X I I Prefαce t ot h e F i r s tE d i t i o n CONTENTS t h e s ec h a p t e r swasc a r e f u l l ys e l e c t e dt oc o n t a i no n l ywhati se s s e n t i a l . Thel a s ttwoando n e ‑ h a l fc h a p t e r smaybeusedi nas e m e s t e rc o u r s eo r og i v eac l e a r a sa d d i t i o n a lr e a d i n g .C o n s i d e r a b l e E圧ort was made t e x p l a n a t i o no fLandaudamping‑onet h a tdoesn o tdependonaknow!ュ edgeo fcontouri n t e g r a t i o n .Iami n d e b t e dt oTomO ’ Neil andGeorge Schmidtf o rh e l pi ns i m p l i f y i n gt h ep h y s i c a lp i c t u r eo r i g i n a l l yg i v e nb y JohnDawson. Somer e a d e r sw i l lbed i s t r e s s e dbyt h eu s eo fc g se l e c t r o s t a t i cu n i t s . I ti s ,o fc o u r s e ,s e n s e l e s st oargueaboutu n i t s ;anyexperiencedp h y s i c i s t candefendh i sf a v o r i t es y s t e me l o q u e n t l yandw i t hf a u l t l e s sl o g i c .The system here i se x p l a i n e di n Appendix I and was chosen t oa v o i d unnecessaryw r i t i n go fc ,オ,,h andε0・ dS well 昌s tobec o n s i s t e n tw i t ht h e m a j o r i t yo fr e s e a r c hp a p e r si nplasmap h y s i c s . Iwouldl i k et othankM i s sL i s aTatarandM r s .B e t t yRaeBrown f o rah i g h l yi n t u i t i v ej o bo f deciphering m y h a n d w r i t i n g , Mr. Tim Lambertf o ras i m i l a rdegreeo funderstandingi nt h ep r e p a r a t i o no f t h ed r a w i n g s ,andmosto fa l lAndeChenf o rp u t t i n gupw i t hal a r g e numbero fd e s e r t e de 1 キ e n i n g s . F r a n c i . sF .Chen LosA n g e l e s ,1974 Prefacetot h eSecondE d i t i o n Prefacet ot h eF i r s tE d i t i o n 1 . INTRODUCTION ¥ ' l l Xl 1 O c c u r r e i t c e o fP l a s m a s i 1 1 Natu問 1 ・ Definition o f Pl山ma 3 • C o n c e p to fT e m f 1 e r a t u r e 4 ・ Debye S h i e l d i n g 8 ・ The Plasma Pa叩meter I1 ・ Criteria f o rP l a s m a s I 1 ・ Applications o fPlasmaP h y s i c s 1 3 19 9 • .Vonuηifoγm E andB F i e l d s l ・ Time- ¥ ' a r y i n gE ・九’onuniform E F i e l d 36 Summaryo fGuiding Time-\ ’arying B F i e l d 4 1 • ・ Adiabatic I n v a r i a n t s 43 2 . SINGLE‑PARTICLE MO’TIONS I n t r o d u c t i o n 19 B F i e l d 26 F i e l d 39 ・ C刊 /er Dγifts 43 ・ Cniform 3 . PLASMAS AS FLUIDS I n t r o d u c t i o n 53 n e t i c s 54 ・ 53 o fPlasmaP h y s i c st o Oγdinary E l e c t r o m a g ュ The F l u i dEqu温tion o fMotion 58 ・ Fluid Driβs Perpendiculaγ to B 6 8 • F l u i dD r i f t sP a r a l l e lt o B 75 ・ The PlasmaA戸proximaiion 7 7 ・ Relation X l l ! XIV Conteη釘 4. もVAVES INPLASMAS Representatioη of W aves 79 ・ ・ Electron O s c i l l a t i o n s 82 Waves 9 4 ・ I o nWaves 9 5 79 V e l o c i t y 8 1 • Plasma Plasma Waves 8 7 • Sound ・ V a l i d i t yo ft h ePlasmaA背骨γ·oxi間at i o n 9 8 • Comparisono fI o nandE l e c t r o nWaves 99 ・ Electros t a t i cE l e c t r o nO s c i l l a t i o n . <Perpendiculaγ to B 100 ・ Electrostatic I o nWaves Perpendiculaγ to B 109 ・ The L ower Hybrid Frequeη cy 112 ・ E l e c t r o m a g n e t i c Waves 山ith B。= 0 1 1 4 ・ Ex戸erimental A合戸lica­ l i o n s 117 ・ Electromagnetic W aves P e r p e n d i c u l a rt oB o 122 ・ C u t o f f s and R e s o n a n c e s 126 ・ Electromagnetic W aves P a r a l l e lt o B。 128 ・ Experimental C o n s e q u e n c e s 1 31 ・ Hydro間agnetic Waves 136 ・ Magnetosonic W aves 142 ・ Summary o fE l e m e n t a r y P l a . < m aWaves 144 ・ TheCMA Diagγ町n 1 4 6 Group 5 . DIFFUSIONAND RESISTIVITY 155 M o b i l i t yin 日々akly I o n i z e dG a s e s 1 5 5 ・ Decayo faPl,山市a 1 5 9 ・ S t e a d yS t a t eS o l u t i o n s 1 6 5 ・ Recombina‑ t i o n 1 6 7 ・ Diffi山間ηαcross aMα gnetic F i e l d 1 6 9 • C o l l i s i o n si n ・ The S i n g l e ‑ F l u i dMHD E q u a t i o n s 1 8 4 F u l l yI o n i z e dP l a s m a s 176 ・ Diffusion i nF u l l yI o n i z e dP l a s m a s 186 ・ Solutiaηs o ft h eD i f f u s i o n E q u a t i o n 188 ・ BohmDiffi山ioη and N e o c l a s s i c a lD i f f u s i o n I 90 Di子山ioη and b y Di子山ion 6 . EQUILIBRIUM AND STABILITY Introductioη199 ・ 199 Hydγ·omagnetic Equilib円um 201 c e p tof ・ The β203 ・ Diff;山 ion o fM a g n e t i cF i e l diηto aPlasma 205 Classがcation o fI n s t a b i l i t i e s 2 0 8 ・ ア町o-Stream I n s t a b i l i t y 2 1 1 The“Gγ·avitational ” Instability 2 1 5 ・ R e s i s t i v eD門戸 Waves 2 18 Conュ ・ ・ ・ TheW e i b e lI n s t a b i l i t y 2 2 3 7 . KINETIC THEORY The Meaningo ff ( v ) 225 225 Equations o fK i n e t i c Theoγy 230 ・ D e r i v a t i o no ft h eF l u i dE q u a t i o n s 236 ・ Plasma O s c i l l a t i o n sandLandau ・ The M eaningo fLandauDαmping 245 ・ A Damping 240 P h y s i c a lD e r i v a t i o no fLandauDam戸仇g 2 56 ・ BGKandVanKam世間 Modes 2 6 1 ・ Expeγimental Verificαtion 2 62 ・ Io nLandauDa前世- i n g 2 6 7 • K i n e t i cEffecぉ in a1 W a g n e t i cF i e l d 2 74 ・ 8 . NONLINEAR EFFECTS I n t r o d u c t i o n 287 Wavι297 ・ Iηstabilities 309 Damping 328 ・ ・ The ・ 287 Sheaths 290 ・ Io n P o n d e r o m o t i v eF o r c e 3 05 A c o u s t i c S h o c k • P a r a m e t r i c Plasma E c h o e s 324 ・ Nonlineaγ Landau Equations o fNonlineaγ Plasma P h y s i c s 3 30 x v APPENDICES C o n t e n t s AppendixA. U n i t s ,C o n s t a n t sandFoγmulas, Vectoγ Relati側s 349 AppendixB .T h e o r yo fWavesi naC o l dUniformPlasma 3 55 AP世間diχ C. S ampleThree-Houγ Final Eχam Append悶 D. Ans山ers t oSomeP r o b l e m s 3 6 1 369 Index 417 Indext oProblems 421 INTRODUCTIONTO PLASMAPHYSICS ANDCONTROLLED FUSION SECONDEDITION Volume1 :PlasmaPhysics C h a p t e rOne INTRODUCTION OCCURRENCE OFPLASMAS INNATURE 1 . 1 I th a so f t e nbeens a i dt h a t99% o ft h ematteri nt h eu n i v e r s ei si nt h e plasmas t a t e ;t h a ti s ,i nt h eformo fane l e c t r i f i e dg a sw i t ht h eatoms d i s s o c i a t e di n t op o s i t i v ei o n sandn e g a t i v ee l e c t r o n s .Thise s t i m a t emay ti sc e r t a i n l yar e a s o n a b l eonei nv i e wo ft h e n o tbev e r yaccur呂町, but i f a c tt h a ts t e l l a ri n t e r i o r sandatmospheres,g a s e o u sn e b u l a e ,andmuch o ft h ei n t e r s t e l l a rhydrogena r ep l a s m a s .I nourownneighborhood,a s soona sonel e a v e st h eearth ’s atmosphere,onee n c o u n t e r st h eplasma comprisingt h eVanA l l e nr a d i a t i o nb e l t sandt h es o l a rw i n d . Ont h e o t h e rhand,i noureverydayl i v e sencountersw i t hplasmasa r el i m i t e d t oafewe x a m p l e s :t h ef l a s ho fal i g h t n i n gb o l t ,t h es o f tglowo ft h e AuroraB o r e a l i s ,t h econductingg a si n s i d eaf l u o r e s c e n tt u b eo rneon s i g n ,andt h es l i g h tamounto fi o n i z a t i o ni nar o c k e te x h a u s t .I twould ft h eu n i v e r s ei nwhichplasmasdonot seemt h a twel i v ei nt h e 1% o occurn a t u r a l l y . Ther e a s o nf o rt h i scanbeseenfromt h eSahae q u a t i o n ,whicht e l l s u st h eamounto fi o n i z a t i o nt obee x p e c t e di nag a si nthermale q u i l i b r i u m : ~3/2 百n n; ’ -- I l ” ー土"" 2 4x1 021 二一- e - UJKT Heren ;andnna r e ,r e s p e c t i v e l y ,t h ed e n s i t y(numberperm3)o fi o n i z e d st h eg a s temperature i n 。 K, K i s atoms and o fn e u t r a la t o m s ,T i Boltzmann ’s c o n s t a n t ,andU ;i st h ei o n i z a t i o nenergyo ft h egas‑that 2 C h a p t e r One i s ,t h enumbero fe r g sr e q u i r e dt oremovet h eoutermoste l e c t r o nfrom anatom.(ThemksorI n t e r n a t i o n a lSystemo fu n i t sw i l lbeusedi nt h i s b o o k . ) For o r d i n a r ya i ra t room t e m p e r a t u r e , we may t a k e nn= 25 3 3X 1 0 m ( s e e Problem 1 ‑ 1 ) , T = 300ーK, and U ;= 1 4 . 5eV ( f o r 0 ‑ 1 9J .ThefractionalionizationnJ(nn+ n i t r o g e n ) ,where1eV= 1 . 6X 1 n ; )=ndnnp r e d i c t e dbyE q .[ 1 ‑ 1 ]i sr i d i c u l o u s l yl o w : ! : ' : ! .= 10‑122 ηn Ast h etemperaturei sr a i s e d ,t h edegreeo fi o n i z a t i o nremainslow u n t i lU;i so n l yafewt i m e sKT.ThennJnnr i s e sa b r u p t l y ,andt h eg a s "l e s sthan i si naplasmas t a t e .Furtheri n c r e a s ei ntemperaturemakesn n ; ,a ndt h eplasmae v e n t u a l l ybecomesf u l l yi o n i z e d .Thisi st h er e a s o n plasmase x i s ti na s t r o n o m i c a lb o d i e sw i t htemperatureso fm i l l i o n so f d e g r e e s , but n o t on t h ee a r t h .L i f e could n o te a s i l yc o e x i s tw i t ha plasma‑atl e a s t ,plasmao ft h et y p ewea r et a l k i n ga b o u t .Then a t u r a l o c c u r r e n c eo fplasmasa th i g htemperaturesi st h ereasonf o rt h ed e s i g n a ュ o u r t hs t a t eo fmatter. ” t ion“ the f Althoughwedon o ti n t e n dto emphasizet h eSahae q u a t i o n ,we shouldp o i n touti t sp h y s i c a lmeaning.Atomsi nag a shaveaspreado f t h e r m a le n e r g i e s ,andanatomi si o n i z e dwhen,byc h a n c e ,i ts u f f e r sa FIGURE1 ‑ 1 I l l u s t r a t i n gt h el o n gr a n g eo fe l e c t r o s t a t i cf o r c e si nap l a s m a . c o l l i s i o no fhighenoughenergyt oknockoutane l e c t r o n .I nac o l dg a s , such e n e r g e t i cc o l l i s i o n s occur i n f r e q u e n t l y ,s i n c e an atom mustbe a c c e l e r a t e dt o much higher t h a nt h ea v e r a g e energy by as e r i e so f “ favorable ” collisions. Theexponentialf a c t o ri nE q .( 1 ‑ 1 ]e x p r e s s e st h e f a c tt h a tt h enumbero ff a s tatomsf a l l se x p o n e n t i a l l yw i t hUJKT.Once anatomi si o n i z e d ,i tremainsc l 1 a r g e du n t i li tmeetsane l e c t r o n ;i tt h e n v e r yl i k e l yrecombinesw i t ht h ee l e c t r o nt obecomen e u t r a la g a i n .The recombinationr a t ec l e a r l ydependsont h ed e n s i t yo fe l e c t r o n s ,which wecant a k ea se q u a lt o n ; .Thee q u i l i b r i u mi o nd e n s i t y ,t h e r e f o r e ,should d e c r e a s ew i t h n;; and t h i si st h er e a s o nf o rt h ef a c t o r πi1 on t h e right町hand s i d eo fE q .[ l ‑ 1 ] .Theplasmai nt h ei n t e r s t e l l a rmediumowes i t se x i s t e n c et ot h elowv a l u eo fn ;( a b o u t1perc m 3 ) ,andhencet h elow recombinationr a t e . DEFINITIONOFPLASMA 1 . 2 Anyi o n i z e dg a scannotbec a l l e dap l a s m a ,o fc o u r s e ;t h e r ei sa l w a y s somes m a l ldegreeo fi o n i z a t i o ni nanyg a s .A u s e f u ld e f i n i t i o ni sa s f o l l o w s : A 世lasma i sa quasi百四 tral e x h i b i t sc o l l e c t i v ebehavio·γ. gαs o fc h a r g e dandneutγal particles 四hich Wemustnowdefine “ quasineutral ” and “ collective behavior. ” The meaningo fq u a s i n e u t r a l i t yw i l lbemadecl田r i nS e c t i o n1 . 4 .Whati s sf o l l o w s . meantby“ collective behavior ” is a Considert h ef o r c e sa c t i n gonamoleculeo f ,s a y ,o r d i n a r ya i r .S i n c e t h emoleculei sn e u t r a l ,t h e r ei snon e te l e c t r o m a g n e t i cf o r c eoni t ,and t h ef o r c eo fg r a v i t yi sn e g l i g i b l e .Them o l e c u l emovesundisturbedu n t i l i tmakesac o l l i s i o nw i t hanotherm o l e c u l e ,andt h e s ec o l l i s i o n sc o n t r o l t h eparticle ’s m o t i o n .A macroscopicf o r c ea p p l i e dt oan e u t r a lg a s ,such a sfromaloudspeakerg e n e r a t i n gsoundw a v e s ,i st r a n s m i t t e dt ot h e i n d i v i d u a l atoms by c o l l i s i o n s . The s i ' t u a t i o ni st o t a l l y di 圧erent i na a r t i c l e s .Ast h e s ec h a r g e smovearound,t h e y p l a s m a ,whichh a schargedp cang e n e r a t el o c a lc o n c e n t r a t i o n so fp o s i t i v eo rn e g a t i v ec h a r g e ,which g i v er i s et oe l e c t r i cf i e l d s .Motiono fc h a r g e sa l s og e n e r a t e sc u r r e n t s ,and hencemagneticf i e l d s .These 五elds a f f e c tt h emotiono fo t h e rcharged p a r t i c l e sf a ra w a y . t h e ro ftwos l i g h t l ycharged Letu sc o n s i d e rt h eE ぼect oneacho r e g i o n so fplasmas e p a r a t e dbyad i s t a n c er( F i g .1 ‑ 1 ) .TheCoulomb i m i n i s h e sa sl / r 2 .However,f o rag i v e ns o l i d f o r c ebetweenA andB d a n g l e( t h a ti s ,t i r / r= c o n s t a n t ) ,t h evolumeo fplasmai nB t h a tcana妊ect 3 I n t r o d u c t i o n C h a p t e r One , el Ai n c r e a s e sa sr 3 .T h e r e f o r e ,e l e m e n t so fplasmae x e r taf o r c eonone anotherevena tl a r g ed i s t a n c e s .I ti st h i slong‑rangedCoulombf o r c e t h a tg i v e st h eplasmaal a r g er e p e r t o i r eo fp o s s i b l emotionsande n r i c h e s t h ef i e l do fs t u d yknowna splasmap h y s i c s .I nf a c t ,t h emosti n t e r e s t i n g nwhicht h el o n g ‑ r a n g e r e s u l t sconcerns o ‑ c a l l e d“ collision less ” plasmas, i e l e c t r o m a g n e t i cf o r c e sa r es omuchl a r g e rthant h ef o r c e sduet oo r d i n a r y l o c a lc o l l i s i o n st h a tt h el a t t e rcanben e g l e c t e da l t o g e t h e r .By“ collective behavior” we meanmotionst h a tdependn o to n l yonl o c a lc o n d i t i o n s butont h es t a t eo ft h eplasmai nremoter e g i o n sa sw e l l . Theword“ plasma ” seems t obeamisnomer 目 It comesfromt h e 6 ,whichmeanssomethingmoldedorf a b r i c a t e d . Greekfλdσμ日, - aro~. r Becauseo fc o l l e c t i v eb e h a v i o r ,aplasmadoesnottendt oconformt o a t h e r ,i to f t e nbehavesa si fi thadamindo fi t sown. e x t e r n a lin 日 uences; r f(u)=Aexp(‑4mu2/KT) 。 wherefdu i st h enumbero fp a r t i c l e sperm3w i t hv e l o c i t ybetweenu andu+du,4mu2 i st h ek i n e t i ce n e r g y ,andK i sBoltzmann ’s c o n s t a n t , computet h ea v e r a g ek i n e t i cenergyo fp a r t i c l e si nt h i sd i s t r i b u t i o n : Thed e n s i t yn ,ornumbero fp a r t i c l e sperm3,i sg i v e nby( s e eF i g .1 ‑ 2 ) 1 ‑ 5 1 に f(u) du D e f i n i n g y= u/1’山[ l-61 and v , ,= (2KT/m ) > 12 wecanw r i t eE q .[ 1 ‑ 2 ]a s f ( u )= Aexp(-u2/v~h) : L [叫(子)]/ andE q .[ l ‑ 5 ]a s 4mAv~h E d y =三 Av,hL:叫(一戸)の av L ~y M一戸)]ydy = 司 [ー;[exp (一戸)]y ]ユ- L:-~exp(-/)d)' = ~ ( 1 ‑ 3 ] Thec o n s t a n tA i sr e l a t e dt ot h ed e n s i t ynby( s e eProblem1 ‑ 2 ) A = η 佳子) 1/2 L:~川U Thei n t e g r a li nt h enumeratori si n t e g r a b l ebyp a r t s: K=1 . 3 8x10‑23JI。 K n = にf川 u ‑ 2 AM a x w e l l i a nv e l o c i t yd i s t r i b u t i o n . FIGURE1 E . , [!・2] ! J lntrodu沼lion 1 . 3 CONCEPTOFTEMPERATURE Beforeproceedingf u r t h e r ,i ti sw e l lt or e v i e wandextendourp h y s i c a l a si nthermale q u i l i b r i u mh a sp a r t i c l e so f n o t i o n so f“ temperature. ” A g a l lv e l o c i t i e s ,andt h emostp r o b a b l ed i s t r i b u t i o no ft h e s ev e l o c i t i e si s knowna st h eM a x w e l l i a nd i s t r i b u t i o n .Fors i m p l i c i t y ,c o n s i d e rag a si n whicht h ep a r t i c l e scanmoveo n l yi noned i m e n s i o n .( T h i si snote n t i r e l y f r i v o l o u s ;as t r o n gmagneticf i e l d ,f o ri n s t a n c e ,canc o n s t r a i ne l e c t r o n s t omoveo n l yalongt h ef i e l dl i n e s . )Theone‑dimensionalMaxwellian d i s t r i b u t i o ni sg i v e nby HU ( 4 : L exp (一戸) dy C a n c e l l i n gt h ei n t e g r a l s ,wehave [!・ 4] ! A 3! 2m 斤‘”ムh 2 I 2 Eavキ =一二二一一=う mv:h Av,h Thewidtho ft h ed i s t r i b u t i o ni sc h a r a c t e r i z e dbyt h ec o n s t a n tT , whichwec a l lthet e m p e r a t u r e .Tos e et h ee x a c tmeaningo fT ,wecan .… Thust h ea v e r a g ek i n e t i cenergyi s~KT. l =さ KT [ l ‑ 7 ] 6 Chapleγ One Maxwelliand i s t r i b u t i o n sw i t hd i f f e r e n ttemperatures T iand T , .This cancomeaboutbecauset h ec o l l i s i o nr a t eamongi o n soramonge l e c t r o n s thPmselvesi sl a r g e rthant h er a t eo fc o l l i s i o n sbetweenani o nandan e l e c t r o n .Theneachs p e c i e scanbei ni t sownthermale q u i l i b r i u m ,but t h eplasmamayn o tl a s tlongenoughf o rt h etwotemperaturest oe q u a l i z e . 、γhen t h e r ei sama耳netic f i e l dB ,evenas i n g l es p e c i e s ,s a yi o n s ,can havetwot e m p e r a t u r e s .Thisi sbecauset h ef o r c e sa c t i n gonani o nalong Baredi 圧erent fromt h o s ea c t i n gperpendiculart oB(duet ot h eLorentz f o r c e ) .Thecomponell[So fv e l o c i t yp e r p e n d i c u l a rt oB andp a r a l l e lt o B may then belong t od i f f e r e n t Maxwellian d i s t r i b u t i o n sw i t h tem‑ p e r a t u r e sTょ and T 1 1 . Beforel e a v i n gourr e v i e wo ft h en o t i o no ft e m p e r a t u r e ,weshould d i s p e lt h e popular misconception t h a t high temperature n e c e s s a r i l y meansal o to fh e a t .Peoplea r eu s u a l l yamazedt ol e a r nt h a tt h ee l e c t r o n t temperaturei n s i d eaf l u o r e s c e n tl i g h tbulbi sabout20,000°K. “ My, i d o e s n ' tf e e lt h a thot !” Of c o u r s e ,t h eh e a tc a p a c i t ymusta l s obet a k e n i n t oa c c o u n t .Thed e n s i t yo fe l e c t r o n si n s i d eaf l u o r e s c e n ttubei smuch l e s sthant h a to fag a sa tatmosphericp r e s s u r e ,andt h et o t a lamounto f heat t r a n s f e r r e dt ot h ew a l l bye l e c t r o n ss t r i k i n gi ta tt h e i rthermal v e l o c i t i e si sn o tt h a tg r e a t .Everyoneh a shadt h ee x p e r i e n c eo fac i g a r e t t e ashdroppedinnocuouslyonh i shand.Althought h etemperaturei shigh enought oc a u s eaburo,t h et o t a lamounto fh e a ti n v o l v e di sn o t .Many l a b o r a t o r y plasmas have temperatures o ft h e order o fl ,000,000ーK (100e V ) ,buta td e n s i t i e so f1 0 1 8 ‑ 1 0 1 9perm 3 ,t h eh e a t i n go ft h ew a l l si s notas e r i o u sconsider旦 ti on 目 I ti se a s yt oextendt h i sr e s u l tt ot h r e ed i m e n s i o n s .Maxwell ’s distribtト t i o ni sthen f ( u ,v,山) =A3exp[一』m(u2+v2 + 山 2)/KT] [I ・ 8] where A3 = η (品) 3/2 [ l ‑ 9 ] Theaveragek i n e t i cenergyi s J IL~ A3~m(u2 +v2+ぷ) exp 同(u2 +v2+w2)/KT]dudvd叩 E a v= ~・・ a 国 1 1 1 Agexp[一;m(u2 +v2 十回 2)/ KT]dudvdw Wenotet h a tt h i se x p r e s s i o ni ssymmetrici nu ,v ,and 叩, since aMaxwellian d i s t r i b u t i o ni si s o t r o p i c . Consequently,eacho ft h et h r e etermsi nt h e numerator 凶 the s amea st h eo t h e r s .Weneedo n l yt oe v a l u a t et h ef i r s t termandm u l t i p l ybyt h r e e : E 3A3J ~mu2 exp(ー;mu2/KT) duJ Sexp[- ~m(v2 +山 2)/KT]dvd叩 a v‑ A dexp(- ~mu2/KT) duJ Sexp[- ~m(v2 +w2)/KT]dvdw - Usingourp r e v i o u sr e s u l t ,wehave E a v= ~KT [ 1 ‑ 1 0 ] Theg e n e r a lr e s u l ti st h a tE a ve q u a l s~KT perdegreeo ffreedom. S i n c e T andE a va r es oc l o s e l yr e l a t e d ,i ti scustomaryi nplasma p h y s i c st og i v etemperaturesi nu n i t so fe n e r g y .Toa v o i dc o n f u s i o non t h enumbero fdimensionsi n v o l v e d ,i ti sn o tE a vbutt h eenergyc o r r e s ュ h a ti susedt odenotet h et e m p e r a t u r e .ForKT=1eV= pondingt oK Tt 1 . 6ラ 1 0ー 19 J,wehave 1 ・ 1. C omputet h ed e n s i t y( i nu n i t so fm•) o fa ni d e a lg a sundert h ef o l l o w i n g PROBLEMS c o n d 1 t 1 o n s T T ( a ) At O。c and 7 6 0Torr p r e s s u r e( lTorr=ImmH g ) .T h i si sc a l l e dt h e L o s c h m i d tnumber. 1 . 6ラ 1 0 ‑ 1 9 =一一一一一一一「百= 1 . 6 0 0 1 . 3 8X 1 0 ‑ ' o 1 ' ( b )I na 、acuum o f1 0'Torra troomt e m p e r a t u r e( 2 0 ー C ) .T h i snumberi sa u s e f u lonef o rt h ee x p e r i m e n t a l i s tt oknowb yh e a r t( I0'Torr=Im i c r o n ) . Thust h ec o n v e r s i o nf a c t o ri s 1 ‑ 2 .D e r i ¥ ' et h ec o n s t a n tA f o ran o r m a l i z e do n e ‑ d i m e n s i o n a lM a x w e l l i a nd i s t r i ュ b u t i o n l -- I l 1eV= ll,600ーK 六u) =Ae x p(一明u2/2KT) By a 2‑eV plasmawe mean t h a tKT=2eV, orE a v=3eV i nt h r e e d i m e n s i o n s . I ti si n t e r e s t i n gt h a taplasmacanhaves e v e r a ltemperaturesa tt h e samet i m e .I to f t e nhappenst h a tt h ei o n sandt h ee l e c t r o n shaves e p a r a t e 岡田掴圃圃圃園田園 7 I n t r o d u c t i o n s u c ht h a t 語圏量 8 9 Chai争ter I n t r o d u c t i o n One PLASMA 0 FIGURE1 ・3 Debyes h i e l d i n g . 1 . 4 DEBYESHIELDING t h ei n e r t i ao ft h ei o n sp r e v e n t sthemfrommovings i g n i f i c a n t l yont h e q u a t i o ni nonedimensioni s t i m es c a l eo ft h ee x p e r i m e n t .Poisson ’s e 0 A fundamentalc h a r a c t e r i s t i co ft h ebehavioro faplasm旦 is i t sa b i l i t yt o s h i e l doute l e c t r i cp o t e n t i a l st h a ta r ea p p l i e dt oi t .Supposewet r i e dt o put an e l e c t r i cf i e l di n s i d e a plasma by i n s e r t i n g two charged b a l l s a l l swoulda t t r a c tp a r t i c l e so ft h e connectedt oab a t t e r y(Fig目ト 3). Theb o p p o s i t ec h a r g e ,anda l m o s timmediatelyac l o u do fi o n swouldsurround t h en e g a t i v eb a l landac l o u do fe l e c t r o n swouldsurroundt h ep o s i t i v e b a l l .(Weassumet h a tal a y e ro fd i e l e c t r i ckeepst h eplasmafroma c t u a l l y recombiningon t h es u r f a c e ,o rt h a tt h eb a t t e r yi sl a r g e enough t o m a i n t a i nt h ep o t e n t i a li ns p i t eo ft h i s . )I ft h eplasmawerec o l dandt h e r e werenot h e r m a lm o t i o n s ,t h e r ewouldbej u s ta smanyc h a r g e si nt h e c l o u da si nt h eb a l l ;t h es h i e l d i n gwouldbep e r f e c t ,andnoe l e c t r i cf i e l d wouldbep r e s e n ti nt h ebodyo ft h eplasmao u t s i d eo ft h eclouds 目 On t h eo t h e rhand,i ft h etemperaturei sf i n i t e ,t h o s ep a r t i c l e st h a ta r ea t t h eedgeo ft h ec l o u d ,wheret h ee l e c t r i cf i e l di sweak, haveenough thermalenergytoe s c a p efromt h ee l e c t r o s t a t i cp o t e n t i a lw e l l .The“ edge ” o ft h ec l o u dtheno c c u r sa tt h er a d i u swhere t h ep o t e n t i a lenergyi s a p p r o x i m a t e l ye q u a lt ot h et h e r m a lenergyK To ft h ep a r t i c l e s ,andt h e e a ki n t o s h i e l d i n gi sn o tc o m p l e t e .P o t e n t i a l so ft h eordero fKT/ecanl t h eplasmaandc a u s ef i n i t ee l e c t r i cf i e l d st oe x i s tt h e r e . L e tu scomputet h eapproximatet h i c k n e s so fsuchachargec l o u d . Imaginet h a tt h ep o t e n t i a lφon t h ep l a n ex= 0i sh e l da tavalueφ D by ap e r f e c t l yt r a n s p a r e n tg r i d( F i g .1 ‑ 4 ) .Wewisht ocomputeφ (x). For 1 1 / mi si n f i n i t e , s i m p l i c i t y ,weassumet h a tt h ei o n ‑ e l e c t r o nmassr a t i o1 s ot h a tt h ei o n sdon o tmovebutformauniformbackgroundo fp o s i t i v e sl a r g eenought h a t c h a r g e .Tob emorep r e c i s e ,wecans a yt h a tM/mi x P o t e n t i a ld i s t r i b u t i o nn e a rag r i di nap l a s m a . F I G U l l . E1 ‑ 4 ' d 2φ εFφ = εu-;;Jz =ー仰z ー叫) (Z=I ) n ・ 12] I ft h ed e n s i t yf a rawayi sn o o ,wehave n ,= n o o I nt h epresenceof t I O nIS 旦 potential energyqφ, f(u)=Aexp [ー(~mu2 the e l e c t r o nd i s t r i b u t i o nf u n c ュ +qφ )/KT,] I twouldnotbeworthwhilet oprovet h i sh e r e .Whatt h i se q u a t i o ns a y s i si n t u i t i v e l yo b v i o u s : There a r e fewer p a r t i c l e sa tp l a c e s where t h e p o t e n t i a lenergyi sl a r g e ,s i n c en o ta l lp a r t i c l e shaveenoughenergyt o g e tt h e r e .I n t e g r a t i n gf(u)o v e ru ,s e t t i n gq= ‑ e ,andn o t i n gthatη,(φ → 0 )= n o o ,wef i n d n ,=n 司 exp (eφ/ KT,) Thise q u a t i o nw i l lbed e r i v e dw i t hmorep h y s i c a li n s i g h ti nS e c t i o n3 目 5. S u b s t i t u t i n gf o rn ;andn ,i nE q .(1 ・ 12), wehave d2φI 「 ( eφ \ l ' l e n 0 0 1 1expt 一一一l 1‑q a x L L ¥KT,JJ J co -;-τ = I nt h er e g i o nwhereI eφ/ KT,I 《 1, wec anexpandt h ee x p o n e n t i a li na Taylors e r i e s : d2φr eφ1 (eφ \ 2' l €0 -;;;;す=四"" Lrr 十 E \K王/十 j [I ・ 13] 一一、・・ー”一一一 一 10 Chαpter One Nos i m p l i f i c a t i o ni sp o s s i b l ef o rt h er e g i o nneart h eg r i d ,whereJ eφ/ KT,J maybel a r g e .F o r t u n a t e l y ,t h i sr e g i o ndoesnotc o n t r i b u t emucht ot h e t h i c k n e s so ft h ecloud( c a l l e das h e a t h ) ,becauset h ep o t e n t i a lf a l l sv e r y r a p i d l yt h e r e .Keepingo n l yt h el i n e a rtermsi nE q .[ l ‑ 1 3 ] ,wehave d2φη "'e2 , [ 1 ‑ 1 4 ] 一ーす=ー一一一 φ ax KT, γ De白 ning λo =(寄手) 1/2 [l ・ 15] d e n s i t y ,b utnots on e u t r a lt h a ta l lt h ei n t e r e s t i n ge l e c t r o m a g n e t i cf o r c e s v a n i s h . Ac r i t e r i o nf o rani o n i z e dg a st ob eaplasmai st h a ti tbedense smuchs m a l l e rt h a nL . enoughthatλD i The phenomenon o f Debye s h i e l d i n ga l s o occursーin modi 自ed form‑ins i n g l e ‑ s p e c i e ss y s t e m s ,sucha st h ee l e c t r o ns t r e a m si nk l y s t r o n s andmagnetronso rt h eprotonbeami nac y c l o t r o n .I nsuchc a s e s ,any l o c a lbunchingo fp a r t i c l e sc a u s e sal a r g eu n s h i e l d e de l e c t r i cf i e l du n l e s s t h ed e n s i t yi se x t r e m e l ylow( w h i c hi to f t e ni s ) .Ane x t e r n a l l yimposed ¥ V i r ep r o b e ,f o rinstance‑wouldbes h i e l d e doutby potential‑froma anadjustmento ft h ed e n s i t yn e a rt h ee l e c t r o d e .S i n g l e ‑ s p e c i e ss y s t e m s , o ru n n e u t r a l i z e dp l a s m a s ,a r en o ts t r i c t l yp l a s m a s ;butt h emathematical t o o l so fplasmap h y s i c scanbeusedt os t u d ysuchs y s t e m s . wherens t a n d sf o rn o o ,wecanw r i t et h es o l u t i o no fE q .[ 1 ‑ 1 4 ] . a s φ = φoexp (一 JxJ /λo) [ l ‑ 1 6 ] Theq u a n t i t yλo, c a l l e dt h eDebyel e n g t h ,i sameasureo ft h es h i e l d i n g d i s t a n c eo rt h i c k n e s so ft h es h e a t h . Notet h a ta st h ed e n s i t yi sincreased , λo d e c r e a s e s ,a sonewould e x p e c t ,s i n c eeachl a y e ro fplasmac o n t a i n smoree l e c t r o n s .Furthermore, λ 口 increases w i t hi n c r e a s i n gKT,.Withoutthermala g i t a t i o n ,t h echarge 仁 loud w ouldc o l l a p s et oani n f i n i t e l yt h i nl a y e r .F i n a l l y ,i ti st h eelectγon temperaturewhichi susedi nt h ed e f i n i t i o no fλD becauset h ee l e c t r o n s , beingmoremobilethant h ei o n s ,g e n e r a l l ydot h es h i e l d i n gbymoving s oa st oc r e a t eas u r p l u so rd e f i c i to fn e g a t i v ec h a r g e .Onlyi ns p e c i a l s i t u a t i o n si st h i snott r u e( s e eProblem1 ‑ 5 ) . Thef o l l o w i n ga r eu s e f u lformso fE q .[ 1 ‑ 1 5 ] : λo = 69(T/n)112m, λ0=7430(KT/n)112m, Thep i c t u r eo fDebyes h i e l d i n gt h a twehaveg i v e nabovei sv a l i do n l y i ft h e r ea r eenoughp a r t i c l e si nt h echargec l o u d .C l e a r l y ,i ft h e r ea r e o n l yoneo rtwop a r t i c l e si nt h es h e a t hr e g i o n ,Debyes h i e l d i n gwould n o tbeas t a t i s t i c a l l yv a l i dc o n c e p t .UsingE q .[ l ‑ 1 7 ] ,wecancomputet h e number 入'0 o fp a r t i c l e si na “ Debye sphere ”: No=n~1Tλ 色= 1 . 3 8ラ J 0 6 T 3 1 2/n1 1 2 (Tinー K ) [I・ 18] I na d d i t i o ntoλD 《 L,“collective behavior ” requires N0> サ1 TinーK KTineV THEPLASMA PARAMETER 1 . 5 [ 1 ‑ 1 9 ] [ l ‑ 1 7 ] We a r e now i nap o s i t i o nt o define “ quasi neutrality 目” If t h e fasystema r emuchl a r g e rthanλ0, thenwheneverl o c a l dimensionsL o c o n c e n t r a t i o n so fchargea r i s eo re x t e r n a lp o t e n t i a l sa r ei n t r o d u c e di n t o t h es y s t e m ,t h e s ea r es h i e l d e do u ti nad i s t a n c es h o r tcomparedw i t hL , l e a v i n gt h eb u l ko ft h eplasmaf r e eo fl a r g ee l e c t r i cp o t e n t i a l so rf i e l d s . O u t s i d eo ft h es h e a t hont h ew a l lo ronano b s t a c l e ,'12φis v e r ys m a l l , andn ;i se q u a lton,,t y p i c a l l y ,t ob e t t e rthanonep a r ti n1 0 6 .I tt a k e s o n l yas m a l lchargeimbalancet og i v er i s et op o t e n t i a l so ft h eordero f KT/ιThe p lasmais “ quasineutral ”; that i s ,n e u t r a lenoughs ot h a tone ,wheren i sacommond e n s i t yc a l l e d the 戸lasmα c a n taken ,=叫= n CRITERIAFORPLASMAS 1 . 6 Wehaveg i v e ntwocondi~ions t h a tani o n i z e dg a smusts a t i s f yt obec a l l e d ap l a s m a .A t h i r dc o n d i t i o nh a st odow i t hc o l l i s i o n s .Theweaklyi o n i z e d g a si naj e te x h a u s t ,f o re x a m p l e ,doesn o tq u a l i f ya saplasmab e c a u s e t h echargedp a r t i c l e sc o l l i d es of r e q u e n t l yw i t hn e u t r a latomst h a tt h e i r motioni sc o n t r o l l e dbyo r d i n a r yhydrodynamicf o r c e sr a t h e rt h a nby e l e c t r o m a g n e t i cf o r c e s .I fwi st h ef r e q u e n c yo ft y p i c a lplぉma o s c i l l a t i o n s st h emeant i m ebetweenc o l l i s i o n sw i t hn e u t r a la t o m s ,wer e q u i r e andT i ωγ > If o rt h eg a st obehavel i k eaplasmar a t h e rthanan e u t r a lg a s . 1 1 Intγ·oduction 12 1 ‑ 7 .ComputeλD andN0 f o rt h ef o l l o w i n gc a s e s : Thet h r e ec o n d i t i o n saplasmamusts a t i s f ya r et h e r e f o r e : Chapleγ One 0 1 6m へ ( a )Ag l o wd i s c h a r g e .w i t hn= 1 lλD 《 L. 2eV. 0 1 2m ",KT,= 0 .Ie V . ( b )Thee a r t h " si o n o s p h e r e ,w i t hn= 1 2 . Nn ;;> I. 3 .W T >1 . PROBLEMS KT,= ( c )A 8 ‑ p i n c h ,w i t hn= 1 0 2 "m ",KT,=800eV 目 1 ‑ 3 .Onal o g ‑ l o gp l o to fn ,v s .KT,w i t hn ,from1 0 6t o1 0 2 5m ‑ 3 ,andKT,from 0 . 0 1t o1 0 5e V ,drawl i n e so fc o n s t a n tλD andN0・ On t h i sg r a p h ,p l a c et h e f o l l o w i n gp o i n t s( ni nm ‑ ' ,KTi neV):・ I .T y p i c a lf u s i o nr e a c t o r :n= 1 0 2 1 ,KT=1 0 , 0 0 0 0 1 9 ,KT=1 0 0( t o r u s ) ;n= 1 0 2 3 ,KT= 2 .T y p i c a lf u s i o ne x p e r i m e n t s :n= 1 I 0 0 0( p i n c h ) . 3 .T y p i c a l i o n o s p h e r e :n= 1 0 1 1 ,KT=0 . 0 5 . 4 .T y p i c a lg l o wdischarge :目 n = 1 0 1 5 ,KT=2 . 0 1 4 ,KT=0 . 1 . 5 .T y p i c a lf l a m e :n= 1 6 .T y p i c a lCsplasma ; η = 1 0 1 7 ,KT=0 . 2 0 6 ,KT=0 . 0 1 . 7 .I n t e r p l a n e t a r ys p a c e :n= 1 C o n v i n c ey o u r s e l ft h a tt h e s ea r ep l a s m a s . 1 ‑ 4 .Computet h ep r e s s u r e ,i na t m o s p h e r e sandi nt o n s / f t 2 ,e x e r t e db yat h e r ‑ m o n u c l e a rp l a s m aoni t sc o n t a i n e r .AssumeKT,=KT,= 20k e V ,n= 1 0 2 1m ‑ 3 , ,+T,・ andp= η KT, whereT = T 1・5. In 且 strictly s t e a d ys t a t es i t u a t i o n ,b o t ht h ei o n sandt h ee~ctrons w i l lf o l l o w t h eBoltzmannr e l a t i o n n ;= n 0e x p(ーも φ/ KT;) F o rt h ec a s eo fanin日 nite, t r a n s p a r e n tg r i dc h a r g e dt oapotentialφ, t h es h i e l d i n gd i s t a n c ei st h e ng i v e nap レ roxiπ1ately by show t h a t e I 広) λζ~2 =一n ε一 o2( KT,+ ShowthatλD i sd e t e r m i n e db yt h et e m p e r a t u r eo ft h ec o l d e rs p e c i e s . i l lg i v ef u r t h e ri n s i g h tt oi t sm e a n i n g . 1 ‑ 6 .Ana l t e r n a t i v ed e r i v a t i o no fλD w a r a l l e lp l a t e sa tx= ア d ,s e ta tpotentialφ = 0 .Thes p a c e C o n s i d e rt w oin 五 nite, p fp a r t i c l e so fc h a r g eq . b e t w e e nthemi su n i f o r m l yf i l l e db yag a so fd e n s i t yno ( a )U s i n gPoisson ’s e q u a t i o n ,showt h a tt h ep o t e n t i a ld i s t r i b u t i o nb e t w e e nt h e p l a t e si s φ =ー noム (d 向z 2 E o x 。" ) ( b ) Showt h a tf o rd> λD・ the e n e r g yneeded t ot r a n s p o r tap a r t i c l efroma p l a t et ot h em i d p l a n ei sg r e a t e rt h a nt h ea v e r a g ek i n e t i ce n e r g yo ft h ep a r t i c l e s . APPLICATIONS OF PLASMA PHYSICS 1 . 7 Plasmascanbec h a r a c t e r i z e dbyt h etwoparametersnandKT,.Plasma a p p l i c a t i o n scoveranextremelywiderangeo fnandKT, : ηvaries over 28ordersofmagnitudefrom 1 0 6t oI 0 3 4m‑ 3 ,andK Tcanvaryover sevenordersfrom0 . 1t oI 0 6eV.Someo ft h e s ea p p l i c a t i o n sa r ed i s c u s s e d v e r yb r i e f l yb e l o w .Thetremendousrangeofd e n s i t ycanbea p p r e c i a t e d whenoner e a l i z e st h a ta i randwaterd i f f e ri nd e n s i t ybyo n l y1 0 3 ,w h i l e waterandwhitedwarfs t a r sa r eseparatedbyonlyaf a c t o ro f1 0 5 .Even neutrons t a r sa r eonly1 0 1 5t i m e sdenserthanw a t e r .Yetgaseousplasmas i nt h ee n t i r ed e n s i t yrangeo f1 0 2 8canbedescribedbyt h esames e to f e q u a t i o n s ,s i n c e only t h ec l a s s i c a l (non‑quantum mechanical) l a w so f p h y s i c sa r eneeded. GasDischarges(GaseousE l e c t r o n i c s ) 1 . 7 . 1 Thee a r l i e s tworkwithplasmaswast h a tofLangmuir,Tonks,andt h e i r e s e a r c hwasi n s p i r e dbyt h eneedt o c o l l a b o r a t o r si nt h e 1920’ s. Thisr developvacuum t u b e st h a tcouldc a r r yl a r g ec u r r e n t s , and t h e r e f o r e hadt obef i l l e dw i t hi o n i z e dg a s e s .Ther e s e a r c hwasdonew i t hweakly i o n i z e dglowd i s c h a r g e sandp o s i t i v ecolumnst y p i c a l l yw i t hKT,=2eV 1 8m‑3 I twas here t h a tt h es h i e l d i n gphenomenon and 1014 く η く 1 0 was d i s c o v e r e d ;t h e sheath surrounding an e l e c t r o d e could be seen i s c h a r g e sa r eencountered nowadaysi n v i s u a l l ya sadarklayer 目 Gas d mercuryr e c t i f i e r s ,hydrogent h y r a t r o n s ,i g n i t r o n s ,sparkg a p s ,welding a r c s ,neonandf l u o r e s c e n tl i g h t s ,andl i g h t n i n gd i s c h a r g e s . ControlledThermonuclearFusion 1 .7. 2 Modern plasma p h y s i c s had i tbeginnings around 1 9 5 2 ,when i twas proposedt h a tt h ehydrogenbombf u s i o nr e a c t i o nbec o n t r o l l e dt omake ar e a c t o r . The p r i n c i p a lr e a c t i o n s , which i n v o l v e deuterium ( D ) and 1 3 I n t r o d u c t i o n 一ー『’F一一ー一一 14 t r i t i u m( T )a t o m s ,a r ea sf o l l o w s : Chapteγ One D+D • 3He +n+3 . 2MeV D+D • T+p+4.0MeV D+T • 4He+n+ 17.6MeV Thec r o s ss e c t i o n sf o rt h e s ef u s i o nr e a c t i o n sa r ea p p r e c i a b l eo n l yf o r i n c i d e n te n e r g i e sabove5keV.A c c e l e r a t e dbeamso fdeuteronsbomュ bardingat a r g e tw i l ln o twork,b e c a u s emosto ft h edeuteronsw i l ll o s e t h e i renergybys c a t t e r i n gb e f o r eundergoingaf u s i o nr e a c t i o n .I ti s n e c e s s a r yt oc r e a t eaplasmai nwhicht h ethermale n e r g i e sa r ei nt h e 0・ keV r a n g e .Theproblemo fh e a t i n gandc o n t a i n i n gsuchaplasmai s 1 r e s p o n s i b l ef o rt h er a p i dgrowtho ft h es c i e n c eo fplasmap h y s i c ss i n c e 1 9 5 2 .Theproblemi ss t i l lu n s o l v e d ,andmosto ft h ea c t i v er e s e a r c hi n plasmap h y s i c si sd i r e c t e dtowardt h es o l u t i o no ft h i sp;oblem. 1 .7. 3 SpacePhysics Anotherimportanta p p l i c a t i o no fplasmap h y s i c si si nt h es t u d yo ft h e earth ’s environmenti ns p a c e .A c o n t i n u o u sstreamo fchargedp a r t i c l e s , c a l l e dt h es o l a rw i n d , impingesont h eearth ’ s magnetosphere,which s h i e l d su sfromt h i sr a d i a t i o nandi sd i s t o r t e dbyi ti nt h ep r o c e s s .T y p i c a l 0 6m 3 ,KT;= 1 0eV,KT,= parametersi nt h es o l a rwinda r en= 5ラ 1 50eV,B = 5ラ 1 0 ‑ 9T,andd r i f tv e l o c i t y300kmfsec目 The i o n o s p h e r e , extendingfromana l t i t u d eo f50kmt o1 0e a r t hr a d i i ,i spopulatedby aweaklyi o n i z e dplasmaw i t hd e n s i t yv a r y i n gw i t ha l t i t u d eupt on= 1 0 1 2m‑3 Thetemperaturei so n l y1 0 1e V . The VanA l l e nb e l t sa r e i e l d . composedo fcharged p a r t i c l e strappedbyt h eearth ’s magneticf Here we have n:;;109m‑3, KT,:;;1keV, KT;=1eV, and B = 500X 1 0 ‑ 9T.I na d d i t i o n ,t h e r ei sah o tcomponentwithη = 1 0 3m‑3 andKT,=40keV. ー一一一一一 a r en o tc h a r g e d ,t h e ybehavel i k ep a r t i c l e si n ap l a s m a ; and plasma k i n e t i ct h e o r yh a sbeenusedt op r e d i c tt h edevelopmento fg a l a x i e s . Radioastronomy h a s uncovered numerouss o u r c e so fr a d i a t i o nt h a t mostl i k e l yo r i g i n a t efromp l a s m a s .TheCrabnebulai sar i c hs o u r c eo f t plasmaphenomenabecausei ti sknownt oc o n t a i namagnetic 白eld. I a l s oc o n t a i n sav i s u a lp u l s a r .Currentt h e o r i e so fp u l s a r sp i c t u r ethem a sr a p i d l yr o t a t i n g neutron s t a r sw i t hp l a s m a se m i t t i n gsynchrotron r a d i a t i o nfromt h es u r f a c e . MHDEnergyConversionandIonPropulsion 1 . 7 . 5 G e t t i n gbackdownt oe a r t h ,wecomet otwop r a c t i c a la p p l i c a t i o n so f plasmap h y s i c s .Magnetohydrodynam1c(MHD)energyc o n v e r s i o nu t i l ュ i z e sadenseplasmaj e tp r o p e l l e da c r o s samagneticf i e l dt og e n e r a t e ,wherev i st h ej e tv e l o c i t y , e l e c t r i c i t y( F i g .1 ‑ 5 ) .TheLorentzf o r c eqvxB c a u s e st h ei o n st od r i f tupwardandt h ee l e c t r o n sdownward,charging o t e n t i a l s .E l e c t r i c a lc u r r e n tcanthenb e t h etwoe l e c t r o d e st odi 百erent p fah e a tc y c l e . drawnfromt h ee l e c t r o d e sw i t h o u tt h eine伍ciency o Thesamep r i n c i p l ei nr e v e r s eh a sbeenusedt od e , キ e l o pe n g i n e sf o r u r r e n ti sd r i v e nthroughaplasma i n t e r p l a n e t a r ym i s s i o n s .I nF i g .1 ・6, ac bya p p l y i n gav o l t a g et ot h etwoe l e c t r o d e s .ThejxB f o r c es h o o t st h e plasmaouto ft h er o c k e t ,andt h eensuingr e a c t i o nf o r c ea c c e l e r a t e st h e r o c k e t .Theplasmae j e c t e dmusta l w a y sb en e u t r a l ;o t h e r w i s e ,t h es p a c e s h i pw i l lcharget oahighp o t e n t i a l . S o l i dS t a t ePlasmas 1 .7. 6 The f r e ee l e c t r o n s and h o l e si nsemiconductors c o n s t i t u t e a plasma e x h i b i t i n gt h e same s o r to fo s c i l l a t i o n s and i n s t a b i l i t i e sa sag a s e o u s p l a s m a . Plasmas i n j e c t e di n t o InSb have been p a r t i c u l a r l yu s e f u li n ( B 1 .7.4 ModernAstrophysics 一一寸 ① , a u v + nD x u v 「一一一← - 一一 」』 ー "'‑ aa守 a EEE S t e l l a ri n t e r i o r sandatmospheresa r ehotenought obei nt h eplasma s t a t e .Thetemperaturea tt h ec o r eo ft h es u n ,f o ri n s t a n c e ,i se s t i m a t e d t obe2keV;thermonuclearr e a c t i o n so c c u r r i n ga tt h i stemperaturea r e a d i a t i o n .Thes o l a rcoronai satenuousplasma r e s p o n s i b l ef o rt h esun ’s r w i t htemperaturesupt o200eV.Thei n t e r s t e l l a rmediumc o n t a i n si o n ュ 0 6m‑ s .Variousplasmat h e o r i e shavebeenused i z e dhydrogenw i t hn= 1 t oe x p l a i nt h ea c c e l e r a t i o no fcosmicr a y s .Althought h es t a r si nag a l a x y l 、 15 I n t r o d u c t i o n θ P r i n c i p l eo ft h eMHDg e n e r a t o r . FIGURE1 ‑ 5 1 6 1 7 Cha:争teγ O町 Intγ·oductioη 一一一切』 V s \~~ーーー/ //ー一一一~\ ... ー-向 。 FIGURE1 ‑ 6 P r i n c i p l eo fp l a s m a ‑ j e te n g i n ef o rs p a c e c r a f tp r o p u l s i o n . h ee f f e c t i v e s t u d i e so ft h e s ephenomena.Becauseo ft h el a t t i c eE圧ects, t c o l l i s i o nfrequencyi smuchl e s sthanonewouldexpecti n 'as o l i dw i t h 29 ‑3 n= 10 m .Furthermore, the holesi nasemiconductorcan havea v e r ylowe f f e c t i v emass‑asl i t t l ea s O.Olm,‑and t h e r e f o r e havehigh c y c l o t r o nf r e q u e n c i e seveni nmoderatemagneticf i e l d s .I foneweret o o ras o l i ds t a t eplasma,i twouldbel e s sthanu n i t ybecause c a l c u l a t eN0f o ft h elowtemperatureandhighd e n s i t y .Quantummechanicale百ects ( u n c e r t a i n t yp r i n c i p l e ) , however, g i v et h e plasma an e f f e c t i v e temュ e s p e c t a b l yl a r g e . Certainl i q u i d s , peraturehighenough t omakeNor obehavel i k e sucha ss o l u t i o n sofsodiumi nammonia,h且ve beenfoundt plasmasa l s o . " 1 .7 .7 GasLasers a slaser‑thati s ,t oi n v e r tt h e Themostcommonmethodto “ pump ” a g populationi nt h es t a t e st h a tg i v er i s et ol i g h ta m p l i f i c a t i o n ‑ i st ou s ea g a sd i s c h a r g e .Thiscanbealow‑pressureglowdischargef o radcl a s e r orah i g h ‑ p r e s s u r eavalanchedischargei napulsedl a s e r .TheHe‑Ne l a s e r scommonlyusedf o ralignmentandsurveyingandt h eArandKr l a s e r susedi nl i g h tshowsa r eexampleso fdcg a sl a s e r s .Thepowerful C02l a s e ri sf i n d i n gcommerciala p p l i c a t i o na sac u t t i n gt o o l .Molecular l a s e r s make p o s s i b l es t u d i e so ft h eh i t h e r t oi n a c c e s s i b l ef a ri n f r a r e d r e g i o no ft h ee l e c t r o m a g n e t i cspectrum.Thesecanbed i r e c t l ye x c i t e d byane l e c t r i c a ld i s c h a r g e ,a si nt h ehydrogencyanide(HCN)l a s e r ,or canbeo p t i c a l l ypumped byaC02 l a s e r ,a swith t h emethyl f l u o r i d e (CH3F)ormethyla l c o h o l(CH30H)l a s e r s .Evens o l i ds t a t el a s e r s ,such a sN d ‑ g l a s s , depend on aplasmaf o rt h e i ro p e r a t i o n ,s i n c et h ef l a s h t u b e susedf o rpumpingc o n t a i ng a sd i s c h a r g e s . FIGUREP l ‑ 1 1 1 ‑ 8 .I nl a s e rf u s i o n ,t h ec o r eo fas m a l lp e l l e to fDTi sc o m p r e s s e dt oad e n s i t y o fI O ' "m一九 at at e m p e r a t u r eo f5 0 , 0 0 0 , 0 0 0 ー K .E s t i m a t et h enumbero fp a r t i c l e s i naDebyes p h e r ei nt h i sp l a s m a . 1 ‑ 9 .A d i s t a n tg a l a x yc o n t a i n sac l o u do fp r o t o n sanda n t i p r o t o n s ,e a c hw i t h d e n s i t yn= 1 0 6m "andt e m p e r a t u r e100。K. Whati st h eDebyel e n g t h ? simmersedi nap l a s m aandc h a r g e d 1 ‑ 1 0 .A s p h e r i c a lc o n d u c t o ro fr a d i u sai t oapotentialφ 小 The e l e c t r o n sr e m a i nM a x w e l l i a nandmovet oformaDebye s h i e l d ,b u tt h ei o n sa r es t a t i o n a r yd u r i n gt h et i m eframeo ft h ee x p e r i m e n t . Assumingφ。《 KT,/e, d e r i v eane x p r e s s i o nf o rt h ep o t e n t i a la saf u n c t i o no fr i nt e r m so fa, φ。, and λ0・( Hint: Assumeas o l u t i o no ft h eforme " " / r . ) 1 ‑ 1 1 .A 自eld-effect t r a n s i s t o r(FET)i sb a s i c a l l ya ne l e c t r o nv a h キ et h a to p e r a t e s onaf i n i t e ‑ D e b y e ‑ l e n g t he f f e c t .C o n d u c t i o ne l e c t r o n sf l o wf 1omt h es o u r c eSt o t h ed r a i nD t h r o u g has e m i c o n d u c t i n gm a t e r i a lwhenap o t e n t i a li sa p p l i e d b e t w e e nt h e m .Whenanegati、e p o t e n t i a li sa p p l i e dt ot h ei n s u l a t e dg a t eG ,no c u r r e n tc a nAowt h r o u g hG ,b u tt h ea p p l i e dp o t e n t i a ll e a k si n t ot h es e m i c o n d u c t o r and r e p e l se l e c t r o n s .Thec h a n n e lw i d t hi sn a r r o w e d and t h ee l e c t r o nf l o w impededi np r o p o r t i o nt ot h eg a t ep o t e n t i a l .I ft h et h i c k n e s so ft h ed e v i c ei st o o l a r g e ,Debyes h i e l d i n gp r e v e n t st h eg a t ev o l t a g efromp e n e t r a t i n gf a re n o u g h . E s t i m a t et h emaximumt h i c k n e s so ft h ec o n d u c t i o nl a y e ro fan1 1 ‑ c h a n n e lFET i fi th a sdopingl e v e l{ p l a s m ad e n s i t y )o f1 0 2 2m へ is a troomt e m p e r a t u r e ,and i st c )b enomoret h a n1 0Debyel e n g t h st h i c k .( S e eF i g .P l ‑ 1 1 . ) PROBLEMS C h a p t e rTwo SINGLE‑PARTICLE MOTIONS INTRODUCTION 2 . 1 Whatmakesplasmasp a r t i c u l a r l yd i f f i c u l tt oa n a l y z ei st h ef a c tt h a tt h e d e n s i t i e sf a l li nani n t e r m e d i a t er a n g e .F l u i d sl i k ewatera r es odense t h a tt h emotionso fi n d i v i d u a lm o l e c u l e sdonothavet obec o n s i d e r e d . C o l l i s i o n sdominate,andt h es i m p l ee q u a t i o n so fordinaryf l u i ddynamics SU 伍ce. A tt h eo t h e r extreme i nv e r yl o w ‑ d e n s i t yd e v i c e sl i k et h e a l t e r n a t i n g ‑ g r a d i e n ts y n c h r o t r o n ,o n l ys i n g l e ‑ p a r t i c l et r a j e c t o r i e sneed bec o n s i d e r e d ;c o l l e c t i v eE 庇ects a r eo f t e nunimportant.Plasmasbehave sometimes l i k ef l u i d s , and sometimes l i k e ac o l l e c t i o no fi n d i v i d u a l p a r t i c l e s .Thef i r s ts t e pi nl e a r n i n ghowt od e a lw i t ht h i ss c h i z o p h r e n i c p e r s o n a l i t yi st ounderstandhows i n g l ep a r t i c l e sbehavei ne l e c t r i cand magneticf i e l d s .Thisc h a p t e rd i f f e r sfromsucceedingonesi nt h a tt h eE andBf i e l d sa r ea s s u m e dt ob ep r e s c r i b e dandnota圧ected byt h echarged p a r t i c l e s . UNIFORM E AND B FIELDS 2 . 2 E=O The ラ B 一一 d a v ”川 山一d I nt h i sc a s e , acharged p a r t i c l eh a sas i m p l ec y c l o t r o n gyration 目 e q u a t i o no fmotioni s 2 . 2 . 1 [2・ l] 1 9 r Taking 主 to bet h ed i r e c t i o no fB(B= Bz),wehave mv,=qBvヲ mv,= qBv, ( B nw.= 0 五x =お=一間 v, 2 1 GUIDING CENTER Single-Paγticle M o t i o n s [ 2 ‑ 2 ] ら= ~v, = (ぞf v, This d e s c r i b e s a simple harmonico s c i l l a t o ra tt h ec y c l o t r o nf r e q u e n c y , whichwed e f i n et obe ION ト三千| Larmoro r b i t si nam a g n e t i cf i e l d . FiGURE2 ‑ 1 [ 2 ‑ 3 ] By t h e convention we have chosen, We i sa l w a y sn o n n e g a t i v e .B i s 0 4g a u s s .Thes o l u t i o n measuredi nt e s l a ,orwebers/m2,au n i te q u a lt o1 2 ‑ 2 ]i sthen o fE q .[ v , . ,=v ょ exp (土 iwct +iδ'·') the 士 denoting t h es i g no fq .Wemaychooset h ephase8s ot h a t v ,=v ょ t =x tw t c m l v ,= ~v, =土一九=土 iv ム E 叫=千 qn w, キ [ 2 ‑ 4 b ] I n t e g r a t i n goncea g a i n ,wehave v . l iwl Y‑Yo α> c Thisd e s c r i b e sacir℃ ular o r b i taguidingc e n t e r( x 0 ,y 0 )whichi sf i x e d( F i g . 2 ‑ 1 ) .Thed i r e c t i o no ft h eg y r a t i o ni sa l w a y ssucht h a tt h emagneticf i e l d generatedbyt h echargedp a r t i c l ei so p p o s i t et ot h ee x t e r n a l l yimposed e d u c et h emagneticf i e l d ,and f i e l d .Plasmap a r t i c l e s ,t h e r e f o r e ,tendt or plasmasa r ed i a m a g n e t i c .In 旦ddition t ot h i smotion,t h e r ei sana r b i t r キ a r y v e l o c i t yL 且long Bwhichi sn o ta f f e c t e dbyB .Thet r a j e c t o r yo fac h a 1 キ g e d p a r t i c l ei nspacei s ,i ng e n e r a l ,ah e l i x . v' . . .' = 士一二 g 山E‘ F i n i t eE I fnowwea l l o wane l e c t r i cf i e l dtobep r e s e n t ,t h emotionw i l lbefound t obet h esumo ftwom o t i o n s :t h eu s u a lc i r c u l a rLarmorg y r a t i o np l u s ol i ei nt h ex‑z plane ad r i f to ft h eguidingcenter 目 We maychooseE t .Asb e f o r e ,t h ezcomponento fv e l o c i t yi su n r e l a t e dt ot h e s ot h a tE,=0 t r a n s v e r s ecomponentsandcanbet r e a t e ds e p a r a t e l y .Theequationo f motion1 snow [ 2 ‑ 5 ] av mdt=q(E+vラ B) We [2 司8] Wed e f i n et h eLαrmor r a d i u st obe whosezcomponenti s U ょ廿w ょ d v , q~ d t m~ z [ 2 ‑ 6 ] γL""::-=1qJB or Takingt h er e a lp a r to fE q .( 2 ‑ 5 ] ,wehave x‑Xo=Ti.S i nWei Y‑Yo 也、 [ 2 ‑ 4 a ] wherev.L i sap o s i t i v ec o n s t a n tdenotingt h espeedi nt h eplaneperpenュ d i c u l a rt oB .Then x-x 。= ‑z‑e ' ELECTRON qE二 = 土 rL COSWei [ 2 ‑ 7 ] v ,=一一 f +V,o 行1 [ 2 ‑ 9 ] 2 . 2 . 2 U ω 土 L 一一 一m q 九一 d Thisi sa s t r a i g h t f o r w a r da c c e l e r a t i o n alongB . The t r a n s v e r s e com『 ponentso fE q .[ 2 ‑ 8 ]a r e (2・ 10] dv d t ” ー」=り平 WrV. ‑ L 瓦 [2・ 13] E × B=B ×(v × B) =vB2‑B(vキB) v x=一w;vx (2 ・ ll] ジヲ=+we (~ι 土川)=叶号+ Vy) Eラ B/B2=vE [2・ 15] Wed e f i n et h i st obev E ,t h ee l e c t r i c f i e l dd r i f to ft h eguidingc e n t e r .I n magnitude,t h i sd r i f ti s 手(Vy +わ=市;(vy +わ s ot h a tE q . [2・ 11] i sreducedt ot h ep r e v i o u sc a s ei fwer e p l a c eVy by v y+(EJB).Equation[ 2 ‑ 4 ]i st h e r e f o r er e p l a c e dby iwt Eε (2・ 12] E.管 内 = ±iv.Le·-" 一正 TheLarmormotioni st h esamea sb e f o r e ,butt h e r ei ssuperimposeda d r i f tV g co ft h eguidingc e n t e ri nt h e‑yd i r e c t i o n( f o rE x>0)( F i g .2・2). E -一一ー- ( B -圃冒 T nuu c aZEE v x [2・ 14] Thet r a n s v e r s ecomponentso ft h i se q u a t i o na r e V.Lgc = Wecanw r i t et h i sa s ; , , , , E+vラ B=O Takingt h ec r o s sproductw i t hB ,wehave D i f f e r e n t i a t i n g ,wehave( f o rc o n s t a n tE ) Vx = V ょ Too b t a i nag e n e r a lformulaf o rV g c .wecans o l v eE q .[ 2 ‑ 8 ]i nv e c t o r v / d ttermi nE q .[2 ・ 8], s i n c et h i stermg i v e s form.Wemayomitthemd e , whichwea l r e a d y knowa b o u t . Then o n l yt h ec i r c u l a r motiona tw E q .[ 2 ‑ 8 ]becomes E(V/m) m VE = 五~ i示 [ 2 ‑ 1 6 ] I ti simportantt on o t et h a tVEi sindependento fq ,m,andv . L .The reasoni so b v i o u sfromt h ef o l l o w i n gp h y s i c a lp i c t u r e .Int h ef i r s th a l f ュ c y c l eo ft h eion’s o r b i ti nF i g .2 ‑ 2 ,i tg a i n senergyfromt h ee l e c t r i cf i e l d e n c e ,i nr L .I nt h esecondh a l f ‑ c y c l e ,i tl o s e s andi n c r e a s e si nuょ and, h energyandd e c r e a s e si nrL・ This d i f f e r e n c ei nr Lont h el e f tandr i g h t s i d e so ft h eo r b i tc a u s e st h ed r i f t .VE・ A n e g a t i v ee l e c t r o ng y r a t e si nt h e o p p o s i t ed i r e c t i o nbuta l s og a i n senergyi nt h eo p p o s i t ed i r e c t i o n ;i tends upd r i f t i n gi nt h esamed i r e c t i o n. a sani o n .Forp a r t i c l e so ft h esame v e l o c i t ybutd i f f e r e n tm a s s ,t h el i g h t e ronew i l lhaves m a l l e rr Landhence d r i f tl e s sperc y c l e .However,i t sg y r a t i o nf r e キ q u e n c yi sa l s ol a r g e r ,and t h etwoe f f e c t se x a c t l yc a n c e l .Twop a r t i c l e so ft h esamemassbutd i f f e r e n t energywouldキ h a v et h esamew e ‑Thes l o w e ronew i l lhaves m a l l e rr Land henceg a i nl e s senergyfromEi nah a l f ‑ c y c l e .However,f o rl e s se n e r g e t i c p a r t i c l e st h ef r a c t i o n a lchangei nr Lf o rag i v e nchangei nenergyi s l a r g e r ,andt h e s etwoe f f e c t sc a n c e l(Problem2 ‑ 4 ) . Thet h r e e ‑ d i m e n s i o n a lo r b i ti ns p a c ei st h e r e f o r eas l a n t e dh e l i x w i t hchangingp i t c h( F i g .2 ・3). G r a v i t a t i o n a lF i e l d 2 . 2 . 3 ION RE2 ・2 P a r t i c l ed r i f t si nc r o s s e de l e c t r i candm a g n e t i cf i e l d s . ELECTRON Theforegoingr e s u l tcanbea p p l i e dt oo t h e rf o r c e sbyr e p l a c i n gqEi n t h ee q u a . t i o no fmotion[ 2 ‑ 8 ]byag e n e r a lf o r c eF .Theguidingc e n t e r 23 S i n g l e ‑ P a r t i c l e M o t i o n s ·~· 24 C h a p t e r 2 5 ExB S i n g l e ‑ P a r t i c l i M o t i o r u T町O ①Uj__υ lluu!.000000000000000φ ION @8 B ELECTRON Thed r i f to fag y r a t i n gp a r t i c l ei nag r a v i t a t i o n a lf i e l d . FIGURE2 ‑ 4 o tn e g l i g i b l e ,i sindependentof c e n t r i f u g a lf o r c e .Thisf o r c e ,whichi sn q .[ 2 ‑ 1 8 ] . mass; t h i si swhywedid nots t r e s st h em dependenceofE C e n t r i f u g a lf o r c ei st h eb a s i sofaplasmai n s t a b i l i t yc a l l e dt h e" g r a v i t a ュ tional” instability, whichhasnothingt odowithr e a lg r a v i t y . FIGURE2 ‑ 3 w …f一 d r i f tcausedbyFi stheq ( 2 ‑ 1 7 ] 2・ 1. Computer Lf o rt h ef o l l o w i n gc a s e si fu 1 1i sn e g l i g i b l e : l e c t r o ni nt h eearth ’s m a g n e t i cf i e l do f5xI 0• T. ( a )A 10・ke Ve Inp a r t i c u l a r ,i fFist h ef o r c eofg r a v i t ymg,t h e r ei sad r i f t ( b )キ As o l a rwindp r o t o nw i t hs t r e a m i n gv e l o c i t y300k m / s e c ,B =5X 1 09T . ( c )A 1 ‑ k e V He+ i o ni nt h es o l a ratmosphere n e a r as u n s p o t , where B = 5ラ 1 0 ‑ 2 T . ( 2 ‑ 1 8 ] Thisi ss i m i l a rt ot h ed r i f tVEi nt h a ti ti sperpendiculart obotht h ef o r c e andB,buti td i f f e r si noneimportantr e s p e c t .Thed r i f tv gchangess i g n h a r g e .Underag r a v i t a t i o n a lf o r c e ,i o n sande l e c t r o n s witht h eparticle ’s c d r i f ti nopposited i r e c t i o n s ,sot h e r ei san e tcurrentd e n s i t yi ntheplasma givenby ( d )A 3.5‑MeVHe++a s hp a r t i c l ei nan ふT DTf u s i o nr e a c t o r . I nt h eTFTR(TokamakF u s i o nT e s tR e a c t o r )a tP r i n c e t o n ,t h eplasmaw i l l beh e a t e dbyi n j e c t i o no f2 0 0 ‑ k eVn e u t r a ldeuteriuma t o m s ,w h i c h ,a f t e re n t e r i n g t h em a g n e t i cf i e l d ,a r ec o n v e r t e dt o200‑keVDi o n s(A= 2 )byc h a r g ee x c h a n g e . . 6m i st h eminorr a d i u so f Thesei o n sa r ec o n f i n e do n l yi frL 《 α, where a= 0 t h et o r o i d a lp l a s m a .Computet h emaximumLarmorr a d i u si na5‑Tf i e l dt os e e i ft h i si ss a t i s f i e d . 2・2. ( 2 ‑ 1 9 ] 2 ‑ 3 .Ani o ne n g i n e( s e eF i g .1 ‑ 6 )h a sa 1 ‑ Tm a g n e t i cf i e l d ,andahydrogen plasmai st obes h o to u ta tanExBv e l o c i t yo f1000k m / s e c .Howmuchi n t e r n a l e l e c t r i cf i e l dmustbep r e s e n ti nt h ep l a s m a ? Thep h y s i c a lreasonf o rt h i sd r i f t( F i g .2 ‑ 4 )i sagaint h echangei nLarmor r a d i u sa st h ep a r t i c l eg a i n sandl o s e senergyi nt h eg r a v i t a t i o n a lf i e l d . Nowt h ee l e c t r o n sg y r a t ei nt h eoppositesenset othei o n s ,butt h ef o r c e onthemi si nt h esamed i r e c t i o n ,sot h ed r i f ti si nt h eopposited i r e c t i o n . h e ThemagnitudeofV gi su s u a l l yn e g l i g i b l e(Problem2・6), butwhent l i n e soff o r c ea r ecurved,t h e r ei sane f f e c t i v eg r a v i t a t i o n a lf o r c eduet o 2 ‑ 4 .Showt h a tuEi st h esamef o rtwoi o n so fe q u a lm a s sandc h a r g eb u td i f f e r e n t e n e r g i e s ,byu s i n gt h ef o l l o w i n gp h y s i c a lp i c t u r e( s e eF i g .2 ‑ 2 ) .Approximatet h e r i g h th a l fo ft h eo r b i tbyas e m i c i r c l ec o r r e s p o n d i n gt ot h ei o nenergya f t e r a c c e l e r a t i o nbyt h eEf i e l d ,andt h el e f th a l fbyas e m i c i r c l ec o r r e s p o n d i n gt o t h ee n e r g ya f t e rd e c e l e r a t i o n . Youmayassumet h a tE i sw e a k ,s ot h a tt h e f r a c t i o n a lchangei nu. ci ss m a l l . gラB j=n(M+m)]j"2 PROBLEMS 26 Supposee l e c t r o n so b e yt h eBoltzmannr e l a t i o no fProblemI5i nac y l i n d r i ュ c a l l ys y m m e t r i cp l a s m acolumni nw h i c hn ( r )v a r i e sw i t has c a l el e n g t hλ , that i s ,i i n / i i r= -n /λ 2・5. Chapleγ Two ( a ) UsingE= Vφ, find に久久見)切 t h er a d i a le l e c t r i cf i e l df o rg i v e nA . B ①①①、① ①①① ( b )Fore l e c t r o n s ,showthat 白 nite Larmorr a d i u se百ects a r el a r g ei fvE i sa sl a r g e a sU山・ Specifically, showt h a tr L= 2 Ai fvE= v , h . マ!Bl ①①①① ( c )I s( b )a l s ot r u ef o ri o n s ? 宅〆i x 27 S i n g l e ‑ P a r t i c l e M o t i o n s 。 、 222..Rllllllllllo..Rll J Thed r i f to fag y r a t i n gp a r t i c l ei nanonuniformm a g n e t i cf i e l d . FIGURE2・5 H i n t :Don o tu s ePoisson ’s e q u a t i o n . 2・6. S upposet h a tas o ‑ c a l l e dQ‑machineh a sau n i f o r mf i e l do f0 . 2T anda c y l i n d r i c a lp l a s m aw i t hKT,=KT,= 0 . 2e V .Thed e n s i t yp r o f i l ei sfounde x p e r i ュ m e n t a l l yt ob eo ft h eform e x a c t l y .Tog e tanapproximateanswer,i ti scustomaryt oexpandi nt h e ,whereL i st h es c a l el e n g t ho ft h einhomogeneity.This s m a l lr a t i ordL t y p eo ft h e o r y ,c a l l e do r b i tt h e o r y ,canbecomeextremelyi n v o l v e d .We s h a l lexamineonlyt h es i m p l e s tc a s e s ,whereonlyoneinhomogeneity o c c u r sa tat i m e . n= n 0exp[ e x p( ‑ r 2/ a2 ) I ] Assumet h ed e n s i t yo b e y st h ee l e c t r o nBoltzmannr e l a t i o nn= n 0exp(eφ/ K1二). ( a )C a l c u l a t et h emaximumvEi fa = Ic m . VB. lB :Grad‑BD r i f t 2 . 3 . l ( b )Comparet h i sw i t hv .duet ot h eearth’S g r a v i t a t i o n a lf i e l d . ( c )Towhatv a l u ec a nB .b el o w e r e db e f o r et h ei o n so fp o t a s s i u m(A= 3 9 ,Z = I ) h a v eaLarmorr a d i u se q u a lt oa? 2 ‑ 7 .Anu n n e u t r a l i z e de l e c t r o nbeamh a sd e n s i t yn ,= 1 0 1 4m 3 andr a d i u sa= Icmandf l o w sa l o n ga2‑Tm a g n e t i cf i e l d .I fBi si nt h e+zd i r e c t i o nandEi s t h ee l e c t r o s t a t i cf i e l dduet ot h ebeam’s c h a r g e ,c a l c u l a t et h emagnitudeand i g .P 2 ‑ 7 . ) d i r e c t i o no ft h eExBd r i f tatγ = ι (See F > 2a Heret h el i n e so ff o r c e *a r es t r a i g h t ,butt h e i rd e n s i t yi n c r e a s e s ,s a y ,i n theyd i r e c t i o n( F i g .2 ‑ 5 ) .Wecana n t i c i p a t et h er e s u l tbyusingoursimple p h y s i c a lp i c t u r e .Theg r a d i e n ti nI BI c a u s e st h eLarmorradi山 to be l a r g e ra tt h ebottomo ft h eo r b i tthana tt h et o p ,andt h i sshouldl e a d t oad r i f t ,i no p p o s i t ed i r e c t i o n sf o ri o n sande l e c t r o n s ,perpendicular r i f tv e l o c i t yshouldo b v i o u s l ybep r o p o r t i o n a l t obothB andVB.Thed ov . L . t ordLandt Considert h eLorentzf o r c eF= qvxB,averagedoverag y r a t i o n . C l e a r l y ,F x= 0 ,s i n c et h ep a r t i c l espendsa smuchtimemovingupa sdown. Wewisht oc a l c u l a t ef , .i nanapproximatef a s h i o n ,byusingt h eundistuγbed oγbit o ft h ep a r t i c l et of i n dt h ea v e r a g e .Theundisturbedo r b i ti sgiven by Eqs ・[ 2-4] andキ[ 2 ‑ 7 ]f o rauniformB f i e l d .Takingt h er e a lp a r to f Eq.[ 2 ‑ 4 ] ,wehave r i J B l F ,= ‑qvxB,(y)= ‑ q v . L ( c o s w , t ) lBo 土 γL(cos w,t ) 百j FIGUREP2‑7 2.3 NONUNIFORM B FIELD Nowt h a ttheconceptofaguidingc e n t e rd r i f ti sf i r m l ye s t a b l i s h e d ,we cand i s c u s sthemotiono fp a r t i c l e si ninhomogeneousfields‑EandB f i e l d swhichvaryi nspaceort i m e .Foruniformf i e l d swewerea b l et o o b t a i ne x a c te x p r e s s i o n sf o rt h eguidingc e n t e rd r i f t s .Assoona swe introduceinhomogeneity,t h eproblembecomest o ocomplicatedt os o l v e (2・201 wherewehavemadeaTaylorexpansiono fB f i e l daboutt h ep o i n t x 0=0 ,y 0=0andhaveusedE q .[ 2 ‑ 7 ] : B = Bo+( rキV)B+・-- ( 2 ‑ 2 1 ] B,=Bo+y ( a B J i l y )+・.. *Themagnettc 自eld l i n e sa r eo f t e nc a l l e d“ lines o ff o r c e . "Theya r en o tl i n e so ff o r c e . Them i s n o m e ri sp e r p e t u a t e dh e r et op r e p a r et h es t u d e n tf o rt h et r e a c h e n e so fh i s p r o f e s s i o n , ) (2 ・22] Theguidingc e n t e rd r i f tv e l o c i t yi st h e n v gc lFXB 1 F, A 干 VJ.TL 1iJB, ‑• q B, qI BI‑ B 2a y 一一- --ーで?τ一一一ー一--ーー一一一一一一一 29 S i n g l e ‑ P a r t i c l e M o t i o n s d F r t ,=干qvょγL~(iJB/iJy) - a -- E ・E・-EEE ・ Two Thisexpansiono fc o u r s er e q u i r e sr dL < 1, whereL i st h es c a l el e n g t h o faBJiJy.Thef i r s ttermo fE q .( 2 ‑ 2 0 ]a v e r a g e st oz e r oi nag y r a t i o n , andt h eaverageo fc o s 2w , ti s! ,sothat 、 V C h a p t e r rV1 J,d浮ヨ hJ仏 d卑 m? 28 (2 ・23] R c wherewehaveusedE q .( 2 ‑ 1 7 ] .S i n c et h ec h o i c eo ftheya x i swasa r b i t r a r y , t h i scanbeg e n e r a l i z e dt o 一B B 一 X VT i L Va 一2 士 u V B 一一 V B 一 l Ac u r v e dm a g n e t i cf i e l d . FIGURE2 ‑ 6 ( 2 ‑ 2 4 ] Accordingt oE q .( 2 ‑ 1 7 ] .t h i sg i v e sr i s et oad r i f t Thish a sa l lt h edependenceswee x p e c t e dfromt h ep h y s i c a lp i c t u r e ; a r i s i n gfromt h ea v e r a g i n g )wasn o tp r e d i c t e d .Note o n l yt h ef a c t o r~ ( thatthe 土 stands f o rt h es i g no ft h ec h a r g e ,andl i g h t f a c eB s t a n d sf o r IB 卜 The q u a n t i t yv v 8i sc a l l e dt h eg;rad‑Bbψ ; it i si no p p o s i t ed i r e c t i o n s f o ri o n sande l e c t r o n sandc a u s e sac u r r e n tt r a n s v e r s et oB .Ane x a c t c a l c u l a t i o no fvv8 wouldr e q u i r eu s i n gt h ee x a c to r b i t ,i n c l u d i n gt h e d r i f t ,i nt h ea v e r a g i n gp r o c e s s . 2 . 3 . 2 CurvedB:CurvatureDrift Hereweassumet h el i n e so ff o r c et obecurvedw i t hac o n s t a n tr a d i u s o fc u r v a t u r eR e .andwet a k eI BI t obec o n s t a n t( F i g .2 ‑ 6 ) .Suchaf i e l d doesn o tobeyMaxwell ’S e q u a t i o n si navacuum,s oi np r a c t i c et h egrad‑B d r i f tw i l la l w a y sbeaddedt ot h ee f f e c td e r i v e dh e r e .A guidingc e n t e r d r i f ta r i s e sfromt h ec e n t r i f u g a lf o r c ef e l tbyt h ep a r t i c l e sa st h e ymove alongt h ef i e l dl i n e si nt h e i rthermalm o t i o n .I fv~ d e n o t e st h eaverage s q u a r eo ft h e componento f random v e l o c i t y alongB ,t h e average c e n t r i f u g a lf o r c ei s F 2 mv11, ~ 2 民c cf=一二一r =mv11 三す 4‘、 c .、 c (2・ 25] v , ,= 2 ̲s三~=竺tl R,× B K q B2 qB2 R ; ( 2 ‑ 2 6 ] Thed r i f tV Ri sc a l l e dt h ecurvature 佐伯 Wemustnowcomputet h egrad‑B d r i f twhichaccompaniest h i s whent h ed e c r e a s eo fI BIw i t hr a d i u si stal叩1 i n t oa c c o u n t .I navacuum, wehaveV XB= 0 .I nt h ec y l i n d r i c a lc o o r d i n a t e so fF i g .2 ‑ 6 ,V ラB h a s o n l yazcomponent,s i n c eB h a so n l ya( }componentandVBo n l yanγ component.Wethenhave Ia (VラB ) ,=ーァ (rB6) = 0 γ Boe x : ュ dT r ( 2 ‑ 2 7 ] Thus IBI せ V I E i R , I B I =疋 (2・ 28] UsingE q .( 2 ‑ 2 4 ] .wehave r R, 1v~ Reラ B lm oRcXB V v B=平一己主B × IBI 寸=±ーニー了一一 -vi -寸7 2B Re 2w, K,15 2q R,B ( 2 ‑ 2 9 ] 主廷す恥志向て一 30 Addingt h i st oV R ,wehavet h et o t a ld r i f ti nacurvedvacuumf i e l d : C h a p t e r Two m R,xB /。 ‑ ‑ = ‑ . . ‑ ‑ ‑ ‑ o ‑ ‑ 1V 『 . .+Vu-~n = ‑ q R;B" \ ” V , , 1 。\ 2 ~/ +- v~ I 2 ‑ v , h AγL [ 2 ‑ 3 0 a ] =土 τご v,hy 日ζ We 1a ~l aB. ーァ(γB~ ) +て二= O r oγ dz [2 ・ 30] I ti su n f o r t u n a t et h a tt h e s ed r i f t sa d d .Thismeanst h a ti fonebendsa magneticf i e l di n t oat o r u sf o rt h epurposeo fc o n f i n i n gathermonuclear p l a s m a ,t h ep a r t i c l e sw i l ld r i f to u to ft h et o r u snom a t t e rhowonej u g g l e s t h etemperaturesandmagneticf i e l d s . ForaMaxwelliand i s t r i b u t i o n ,E [ 1 ‑ 7 ]and[ 1 ‑ 1 0 ]i n d i c a t et h a t 一空 iーす , qs. I Iand2vJ. a r eeache q u a lt oKT/m,s i n c euょ involves twod e g r e e so f freedom.E q u a t i o n s[2 “ 3] and[ l ‑ 6 ]thena l l o wu st ow r i t et h ea v e r a g e c u r v e d ‑ f i e l dd r i f ta s VR+VB=土 τご一一 y Wecano b t a i nB , .fromVキ B= 0 : [2 ・ 31] I foBJoz i sg i v e na tr= 0anddoesnotv a r ymuchw i t hr , we h ave approximately γB,=-r γ誓ρ =-抗告l=O [2・ 32] B,= - ~r[担=O Thev a r i a t i o no fI B Iwithr causesagrad‑B driftofguidingcenters aboutt h ea x i so fsymmetry,butt h e r ei snor a d i a lgrad‑Bd r i f t ,b e c a u s e i J B / a O=0 .Thecomponentso ft h eLorentzf o r c ea r e Kc f三= q (v6B,‑v J { i J ) wherey herei st h ed i r e c t i o no fReX B .Thisshowst h a tVR+vadepends ont h echargeo ft h es p e c i e sbutn o toni t sm a s s . ① F6= q(‑v,B,+v , B , ) [2・ 33] ②③ λ =q ( v , f f o‑VoB,) ④ 2 . 3 . 3 V B l ! B :MagneticMirrors Nowwec o n s i d e ramagneticf i e l dwhichi sp o i n t e dp r i m a r i l yi nt h ez d i r e c t i o nandwhosemagnitudev a r i e si nt h ezd i r e c t i o n .L e tt h ef i e l d bea x i s y m m e t r i c ,w i t hB6= 0 ando / i J O= 0 .S i n c et h el i n e so ff o r c e convergeandd i v e r g e ,t h e r ei sn e c e s s a r i l yacomponentB,( F i g .2 ‑ 7 ) .We w i s ht oshowt h a tt h i sg i v e sr i s et oaf o r c ewhichcant r a pap a r t i c l ei n amagneticf i e l d . Twotermsv a n i s hi fB6= 0 ,andterms 1and2g i v er i s et ot h eu s u a l Larmorg y r a t i o n .Term3v a n i s h e sont h ea x i s ;wheni tdoesn o tv a n i s h , t h i sa z i m u t h a lf o r c ec a u s e s :ad r i f ti nt h er a d i a ld i r e c t i o n .Thisd r i f t merelymakest h eg u i d i n gc e n t e r sf o l l o wt h el i n e so ff o r c e .Term4i s t h eonewea r ei n t e r e s t e di n .UsingE q .[ 2 ‑ 3 2 ] ,weo b t a i n え= ~qvor(aBJaz) [2・ 34] 八千 Wemustnowa v e r a g eo v e roneg y r a t i o n . Fors i m p l i c i t y ,c o n s i d e ra p a r t i c l ewhoseg u i d i n gc e n t e rl i e sont h ea x i s .Thenv6 i sac o n s t a n t duringag y r a t i o n ;dependingont h es i g no fq ,v 6is 平Uょ・ Since r= r L , t h ea v e r a g ef o r c ei s ーー一一ーーーー・・F I ¥ z 一 1 2 aB, 1 v~ aB~ 2 We o z 1mえ aB, 2B o z F,= 平一qリL一ー=平一q 一一=一一一一一 a z [2・ 35] Wed e f i n et h emagneticmomento ft h eg y r a t i n gp a r t i c l et obe FIGURE2・7 D r i f to fap町tide i nam a g n e t i cm i r r o rf i e l d . | μ 三かえ/BI (2・ 36] Single” Particle M o t i o n s 32 s ot h a t Cha骨ter F ,=一µ(aBJaz) Two Thisi sas p e c i f i cexampleo ft h ef o r c eon 旦 i ng e n e r a lcanbew r i t t e n diamagnetic p a r t i c l e ,which Fu =一µ aB/as = 一µ. VuB ‑ r r v ie w e lv i e lmv μ =一一E一一一=一一一-=一一一一 We 2 7 T 2 We 2 B As t h ep a r t i c l e moves i n t or e g i o n so fs t r o n g e ro rweakerB ,i t s Larmorr a d i u sc h a n g e s ,butμγ·emains i n v a r i a n t .Toprovet h i s ,c o n s i d e r t h ecomponento ft h eequationo fmotionalongB : d v u d t aB μ キa s [2・ 39] M u l t i p l y i n gbyv uonthel e f tandi t se q u i v a l e n td s /d tont h er i g h t ,wehave d v n d/ l 9¥ aBd s dB ¥‑mvu)=一μ 一一=一μ 一 d t d t¥ 2 ' J a sd t d t mv1戸!= [ 2 ‑ 4 0 ] Hered B / d ti st h ev a r i a t i o no fB a sseenbyt h ep a r t i c l e ;B i t s e l fi s c o n s t a n t .Theparticle’S energymustbec o n s e r v e d ,s owehave dnmtl~ +_!_m11~ ¥= ! ! . J_!_mV~ +U D )= 0 d t¥ 2 キ キ ‑ ‑ u 2 ムJ d t¥ 2 " . J Bπ1 [ 2 ‑ 3 8 ] whered si sal i n eelementalongB .Notet h a tt h ed e f i n i t i o n( 2 ‑ 3 6 ]i st h e samea st h eu s u a ld e f i n i t i o nf o rt h emagneticmomento facurrentloop witha r e aA andc u r r e n t/ :オ =I A .Int h ec a s eo fas i n g l ychargedi o n , Ii sgeneratedbyachargeecomingaroundw)27r t i m e s as e c o n d : I=e w c / 2 T T .TheareaA i sT T r E= -rrv~ /w~. Thus 符1 一一ー= 径三診 [ 2 ‑ 3 7 ] 33 S i n g l e ‑ P a r t i c l e M o t i o n s [ 2 ‑ 4 1 ] Ap l a s m at r a p p e db e t w e e nm a g n e t i cm i r r o r s . FIGURE2 ・8 motion,i ts e e sani n c r e a s i n gB,andt h e r e f o r ei t sv.L musti n c r e a s ei n ordert okeepオ c o n s t a n t .S i n c ei t st o t a lenergymustremainc o n s t a n t , v umustn e c e s s a r i l yd e c r e a s e .I fB i shighenoughi nt h e“ throat” of t h e ue v e n t u a l l ybecomesz e r o ;andt h ep a r t i c l eis “ reflected ” back m i r r o r ,v t ot h ew e a k ‑ f i e l dr e g i o n .I ti s ,o fc o u r s e ,t h ef o r c eF uwhichc a u s e st h e r e f l e c t i o n .Thenonuniformf i e l do fasimplep a i ro fc o i l sformstwo magneticm i r r o r sbetweenwhichaplasmacanbetrapped ( F i g .2 ‑ 8 ) . Thise f f e c tworksonbothi o n sande l e c t r o n s . Thetrappingi snotp e r f e c t ,however.Fori n s t a n c e ,ap a r t i c l ew i t h Uム= 0w i l lhavenomagneticmomentandw i l lnotf e e lanyf o r c ealong . L / v na tt h emidplane( B=Bo)w i l la l s oescape B .A p a r t i c l ew i t hs m a l lv sn o tl a r g eenough. Forg i v e nB0andB m, i ft h emaximumf i e l dBmi whichp a r t i c l e sw i l le s c a p e ?A p a r t i c l ew i t huょ = v ムo andv u=v u oa tt h e midplanew i l lhavev ょ= v~ andv u=0a ti t sturningp o i n t .Lett h ef i e l d h ei n v a r i a n c eofオy i e l d s beB ’ there. Thent ;間百i。/Bo= ~mv~2 / B’ Conservationo fenergyr e q u i r e s 1 2 2 .2 2 v . L = v ょ0 寸 VUo = " V o WithE q .[ 2 ‑ 4 0 ]t h i sbecomes [ 2 ‑ 4 3 ] [ 2 ‑ 4 4 ] CombiningE q s .( 2 ‑ 4 3 ]and( 2 ‑ 4 4 ] ,wef i n d dB d μ 一+ー (µB) = 0 d t d t s ot h a t d オ / d t= 0 Bn n V~n n Jj vム ゴ=一苦= [ 2 ‑ 4 2 ] Thei n v a r i a n c eofオi st h eb a s i sf o roneo ft h eprimaryschemesf o r plasmaconfinement :・ the m a g n e t i cm i r r o r .Asap a r t i c l emovesfroma w e a k ‑ f i e l dr e g i o nt oas t r o n g ‑ f i e l dr e g i o ni nt h ecourseo fi t sthermal V~の。 n " ‑T=sinιO [2・ 45] U0 where) (i st h ep i t c ha n g l eo ft h eo r b i ti nt h ew e a k ‑ f i e l dr e g i o n .P a r t i c l e s w i t hs m a l l e r( )w i l lmirrori nr e g i o n so fhigherB.I f) (i st o os m a l l ,B ’ exceedsBm;andt h ep a r t i c l edoesnotmirrora ta l l .ReplacingB ’ by Bm i nE q .[ 2 ‑ 4 5 ] ,wes e et h a tt h es m a l l e s t ( )o faconfinedp a r t i c l ei sg i v e nby s i n 2Om=Bo/Bm 三 l/Rm [ 2 ‑ 4 6 ] 34 C h a p t e r Vu 35 ( a ) Computet h ei o na n キ de l e c t r o nVBd r i f tv e l o c i t i e s . Two Single-Paγticle ( b )Doesane l e c t r o nd r i f te a s t w a r do rw e s t w a r d ? ~、 M o t i o n s ( c ) Howl o n gd o e si tt a k eane l e c t r o nt oe n c i r c l et h ee a r t h ? 、 ( d )Computet h er i n gc u r r e n td e n s i t yi nA/m2. N o t e :Thec u r v a t u r ed r i f ti sn o tn e g l i g i b l eandw i l la f f e c tt h en u m e r i c a la n s w e r , b u tn e g l e c ti ta n y w a y . v vx FIGURE2 ‑ 9 Thel o s sc o n e . ど一人 y whereRmi sthemirγ·or r a t i o .Equation[ 2 ‑ 4 6 ]d e f i n e st h eboundaryofa regioni nv e l o c i t yspacei nt h eshapeofac o n e ,c a l l e dal o s sc o n e( F i g . 2・9). P a r t i c l e sl y i n gwithinthel o s sconea r enotc o n f i n e d .Consequently, amirror‑confinedplasmai sneveri s o t r o p i c .Notet h a tthel o s sconei s .Withoutc o l l i s i o n s ,bothi o n sande l e c t r o n sare independentofqorm e q u a l l yw e l lc o n f i n e d .Whenc o l l i s i o n so c c u r ,p a r t i c l e sarel o s twhenthey changet h e i rp i t c hanglei nac o l l i s i o nanda r es c a t t e r e di n t othel o s s cone.G e n e r a l l y ,e l e c t r o n sarel o s tmoree a s i l ybecausetheyhaveahigher c o l l i s i o nfrequency. The magnetic mirror was f i r s t proposed by Enrico Fermi a sa mechanismf o rthea c c e l e r a t i o nofcosmicr a y s .Protonsbouncingbetween magneticmirrorsapproachingeachothera thighv e l o c i t ycouldgain energya teachbounce.Howsuchmirrorscoulda r i s ei sanothers t o r y . A furtherexampleofthemirrore f f e c ti st h econfinementofp a r t i c l e s i ntheVanAllenb e l t s .Themagneticf i e l doft h ee a r t h ,beingstronga t thep o l e sandweaka tt h ee q u a t o r ,formsan a t u r a lmirrorwithrather m. l a r g eR PROBLEMS 2 ‑ 8 . s日ppose t h eearth’s m a g n e t i cf i e l di s3xI O5Tatt h ee q u a t o randf a l l so f f a sl / r ' ,a sf o rap e r f e c td i p o l e .L e tt h e r eb eani s o t r o p i cp o p u l a t i o no fl ‑ e V p r o t o n sand30・keV e l e c t r o n s ,e a c hw i t hd e n s i t yn = 1 0 7m‑3a tr= 5e a r t hr a d i i i nt h ee q u a t o r i a lp l a n e . 2・9. Ane l e c t r o nl i e sa tr e s ti nt h em a g n e t i cf i e l do fani n f i n i t es t r a i g h tw i r e c a r r y i n gac u r r e n tI .Att= 0 ,t h ew i r ei ss u d d e n l yc h a r g e dt oap o s i t i v ep o t e n t i a l φwithout a百ecting I .Thee l e c t r o ng a i n senergyfromt h eelectric 自eld and b e g i n st od r i f t . ( a ) Drawadiagramshowingt h eo r b i to ft h ee l e c t r o nandt h er e l a t i v ed i r e c t i o n s ,VE, v v B .andv R o fI ,B ( b )C a l c u l a t et h em a g n i t u d e so ft h e s ed r i f t sa tar a d i u so flcmi fI= 500A , φ = 4 60V ,andt h er a d i u so ft h ew i r ei slmm.Assumet h a tφis h e l da t0Von t h evacuumchamberw a l l sI Ocma w a y . H i n t :Agoodi n t u i t i v ep i c t u r eo ft h emotioni sneededi na d d i t i o nt ot h ef o r m u l a s g i v e ni nt h et e x t . 2 ‑ 1 0 .A 20‑keVd e u t e r o ni nal a r g em i r r o rf u s i o nd e v i c eh a sap i t c ha n g l e ( }o f 45。 at t h emidp l a n e ,whereB =キ o . 7T.Computei t sLarmorr a d i u s . Ap l a s m aw i t hani s o t r o p i cv e l o c i t yd i s t r i b u t i o ni sp l a c e di nam a g n e t i c m i r r o rt r a pw i t hm i r r o rr a t i oRm= 4 .Therea r enoc o l l i s i o n s ,s ot h ep a r t i c l e si n t h el o s scones i m p l ye s c a p e ,andt h er e s tr e m a i n ‑t r a p p e d .Whatf r a c t i o ni s t r a p p e d ? 2・ 11. Ac o s m i cr a yp r o t o ni st r a p p e dbetweentwomovingm a g n e t i cm i r r o r s w i t hRm= 5andi n i t i a l l yh a sW = lk eVanduょ= v 1 1a tt h emidp l a n e .Eachm i r r o r Okm/sec( F i g .2 ‑ 1 0 ) . movest o w a r dt h emidplanew i t hav e l o c i t yVm = I 2・ 12. ヅ「一一一一一雨示一一一一- ~vm \\一一一一一一一一一一一一一一一メ L= 1010km A c c e l e r a t i o no fcosmicr a y s . FIGURE2・ 10 U O一間 ・ u 一一 x 一肌 q + E 1 .T r e a tt h em i r r o r sa sf l a tp i s t o n sandshowt h a tt h ev e l o c i t yg a i n e da te a c h bouncei s2 v m . 2 .Computet h enumbero fb o u n c e sn e c e s s a r y . 3 .Computet h et i m eTitt a k e st ot r a v e r s eLt h a tmanyt i m e s .F a c t o r ‑ o f ‑ t w o a c c u r a c yw i l lsu 伍ce. U U x ( b ) Howl o n gw i l li tt a k et or e a c ht h a tenergyコ 一一 . 吋一 T日。 37 whoset r a n s v e r s ecomponentsa r e 空間 ( a )U s i n gt h el o s sc o n ef o r m u l aandt h ei n v a r i a n c eo fμ,日nd t h ee n e r g yt o w h i c ht h ep r o t o nw i l lb ea c c e l e r a t e db e f o r ei te s c a p e s . Chα争ter 実喰Ftp 36 」 , 9 v ,=一 w~v. 土 w,8 2E,(x) 2 ii,= ーω¢ 町一 w,--s 2 . 4 NONUNIFORME FIELD Nowwe l e tt h e magnetic f i e l d be uniform and t h ee l e c t r i cf i e l d be nonuniform.Fors i m p l i c i t y ,weassumeEt obei nt h exd i r e c t i o nandt o v a r ys i n u s o i d a l l yi nt h exd i r e c t i o n( F i g .2 ‑ 1 1 ) : E=E0(coskx )圭 m(dv/dt)= q[E(x)+vX B J - L x=x。+ r L s i nwJ (2・ 51] [2・ 52] FromE q s .[ 2 ‑ 5 1 ]and[ 2 ‑ 4 7 ] ,wenowhave ii,= 一ω 内 2"キ0 w , ~cos 的。+ r L s i nw , t ) ( 2 ‑ 5 3 ] A n t i c i p a t i n gt h er e s u l t ,wel o o kf o ras o l u t i o nwhichi st h esumo fa ,andas t e a d yd r i f tVE・ Since wea r ei n t e r e s t e di nf i n d i n g g y r a t i o na tw a k eoutt h eg y r a t o r ymotionbyaveragingover ane x p r e s s i o nf o rV」,wet ,=0.InEq.[2‑53],theoscillating ac y c l e .Equation[ 2 ‑ 5 0 ]theng i v e su l e a r l ya v e r a g e st oz e r o ,andwehave term c え= 0 =ーω九 - w ;~<:州日L Si 3 Ex (2・ 50] v , fppp y ( 2 ‑ 4 8 ] (2 ・ 49] HereE,(x)i st h ee l e c t r i cf i e l da tt h ep o s i t i o no ft h ep a r t i c l e .Toe v a l u a t e t h i s ,weneedt oknowt h eparticle’s o r b i t ,whichwea r et r y i n gt os o l v e ft h ee l e c t r i cf i e l di sweak,wemay,a sanapproximaュ f o ri nt h ef i r s tp l a c e .I t i o n ,uset h eundisturbedoγbit t oe v a l u a t eE,(x).Theo r b i ti nt h ea b s e n c e i e l dwasg i v e ni nE q .[ 2 ‑ 7 ] : o ft h eE f ( 2 ‑ 4 7 ] Thisf i e l dd i s t r i b u t i o nhasawavelengthA=2 ‑ r r / kandi st h er e s u l to fa s i n u s o i d a ld i s t r i b u t i o no fc h a r g e s ,whichweneednots p e c i f y .Inp r a c t i c e , suchacharged i s t r i b u t i o ncana r i s ei naplasmaduringawavemotion. Theequationo fmotioni s S i n g l e ‑ P a r t i c l e M o t i o n s ( 2 ‑ 5 4 ] Expandingt h ec o s i n e ,wehave B qJ e、吋吋 ( c o sk( x 0+r Ls i nw , t )=cos(kx0)c o s( k r Ls i nw , t ) ‑s i n( k x 0 )s i n(kγL s i nw , t ) I tw i l lsu 伍ce t ot r e a tt h es m a l lLarmorr a d i u sc a s e ,krL くく 1 .TheTaylor expans10ns cos€ = 1‑~€2 +・ FIGURE2 ‑ 1 1 D r i f to fag y r a t i n gp a r t i c l ei nanonuniforme l e c t r i cf i e l d . [ 2 ‑ 5 5 ] sin€ = ε +・・・ ( 2 ‑ 5 6 ] 38 a l l o wu st ow r i t e s c a l el e n g t h so ft h ei n h o m o g e n e i t y .Fort h i sr e a s o n ,d r i f ti n s t a b i l i t i e s belongt oamoreg e n e r a lc l a s sc a l l e dm i c r o i n s t a b i l i t i e s . Chapleγ T加。 x o+TLs i nw e t )= ( c o skx0)(1 ーお 2γi s i n 2w ; t ) c o sk( 一(sin k x 0 ) k r Ls i nW e t Thel a s ttermv a n i s h e supona v e r a g i n go v e rt i i n e ,andE q .[ 2 ‑ 5 4 ]g i v e s Eo L { 1 22 ¥ v ,= ‑ B(coskx0) い - 4k サ= E . ( x o )I 1 22 ¥ -----n~1-4k"rf) [ 2 ‑ 5 7 ] Thust h eu s u a lEX Bd r i f ti sm o d i f i e dbyt h einhomogeneityt oread ‑ ‑ ‑ ‑ s r , Eラ BI VE̲ I ,2 2.) 4 ) L e tu snowt a k eE andB t obeuniformi ns p a c eb u tv a r y i n gi nt i m e . F i r s t ,c o n s i d e rt h ec a s ei nwhichEa l o n ev a r i e ss i n u s o i d a l l yi nt i m e ,and l e ti tl i ealongt h exa x i s : E=Eoeiw<x̲ [ 2 ‑ 5 8 ] V x= -w~ (Vx 平ごわ [ 2 ‑ 6 2 ] wheret h et i l d eh a sbeenaddedmerelyt oemphasizet h a tt h ed r i f ti s o s c i l l a t i n g .Theupper( l o w e r )s i g n ,a su s u a l ,d e n o t e sp o s i t i v e( n e g a t i v e ) q .NowE q s .[ 2 ‑ 5 0 ]and[ 2 ‑ 5 1 ]become ら=一w~ (Vx ーら) ら=一w~ ( v ,‑ i i E ) Thesecondtermi sc a l l e dt h efinite‑Larmor‑radiuse f f e c t .Whati st h e s i g n i f i c a n c eo ft h i sc o r r e c t i o n ?S i n c eγL i smuchl a r g e rf o ri o n sthanf o r e l e c t r o n s ,VE i snol o n g e rindependento fs p e c i e s .I fad e n s i t ydump o c c u r si nap l a s m a ,ane l e c t r i cf i e l dcanc a u s et h ei o n sande l e c t r o n st o s e p a r a t e ,g e n e r a t i n ganothere l e c t r i cf i d d .I ft h e r ei safeedbackmechanュ ismt h a tc a u s e st h eseconde l e c t r i cf i e l dt oenhancet h ef i r s to n e ,Egrows i n d e f i n i t e l y ,andt h eplasmai su n s t a b l e .Suchani n s t a b i l i t y ,c a l l e dadriβ i n s t a b i l i t y ,w i l lbed i s c u s s e di nal a t e rc h a p t e r .Thegrad‑Bd r i f t ,o fc o u r s e , i sa l s oafinite輔Larmor-radius e f f e c tanda l s oc a u s e sc h a r g e st os e p a r a t e . Accordingt oE q .[ 2 ‑ 2 4 ] ,however,v v 8i sp r o p o r t i o n a lt ok r L .w hereas n i ュ t h ec o r r e c t i o ntermi nE q .[ 2 ‑ 5 8 ]i sp r o p o r t i o n a lt ok2r~. Thenonu f o r m ‑ E ‑ f i e l dE征ect, t h e r e f o r e ,i simportanta tr e l a t i v e l yl a r g ek ,o rs m a l l [ 2 ‑ 6 1 ] - 一B L 土一 リ・山 一B L- 山一一叫 L e tu sd e f i n e =一一= [ 2 ‑ 5 9 ] [ 2 ‑ 6 0 ] S i n c eEx= iwK,wecanw r i t eE q .[2・50] a s ・ 1 Thep h y s i c a lr e a s o nf o rt h i si se a s yt os e e .Ani o nw i t hi t sguiding c e n t e ra tamaximumo fE a c t u a l l yspendsagoodd e a lo fi t st i m ei n r e g i o n so fweakerE .I t sa v e r a g ed r i f t ,t h e r e f o r e ,i sl e s sthanE/B e v a l u ュ a t e da tt h eguidingc e n t e r .Inal i n e a r l yv a r y i n gEf i e l d ,t h ei o nwould bei nas t r o n g e rf i e l donones i d eo ft h eo r b i tandi naf i e l dweakerby t h esameamountont h eo t h e rs i d e ;t h ec o r r e c t i o nt oVE thenc a n c e l s o u t .Fromt h i si ti sc l e a rt h a tt h ec o r r e c t i o ntermdependsont h esecond d e r i v a t i v eo fE .Fort h es i n u s o i d a ld i s t r i b u t i o nweassumed,t h esecond d e r i v a t i v ei sa l w a y sn e g a t i v ew i t hr e s p e c tt oE .F orana r b i t r a r yv a r i a t i o n o fE ,weneedo n l yr e p l a c ei kbyVandw r i t eE q .[ 2 ‑ 5 8 ]a s E=(l +~伊)ヰ旦 TIME‑VARYINGE FIELD 2 . 5 [ 2 ‑ 6 3 ] Bya n a l o g yw i t hE q .[ 2 ‑ 1 2 ] ,wet r yas o l u t i o nwhichi st h esumo fad r i f t andag y r a t o r ym o t i o n : V x= V j ̲e ' w ォ+V p v ,=土ivJ. e ' w ォ+VE [ 2 ‑ 6 4 ] I fwenowdi江erentiate t w i c ew i t hr e s p e c tt ot i m e ,wef i n d 2 V x=ーw,vx +(w , 2 一w 2 ) v p 宮 [2・ 65] 内=ーw,v,+(w , 一 lLI ) V E Thisi sn o tt h esamea sE q .[ 2 ‑ 6 3 ]u n l e s sw2 《 w~. I fwenowmaket h e assumptiont h a tE v a r i e ss l o w l y ,s ot h a tw2 《 w~, thenE q .[ 2 ‑ 6 4 ] ーi st h e approximates o l u t i o nt oE q .[ 2 ‑ 6 3 ] . ~9 S i n g l e ‑ P a r t i c l e M o t i o n s Equation [ 2 ‑ 6 4 ]t e l l su st h a tt h eg u i d i n gc e n t e rmotionh a stwo components.Theycomponent,p e r p e n d i c u l a rt oB andE ,i st h eu s u a l ExBd r i f t ,e x c e p tt h a tVE nowo s c i l l a t e ss l o w l ya tt h efrequencyw.The xcomponent,anewd r i f ta l o n gt h ed i r e c t i o no fE ,i sc a l l e dt h ep o l a r i z a t i o n e p l a c i n gi wbya / a t ,wecang e n e r a l i z eE q .[ 2 ‑ 6 2 ]andd e f i n e d r i f t .Byr t h ep o l a r i z a t i o nd r i f ta s 吋矧刻川町内主 ザ ム 、 ミ 40 C h a p t e r Two e l e c t r o n ss e p a r a t e dbyad i s t a n c eγL・ But s i n c ei o n sande l e c t r o n scan movearoundt op r e s e r v eq u a s i n e u t r a l i t y ,t h ea p p l i c a t i o no fas t e a d yE f i e l ddoesn o tr e s u l ti nap o l a r i z a t i o nf i e l dP .However,i fE o s c i l l a t e s , ano s c i l l a t i n gc u r r e n tj pr e s u l t sfromt h el a gduet ot h ei o ni n e r t i a . TIME‑VARYINGB FIELD 2 . 6 1 dE [ 2 ‑ 6 6 ] Vぬ=土ー一一一- ' WcB d i S i n c e vp i si no p p o s i t ed i r e c t i o n sf o ri o n sand e l e c t r o n s ,t h e r ei sa polarizatio托 current ; f o rZ 1 ,t h i si s = n e dE p dE j p= ne (向 - v叩)=語吉 (M +m ) d t= B 1d t [ 2 ‑ 6 7 ] wherep i st h emassd e n s i t y . Thep h y s i c a lr e a s o nf o rt h ep o l a r i z a t i o nc u r r e n ti ss i m p l e( F i g .2 ‑ 1 2 ) . Considerani o na tr e s ti namagneticf i e l d .I faf i e l dE i ssuddenly a p p l i e d ,t h ef i r s tt h i n gt h ei o ndoesi st omovei nt h ed i r e c t i o no fE . Onlya f t e rp i c k i n gupav e l o c i t yvdoest h ei o nf e e laLorentzf o r c eevxB andbegint omovedownwardi nF i g .( 2 ‑ 1 2 ) .I fEisnowk eptc o n s t a n t , t h e r ei snof u r t h e rvp d r i f tbuto n l yavEd r i f t .However,i fEisr e v e r s e d , t h e r ei sa g a i namomentaryd r i f t ,t h i st i m etot h el e f t .ThusVpi sas t a r t u p d r i f tduet oi n e r t i aando c c u r so n l yi nt h ef i r s th a l f ‑ c y c l eo feachg y r a t i o n duringwhichEc h a n g e s .C o n s e q u e n t l y ,vρgoes t oz e r ow i t hw/wc・ The p o l a r i z a t i o ne f f e c ti na plasmai ss i m i l a rt ot h a ti na s o l i d d i e l e c t r i c ,whereD = ε0E +P .Thed i p o l e si naplasmaa r ei o n sand F i n a l l y ,wea l l o wt h emagneticf i e l dt ov a r yi nt i m e .S i n c et h eLorentz f o r c ei sa l w a y sp e r p e n d i c u l a rt ov ,amagneticf i e l di t s e l fcannotimpart energyt oachargedp a r t i c l e .However,a s s o c i a t e dw i t hB i sane l e c t r i c f i e l dg i v e nby vX E =‑B [ 2 ‑ 6 8 ] andt h i scana c c e l e r a t et h ep a r t i c l e s .Wecannol o n g e rassumet h ef i e l d s t obec o m p l e t e l yu n i f o r m .L e tvょ= d l / d t bet h etでansverse v e l o c i t yl beingt h eelemento fp a t ha l o n gap a r t i c l et r a j e c t o r y( w i t hv uneglected). Takingt h es c a l a rproducto ft h ee q u a t i o no fmotion[2・8] w i t hv . L ,wehave d{1 。\ d i ートmv~ I =aEキv,=aEキ‑:ュ d t\2 . ゐ/皐~ [ 2 ‑ 6 9 ] d t Thechangei noneg y r a t i o ni so b t a i n e dbyi n t e g r a t i n go v e ronep e r i o d : δ(~mι)=了〉か I ft h ef i e l dchangess l o w l y ,wecanr e p l a c et h et i m ei n t e g r a lbyal i n e i n t e g r a lo v e rt h eunperturbedo r b i t : f L s (~mvi) = qEキdl=q (VラE)キdS E ーーーー”F [ 2 ‑ 7 0 ] HereSi st h es u r f a c ee n c l o s e dbyt h eLarmoro r b i tandh a sad i r e c t i o n g i v e nbyt h er i g h t ‑ h a n dr u l ewhent h ef i n g e r sp o i n ti nt h ed i r e c t i o no f v .S i n c et h eplasmai sd i a m a g n e t i c ,wehaveBキ dS く 0 f o ri o n sand>O f o re l e c t r o n s .ThenE q .[ 2 ‑ 7 0 ]becomes fl o l a r i z a t i o nd r i f t . FIGURE2 ‑ 1 2 Thep 。\ .。 .v~ m }mv~ 2π8 8(-mv~ ) =土qB1TT~ =土q7TB ニ一一一=:::....ーニ・一一 ¥ 2 J We 土qB B w, [ 2 ‑ 7 1 ] 4 1 S i n g l e ‑ P a r t i c l e M o t i o n s 42 C h a p t e r Two A 図 c 図 o fl a s e r ‑ d r i v e nf u s i o n schemes u s i n ge i t h e r magnetic o ri n e r t i a l c o n f i n e m e n t . D SUMMARYOFGUIDINGCENTERDRIFTS 2 . 7 臼 日 G e n e r a lf o r c eF : IFラB q B FIGURE2‑13 T w o ‑ s t a g ea d i a b a t i cc o m p r e s s i o no fap l a s m a . EXB 7 T B / w ,= B / f ,i sj u s tt h echange8Bduringonep e r i o do f Theq u a n t i t y2 g y r a t i o n .Thus o (~mvi) = µ, δB [2・ 72] VE=B了 Gγavitatio百al f i e l d : Noni肌 iform E : E = S i n c et h eleft』hand s i d ei s8(オ,B),wehavet h ed e s i r e dr e s u l t NonuniformBf i e l d B q キ B qー [2・ 24] [ 2 ‑ 2 6 ] [ 2 ‑ 3 0 ] [ 2 ‑ 6 6 ] [ 2 ‑ 7 4 ] c o n s t a n ti f オ ,i sc o n s t a n t . Thisp r o p e r t yi susedi namethodo fplasmah e a t i n gknowna s a d i a b a t i ccom戸時·ssioη. F i g u r e2‑13showsas c h e m a t i co fhowt h i si sdone. A plasmai si n j e c t e di n t ot h er e g i o nbetweent h em i r r o r sA andB.C o i l s A andB a r et h e np u l s e dt oi n c r e a s eBandhenceιThe h e a t e dplasma c a nt h e nbet r a n s f e r r e dt ot h er e g i o nC‑D byaf u r t h e rp u l s ei nA, i n c r e a s i n gt h em i r r o rr a t i ot h e r e .Thec o i l sC andD a r et h e np u l s e dt o f u r t h e rcompressandh e a tt h ep l a s m a .E a r l ymagneticmirrorf u s i o n d e v i c e semployedt h i st y p eo fh e a t i n g .A d i a b a t i ccompressionh a sa l s o beenuseds u c c e s s f u l l yont o r o i d a lp l a s m a sandi sane s s e n t i a lelement Therefore , φis 担一 d qB [ 2 ‑ 5 9 ] 12~ V.i V ょηZ :27Tηl EηW.i : 2 φ = B7T 一言 = Bπ~一言==..:γ 一一一=ーすμ w, 一ω 土 22~ 19¥RXB q ‑ ¥ v 1 T+2v'.i.}~ l一 2 ム 間/ 9 VR+vvB = v P o l a r i z a t i o nd r i f t : γ mv~ R ,× B q KB VR =一一ー一~「 Them a g n e t i cf l u xthγ·ough aLarmoroγbit i sc o n s t a n t . Thef l u xφis g i v e nbyBS,w i t hS = 7Tγ~.Thus 一2 Curvedvacuumf i e l d : U d r i f t : 土 C祉問at祉γe B 一 l Grad‑Bd r i f t : Ast h eB 自eld v a r i e si ns t r e n g t h ,t h eLarmoro r b i t sexpandand c o n t r a c t ,andt h ep a r t i c l e sl o s eandg a i nt r a n s v e r s ee n e r g y .Thisexchange o fenergybetweent h ep a r t i c l e sandt h ef i e l di sd e s c r i b e dv e r ys i m p l yby E q .[ 2 ‑ 7 3 ) .Thei n v a r i a n c eofオ, a l l o w su st oprovee a s i l yt h ef o l l o w i n g well‑knowntheorem: 一一 B V V Them a g n e t i cmomenti si n v a r i a n ti ns l o w l yv a r y i n gm a g n e t i cf i e l d s . VT [ 2 ‑ 7 3 ] [ 2 ‑ 1 8 ] (I +.!.γ~v2)~ 4 B B X一 B 一 L 0 [ 2 ‑ 1 5 ] 山一ポ Electric 戸eld: δµ, = [ 2 ‑ 1 7 ] V f=一一一一言一 ADIABATICINVARIANTS 2 . 8 I ti sw e l lknowni nc l a s s i c a lmechanicst h a twheneveras y s t e mh a sa p e r i o d i cmotio凡 the a c t i o ni n t e g r a lT pdqtakenoveraperiodi sac o n s t a n t o ft h em o t i o n .Herepandqa r et h eg e n e r a l i z e dmomentumandc o o r d i n ュ a t ewhichr e p e a tt h e m s e l v e si nt h em o t i o n .I fas l o wchangei smadei n t h es y s t e m ,s ot h a tt h emotioni sn o tq u i t ep e r i o d i c ,t h ec o n s t a n to ft h e motiondoesn o tchangeandi st h e nc a l l e dana d i a b a t i ci n v a r i a n t .Bys l o w herewemeans l o wcomparedw i t ht h ep e r i o do fm o t i o n ,s ot h a tt h e i n t e g r a l9 戸 dq i sw e l l de白r d eventhoughi ti ss t r i c t l ynol o n g e ran 1 3 S i n g l e ‑ P a r t i c l e M o t i o n s 44 Cha戸ter Two / i n t e g r a loverac l o s e dp a t h .A d i a b a t i ci n v a r i a n t sp l a yanimportantr o l e i n plasma p h y s i c s ;t h e ya l l o wu st oo b t a i ns i m p l e answers i n many i n s t a n c e si n v o l v i n gc o m p l i c a t e dm o t i o n s . There a r et h r e ea d i a b a t i c i n v a r i a n t s ,eachcorrespondingt oadi 百erent t y p eo fp e r i o d i cm o t i o n . 45 S i n g l e ‑ P a r t i c l e Motio叫S 0 M 2 . 8 . 1 TheF i r s tAdiabaticI n v a r i a n t , オ , l o /ノt ·'.·÷;\\、 AXISOF Wehavea l r e a d ymett h eq u a n t i t y オ ,= mv~ / 2B andhaveprovedi t si n v a r i a n c ei ns p a t i a l l yandt e m p o r a l l yv a r y i n gB f i e l d s .Thep e r i o d i cmotioninvolved ,。f c o u r s e ,i st h eLarmorg y r a t i o n . I fwet a k ept obeangularmomentummvj̲randdqt obet h ec o o r d i n a t e d 8 ,t h ea c t i o ni n t e g r a lbecomes f f pdq= mv1‑rLd8=加L Uょ= 27Tー=一 w, l q l [2・ 75) Thusオ ,i sac o n s t a n to ft h emotiona slonga sq/mi sn o tchanged.We ,o n l yw i t ht h ei m p l i c i t assumption have proved t h ei n v a r i a n c eo fオ w/w , < 1, wherew i safrequencyc h a r a c t e r i z i n gt h er a t eo fchangeo fB a ss e e nbyt h ep a r t i c l e .A proofe x i s t s ,however,t h a t オ ,i si n v a r i a n teven h e o r i s t s 'l a n g u a g e ,オ ,i si n v a r i a n t“ to a l lo r d e r si nan whenw 主主 w,. Int expansioni nw / w , . "Whatthismeansinpracticei st h a t オ ,remainsmuch moren e a r l yc o n s t a n tthanBdoesduringonep e r i o do fg y r a t i o n . I ti sj u s ta simportantt oknowwhenana d i a b a t i ci n v a r i a n tdoesn o t e x i s ta st oknowwheni td o e s .A d i a b a t i ci n v a r i a n c eofオ.i sv i o l a t e dwhen wi sn o ts m a l lcomparedw i t hw , .Weg i v et h r e eexampleso ft h i s . h es t r e n g t ho fB i namirrorconfinement ( A ) Magnetic Pumping・ If t s c i l l a t e ;butt h e r e systemi sv a r i e ds i n u s o i d a l l y ,t h ep a r t i c l e s 'vj̲ wouldo wouldbenog a i no fenergyi nt h elongr u n .However,i ft h ep a r t i c l e s makec o l l i s i o n s ,t h ei n v a r i a n c eo fオ .i sv i o l a t e d ,andt h eplasmacanbe h e a t e d .I np a r t i c u l a r ,ap a r t i c l emakingac o l l i s i o nduringt h ecompresュ s i o nphasecant r a n s f e rp a r to fi t sg y r a t i o nenergyi n t ov 1 1e n e r g y ,and t h i si sn o tt a k e nouta g a i ni nt h eexpansionp h a s e . (B) C y c l o t r o nH e a t i n g . Nowi maginet h a tt h eB f i e l di so s c i l l a t e da tt h e frequencyw ' "Theinducede l e c t r i cf i e l dw i l lt h e nr o t a t ei nphasew i t h someo ft h ep a r t i c l e sanda c c e l e r a t et h e i rLarmormotionc o n t i n u o u s l y . Thec o n d i t i o nω 《 w,is v i o l a t e d ,オ .i sn o tc o n s e r v e d ,andt h eplasmacan beh e a t e d . Plasmac o n f i n e m e n ti nac u s p e dm a g n e t i cf i e l d . FIGURE2‑14 ~:r~a~:;!~~:~:ニ:;,C:立;:t~cn~:::.~:~:~l~i::品?:立)?立: ~~it完:;(~~~J~:fi~!\~:古:f主~;~~~~t:~~ :~ f f~~:~::~~j:\?:~tr~主主主主出;\g confi 何u : .~' ; ~d~;~~n:;;::;;;江主立す;出::~~~~n~'s :o;;~i~~:~~; ~i~~e~hi: I : X f t h e ~onadiabatic r e g i o n . Fortunate弘山re 1 s in 帥 C蹴Aao~o;:i: i n v a r i a n t :t h ec a n o n i c a l angular momentum P o= mrvo‑e r e n s u r e st h a tt h e r ew i l lbeap o p u l a t i o no fp a r t i c l e strappedi n d e f i n i t e l y u n t i lt h e ymakeac o l l i s i o n . TheSecondA d i a b a t i cI n v a r i a n t ,I 2 . 8 . 2 ~;t::!~~r t~::t~~~ t:~~;:f:ごむ: tエロヶおごす立?;:;;:; :::~:~::・山口;;:::応出店主;:出品おこ;::~~~ s i n c et h eg u i d i n gc e n t e rd r i f t sa c r o s sf i e l dl i n e s ,t h emotioni sn o tex~ctly p e r i o d i c ,andt h ec o n s t a n to ft h emotionbecomesana d i a b a t i cinvanant・ Thisi sc a l l e dt h el o n g i t u d i n a li n v a r i a n tIandi sd e f i n e df o rah a l f ‑ c y c l e 46 C h a p t e r T出O Jバト~一 l o n g i t u d e ,ap a r t i c l emayf i n di t s e l fonanotherl i n eo ff o r c ea tad i f f e r e n t a l t i t u d e .Thiscannothappenif]i sconserved.]determinest h el e n g t h o ft h el i n eo ff o r c ebetweent u r n i n gp o i n t s ,andnotwol i n e shavet h e samel e n g t hbetweenp o i n t sw i t ht h esameI BI C o n s e q u e n t l y ,t h ep a r t i c l e r e t u r n st ot h esamel i n eo ff o r c eeveni nas l i g h t l yasymmetricf i e l d . Toprovet h ei n v a r i a n c eo f] ,wef i r s tc o n s i d e rt h ei n v a r i a n c eo f v 1 1 8 s , .where8 si sasegmento ft h epathalongB ( F i g .2 ‑ 1 7 ) .Becauseo f i l lf i n di t s e l fonanotherl i n eo f guidingc e n t e rd r i f t s ,ap a r t i c l eonsw f o r c eos ’ after at i m et : i . t .Thel e n g t ho f8s ’ is d e f i n e dbyp a s s i n gp l a n e s s .Thel e n g t ho f8 si s perpendiculart oB throught h eendp o i n t so f8 o b v i o u s l yp r o p o r t i o n a lt ot h er a d i u so fc u r v a t u r e : 一~ー FIGURE2 ‑ 1 5 Ap a r t i c l eb o u n c i n gb e t w e e nt u r n i n gp o i n t sa andbi nam a g n e t i cf i e l d . betweent h etwot u r n i n gp o i n t s( F i g .2 ‑ 1 5 ) : 1~ r.,,ゐ l / 47 Siηgle・Particle O S Os ’ [2・ 76] K R; s ot h a t - R;-Rε Os ’ 8s t : i . t 8 s [ 2 ‑ 7 7 ) t : i . t K The“ radial ” component o fVgci sj u s t R, R;‑K [ 2 ‑ 7 8 ) vgc-一一=一一一一- R , t : i . t FromE q s .[ 2 ‑ 2 4 )and[ 2 ‑ 2 6 ) ,wehave ×一B q BT 9 -” uE R一R + 剛一 B 一 ×一B VT 一一 B 一 L T 4 U l 一2 土 + R V B V V 一一 vg [ 2 ‑ 7 9 ) R .一。に B ラ V 一。 4 間一 q 一一 vA 一一 p a 疋 一d vg 一ゐ 。。 l d B 2一 h t Thel a s ttermh a snocomponentalongR , .UsingEqs ・[ 2-78) and[ 2 ‑ 7 9 ) , wecanw r i t eE q .[ 2 ‑ 7 7 )a s R i e l d ;t h e Wes h a l lprovethat]i si n v a r i a n ti nas t a t i c ,nonuniformB f r e s u l ti sa l s ot r u ef o ras l o w l yt i m e ‑ v a r y i n gB f i e l d . Beforeembarkingont h i ssomewhatl e n g t h yp r o o f ,l e tu sc o n s i d e r anexampleo ft h et y p eo fproblemi nwhichatheoremont h ei n v a r i a n c e o f ̲ Jwouldbeu s e f u l .Aswehavea l r e a d ys e e n ,t h eearth’s magneticf i e l d m i r r o r ‑ t r a p schargedp a r t i c l e s ,whichs l o w l yd r i f ti nl o n g i t u d earound e eF i g .2・ 16). I ft h emagneticf i e l dwerep e r f e c t l y t h ee a r t h(Problem2・ 8; s s y m m e t r i c ,t h ep a r t i c l ewoulde v e n t u a l l yd r i f tbackt ot h esamel i n eo f f o r c e .However,t h ea c t u a lf i e l di sd i s t o r t e dbysuche f f e c t sa st h es o l a r w i n d .I nt h a tc a s e ,w i l lap a r t i c l ee v e rcomebackt ot h esamel i n eo f f o r c e ?S i n c et h eparticle’s energyi sc o n s e r v e dandi se q u a lt o~mv~ a t t h eturningp o i n t ,t h ei n v a r i a n c eo fオ i n d i c a t e st h a tI B Iremainsthe samea tt h et u r n i n gp o i n t .However,upond r i f t i n gbackt ot h esame [ 2 ‑ 8 0 ) Thisi st h er a t eo fchangeo fo sasseenbytheparticle.Wemust'now J Ia ss e e nbyt h ep a r t i c l e .Thep a r a l l e land g e tt h er a t eo fchangeo fV B B ‑ 1 6 Motiono FIGURE2 a g n e t i cf i e l d . fac h a r g e dp a r t i c l ei nt h eearth’s m ‑ 1 7 P r o o fo ft h ei n v a r i a n c eo f] . FIGURE2 M o t i o n s 48 C h a p t e r Two TheThirdAdiabaticInvariant, φ perpendiculare n e r g i e sa r edefinedby W = ~mv~ +~mv~ = ~mv~ +オ.B=Wu+Wょ ( 2 ‑ 8 1 ) Thusv ucanbew r i t t e n vu=[(2/m)(W 一 µ.B)]112 [ 2 ‑ 8 2 ) HereW andオ .arec o n s t a n t ,andonlyB v a r i e s .Therefore, 内 vu ー 1 オ . B 1オ . B オ . B 2F士五五= 2W11 一戸了 ( 2 ‑ 8 3 ) snotzeroo n l ybecauseo ft h eguiding S i n c eB wasassumeds t a t i c ,B i c e n t e rmotion: ̲mv~ ReX B dB d r B = ー・ー= d r dt V,,r" 酔 VB 一一一一τ7 q R:W ・ VB [ 2 ‑ 8 4 ) Nowwehave t i 1 1 オ .(R,× B)·VB lmv~ (BXVB )・ Re v u‑ :q R~B2 ‑ 2q R~B2 B Referringagaint oF i g . 2・ 16, wes e et h a tt h eslowd r i f to faguiding c e n t e raroundt h ee a r t hc o n s t i t u t e sat h i r dt y p eo fp e r i o d i cmotion.The a d i a b a t i ci n v a r i a n tconnectedw i t ht h i st u r n soutt obet h et o t a lmagnetic f l u xφenclosed byt h ed r i f ts u r f a c e .I ti salmostobviousth主t, a sB v a n e s , t h ep a r t i c l ew i l ls t a yonas u r f a c esucht h a tt h et o t a lnumbero fl i n e so f p p l i c a t i o n s f o r c eenclosedremainsc o n s t a n t .Thisinvariant, φ, has fewa becausemostf l u c t u a t i o n so fB occuronatimes c a l es h o r tcompared witht h ed r i f tp e r i o d .Asanexampleo ft h ev i o l a t i o no fφinvariance, wecanc i t esomer e c e n tworkont h ee x c i t a t i o nofhydromagneticwaves i nt h eionosphere.Thesewaveshavealongperiodcomparablet ot h e d r i f ttimeo fap a r t i c l earoundt h ee a r t h .Thep a r t i c l e scant h e r e f o r e encountert h ewavei nt h esamephaseeachtimearound.I fthephase i sr i g h t ,t h ewavecanbee x c i t e dbyt h econversiono fp a r t i c l ed r i f tenergy 49 2 . 8 . 3 Single-Paγticle M o t i o n s t owavee n e r g y . [ 2 ‑ 8 5 ) Thef r a c t i o n a lchangei nv u8 si s I d 1d 8 s 1d v 1 1 一一一( vu &)=一 v uO sd t " +ーー- O Sd t v ud t 2・ 13. [2 ・ 86) FromE q s .[ 2 ‑ 8 0 )and[ 2 ‑ 8 5 ) ,wes e et h a tt h e s etwotermsc a n c e l ,s ot h a t sc o n s t a n t ,however. In Thisi snote x a c t l yt h esamea ss a y i n gt h a tIi t a k i n gt h ei n t e g r a lo fv 1 18 sbetweentheturningp o i n t s ,i tmaybet h a t t h eturningp o i n t son8s ’ do notc o i n c i d ew i t ht h ei n t e r s e c t i o n so ft h e r i s i n gfrom perpendicularp l a n e s( F i g .2 ‑ 1 7 ) .However,anye r r o ri nIa ui s suchadiscrepancyi sn e g l i g i b l ebecauseneart h eturningp o i n t s ,v n e a r l yz e r o .Consequently,wehaveproved f =… v u d s v 1 1d s= viιand ( a )L e tJ di百erentiate w i t hr e s p e c tt ot i m e . ( b )Fromt h i s ,g e tane x p r e s s i o nf o rTint e r m so fd L / d t .S e td L / d t= ‑2vmt o o b t a i nt h ea n s w e r . ( 2 ‑ 8 7 ) v u8 s= constant I= D e r i v et h er e s u l to fProblem2 ‑ 1 2 ( b )d i r e c t l ybyu s i n gt h ei n v a r i a n c eo f ] . nt [ 2 ‑ 8 8 ) Anexampleo ft h ev i o l a t i o no fJi n v a r i a n c ei sgivenbyaplasma heatingschemec a l l e dt r a n s i t ‑ t i m em a g n e t i cp u m p i n g .Supposeanoscillat” i n gcurrenti sa p p l i e dt ot h ec o i l so famirrorsystems ot h a tthemirrors a l t e r n a t e l yapproachandwithdrawfromeachotherneart h ebounce f r e q u e n c y .Thosep a r t i c l e st h a thavet h er i g h tbouncefrequencyw i l l a l w a y ss e eanapproachingmirrorandw i l lt h e r e f o r eg a i nvu・ f i snot conservedi nt h i sc a s ebecausethechangeo fB o c c u r sonatimes c a l e notlongcomparedwitht h ebouncet i m e . 2 ‑ 1 4 .I np l a s m ah e a t i n gbya d i a b a t i cc o m p r e s s i o n ,t h ei n v a r i a n c eo f オ ,r e ' q u i r e s sB i n c r e a s e s .Them a g n e t i cf i e l d ,h o w e v e r ,c a n n o ta c c e l e r a t e t h a tKTょ increase a l w a y sp e r p e n d i c u l a rt ot h ev e l o c i t y . p a r t i c l e sb e c a u s et h eL o r e n t zf o r c eqvXBisa Howdot h ep a r t i c l e sg a i ne n e r g y ? 2・ 15. Thep o l a r i z a t i o nd r i f tv• c a na l s ob ed e r i v e dfrome n e r g yc o n s e r v a ̲ t i o n : I fE i so s c i l l a t i n g ,t h eExB d r i f ta l s oo s c i l l a t e s ;andt h e r ei sanenergy 古mvf; a s s o c i a t e dw i t ht h eg u i d i n gc e n t e rm o t i o n .S i n c ee n e r g yc a nbeg a i n e dfroman E 白eld o n l yb ym o t i o na l o n gE ,t h e r emustb ead r i f tv• i nt h eEd i r e c t i o n .By i t ht h er a t eo fe n e r g yg a i nfromv• キ E , e q u a t i n gt h er a t eo fchangeo f~mv~ w f i n dt h er e q u i r e dv a l u eo fv•. 2・ 16. A h ydrogenp l a s m ai sh e a t e db ya p p l y i n gar a d i o f r e q u e n : ywavew i t hE p e r p e n d i c u l a rt o B and w i t h an a n g u l a rf r e q u e n c y w = 10ヨ rad/sec. The con品ning m a g n e t i cf i e l di s1T .I st h em o t i o no f( a )t h ee l e c t r o n sand( b )t h e i o n si nr e s p o n s et ot h i swavea d i a b a t i c ? A1 ‑ k eV p r o t o nw i t hv 1 1= 0i nauniformm a g n e t i cf i e l dB= 0 . 1T i s ss l o w l yi n c r e a s e dt oIT .I tt h e nmakesane l a s t i cc o l l i s i o nw i t h a c c e l e r a t e da sB i ah e a v yp a r t i c l eandc h a n g e sd i r e c t i o ns ot h a tUょ= v 1 1TheB -白eld i st h e ns l o w l y n e r g ynow? d e c r e a s e db a c kt o0 . 1T .Whati st h eproton ’s e 2・ 17. PROBLEMS 5CT hv z r -‘ ρ I ,世 ’UM T ( a ) Drawt y p i c a lo r b i t sf o ri o n sande l e c t r o n sw ) t hv 1 1= 0d r i f t i n gi nt h enonunト formB f i e l d . ( b )C a l c u l a t et h er a t eo fchargea仁cumulation ( i ncoulombspers e c o n d )ont h e zニ:江口:止に立~:fi:」コニむご0~:=~ぷua'~a;~~;どl~~: nu asp~ct 凶io(R 》 a) a pproximationwheren e c e s s a r y . 2-20・ Suppose themagneticf i e l dalongt h ea x i so famagneticmirrori sg i v e nby B ,= B0(1+a 2 z 2 ) . 件) I fane l e c t r o na tz= Oh a sav e l o c i t yg i v e nbyv2 =叫= 1.5山t whatv a l u B o fzi st h ee l e c t r o nre日ected? ( b ) Writet h ee q u a t i o no fmotiono ft h eguidingc e n t e rf o rt h ed i r e c t i o np a r a l l e l t othe 自eld ( c ) Showt h a tt h emotioni ss i n u s o i d a l ,andc a l c u l a t ei t sf r e q u e n c y . FIGUREP2‑18 2 ‑ 1 8 .A c o l l i s i o n l e s shydrogenplasmai scon 五ned i nat o r u si nwhiche x t e r n a l windingsprovideamagneticf i e l dB l y i n ga l m o s te n t i r e l yi nt h eφdirection The plasma i si n i t i a l l y Maxwellian a t KT=IkeV. At t= 0 ,B i sg r a d u a l l y i n c r e a s e dfromIT t o3TinJOOオ s e c ,andt h eplasmai scompressed ( a ) Show t h a tt h e magnetic momentオ remains i n v a r i a n tf o rboth i o n s and e l e c t r o n s ( b )C a l c u l a t et h etemperaturesTょ and T 1 1a f t e rc o m p r e s s i o n . 2 ‑ 1 9 . A uniform plasma i sc r e a t e di nat o r o i d a l chamberw i t h square c r o s s s e c t i o n ,a sshown.Themagneticf i e l di sprovidedbyac u r r e n tIalongt h ea x i s 0cm.Theplasmai sMaxwellian o fsymmetry.Thedimensionsa r ea= Icm,R = 1 a sd e n s i t yn= 1 0 1 9m ‑ 3 .Therei snoelectric 品eld. a tKT=100eVandh alfila --|也, 司ト一一一 a 一一一ー FIGUREP2‑19 ( d )C a l c u l a t et h el o n g i t u d i n a li n v a r i a n tfcorrespondingt ot h i smotion 忠21. A口 in 白 ni Att=0 ,ane l e c t r o no fs m a l lg y r o r a d i u si sa tz=0andγ = γ0 withυよo=V 仙 1ム and¥ Irefert ot h edire仁ti onrεlative t ot h emagneticf i e l d . ) 伺己al仁ulate themagn velo仁ity. ~~!c;r~~~~~~ ~~a~~:e±czu工::::c:~:::コ;::;Y ロロ:;~c: ~i:::a~a::.ココ: d i r e c t i o n so fI ,B ,E ,andVE ( c ) Dov'andv ni n c r e a s e ,d e c r e a s e ,o rremaint h esamea st h ec u r r e n tincreasesコ Whyコ 5 1 S i n g l e ‑ P a r t i c l e M o t i o n s C h a p t e rT h r e e PLASMAS ASF L U I D S INTRODUCTION 3 . 1 I naplasmat h es i t u a t i o ni smuchmorec o m p l i c a t e dthant h a ti nt h el a s t c h a p t e r ;t h eE andB f i e l d sa r en o tp r e s c r i b e dbuta r edeterminedby t h ep o s i t i o n sandmotionso ft h ec h a r g e st h e m s e l v e s .Onemusts o l v ea s e l f ‑ c o n s i s t e n tproblem;t h a ti s ,f i n das e to fp a r t i c l et r a j e c t o r i e sand 自 eld p a t t e r n ssucht h a tt h ep a r t i c l e sw i l lg e n e r a t e the 自elds a st h e ymove alongt h e i ro r b i t sandt h ef i e l d sw i l lc a u s et h ep a r t i c l e st omovei nt h o s e e x a c to r b i t s .Andt h i smustbedonei nat i m e ‑ v a r y i n gs i t u a t i o n ! 1 2 Wehaves e e nt h a tat y p i c a lplasmad e n s i t ymightbe1 0 i o n ‑ e l e c t r o n feacho ft h e s ep a r t i c l e sf o l l o w sac o m p l i c a t e dt r a j e c t o r y p a i r spercm3 I andi ti sn e c e s s a r yt of o l l o weacho ft h e s e ,p r e d i c t i n gt h eplasma’s b e h a v i o r would be a h o p e l e s st a s k .F o r t u n a t e l y ,t h i si sn o tu s u a l l yn e c e s s a r y b e c a u s e ,s u r p r i s i n g l y ,t h emajority‑perhapsa smucha s80%‑ofplasma phenomenaobservedi nr e a lexperimentscanbee x p l a i n e dbyar a t h e r crudemodel.Thismodeli st h a tusedi nf l u i dm e c h a n i c s ,i nwhicht h e i d e n t i t yo ft h ei n d i v i d u a lp a r t i c l ei sn e g l e c t e d ,ando n l yt h emotiono f f l u i delementsi st a k e ni n t oa c c o u n t .Ofc o u r s e ,i nt h ec a s eo fp l a s m a s , t h ef l u i dc o n t a i n se l e c t r i c a lc h a r g e s .I n an o r d i n a r yf l u i d ,f r e q u e n t c o l l i s i o n sbetweenp a r t i c l e skeept h ep a r t i c l e si naf l u i delementmoving t o g e t h e r .I ti ss u r p r i s i n gt h a tsuchamodelworksf o rp l a s m a s ,which g e n e r a l l y havei n f r e q u e n tc o l l i s i o n s . Butwes h a l ls e et h a tt h e r ei sa r e a s o nf o rt h i s . I nt h eg r e a t e rp a r to ft h i sb o o k , we s h a l l be concerned w i t h whatcanbel e a r n e dfromt h ef l u i dt h e o r yo fp l a s m a s .A morer e f i n e d ーム←ー 5 3 5 4 Chapleγ T h r e e treatment‑thek i n e t i ct h e o r yo fplasmas‑requiresmoremathematical c a l c u l a t i o nt h a ni sa p p r o p r i a t ef o rani n t r o d u c t o r yc o u r s e .Ani n t r o d u c ュ t iont ok i n e t i ct h e o r yi sg i v e ni nChapter7 . I nsomeplasmap r o b l e m s ,n e i t h e rf l u i dt h e o r ynork i n e t i ct h e o r y i ss u f f i c i e n tt od e s c r i b et h eplasma’s b e h a v i o r .Thenoneh a st of a l lback ont h et e d i o u sp r o c e s so ff o l l o w i n gt h ei n d i v i d u a lt r a j e c t o r i e s .Modern computerscandot h i s ,althought h e yhaveo n l yenoughmemoryt os t o r e t h ep o s i t i o nandv e l o c i t ycomponentsf o rabout1 0 4p a r t i c l e sa n d ,e x c e p t i n a few c a s e s , can s o l v e problems o n l yi n one o r two d i m e n s i o n s . N o n e t h e l e s s ,computers i m u l a t i o nh a sr e c e n t l ybegunt op l a yanimporュ t a n tr o l ei nf i l l i n gt h e gap between t h e o r yand experimenti nt h o s e i n s t a n c e swhereevenk i n e t i ct h e o r ycannotcomec l o s et oe x p l a i n i n gwhat i so b s e r v e d . o ft h eq u a n t i t i e sD andH i ntermso fEandオ , .I naplasm昌, the i o n s ande l e c t r o n scomprisingt h eplasmaa r et h ee q u i v a l e n to ft h e“ bound ” c h a r g e sandc u r r e n t s .S i n c et h e s ec h a r g e smovei nac o m p l i c a t e dw a y , , . i ti si m p r a c t i c a lt ot r yt olumpt h e i re f f e c t si n t otwoc o n s t a n t sEandオ C o n s e q u e n t l y ,i nplasmap h y s i c s ,oneg e n e r a l l yworksw i t ht h evacuum e q u a t i o n s[ 3 ‑ l ] ‑ ( 3 ‑ 4 ] ,i nwhichσand ji n c l u d ea l lt h ec h a r g e s and c u r r e n t s ,bothe x t e r n a landi n t e r n a l . Notet h a twehaveusedE andB i nt h evacuume q u a t i o n sr a t h e r thant h e i rc o u n t e r p a r t sD andH,whicha r er e l a t e dbyt h econstantsεo andµ,0・ This i sbecauset h ef o r c e sqEandjラB dependonE andB r a t h e rthanD and H, andi ti sn o tn e c e s s a r yt oi n t r o d u c et h el a t t e r q u a n t i t i e sa slonga sonei sd e a l i n gw i t ht h evacuume q u a t i o n s . C l a s s i c a lTreatmento fMagneticM a t e r i a l s 3 . 2 . 2 3 . 2 RELATIONOFPLASMA PHYSICSTOORDINARY ELECTROMAGNETICS 3 . 2 . l Maxwell’s Equations I nvacuumキ E o ' i lキ E= σ 'i/xE= B v 、 B=O マ× B = µ,。( j + εoEl [3 ・ I] [ 3 ‑ 2 ] [ 3 ‑ 3 ] [ 3 ‑ 4 ] I namedium: 'i/·D = σ S i n c eeachg y r a t i n gp a r t i c l eh a samagneticmoment,i twouldseemt h a t t h el o g i c a lt h i n gt odowouldbet oc o n s i d e raplasmaa samagnetic m a t e r i a lw i t hap e r m e a b i l i t y/ 1 ‑ m キ (Weh aveputas u b s c r i p tm ont h e p e r m e a b i l i t yt od i s t i n g u i s hi tfromt h ea d i a b a t i ci n v a r i a n t オ , . )Tos e ewhy t h i si sn o tdonei np r a c t i c e ,l e tu sr e v i e wt h ewaymagneticm a t e r i a l sa r e u s u a l l yt r e a t e d . Thef e r r o m a g n e t i cdomains,s a y ,o fap i e c eo fi r o nhavemagnetic momentsµυgiving r i s et oabulkm a g n e t i z a t i o n [3 ・ 5] M= ‑ & r :オ, [ 3 ‑ 1 1 ] peru n i tvolume Thish a st h esamee f f e c ta saboundc u r r e n td e n s i t y e q u a lt o j 6= ' i ixM [ 3 ‑ 1 2 1 ' ixE=‑B [ 3 ‑ 6 ] ' iキB=0 [ 3 ‑ 7 ] I nt h evacuume q u a t i o n(3 ・4], wemusti n c l u d ei njbotht h i sc u r r e n t andt h e“ free ,” or e x t e r n a l l ya p p l i e d ,c u r r e n tj r : 'i/xH=j+D [ 3 ‑ 8 ] オ , ( j ' VxB=j r+j .+ εoE D = εE [ 3 ‑ 9 ] B=オ,H [ 3 ‑ 1 0 ] I nE q s .[ 3 ‑ 5 ]and(3-8 ], σand js t a n df o rt h e“ free ” charge andc u r r e n t u r r e n td e n s i t i e sa r i s i n gfrompolariz・ d e n s i t i e s .The“ bound ” charge andc a t i o nandm a g n e t i z a t i o no ft h emediuma r ei n c l u d e di nt h ed e f i n i t i o n [3 ・ 13] Wew i s ht ow r i t eE q .( 3 ‑ 1 3 ]i nt h es i m p l eform V xH =j r+ εoE [ 3 ‑ 1 4 ] byi n c l u d i n gj 6i nt h ed e f i n i t i o no fH.Thiscanb edonei fwel e t H =オ , 0 1 B‑ M [ 3 ‑ 1 5 ] 5 5 P l a s m a s AsF l u i d s = B= オ , o ( l+Xm)H !LmH [ 3 ‑ 1 6 ] . 2 . 4 TheD i e l e c t r i cConstantofaPlasma 3 [ 3 ‑ 1 7 ] . 5t h a taf l u c t u a t i n gE f i e l dg i v e sr i s et oa Wehaveseeni nS e c t i o n2 p o l a r i z a t i o ncurrentj p .Thisl e a d s ,i nt u r n ,t oap o l a r i z a t i o nchargeg i v e n byt h eequationo fc o n t i n u i t y : Thiss i m p l er e l a t i o nbetweenB andH i sp o s s i b l ebecauseo ft h el i n e a r formo fE q .[ 3 ‑ 1 6 ] . In aplasmaw i t hamagneticf i e l d ,each p a r t i c l ehas a magnetic momentµα, and t h eq u a n t i t yMist h esumo fa l lt h e s eμα ’sinlm3.But wenowhave ヨ, ηiv ょα ー- μ l =一一一比一 B α2B a ,アh "= 0 -ーと+ V ・ i. a t [3 ・ 24] Thisi st h ee q u i v a l e n to fE q .[3・ 18], e x c e p tt h a t ,a swenotedb e f o r e ,a p o l a r i z a t i o ne f f e c tdoesnota r i s ei naplasmau n l e s st h ee l e c t r i cf i e l di s timev a r y i n g .S i n c ewehaveane x p l i c i te x p r e s s i o nf o rj 9butnotf o rσ炉 i ti se a s i e rt oworkw i t ht h efourthMaxwelle q u a t i o n ,Eq目( 3-4]: M ぽま Ther e l a t i o nbetweenMandH ( o rB)i snolongerl i n e a r ,andwecannot " mc o n s t a n t .I ti st h e r e f o r enotu s e f u lt oc o n s i d e ra w r i t eB=!"ml王 with l plasmaa samagneticmedium. V xB = 1 L o ( i 1+j p+ εoE) [3・ 25] Wewisht ow r i t et h i si nt h eform 3 . 2 . 3 ClassicalTreatmentofDielectrics VxB =µ,。Cit + εE) Thep o l a r i z a t i o nP peru n i tvolumei st h esumovera l lt h ei n d i v i d u a l momentsp ;o ft h ee l e c t r i cdipoles ・ This g i v e sr i s et oaboundcharge [ 3 ‑ 2 6 ] Thiscanbedonei fwel e t .j p d e n s i t y [ 3 ‑ 2 7 ] t: = εo 十 E σb =‑ v .p [ 3 ‑ 1 8 ] FromE q .( 2 ‑ 6 7 ]f o rj p ,wehave Int h evacuume q u a t i o n[ 3 ‑ 1 ] ,wemusti n c l u d ebotht h eboundcharge andt h ef r e ec h a r g e : ε0V·E= (σ1 + σb) ε = εn"+と B" [3 ・ 19] [3 ・ 20] byi n c l u d i n gσb i nt h ed e f i n i t i o no fD.Thiscanbedonebyl e t t i n g D = <oE+P= εE [ 3 ‑ 2 1 ] I fPi sl i n e a r l yp r o p o r t i o n a lt oE , P= <ox,E [ 3 ‑ 2 2 ] then€ i sac o n s t a n tg i v e nby ε = ! L o P C 2 ( 1+x,)ε。 ε !Lo 2 PC 匂三一= 1 十一亡す一 ε0 [3 ・28] fj Thisi st h elow-f作quency 戸las情。 dielectric c o n s t a n tfoγ transverse 明otions. The q u a l i f i c a t i o n sa r en e c e s s a r ybecauseoure x p r e s s i o nf o rj 9i sv a l i do n l y 2 2 f o rω 《 w, andf o rE perpendiculart oB .Theg e n e r a le x p r e s s i o nf o r ε, of c o u r s e ,i sv e r ycomplicatedandhardlyf i t sononep a g e . t svacuumv a l u e ,u n i t y ,a si t Note t h a ta sp → O, εR approaches i s h o u l d .AsB →∞, εR a l s oapproachesu n i t y .Thisi sbecauset h ep o l a r i z ュ a t i o nd r i f tv pthenv a n i s h e s ,andt h ep a r t i c l e sdonotmovei nrespons告 t ot h et r a n s v e r s ee l e c t r i cf i e l d .Inau s u a ll a b o r a t o r yp l a s m a ,t h esecond termi nEq. [ 3 ‑ 2 8 ]i sl a r g ecomparedw i t hu n i t y .Fori n s t a n c e ,i fn= 1016m‑ 3andB = 0.1T wehave( f o rhydrogen) Wewisht ow r i t et h i si nt h es i m p l eform V·D = σf or 一てす一- [ 3 ‑ 2 3 ] Bι よ ( 4 7 Tラ 1 0 ‑ 7 ) ( 1 0 1 6 ) ( 1 . 6 7ラ 1 0 ‑ 2 7 ) ( 9ラ 1 0 1 6 ) " =1 89 ( 0.1)" 7 出ゐ M=xmH Thec o n s t a n tXmi st h emagnetics u s c e p t i b i l i t y .Wenowhave Therei snoaprioγi reasonwhyar e l a t i o nl i k e[ 3 ‑ 2 2 ]cannotbev a l i di n :i nap l a s m a . aplasma,s owemayproceedt ot r yt og e tane x p r e s s i o nf o r< 5m 一凶 hF A iT h r e e Tog e tas i m p l er e l a t i o nbetweenB andH,weassumeM t obeproporュ t i o n a lt oBorH: ps i 56 l C h a p t e r den、rative i stobet a k e na tt h ep o s i t i o no fthe 戸articles. Ont h eo t h e rhand. wew凶 to haveane q u a t i o nf o rf l u e l e m e r wouldbei m p r a c t i c a lt odoo t h e r w i s e .Consideradrop一 of creami na ~up o fco圧ee a saf l u i de l e m e n t .Ast h eco仔ee i ss t i r r e d ,t h edropd i s t o r t s mtoaf i l a m e n tandf i n a l l yd i s p e r s e sa l lo v e rt h ec u p ,l o s i n gi t si d e n t i t y . Af l u i delementa taf i x e ds p o ti nt h ec u p ,however,r e t a i n si t si d e n t i t y althoughp a r t i c l e sc o n t i n u a l l ygoi nandouto fi t . Tomaket h et r a n s f o r m a t i o nt ov a r i a b l e si naf i x e df r a m e ,c o n s i d e r G ( x ,t )t obeanyp r o p e r t yo faf l u i di no n e ‑ d i m e n s i o n a lxspace・ The changeo fG w i t ht i m ei naframemovingw i t ht h ef l u i di st h esumo ftwo t e r m s : ft h ei o nc y c l o t r o nf r e q u e n c yi sd e n o t e db yn ,andtheionplasmafrequency 3 ‑ 2 .I i sd e f i n e db y n .= (ne2 /ε。品,f)l/2 whereM i st h ei o nm a s s ,underw h a tc i r c u m s t a n c e si st h ed i e l e c t r i cc o n s t a n tε a p p r o x i m a t e l ye q u a lt on~ ; n~ ? 3 . 3 THEFLUID EQUATIONOFMOTION d G ( x ,t ) aG aGd x aG aG づ「 = a1 + 耳石 = a1 + 叫xa; Maxwell ’S e q u a t i o n st e l lu swhatE andB a r ef o rag i v e ns t a t eo ft h e p l a s m a . To s o l v et h es e l f ‑ c o n s i s t e n t problem, we musta l s o have an og i v e nE andB .I nt h ef l u i d e q u a t i o ng i v i n gt h eplasma’s responset approximation,wec o n s i d e rt h eplasmat obecomposedo ftwoo rmore inteψenetratiπE f l u i d s ,onef o reachs p e c i e s .Int h es i m p l e s tc a s e ,when t h e r ei so n l yones p e c i e so fi o n ,wes h a l lneedtwoe q u a t i o n so fm o t i o n , onef o rt h ep o s i t i v e l ychargedi o nf l u i dandonef o rt h en e g a t i v e l ycharged e l e c t r o nf l u i d .Inap a r t i a l l yi o n i z e dg a s ,wes h a l la l s oneedane q u a t i o n f o rt h ef l u i do fn e u t r a la t o m s .Then e u t r a lf l u i dw i l li n t e r a c tw i t ht h e i o n sande l e c t r o n so n l ythroughc o l l i s i o n s .Thei o nande l e c t r o nf l u i d s w i l li n t e r a c tw i t heacho t h e reveni nt h eabsenceo fc o l l i s i o n s ,because o ft h eEandB f i e l d st h e yg e n e r a t e . (3訓] !hefirst ほm ont h er i g h trepres側S t h echangeo fG a taf i x e dp o i n t ms p a c e ,andt h esecondtermr e p r e s e n t st h echangeo fGast h eo b s e r v e r movesw i t ht h ef l u i di n t oar e g i o ni nwhichG i sd i f f e r e n t .I nt h r e e ]g e n e r a l i z e st o d i m e n s i o n s ,E q .(3・3 I dG aG d t a t -一=ー+(u·V)G [ 3 ‑ 3 2 ] Thisi sc a l l e dt h ec o n v e c t i v ed e r i v a t i v eandi ssometimesw r i t t e nDG/ D t . Notet h a t( uキV )i sas c a l a rd i f f e r e n t i a lo p e r a t o r .S i n c et h es i g no ft h i s termi ssometimesas o u r c eo fc o n f u s i o n ,weg i v etwos i m p l ee x a m p l e s . l e c t r i cwaterh e a t e ri nwhicht h eh o tw a t e r Figure3・ 1 showsane h a sr i s e nt ot h etopandt h ec o l dwaterh a ssunkt ot h eb o t t o m .LetG ( x ,t ) bet h etemperatureT;VGi sthenupward.Consideraf l u i delement ft h eh e a t e relementi sturnedo n ,t h ef l u i d neart h eedgeo ft h et a n k .I elementi sheated ぉ it moves,andwehavedT/dt>0 .I f ,i na d d i t i o n ,a i x e d paddlewheels e t supaf l o wp a t t e r na sshown,t h etemperaturei naf f l u i delementi sloweredbyt h econvec出n 。f c o l dwa町 from t h ebot~om. I nt h i sc a s e ,we haveoT/ax>0 andUx>0 ,s ot h a tuキVT>O .The T / a t ,i sg i v e nbyab a l a n c e temperaturechangei nt h ef i x e de l e m e n t ,a 3 . 3 . 1 TheConvectiveDerivative Thee q u a t i o no fmotionf o ras i n g l ep a r t i c l ei s d t (3・30] ~hi.s 爪 however, notaco同町1t formt ou s e .I nE q .(臼9), t h et i m e 3・ 1. D e r i v et h euniform司plasma l o w ‑ f r e q u e n c yd i e l e c t r i cc o n s t a n t ,E q .[3羽], b yr e c o n c i l i n gt h et i m ed e r i v a t i v eo ft h ee q u a t i o nVキ D= Vキ (εE) = 0w i t ht h a t o ft h evacuumP o i s s o ne q u a t i o n[ 3 ‑ 1 ] ,w i t ht h eh e l po fe q u a t i o n s[ 3 ‑ 2 4 ]a nd[ 2 ‑ 6 7 ] . 市立= q(E+vxB) qη ( E+u × B) [ 3 ‑ 2 9 ] Assumef i r s tt h a tt h e r ea r enoc o l l i s i o n sandnothermalm o t i o n s .Then a l lt h ep a r t i c l e si naf l u i delementmovet o g e t h e r ,andt h eaveragev e l o c i t y uo ft h ep a r t i c l e si nt h eelementi st h esamea st h ei n d i v i d u a lp a r t i c l e 一」』ー A PROBLEMS du mn 一一 = d t ELm Dais v e l o c i t yv .i : h efluid 叩ation i so b t a i n e ds i m p l ybym u l t i p l y i n gE q .( 3 ‑ 2 9 ] byt h ed e n s i t yn: Thismeanst h a tt h ee l e c t r i cf i e l d sduet ot h ep a r t i c l e si nt h eplasma g r e a t l ya l t e rt h ef i e l d sa p p l i e de x t e r n a l l y .A plasmaw i t hl a r g eεshields outa l t e r n a t i n gf i e l d s ,j u s ta saplasmaw i t hs m a l lλD s h i e l d soutdcf i e l d s . C h a p t e r T h r e e 9 出ゐ 58 - m 一ー司-一ーー← meaningt h a tt h es a l i n i t yi n c r e a s e sa tanyg i v e np o i n t .Ofc o u r s e ,i fi t S / d ti st o r a i n s ,t h es a l i n i t yd e c r e a s e severywhere,andan e g a t i v etermd beaddedt ot h emiddlep a r to fE q .[3司34]. Asaf i n a lexample,t a k eG t obet h ed e n s i t yo fc a r snearafreeway e n t r a n c ea trushhour.Ad r i v e rw i l ls e et h ed e n s i t yaroundhimi n c r e a s i n g a s he approaches t h e crowded f r e e w a y . This i st h ec o n v e c t i v e term ( uキ V)C.Att h esamet i m e ,t h el o c a ls t r e e t smaybef i l l i n gw i t hc a r st h a t e n t e rfromd r i v e w a y s ,s ot h a tt h ed e n s i t yw i l li n c r e a s eeveni ft h eo b s e r v e r doesn o tmove.Thisi st h ea G / a tterm.Thetotalincreaseseenbythe o b s e r v e ri st h esumo ft h e s ee f f e c t s . I nt h ec a s eo fap l a s m a ,wet a k eG t obet h ef l u i dv e l o c i t yuand s w r i t eE q .[3 ・30] a FIGURE3 ‑ 1 Motiono ff l u i de l e m e n t si na h o tw a t e rh e a t e r . r a u a t +(u V)uJ = qn( E+uxB) o ft h e s ee狂ects, mnj dT 一一=ーー- u キVT a t d t 。T 1 [ 3 ‑ 3 5 1 wherea u / a ti st h etimed e r i ¥ ' a t i v ei na 五xed f r a m e . [3 ・33] I ti sq u i t ec l e a rt h a ta T / a tcanbemadezero,atleastforashorttime. Asasecondexamplewemayt a k eG t obet h es a l i n i t ySo ft h ewater fxi st h eupstreamd i r e c t i o n ,t h e r e neart h emoutho far i v e r(Fig. 与 2). I TheS t r e s sTensor 3 . 3 . 2 Whenthermalmotionsa r etakeni n t oa c c o u n t ,ap r e s s u r ef o r c eh a st o beaddedt ot h er i g h t ‑ h a n ds i d eo fE q .[ 3 ‑ 3 5 ] .Thisf o r c ea r i s e sfromt h e y OCEAN z FIGURE3・2 D i r e c t i o no ft h es a l i n i t yg r a d i e n ta tt h emoutho far i v e r . ノ// x O r i g i no ft h ee l e m e n t so ft h es t r e s st e n s o r . FIGURE3 ・3 上 JaUゐ [ 3 ‑ 3 4 ] Emω a s ax A a s at 一一= -u笠一一> O ‘ bFf i snormallyag r a d i e n to fSsucht h a tas/ax く 0. Whent h et i d ecomes i n ,t h ee n t i r ei n t e r f a c ebetweens a l tandf r e s hwatermovesupstream, andUx>0 .Thus C h a p t e r T h r e e ps 60 [ 3 ‑ 3 9 ] Equation(3喝38] nowbecomes U山 L where6 . n vi st h enumbero fp a r t i c l e sperm3w i t hv e l o c i t yvx ・ もγe c anc a n c e ltwotermsbyp a r t i a ld i f f e r e n t i a t i o n : 6 . n v= 6 . v xJ Sf(v,,v , ,v , )d円 dv, a u x' aη a(nux) mnat 十間'" at= -muχ a;;-. Eachp a r t i c l ec a r r i e samomentumm1ら・ The d e n s i t ynandtemperature K Ti neachcubei sassumedt ohavet h ev a l u ea s s o c i a t e dwitht h ecube’s n t ot h eelementa tx 0throughA c e n t e r .ThemomentumPA+earnedi i sthen PA+=: 2 .6.nvmv!6 . y6 . z= 6 . y6.z[m;;~nlxu-"x 8πa ae- + ζ (i山χ ) = 0 [3品] |円KT PB += ムy ムz [間;; hJxり ん+一九÷= 6 . y6 . zkm ((η之lxu-C.x au~\ a p ¥ a t +Uxa ;)= ‑ a ; [η之Jxり r au mnl 百+(u dX n ; ; . -守 6 . x6 . y6 . z (3羽1 Lett h ev e l o c i t yv xo fap a r t i c l ebedecomposedi n t otwop a r t s , V x= tら + v訂 Ux = V x 1 V)uj=q叫(E+ux B)‑Vp * I ft h er e a d e rh a sn o te n c o u n t e r e dt h i sb e f o r e ,1 1 1 sd e r i v e di nS e c t m n3.3.5 一一一一一一 ( 3 ‑ 4 3 ] ( 3 ‑ 4 4 ] What we have d e r i v e di so n l yas p e c i a lc a s e :t h et r a n s f e ro fx momentumbymotioni nt h exd i r e c t i o n ;andwehaveassumedt h a tt h e f l u i di si s o t r o p i c ,s ot h a tt h esamer e s u l th o l d si ntheyandzd i r e c t i o n s . Buti ti sa l s op o s s i b l et ot r a n s f e rymomentumbymotioni nt h exd i r e c t i o n , f o ri n s t a n c e .Suppose,i nF i g .3 ‑ 3 ,t h a tuヲ is z e r oi nt h ecubea tx= x 0 buti sp o s i t i v eonboths i d e s .Thena sp a r t i c l e smigratea c r o s st h ef a c e s A andB,t h e ybringi nmorep o s i t i v eymomentumthant h e yt a k eo u t , andt h ef l u i delementg a i n smomentumi nt h eyd i r e c t i o n .Thiss h e a r i ¥ " e nbyat e n s o r s t r e s scannotberepresentedbyascalar 合 but mustbeg This r e s u l tw i l l be j u s t doubled by t h ec o n t r i b u t i o no f left‑movmg l s omovei nt h e p a r t i c l e s ,s i n c et h e yc a r r yn e g a t i v exmomentumanda o p p o s i t ed i r e c t i o nr e l a t i v et ot h eg r a d i e n to f The刷al changeo f oi st h e r e f o r e momentumo ft h ef l u i delementa tx a [ 3 ‑ 4 2 ] Thisi st h eu s u a lp r e s s u r e ‑ g r a d i e n tf o r c e .Addingt h eelect附nagn附 eti f o r c e sandg e n e r a l i z i n gt ot h r e ed i m e n s i o n s ,wehavet h ef l u i dequation [ 3 ‑ 3 7 ] ~m(-6.x );.(♂) a x I mn {~Ux =6 . y6 . z 隅ナ(ηVx) [ 3 ‑ 4 1 ] wehavef i n a l l y Thust h en e tg a i ni nxmomentumfromright司moving p a r t i c l e si s n [ 3 ‑ 4 0 ] a l l o w su st oc a n c e lt h etermsn e a r e s tt h ee q u a ls i g ni nE q .( 3 ‑ 4 0 ] .Defining t h ep r e s s u r e 一宮 ( n m u x )6 . x6 . y6 . z= a t a ; Thee q u a t i o no fmassc o n s e r v a t i o n * Thesumover6 . n vr e s u l t si nt h eaverageV xovert h ed i s t r i b u t i o n .The comesfromt h ef a c tt h a to n l yh a l ft h ep a r t i c l e si nt h ecubea t f a c t o rk x 0‑6 . xa r egoingto叩ard f a c eA.S i m i l a r l y ,t h emomentumc a r r i e dout throughf a c eB i s 二'... a u . a m n u x ‑ ; ; : ‑‑ (nKT) 一( 一一一←一一一一 閉山 I E ~ (nmux)=‑m‑/;[n 応札+之)] =-m 子 rn(u; +~) l ¥ m JJ 2 白山ゐ 6 . n vV x6 . y6 . z I 2 m v x r=2KT A whereU xi st h ef l u i dv e l o c i t yandV x ri st h erandomthermalv e l o c i t y .For aone‑d1mensionalMaxwelliand i s t r i b u t i o n ,wehavefromE q .( 1 ‑ 7 ] nU5 randommotiono fp a r t i c l e si nandouto faf l u i delementanddoesn o t . x6 . y6 . z appeari nt h eequationf o ras i n g l ep a r t i c l e .Letaf l u i delement6 becentereda t( x 0 ,~6.y, ~6.z) ( F i g .3・3). Fors i m p l i c i t y ,wes h a l lc o n s i d e r o n l yt h excomponento fmotionthrought h ef a c e sA andB.Thenumber o fp a r t i c l e spersecondp a s s i n gthrought h ef a c eA w i t hv e l o c i t yV xi s H .加 62 C h a p t e r T h r e e t h en e u t r a lf l u i d .I fr ,themeanf r e etimebetweenc o l l i s i o n s ,i sa p p r o x i ュ matelyc o n s t a n t ,t h er e s u l t i n gf o r c e term can be roughly w r i t t e na s ‑mn(u‑u o ) / r .Thee q u a t i o no fmotion ( 3 ‑ 4 4 ]can beg e n e r a l i z e dt o i n c l u d ea n i s o t r o p i cp r e s s u r eandn e u t r a lc o l l i s i o n sa sf o l l o w s : rau 1 明η ( u-uo) LOL 」 T mnJ で+ ( uキV)uI = qn( E+uX B)‑VキP 一一一一一一- 、vntten lρ0 0 ¥ P OJ ¥ O o pI P=IO C o l l i s i o n sbetweenchargedp a r t i c l e shaven o tbeeni n c l u d e d ;t h e s ew i l l b ‑ : :t r e a t e di nChapter5 . [ 3 ‑ 4 5 ] V.pi sj u s tV p .I nS e c t i o n1 . 3 ,wenotedt h a taplasmacouldhavetwo t e m p e r a t u r e sTム and T 1 1i nt h epresenceo famagnetic 自eld. Int h a tc a s e , t h e r ewould be two p r e s s u r e sP ょ = nKTょ and P 1 1= n K T 1 1 . Thes t r e s s ComparisonwithOrdinaryHydrodynamics 3 . 3 . 4 Ordinaryf l u i d sobeyt h eNavier‑Stokese キ q u a t i o n tt , EEE OO li、 t P[~ +(uキV)uJ = ‑Vp+pv¥ 7 2 u [ 3 ‑ 4 6 ] tf -- 九州 ’’’’ 一一 114 aFeaEhEth 』6』 n r oho hoo t e n s o ri st h e n [ 3 ‑ 4 7 ] [ 3 ‑ 4 8 ] Thisi st h esamea st h eplasmae q u a t i o n( 3 ‑ 4 7 )e x c e p tf o rt h eabsence o fe l e c t r o m a g n e t i cf o r c e sandc o l l i s i o n sbetweens p e c i e s( t h e r ebeing o n l yones p e c i e s ) .Thev i s c o s i t ytermpvV2u ,whereνis t h ek i n e m a t i c h eabsence v i s c o s i t yc o e f f i c i e n t ,i sj u s tt h ec o l l i s i o n a lp a r to fVキP‑V台 in t o fmagneticf i e l d s .Equation( 3 ‑ 4 8 )d e s c r i b e saf l u i di nwhicht h e r ea r e frequentc o l l i s i o n sbetweenp a r t i c l e s .Equation( 3 ‑ 47 ] ,ont h eo t h e rhand, wasd e r i v e dwithoutanye x p l i c i tstatemento ft h ec o l l i s i o nr a t e .S i n c e t h etwoe q u a t i o n sa r ei d e n t i c a le x c e p tf o rt h eE andB t e r m s ,canE q . ( 3 ‑ 47 ]r e a l l yd e s c r i b eaplasmas p e c i e s ?Theansweri saguardedy e s , andt h er e a s o n sf o rt h i sw i l lt e l lu st h el i m i t a t i o n so ft h ef l u i dt h e o r y . Int h ed e r i v a t i o no fE q .[ 3 ‑ 4 7 ) ,wed i da c t u a l l yassumei m p l i c i t l y t h a tt h e r ewerec o l l i s i o n s .Thisassumptioncamei nE q .( 3 ‑ 3 9 ]whenwe took t h ev e l o c i t yd i s t r i b u t i o nt o be M a x w e l l i a n . Such a d i s t r i b u t i o n g e n e r a l l ycomesabouta st h er e s u l to ffrequentc o l l i s i o n s .However,t h i s assumptionwasusedonlyt ot a k et h eaverageo fv ;,・ Any o t h e rdistribu・ t i o nw i t ht h esameaveragewouldg i v eu st h esameanswer.Thef l u i d t h e o r y ,t h e r e f o r e ,i sn o tv e r ys e n s i t i v et od e v i a t i o n sfromt h eMaxwellian d i s t r i b u t i o n ,althought h e r ea r ei n s t a n c e si nwhicht h e s ed e v i a t i o n sa r e i m p o r t a n t .K i n e t i ctheorymustthenbeu s e d . Therei sa l s oane m p i r i c a lo b s e r v a t i o nbyI r v i n gLangmuirwhich h e l p st h ef l u i dt h e o r y .Inworkingwitht h ee l e c t r o s t a t i cprobeswhich bearh i sname,Langmuird i s c o v e r e dt h a tt h ee l e c t r o nd i s t r i b u t i o nf u n c ュ t i o nwasf a rmoren e a r l yMaxwellianthancouldbeaccountedf o rbyt h e c o l l i s i o nrate・ This phenomenon,c a l l e dLangmuir ’s p a r a d o x ,hasbeen wheret h ec o o r d i n a t eo ft h et h i r d. r o worcolumni st h ed i r e c t i o no fB . Thisi ss t i l ld i a g o n a landshowsi s o t r o p yi naplaneperpendiculartoB . I nan o r d i n a r yf l u i d ,t h eo f f ‑ d i a g o n a lelements o fP a r eu s u a l l y a s s o c i a t e dw i t hv i s c o s i t y .Whenp a r t i c l e smakec o l l i s i o n s ,t h e ycomeo f f w i t hana v e r a g ev e l o c i t yi nt h ed i r e c t i o no ft h ef l u i dv e l o c i t yu a tt h e p o i n twheret h e ymadet h e i rl a s tc o l l i s i o n .Thismomentumi st r a n s f e r r e d t oanotherf l u i delementupont h en e x tc o l l i s i o n .Thist e n d st oe q u a l i z e ua td i f f e r e n tp o i n t s ,andt h er e s u l t i n gr e s i s t a n c et oshearf l o wi swhat wei n t u i t i v e l yt h i n ko fa sv i s c o s i t y .Thelongert h emeanf r e ep a t h ,t h e f a r t h e rmomentumi sc a r r i e d ,andt h el a r g e ri st h ev i s c o s i t y .Inaplasma t h e r ei sas i m i l a re f f e c twhicho c c u r seveni nt h eabsenceo fc o l l i s i o n s . TheLarmorg y r a t i o no fp a r t i c l e s( p a r t i c u l a r l yi o n s )b r i n g sthemi n t o d i f f e r e n tp a r t so ft h eplasmaandt e n d st oe q u a l i z et h ef l u i dv e l o c i t i e s t h e r e .TheLarmorr a d i u sr a t h e rthant h emeanf r e epaths e t st h es c a l e o ft h i skindo fc o l l i s i o n l e s sv i s c o s i t y .I ti saf i n i t e ‑ L a r m o r ‑ r a d i u se f f e c t whicho c c u r si na d d i t i o nt oc o l l i s i o n a lv i s c o s i t yandi sc l o s e l yr e l a t e dt o t h eV E d r i f ti nanonuniformEf i e l d( E q .[2 ・58)). o l l i s i o n s 3 . 3 . 3 C I ft h e r ei san e u t r a lg a s ,t h echargedf l u i dw i l lexchangemomentum w i t hi t through c o l l i s i o n s . The momentum l o s t per c o l l i s i o nw i l l be p r o p o r t i o n a lt ot h er e l a t i v ev e l o c i t yu‑n o ,whereuoi st h ev e l o c i t yo f -'』』 ん同 H P ,t h es t r e s st e n s o r ,whosecomponentsP ; ;=mηU的 specify botht h e d i r e c t i o no fmotionandt h ecomponento fmomentumi n v o l v e d .I nt h e g e n e r a lc a s et h eterm-V戸 is r e p l a c e dby-V ・ P. Wes h a l ln o tg i v et h es t r e s st e n s o rheree x c e p tf o rt h etwos i m p l e s t cases ・ When t h ed i s t r i b u t i o nf u n c t i o ni sani s o t r o p i cM a x w e l l i a n ,P i s ド。ω ゐ ハ m .山 U C h a p t e r T h r e e RL 品 64 66 Cha戸ter T h r e e whereC i sac o n s t a n tandγis t h er a t i oo fs p e c i f i ch e a t sG p /C"・ The termVpi st h e r e f o r eg i v e nby a t t r i b u t e da tt i m e st oh i g h ‑ f r e q u e n c yo s c i l l a t i o n s .Thereh a sbeenno s a t i s f a c t o r yr e s o l u t i o no ft h ep a r a d o x ,butt h i sseemst obeoneo ft h e fewi n s t a n c e si nplasmap h y s i c swherenatureworksi nourf a v o r . Anotherr e a s o nt h ef l u i dmodelworksf o rplasmasi st h a tt h emagュ n e t i cf i e l d ,whent h e r ei so n e ,canp l a yt h er o l eo fc o l l i s i o n si nac e r t a i n s e n s e .Whenap a r t i c l ei sa c c e l e r a t e d ,s a ybyanE f i e l d ,i twouldc o n ュ t i n u o u s l yi n c r e a s ei nv e l o c i t yi fi twerea l l o w e dt of r e e ‑ s t r e a m .When t h e r ea r ef r e q u e n tc o l l i s i o n s ,t h ep a r t i c l ecomest oal i m i t i n gv e l o c i t y p r o p o r t i o n a lt oE .Thee l e c t r o n si nacopperw i r e ,f o ri n s t a n c e ,d r i f t , E ,whereオ ,i st h em o b i l i t y .A magnetic t o g e t h e rw i t hav e l o c i t yv=オ f i e l da l s ol i m i t sf r e e ‑ s t r e a m i n gbyf o r c i n gp a r t i c l e st og y r a t ei nLarmor o r b i t s . The e l e c t r o n si n a plasma a l s od r i f tt o g e t h e rw i t h av e l o c i t y p r o p o r t i o n a lt oE ,n a m e l y ,v E=ExB/B2.I nt h i ss e n s e ,ac o l l i s i o n l e s s plasmabehavesl i k eac o l l i s i o n a lf l u i d .Ofc o u r s e ,p a r t i c l e sdof r e e ‑ s t r e a m a l o n gt h emagneticf i e l d ,andt h ef l u i dp i c t u r ei sn o tp a r t i c u l a r l ys u i t a b l e ,t h ef l u i d f o rmotionsi nt h a td i r e c t i o n . Foγ 叩otions peゆendiculaγ to B theoγy i sagoodapproximatioη. Vp 合 6 7 P l a s m a s AsF l u i d s Vn [ 3 ‑ 5 2 1 γ7 Fori s o t h e r m a lc o m p r e s s i o n ,wehave Vp= V(nKT)= KTVn s ot h a t ,clearly , γ = 1 .Fora d i a b a t i cc o m p r e s s i o n ,K Tw i l la l s ochange, g i v i n gγa v a l u el a r g e rthano n e .I fN i st h enumbero fdegreeso f freedom , γis g i v e nby γ = (2+N)/N [ 3 ‑ 5 3 1 Thev a l i d i t yo ft h ee q u a t i o no fs t a t er e q u i r e st h a th e a tf l o wben e g l i g i b l e ; t h a ti s ,t h a tthermalc o n d u c t i v i t ybel o w .A g a i n ,t h i si smorel i k e l yt obe t r u ei nd i r e c t i o n sp e r p e n d i c u l a rt oB thanp a r a l l e lt oi t .F o r t u n a t e l y , mostb a s i cphenomenacanb ed e s c r i b e da d e q u a t e l ybyt h ecrudeassumpュ t ! O no fE q .( 3 ‑ 5 1] . 3 . 3 . 5 Equationo fC o n t i n u i t y Thec o n s e r v a t i o no fm a t t e rr e q u i r e st h a tt h et o t a lnumbero fp a r t i c l e s Ni navolumeVcanchangeo n l yi ft h e r ei san e tf l u xo fp a r t i c l e sa c r o s s t h es u r f a c eS boundingt h a tvolume.S i n c et h ep a r t i c l ef l u xd e n s i t yi s n u ,weh a v e ,byt h ed i v e r g e n c etheorem, aN ia n i at=I vatdV= ‑ c pnu 「 必=- Lv (叩) dV TheCompleteS e to fF l u i dEquations 3 . 3 . 7 Fors i m p l i c i t y ,l e tt h eplasmah在ve o n l ytwos p e c i e s :i o n sande l e c t r o n s ; e x t e n s i o nt omores p e c i e si st r i v i a l .Thechargeandc u r r e n td e n s i t i e sa r e theng i v e nby [3・49] σ = 一一 n u η u v 伽一川町 ) S i n c es i n g l e ‑ p a r t i c l emotionsw i l lnol o n g e rbec o n s i d e r e d ,wemaynow u s evi n s t e a do fuf o rthe 自 uid v e l o c i t y .Wes h a l ln e g l e c tc o l l i s i o n sand v i s c o s i t y .Equations[ 3 ‑ l ] ‑ ( 3 ‑ 4 ] ,( 3 ‑ 4 4 ] ,(3 ・50], and( 3 ‑ 5 1 ]formt h ef o l l o w ュ i n gs e t : [ 3 ‑ 5 0 ] Therei sonesuche q u a t i o no fc o n t i n u i t yf o reachs p e c i e s .Anys o u r c e so r s i n k so fp a r t i c l e sa r et obeaddedt ot h er i g h t ‑ h a n ds i d e . +n,q, 3 . 3 . 6 EquationofState εo V キ E= n ; q ; [ 3 ‑ 5 5 ] V xE= ‑B VキB=O [ 3 ‑ 5 6 ] [ 3 ‑ 5 7 ] オ,01VxB = r明, Vi + η,q,v, + ε。主 Onemorer e l a t i o ni sneededtoc l o s et h es y s t e mo fe q u a t i o n s .Fort h i s , wecanu s et h ethermodynamice q u a t i o no fs t a t erelating 世 ton: 争 = Gp" [3 ・54] J= n , q ;v ;+n , q ,v , S i n c et h i smusth o l df o ranyvolumeV ,t h ei n t e g r a n d smustbee q u a l : + n , q ,+n , q , l a / +(v; V)巧/ =q,n;(E+v;xB)‑Vp; IdV' m , n ; [3・51] .』 I [ 3 ‑ 5 8 ] j= i ,e ( 3 ‑ 5 9 ] . . B xVn f o= n e ( v n ;‑V n , )=(KT;+KT,) 一五「 I nt h ep a r t i c l ep i c t u r e ,onewouldnote x p e c tt omeasureac u r r e n ti ft h e of l o w s guidingc e n t e r sdon o td r i f t .I nt h ef l u i dp i c t u r e ,t h ec u r r e n tf wherever t h e r ei sap r e s s u r eg r a d i e n t .These twov i e w p o i n t scanb e r e c o n c i l e di fonec o n s i d e r st h a ta l lexperimentsmustbec a r r i e do u ti n af i n i t e ‑ s i z e dp l a s m a .Supposet h eplasmawerei nar i g i dbox( F i g .3 ‑ 6 ) . I foneweret oc a l c u l a t et h ec u r r e n tfromt h es i n g l e ‑ p a r t i c l ep i c t u r e ,one wouldhavet ot a k ei n t oaccountt h ep a r t i c l e sa tt h eedgeswhichhave c y c l o i d a lp a t h s .S i n c et h e r ea r emorep a r t i c l e sont h el e f tthanont h e i t ht h ef l u i d r i g h t ,t h e r ei s an e tc u r r e n tdownward, i nagreeme ロt w p i c t u r e . Thereadermayn o tbesatis白ed w i t ht h i se x p l a n a t i o nb e c a u s ei twas ft h ew a l l swereabsorbingo ri f n e c e s s a r yt os p e c i f yr e f l e c t i n gw a l l s .I t h e ywereremoved,onewouldf i n dt h a te l e c t r i cf i e l d swoulddevelop O r i g i no ft h ed i a m a g n e t i cd r i f t . r i t et h ediamagneticd r i f ta s Witht h eh e l po fEq目[3-52], wecanw . γ·KTzxVη (3 ・ 66] V n =士一戸一一一一一一一- eB LJ n Inp a r t i c u l a r ,f o rani s o t h e r m a lplasmai nt h egeome~ry o fFig. 九 in whichVn=n ’r, wehavet h efollowi時 formulas f a m i l i a rt oexpenmenュ t a l i s t swhohaveworkedw i t hQ ‑ m a c h i n e s " ' : E- く n u E , ,, 、町、E‘ \ 一 E Vni =di -;:;- σ ”山一千’ lt d no -内 / KT; η ’ Z (3 ・69] ( 3 ‑ 6 7 ] KT,n ’ J di-;:;- σ Vn,= ‑ Themagnitudeo fvni se a s i l ycomputedfromt h eformula V 一) 作一T U一B ( ( 3 ‑ 6 8 ] B whereAi st h edens町 scale l e n g t h!?げがlinm. Thep h y s i c a lr e a s o nf o rt h i sd r i f tcanbes e e nfromF i g .3・5. Here wehavedrawnt h eo r b i t so fi o n sg y r a t i n gi namagneticf i e l d .Therei s ad e n s i t yg r a d i e n ttowardt h el e f t ,a si n d i c a t e dbyt h ed e n s i t yo fo r b i t s . P a r t i c l ed r i f t si n a bounded p l a s m a , i l l u s t r a t i n gt h er e l a t i o nt of l u i dd r i f t s . FIGURE3 ‑ 6 噂AQ ‑ m a c h i n ep r o d u c e saqu四ent p l a s m ab yt h e r m a lionizatio~ ~f 守 or K , " . t 0 m si m p i n e r ef i r s tm e a s t dmυ- macnm白 o n hott u n g s t e np l a t e s .D i a m a g n e t i cd仙s w 、 一一」ムー一 円山ぬ FIGURE3 ・5 コ コ コ A 『←- Vn Throughanyf i x e dvolumeelementt h e r ea r emorei o n smovingdownュ wardthanupward,s i n c et h edownward司moving i o n scomefromar e g i o n o fhigherd e n s i t y .Therei s ,t h e r e f o r e ,af l u i dd r i f tperpendiculart oVn andB ,e v e nt h o u g ht h eg u i d i n gc e n t e r saγe stationaη. Thediamagneticd r i f t r e v e r s e ss i g nw i t hq b e c a u s et h ed i r e c t i o no fg y r a t i o nr e v e r s e s .The magnitudeo fvndoesnotdependonmassb e c a u s ethem‑112dependence o ft h ev e l o c i t yi sc a n c e l l e d by t h em112 dependence o ft h e Larmor radiusーless o ft h ed e n s i t yg r a d i e n ti ssampledduringag y r a t i o ni ft h e massi ss m a l l . S i n c ei o n s and e l e c t r o n sd r i f ti no p p o s i t ed i r e c t i o n s ,t h e r ei sa diamagneticc u r r e n t .Forγ = Z = . l ,t h i si sg i v e nby Jm ’仰 ’伯RI C h a p t e r T h r e e ① ps 。 B コペ) OO Xノ 70 68 C h a p t e r T h r e e 竺t+v ・(n;v;) =0 i ) t , j= i , e j=i,e 金;= C,nj; [ 3 ‑ 6 0 ] [3 司 61] /プ/ Therea r e1 6s c a l a runknowns:n ;,叫, p., p , ,v ; ,v , ,E ,andB .Therea r e a p p a r e n t l y1 8s c a l a re q u a t i o n si fwecounteachv e c t o re q u a t i o na st h r e e s c a l a re q u a t i o n s .However,twoo fMaxwell ’ s e q u a t i o n sa r es u p e r f l u o u s , s i n c eEqs・(3-55] and[ 3 ‑ 5 7 ]canber e c o v e r e dfromt h ed i v e r g e n c e so f E q s .[ 3 ‑ 5 8 ]and[ 3 ‑ 5 6 ](Problem3 ‑ 3 ) .Thesimultaneouss o l u t i o no ft h i s 6e q u a t i o n si n1 6unknownsg i v e sas e l f ‑ c o n s i s t e n ts e to ff i e l d s s e to f1 andmotionsi nt h ef l u i da p p r o x i m a t i o n . 3 . 4 FLUID DRIFTS PERPENDICULARTO B !守 S i n c e af l u i d elementi scomposed o fmanyi n d i v i d u a lp a r t i c l e s , one woulde x p e c tt h ef l u i dt ohaved r i f t sp e r p e n d i c u l a rt oBi ft h ei n d i v i d u a l g u i d i n gc e n t e r shavesuchd r i f t s .However,s i n c et h eVptermappears o n l yi nt h ef l u i de q u a t i o n s ,t h e r ei sad r i f ta s s o c i a t e dw i t hi twhicht h e f l u i de l e m e n t shavebutt h ep a r t i c l e sdonoth a v e .Foreachs p e c i e s ,we haveane q u a t i o no fmotion ( L<ll ( Considert h er a t i oo fterm ( Therefore, F [ 3 ‑ 6 2 ] ( 3 ) J where w to … term (: 百 明η|竺+ (vキV)vj=qη (E+v'.'.< B)一町 D i a m a g n e t i cd r i f t si nac y l i n d r i c a lp l a s m a . FIGURE3 ・4 [ 3 . 6 4 ] ①= I竺E竺主土|=主 ( [3 ・63] Iq n v J ̲ BI w, Herewehavet a k e ni J / i J t=i wanda r eco町erned o n l yw i t hh・ Foぺrifts s l o wcomparedw i t ht h et i m es c a l eo fw口 we mayn e g l e c ttermC J ) .We s h a l la l s on e g l e c tt h e( vキ V)vtermandshowa 世osteriori t h a tt h i si sa l l r a d i e n t .This1 s r i g h t .LetEandBbeuniform,butletπand phaveag t h eu s u a ls i t u a t i o ni nam a g n e t i c a l l yc o n f i n e dplasmacolumn( F i g .3 ‑ 4 ) . Takingt h ec r o s sproducto fE q .[ 3 ‑ 6 2 ]w i t hB ,wehave( n e g l e c t i n gt h e VpXB I VoE 一一一一γ | Diamagneticd r i f t qnB ' Thed r i f tv Ei st h esamea sf o rguidingc e n t e r s ,butt h e r ei snowanew d r i f tv 0 ,c a l l e dt h ediamagneticd r i f t .S i n c ev0i sp e r p e n d i c u l a rt ot h e d i r e c t i o no ft h eg r a d i e n t ,ourn e g l e c to f( vキV)vi sj u s t i f i e di fE=0 .I f E=-Vφ ¥ 0 ,( vキV)vi ss t i l lz e r oi fVφand Vpa r ei nt h esamed i r e c t i o n ; o t h e r w i s e ,t h e r ecouldbeamorec o m p l i c a t e ds o l u t i o ni n v o l v i n g( vキV ) v . l e f t ‑ h a n ds i d e ) O=qn[ExB+(vム× =qn[ExB+ザ B) [ 3 ‑ 6 5 ] xB]‑VpxB B)-vJ.B2]-VpxB ~』』 I nanonuniformBf i e l dt h eg u i d i n gc e n t e r sd r i f tb u tt h ef l u i de l e m e n t sdon o t . FIGURE3 ‑ 8 ~/R,= ηKT11/ R,hastobeaddedtotheright‑handsideofthefluid e q u a t i o n-~f motion.Thisi se q u i v a l e n tt oag r a v i t a t i o n a lf o r c eA f n g ,w i t h ~ ~ KT11/MR"andl e a d st oad r i f tv .= ( m / q ) ( gラ B)/B2,a si nt h ep a r ュ t 1 c l ep i c t u r e( E q .[ 2 ‑ 1 8 ] ) . Thegrad‑Bd r i f t ,however,doesnote x i s tf o rf l u i d s .I tcanbeshown on thermodynamic grounds t h a t a magnetic f i e l d does not a f f e c ta Maxwelliand i s t r i b u t i o n .Thisi sbecauset h eLorentzf o r c ei sperpenュ d i c u l a rt ovandcannotchanget h eenergyo fanyp a r t i c l e .Themost probabled i s t r i b u t i o nf ( v )i nt h eabsenceo fB i sa l s ot h emostp r o b a b l e d i s t r i b u t i o ni nt h epresenceo fB .I ff ( v )remainsMaxwelliani nanonu n i ュ formB f i e l d ,andt h e r ei snod e n s i t yg r a d i e n t ,thent h en e tmomentum c a r r i e di n t oanyf i x e df l u i delementi sz e r o .Therei snof l u i dd r i f teven thought h ei n d i v i d u a lguidingc e n t e r shaved r i f t s ;t h ep a r t i c l ed r i f t si n any 五xed f l u i delementc a n c e lo u t .Tos e et h i sp i c t o r i a l l y ,c o n s i d e rt h e o r b i t so ftwop a r t i c l e smovingthroughaf l u i delementi nanonuniform Bf i e l d(Fig. 与8). S i n c et h e r ei snoE f i e l d ,t h eLarmorr a d i u schanges o n l ybecauseo ft h eg r a d i e n ti nB ;t h e r ei snoa c c e l e r a t i o n , andt h e p且rticle energyremainsc o n s t a n tduringt h em o t i o n .I ft h etwop a r t i c l e s h a v ̲ et h esamee n e r g y ,t h e yw i l l havet h esamev e l o c i t yand Larmor h ef l u i de l e m e n t .Therei st h u sap e r f e c tc a n c e l l a t i o n radmsw h i l einそiδe t be~tween p a r t i c l ep a i r swhent h e i rv e l o c i t i e sa r eaddedt og i v et h ef l u i v e l o c i t y . FIGURE3・7 Whent h e r ei sanonuniformE f i e l d ,i ti sn o te a s yt or e c o n c i l et h e 臼 uid andp a r t i c l ep i c t u r e s .Thent h ef i n i t e ‑ L a r m o r ‑ r a d i u se f f e c to fS e c ュ t i o n2 . 4c a u s e sbothaguidingc e n t e rd r i f tandaf l u i dd r i f t ,butt h e s e M e a s u r i n gt h ed i a m a g n e t i cc u r r e n ti naninhomogeneousp l a s m a . __...』ー- 7m 同H A e VBt Js p becausemoreo fonespecies‑theonew i t hl a r g e rLarmorradius‑would bec o l l e c t e dthant h eo t h e r .Thent h eguidingc e n t e r swouldd r i f t ,and t h es i m p l i c i t yo ft h emodelwouldbel o s t .A l t e r n a t i v e l y ,onecouldimagine t r y i n gt omeasuret h ediamagneticc u r r e n tw i t hacurrentprobe( F i g . 3 ‑7 ) .Thisi sj u s tatransformerwithac o r eo fmagneticm a t e r i a l .The primarywindingi st h e plasma currentthreadingt h ec o r e , and t h e secondaryi sam u l t i t u r nwindinga l laroundt h ec o r e . Lett h ewhole t h i n gbei n f i n i t e s i m a l l yt h i n ,s oi tdoesnoti n t e r c e p tanyp a r t i c l e s .I ti s c l e a rfromF i g .3 ‑ 7t h a tan e tupwardc u r r e n twouldbemeasured,t h e r e beinghigherd e n s i t yont h el e f tthanont h er i g h t ,s ot h a tt h ediamagnetic 印rrent i sar e a lc u r r e n t .Fromt h i sexample,onecans e et h a ti tcanbe i t ht h es i n g l e ‑ p a r t i c l ep i c t u r e .Thef l u i dt h e o r y q u i t et r i c k ytoworkw u s u a l l yg i v e st h er i g h tr e s u l t s when a p p l i e ds t r a i g h t f o r w a r d l y , even thoughi tcontains “ fictitious ” drifts l i k et h ediamagneticd r i f t . Whataboutt h egrad‑Bandc u r v a t u r ed r i f t swhichappearedi nt h e s i n g l e ‑ p a r t i c l ep i c t u r e ?Thec u r v a t u r ed r i f ta l s oe x i s t si nt h ef l u i dp i c t u r e , s i n c et h ec e n t r i f u g a lf o r c ei sf e l tbya l lt h ep a r t i c l e si naf l u i delement a st h e y move around a bend i nt h e magnetic f i e l d . A term fミr= C h a p t e r T h r e e . M 3 山ゐ 72 a r enott h esame;i nf a c t ,t h e yhaveo p p o s i t es i g n s !Thep a r t i c l ed r i f t wasc a l c u l a t e di nChapter2 ,andt h ef l u i dd r i f tcanbec a l c u l a t e dfrom fP .I ti sextremelyd i f f i c u l tt oe x p l a i nhow t h eoιdiagonal elementso thef i n i t e ‑ L a r m o r ‑ r a d i u se f f e c t sd i f f e r .A simplep i c t u r el i k eF i g .3 ‑ 6w i l l a k ei n t oaccounts u b t l ep o i n t sl i k et h e notworkbecauseone h a sto t f o l l o w i n g :Int h epresenceo fad e n s i t yg r a d i e n t ,t h ed e n s i t yo fguiding c e n t e r si snott h esamea st h ed e n s i t yo fp a r t i c l e s ! 74 ; Chapleγ : T h r e e ( c )I nt h el a bf r a m e ,i st h i sc u r r e n tc a r r i e db yi o n so rb ye l e c t r o n so rbyboth コ 75 P l a s m a s AsF l u i d s I nt h ep r e c e d i n gp r o b l e m ,b yhowmuchd o e st h ed i a m a g n e t i cc u r r e n t r e d u c e B on t h e axisコ Hint: You may u s e Ampere ’s c i r c u i t a ll a wo v e ran a p p r o p r i a t ep a t h . 3・9. FLUID DRIFTS PARALLEL T O B 3 . 5 ft h ef l u i dequationofmotioni s Thezcomponento PROBLEMS ~ふ Show t h a tE q s .[ 3 ‑ 5 5 ]and(3・57] a r eredundanti nt h es e to fM a x w e l l ' s e q u a t i o n s . mn[子(v キV)v,J= qnE,‑~ 3司4. Showt h a tt h ee x p r e s s i o nf o rf oont h er i g h t ‑ h a n ds i d eo fE q .( 3 ‑ 6 9 ]h a s Thec o n v e c t i v etermcano f t e nben e g l e c t e dbecausei ti smuchs m a l l e r v , / a tt e r m .Wes h a l lavoidcomplicatedargumentshereand thant h ea ,i ss p a t i a l l yuniform.UsingE q .( 3 ‑ 5 2 ] , simplyc o n s i d e rc a s e si nwhichv wehave t h ed i m e n s i o n so fac u r r e n td e n s i t y . 3 ・5. Showt h a ti ft h ec u r r e n tc a l c u l a t e dfromt h ep a r t i c l ep i c t u r e( F i g .3 ‑ 6 )a g r e e s w i t ht h a tc a l c u l a t e dfromt h ed i a m a g n e t i cd r i f tf o ronew i d t ho ft h eb o x ,t h e n i tw i l la g r e ef o ra l lw i d t h s . [ 3 ‑ 7 1 ] Thisshowst h a tt h ef l u i di sa c c e l e r a t e dalongB undert h ecombined e l e c t r o s t a t i candpressureg r a d i e n tf o r c e s .A p a r t i c u l a r l yimportantr e s u l t i sobtainedbyapplyingE q .( 3 ‑ 7 1 ]t om a s s l e s se l e c t r o n s .Takingt h el i m i t m • O ands p e c i f y i n gq= ‑ eandE= -Vφ , we have* π = n0(1-x2 /α2) ( a )D e r i v ea ne x p r e s s i o nf o rt h ee l e c t r o nd i a m a g n e t i cd r i f tv e l o c i t yv v ,a sa . funcuono fx ( b ) Drawad i a g r a mshowingt h ed e n s i t yp r o f i l eandt h ed i r e c t i o no fV v ,onb o t h s i d e so ft h em i d p l a n ei fB i so u to ft h ep a p e r . 。φγKT, aη q E ,= e で一=一一一ーでー 。Z n <!Z 0 ,a tx=a / 2i fB =0 . 2T ,KT,=2e V ,anda=4c m . ( c )E v a l u a t ev [ 3 ‑ 7 2 ] E l e c t r o n sa r es omobilet h a tt h e i rh e a tc o n d u c t i v i t yi salmosti n f i n i t e . .I n t e g r a t i n g , Wemaythenassumei s o t h e r m a le l e c t r o n sandt a k eγ = 1 wehave 3 ‑ 7 .Ac y l i n d r i c a l l ys y m m e t r i cp l a s m acolumni nauniformBf i e l dh a s and qFγKT Oη 。v, at 市, mη az 一一一一- 3・6. Ani s o t h e r m a lp l a s m ai sc o n f i n e db e t w e e nt h ep l a n e sx=土αin am a g n e t i c J , .Thed e n s i t yd i s t r i b u t i o ni s f i e l dB= B η (r) = ηo e x p(一戸/r~) [ 3 ‑ 7 0 ] n ,= n ,= n oexp(eφ/ KT,) eφ = KT, ( a )Showt h a tV Eandv 0 ,a r ee q u a lando p p o s i t e . o d y . ( b )Showt h a tt h ep l a s m ar o t a t e sas 且 solid b lnn+ C or ( c )I nt h ef r a m ew h i c hr o t a t e sw i t hv e l o c i t yv E ,somep l a s m aw a v e s( d r i f tw a v e s ) p r o p a g a t ew i t hap h a s ev e l o c i t yvφ = 0.5vv.・ What i svφin t h el a bf r a m e ?Ona dia耳ram o ft h eγ - ( Jp l a n e ,drawa r r o w si n d i c a t i n gt h er e l a t i v em a g n i t u d e sand diだctions o fv E ,vv .andvφin t h el a bf r a m e . |… (e<p問| o exp [3・ 73] Thisi sj u s tt h eBoltzmann γelation f o re l e c t r o n s . Whatt h i smeansp h y s i c a l l yi st h a te l e c t r o n s ,beingl i g h t ,a r every mobileandwouldbea c c e l e r a t e dt ohighe n e r g i e sveryq u i c k l yi ft h e r e v 3 ‑ 8 .( a )F o rt h ep l a s m ao fProblem3 ‑ 7 ,f i n dt h ed i a m a g n e t i cc u r r e n td e n s i t yi a saf u n c t i o no fr a d i u s . 0i nA/m2 f o rB =0 . 4T ,no=1 0 1 5m ‑ 3 ,KT,=KT‘= 0 . 2 5e V , ( b )E v a l u a t ej c m . ~hy 叩1’tu,→ oo, k e e p i n gm u , γ = γ。= I ム 一-一一一一一一一一---一一一一----------由園---園-.-目----圃圃圃圃圃. . . . . . . ァー一 一一一ー』 Thep r e v i o u sexampler e v e a l sanimportantc h a r a c t e r i s t i co fplasmas t h a th a swidea p p l i c a t i o n .Wea r eusedt os o l v i n gf o rE fromPoisson ’s nap l a s m a ,t h e e q u a t i o n whenwe a r eg i v e nt h echarged e n s i t yσ. I o p p o s i t eprocedurei sg e n e r a l l yu s e d .Ei sfoundfromt h ee q u a t i o n so f q u a t i o ni susedo n l yt of i n dσ. Ther e a s o ni st h a t mot10n,andPoisson ’s e aplasmah a sano v e r r i d i n gtendencyt oremainn e u t r a l .I ft h ei o n smove, t h ee l e c t r o n sw i l lf o l l o w .E musta d j u s ti t s e l fs ot h a tt h eo r b i t so ft h e e l e c t r o n sandi o n sp r e s e r v en e u t r a l i t y .Thecharged e n s i t yi so fsecondary importance;i tw i l la d j u s ti t s e l fs ot h a tPoisson ’s e q u a t i o ni ss a t i s f i e d .This i st r u e ,o fc o u r s e ,o n l yf o rlow‑frequencymotionsi nwhicht h ee l e c t r o n i n e r t i ai sn o taf a c t o r . I nap l a s m a ,i ti su s u a l l yp o s s i b l et oassumen; =叫 and V Er=0a t t h esamet i m e .Wes h a l lc a l lt h i st h eplasmaapψroximation. I ti safundaュ ment旦i t r a i to fp l a s m a s ,onewhichi sd i f f i c u l tf o rt h en o v i c et ou n d e r s t a n d . Don o tu s eP o i s s o n ' se q u a t i o nt oo b t a i nEuηless i ti su n a v o i d a b l e !I nt h es e t o ff l u i de q u a t i o n s[3-55]ー[3-61], wemaynowe l i m i n a t ePoisson ’s e q u a t i o n ;=n ,=n . anda l s oe l i m i n a t eoneo ft h eunknownsbys e t t i n gn The 戸las maa台。γ·oximation i sa l m o s tt h esamea st h ec o n d i t i o no f q u a s i n e u t r a l i t yd i s c u s s e de a r l i e rbuth a samoree x a c tmeaning.Whereas q u a s i n e u t r a l i t yr e f e r st oag e n e r a ltendencyf o raplasmat oben e u t r a l i ni t ss t a t eo fr e s t ,t h eplasmaapproximationi samathematicals h o r t c u t t h a tonecanu s eevenf o rwavem o t i o n s .Aslonga st h e s emotionsa r e s l o wenought h a tbothi o n sande l e c t r o n shavet i m et omove,i ti sagood q u a t i o nbyt h ee q u a t i o nn; =叫・ Of approximationt or e p l a c ePoisson ’s e c o u r s e ,i fo n l yones p e c i e scanmoveandt h eo t h e rcannotf o l l o w ,such a si nhigh‑frequencye l e c t r o nw a v e s ,thent h eplasmaapproximationi s notv a l i d ,andE mustbefoundfromMaxwell ’s e q u a t i o n sr a t h e rthβn fromt h ei o nande l e c t r o ne q u a t i o n so fm o t i o n .Wes h a l lr e t u r nt ot h e q u e s t i o no ft h ev a l i d i t yo ft h eplasmaapproximationwhenwecomet o t h et h e o r yo fi o nw a v e s .Att h a tt i m e ,i tw i l lbecomec l e a rwhywehad q u a t i o ni nt h ed e r i v a t i o no fDebyes h i e l d i n g . t ousePoisson ’ S e 『骨一一一ー F P 4唖ー一一一一 一一一一- FE -一一ー一昔』 『噌一一一一一 モー唾一一一一 ゆ一 B ー一一一暑F + h y s i c a lr e a s o nf o rt h eBoltzmannr e l a t i o nb e t w e e nd e n s i t y and FIGURE3 ‑ 9 P p o t e n t i a l . werean e tf o r c eonthem.S i n c ee l e c t r o n scannotl e a v ear e g i o ne nm a s s e w i t h o u tl e a v i n gbehindal a r g ei o nc h a r g e ,t h ee l e c t r o s t a t i candp r e s s u r e g r a d i e n tf o r c e sont h ee l e c t r o n smustbec l o s e l yi nb a l a n c e .Thisc o n d i t i o n oe a c hl i n e l e a d st ot h eBoltzmannr e l a t i o n .Notet h a tE q .[3・73] ap戸lies t i f f e r e n tl i n e so ff o r c emaybechargedt od i f f e r e n t o ff o r c ese戸arately. D p o t e n t i a l sa r b i t r a r i l yu n l e s samechanismi sprovidedf o rt h ee l e c t r o n s t omovea c r o s sB .Theconductorsonwhichl i n e so ff o r c et e r m i n a t ecan p r o v i d esuchamechanism,andt h ee x p e r i m e n t a l i s thast ot a k et h e s e ende f f e c t si n t oaccountc a r e f u l l y . F i g u r e3 ‑ 9showsg r a p h i c a l l ywhato c c u r swhent h e r ei sal o c a ld e n s i t y clumpi nt h ep l a s m a .Lett h ed e n s i t yg r a d i e n tbetowardt h ec e n t e ro f sc o n s t a n t .Therei s thenap r e s s u r e t h ediagram,andsupposeK Ti g r a d i e n ttowardt h ec e n t e r .S i n c et h eplasmai sq u a s i n e u t r a l ,t h eg r a d i e n t e x i s t sf o rbotht h ee l e c t r o nandi o nf l u i d s .Considert h ep r e s s u r eg r a d i e n t pont h ee l e c t r o nf l u i d .I td r i v e st h emobilee l e c t r o n sawayfrom f o r c eF t h ec e n t e r ,l e a v i n gt h ei o n sb e h i n d .Ther e s u l t i n gp o s i t i v echargeg e n e r ュ a t e saf i e l dEwhosef o r c eFEont h ee l e c t r o n sopposesF合 Only whenFE i se q u a lando p p o s i t et oF pi sas t e a d ys t a t ea c h i e v e d .I fBisc o n s t a n t ,E a r g ea tt h ec e n t e r ,where i sane l e c t r o s t a t i cf i e l dE=-Vφ, and φmust bel ηis l a r g e .Thisi sj u s twhatE q .( 3 ‑ 7 3 ]t e l l su s .Thed e v i a t i o nfroms t r i c t n e u t r a l i t ya d j u s t si t s e l fs ot h a tt h e r ei si u s tenoughcharget os e tupt h e Ef i e l dr e q u i r e dt ob a l a n c et h ef o r c e sont h ee l e c t r o n s . ーム』 閉山 マp THE PLASMAAPPROXIMATION 3.6 ーーーーーーー- 内 J •a・ o~・~·勾議総 •J:o°- i. 。 γ ウ出ゐ C h a p t e r T h r e e ω 円打 RLm 7 6 ChapterFour Wf町ESIN PLASMAS REPRESENTATIONOF司有TAVES 4 . 1 Anyp e r i o d i cmotiono faf l u i dcanbedecomposedbyF o u r i e ra n a l y s i s i n t oas u p e r p o s i t i o no fs i n u s o i d a lo s c i l l a t i o n sw i t hd i f f e r e n tf r e q u e n c i e s w andwavelengthsλ. A s i m p l ewavei sanyoneo ft h e s ecomponents. When t h eo s c i l l a t i o n amplitude i ss m a l l ,t h e waveform i sg e n e r a l l y s i n u s o i d a l ;andt h e r ei so n l yonecomponent.Thisi st h es i t u a t i o nwe s h a l lc o n s i d e r . Anys i n u s o i d a l l yo s c i l l a t i n gquantity‑say, t h ed e n s i t y nー-can be r e p r e s e n t e da sf o l l o w s : nz 江 exp [ i ( kキr 一 wt)] [ 4 ‑ 1 ] where,i nC a r t e s i a nc o o r d i n a t e s , kキr= k , x+k , y+k~z [ 4 ‑ 2 ] Here 百 is ac o n s t a n td e f i n i n gt h eamplitudeo ft h ewave,andki sc a l l e d ft h ewavepropagatesi nt h exd i r e c t i o n ,k t h epropagationconst且nt. I h a so n l yanxcomponent,andE キ q .[4司 l] becomes ‑ •(kx-w<) n= n e Byc o n v e n t i o n ,t h ee x p o n e n t i a ln o t a t i o nmeanst h a tt h er e a lp a r to ft h e e x p r e s s i o ni st obet a k e na st h emeasurableq u a n t i t y .L e tu schoose 而 to ber e a l ;wes h a l lsoons e et h a tt h i scorrespondst oac h o i c eo ft h eo r i g i n s 79 cos ( k x w t ) [ 4 ‑ 3 ] Ap o i n to fc o n s t a n tphaseont h ewavemovess ot h a t(d/dt)(kx ー wt)= 0 , or 一 - 明 一 ω 一k u 4・ l. [4・ 4] ψ Theo s c i l l a t i n gdens町 n 1andpotentialφl i na “ drift wave” are r e l a t e db y PROBLEM : : i ,̲ eゆ1 竺主土主 KT, w +i a - 一命一d-一 - 山由 Re(n)=而 Fouγ comp]山 h h g d f ;h h i e x p r e s s i o n[ 4 ‑ 7 ] . Therecanbenoc o n f u s i o n ,b e c a u s ei nl i n e a rwave t h e o r yt h esamee x p o n e n t i a lf a c t o rw i l loccuronboths i d e so fanye q u a t i o n andcanbec a n c e l l e do u t . ηo Thisi scall巴d t h ep h a s ev e l o c i t y .I fw/ki sp o s i t i v e ,t h ewavemovest ot h e r i g h t ;t h a ti s ,x i n c r e a s e sa sti n c r e a s e s ,s oa st okeepkx ー wt c o n s t a n t . I fw /ki sn e g a t i v e ,t h ewavemovest ot h el e f t .Wec o u l de q u a l l yw e l l havetaken 回 η = πe wherei ti so n l yn e c e s s a r yt oknowt h a ta l lt h eo t h e rs y m b o l s( e x c e p ti )s t a n df o r p o s t t 1 v ec o n s t a n t s . ( a )F i n da ne x p r e s s i o nf o rt h ep h a s e { )ofφ1 r e l a t i v et o n , .( F o rs i m p l i c i t y ,a s s u m e t h a tn1i sr e a l . ) fw ( b )I .Ckχ + wt) i nwhichc a s ep o s i t i v ew/k wouldhavemeantn e g a t i v ephasev e l o c i t y . Thisi saconventiont h a ti ssometimesu s e d ,butwes h a l ln o tadopti t . o t hw andkmakes FromEq.[ 4 ‑ 3 ] ,i ti sc l e a rt h a tr e v e r s i n gt h es i g no fb nodi征erence. Considernowanothero s c i l l a t i n gq u a n t i t yi nt h ew a v e ,s a yt h ee l e c t r i c f i e l dE .S i n c ewehavea l r e a d ychosent h ephaseo fnt ob ez e r o ,wemust : a l l o wEt ohavead i f f e r e n tphase8 E =Ecos(kx ー wt +8) ‑ <(kx-wt + δ ) E =Ee o r Thephasev e l o c i t yo fawavei naplasmao f t e ne x c e e d st h ev e l o c i t yo f l i g h tc .Thisd oesnotv i o l a t et h et h e o r yo fr e l a t i v i t y ,b e c a u s eani n f i n i t e l y longwavet r a i no fc o n s t a n tamplitudecannotc a r r yi n f o r m a t i o n .The c a r r i e ro far a d i owave,f o ri n s t a n c e ,c a r r i e snoi n f o r m a t i o nu n t i li ti s modulated.Themodulationi n f o r m a t i o ndoesnott r a v e la tt h ephase .Toi l l u s t r a t e v e l o c i t ybuta tt h egroupv e l o c i t y ,whichi sa l w a y sl e s sthanc t h i s ,wemayc o n s i d e ramodulatedwaveformedbyadding(“ beating'”) twowaveso fn e a r l ye q u a lf r e q u e n c i e s .Lett h e s ewavesbe [ 4 ‑ 5 ] ei(kx-w。 where 主c i sacomplexa m p l i t u d e .Thephase8canber e c o v e r e dfrom 孟,, s i n c eRe(孟cl =孟 cos 8andIm(孟,) =孟 sin 8 ,s ot h a t ̲ Im(E,) tan ()=一一一=一一 ’ Re(E,) Ei=E0c o s[ ( k+D.k)x ー (w+llw)t] E2=Eoc o s[ ( k‑M)x 一(ω ームw)t] [ 4 ‑ 8 ] E,andE2d i f f e ri nfrequencyby2 . : l w .S i n c eeachwavemusthavet h e phasev e l o c i t yw/ka p p r o p r i a t et ot h emediumi nwhicht h e yp r o p a g a t e , onemusta l l o wf o rad i f f e r e n c e2 . : l ki npropagationc o n s t a n t .Usingt h e a b b r e v i a t i o n s [ 4 ‑ 6 ] Fromnowo n ,wes h a l lassumet h a ta l lamplitudesa r ecomplexanddrop .Anyo s c i l l a t i n gq u a n t i t yg 1w i l lbew r i t t e n t h es u b s c r i p tc g 1=g 1exp[ i ( kキ r‑wt)] d o e sφ1 l e a do r l a g n 1 ? GROUPVELOCITY 4 . 2 whereEi sar e a l ,c o n s t a n tv e c t o r . I ti s customaryt oi n c o r p o r a t et h e phase i n f o r m a t i o ni n t oE by a l l o w i n gEt obecomplex.Wecanw r i t e E =孟 eiB ei<kx ーwt )= 孟c く w*, a=kx [ 4 ‑ 7 ] 一 wt b= (Ak)x ム ー (Aw)t 31nu I 附川口 o fxand. tTher e a lp a r to fni sthen C h a p t e r 8mm 8 0 アー 図口 Cha戸ter F o u r FIGURE4‑l S p a t i a lv a r i a t i o no ft h eelectric d i f f e r e n c e . 自eld 園口 o ftwow a v e sw i t haf r e q u e n c y wehave E1+E2= Eoc o s(a+b )+E0c o s( a‑b ) =E o ( c o sac o sb‑s i nas i nb+cosac o sb+s i nas i nb ) = E 2」0c o sac o sb E1+」2= 2Eoc o s[ ( i l k)x +門 門U U 一問問m 凶mμ 一 mM 凶m 悶凶 +門 U 門U 82 日園 口図 園口 口図園口 口図 図口 口図園口 口図 『司トーー ーーーーヨーー ーーー掴ー- 『咽屠一ーー Mechanismo fp l a s m ao s c i l l a t i o n s . FIGURE4‑2 J 一 (ilw ) tc o s(kx ー wt) [4・ 9] Thisi sas i n u s o i d a l l ymodulatedwave( F i g .4 ‑ 1 ) .Theenvelopeo ft h e t ] ,i swhatc a r r i e si n f o r m a t i o n ;i tt r a v e l s w a v e ,g i v e nbyc o s[(ilk)x 一 ( ilw ) l w /i l k .Takingt h el i m i tilw • 0, wed e f i n et h eg r o u pv e l o c i t y a tv e l o c i t yi t ob e lvg=dw/d h e Wes h a l ld e r i v eane x p r e s s i o nf o rt h eplasmafrequencywρin t 1 )Therei snomagnetic s i m p l e s tc a s e ,makingt h efollowing ぉsumptions: ( ) ;( 3 )t h ei o n sa r ef i x e d f i e l d ;( 2 )t h e r ea r enothermalmotions(KT=0 i ns p a c ei nauniformd i s t r i b u t i o n ;( 4 )t h eplasmai si n f i n i t ei ne x t e n t ; i r e c t i o n .Asac o n ュ and( 5 )t h ee l e c t r o nmotionsoccuro n l yi nt h exd sequenceo ft h el a s ta s s u m p t i o n ,wehave [ 4 ‑ 1 0 ] V =走。/δx I ti st h i sq u a n t i t yt h a tcannote x c e e dc . E=E去 VXE=O E =-Vφ ( 4 ‑ 1 1 ] Therei s ,t h e r e f o r e ,nof l u c t u a t i n gmagneticf i e l d ;t h i si sane l e c t r o s t a t i c o s c i l l a t i o n . Thee l e c t r o ne q u a t i o n so fmotionandc o n t i n u i t ya r e 4 . 3 PLASMAOSCILLATIONS mn,[守+仇叫=一四, E I ft h ee l e c t r o n si naplasmaa r ed i s p l a c e dfromauniformbackground o fi o n s ,e l e c t r i cf i e l d sw i l lb eb u i l tupi nsuchad i r e c t i o na st or e s t o r e t h en e u t r a l i t yo ft h eplasmabyp u l l i n gt h ee l e c t r o n sbackt ot h e i ro r i g i n a l p o s i t i o n s . Because o ft h e i ri n e r t i a ,t h ee l e c t r o n sw i l lo v e r s h o o t and o s c i l l a t e around t h e i re q u i l i b r i u mp o s i t i o n sw i t hac h a r a c t e r i s t i c r e q u e n c y .Thiso s c i l l a t i o ni ss of a s tt h a t f r e q u e n c yknowna st h eμω市a f t h em a s s i v ei o n sdonothavet i m et orespondt ot h eo s c i l l a t i n gf i e l dand maybec o n s i d e r e da sf i x e d .I nF i g .4 ‑ 2 ,t h eopenr e c t a n g l e sr e p r e s e n t t y p i c a lelementso ft h ei o nf l u i d ,andt h edarkenedr e c t a n g l e st h ea l t e r ュ n a t e l yd i s p l a c e delementso ft h ee l e c t r o nf l u i d .Ther e s u l t i n gcharge bunchingc a u s e sas p a t i a l l yp e r i o d i cE f i e l d ,whicht e n d st or e s t o r et h e h e i rn e u t r a lp o s i t i o n s . e l e c t r o n stot 生~+ v ・(n,v,) a t =0 [4・ 12] [4・ 13] Theo n l yMaxwelle q u a t i o nwes h a l lneedi st h eonet h a tdoesnoti n v o l v e B : Poisson ’s e q u a t i o n .Thisc a s ei sane x c e p t i o nt ot h eg e n e r a lr u l eo f q u a t i o ncannotbeusedtof i n dE .Thisi sa S e c t i o n3 . 6t h a tPoisson ’s e h i g h ‑ f r e q u e n c yo s c i l l a t i o n ;e l e c t r o ni n e r t i ai si m p o r t a n t ,andt h ed e v i ュ a t i o n from n e u t r a l i t yi st h emain elfεct i nt h i sp a r t i c u l a rc a s e . Conュ s e q u e n t l y ,wew r i t e ε0V· ムー E= εoaE/ax=e (ηs 一 η,) ( 4 ‑ 1 4 ] 8 3 W a v e si n P l a s m a s ナー- 84 C h a p t e r F o u r E q u a t i o n s[ 4・2]-[4-14] φn e a s i l y be s o l v e d by t h e procedure o f l i n e a r i z a t i o n .Byt h i swemear¥t h a tt h eamplitudeo fo s c i l l a t i o ni ss m a l l , andtermsc o n t a i n i n ghigherpowerso famplitudef a c t o r scanbeneglec・ t e d .Wef i r s ts e p a r a t et h edep台ndent v a r i a b l e si n t otwop a r t s :an “ equilibrium ” part i n d i c a t e dbyas t J . b s c r i p t0 ,anda “ perturbation ” part i n d i ‑ c a t e dbyasubscr明 1: Thet i m ed e r i v a t i v ea / a t can t h e r e f o r eber e p l a c e dby ‑iw, and t h e q u a t i o n s[ 4 ‑ 1 7 ] ‑ [4 ‑ 1 9 ]nowbecome g r a d i e n tVbyik圭. E ‑imwv1= ‑eE1 ‑iwn1= ‑n0ikv1 1 ' n ,= ' I v , =Vo+V 1 πo + ηl E=E0+E 1 ikε0E1 [4” 15] a n 0 a v o aEo a i a t a t ‑e ‑ n . i k v1 n 0 e2 ‑imwv1= -e τ7一一一一ァー=- i 一- vi l l l c o -iα) €。αJ Theplasmaf r e q u e n c yi st h e r e f o r e v )」 i 叫=(号) ω合/ 2Tr =ん""' g,;; : 0 ん= 9 ( 1 0 1 8 ) 1 1 2=9x 1 0 9s e c ‑ 1=9GHz [ 4 ‑ 1 8 ] 竺.!.+ η。ヤ・ Vt ‘+v1 n =0 a t -: . ・叫 I ‑ R a d i a t i o nat ん normally l i e si nt h emicrowaver a n g e .Wecancompare t h i sw i t hanothere l e c t r o nf r e q u e n c y :w, A u s e f u lnumericalformulai s I nPoisso山quation 山],中en悦 that n ; 0=叫o i nequi刷um and t h a tn;1=0byt h eassumptioni o ff i x e di o n s ,s owehave c o ' Vキ E 1= ‑ eni ん= Vt 冗 1 干叫 1 ei(kx一叫 •(kx-w<) e [ 4 ‑ 2 0 ] E= Eei<«-wo 圭 J」』』 i 一一一ーー 一一ー-ーー一一一ーーー~日一 一ー一ー-『一一 28GHz/Tesla [4・27] Thusi fB = 0 . 3 2Tandn= 1 0 1 8m ‑ 3 ,t h ec y c l o t r o nfrequencyi sa p p r o x i ュ matelye q u a lt ot h eplasmafrequencyf o re l e c t r o n s . Equation[ 4 ‑ 2 5 ]t e l l su st h a ti faplasmao s c i l l a t i o ni st ooccura ta l l , .Inp a r t i c u l a r ,w doesn o t i tmusthaveafrequencydependingo n l yonn dependonk ,s ot h egroupv e l o c i t ydw/dki sz e r o .Thed i s t u r b a n c edoes notp r o p a g a t e .Howt h i scanhappencanbemadec l e a rw i t hamechanical analogy( F i g .4 ‑ 3 ) .Imagineanumbero fheavyb a l l ssuspendedbys p r i n g s [ 4 ‑ 1 9 ] Theo s c i l l a t i n gq u a n t i t i e sa r eassumedt obehaves i n u s o i d a l l y : • [4・ 26] Thisf r e q u e n c y ,dependingo n l yont h eplasmad e n s i t y ,i soneo f t h efundamentalparametersof 旦 plasma. Becauseo ft h es m a l l n e s so f m ,t h eplasmafrequencyi su s u a l l yv e r yh i g h .Fori n s t a n c e ,i naplasma o fd e n s i t yn= 1 0 1 8m‑ 3 ,wehave ~+~'"(ηoVt +叫, 1V1) a e , . v [4・ 25] N u m e r i c a l l y ,onecanu s et h eapproximateformula 7 =0 I r a d / s e c [ 4 ‑ 1 7 ] Theterm( v 1 V)v s e e r wes h a l ll i n e a r i z ebyneglecti~g i t .Thelineaγ theoγy i sv a l i da slonga s Jv i ii ss m a l lenought h a tsucpq u a d r a t i ctermsa r eindeedn e g l i g i b l e . S i m i l a r l y ,E q .[ 4 ‑ 1 3 ]becomes,: A百, [4・ 24] w2= n0e2/mc0 Equation 山J nowbecd1mes La t [4・ 23] I fv1doesnotv a n i s h ,wemusthave [ 4 ‑ 1 6 ] ~ r a v ,!v ~- 1 mJ -」+ ( 1, キV ) v 1I =‑eE1 [ 4 ‑ 2 2 ] E l i m i n a t i n gn 1andE 1 ,wehavef o rE q .[ 4 ‑ 2 1 ] The e u t r a lplasmaa t o ft h eo s c i l l a t i o nS i n c eweh~ve assumedauniformn r e s tb e f o r et h eele町ons a r e~isplaced, wehave v10=V o=Eo= 0 =‑en1 [ 4 ‑ 2 1 ] 85 W a v e si n P l a s m a s アー d e r i v ea ne x p r e s s i o nf o rt h edielec < ric c o n s t a n tE a p p l i c a b l et oh i g h ‑ f r e q u e n c y l o n g i t u d i n a lm o t i o n s . ELECTRONPLASMA 、'VAVES Therei sanothere f f e c tt h a tcancauseplasmao s c i l l a t i o n st opropagate, andt h a ti sthermalmotion.E l e c t r o n sstreamingi n t oadjacentl a y e r so f plasm且 with t h e i rthermalv e l o c i t i e sw i l lc a r r yinformationaboutwhat i shappeningi nt h eo s c i l l a t i n gr e g i o n .Theplasmaoscillation canthen a s i l yt r e a tt h i se f f e c tbyadding properlybec a l l e daplasma 山al'e. Wecane h eequationofmotion[4-12 ]目 In t h eone‑dimensional aterm-Vム to t problem , γwill b et h r e e ,accordingt oE q .[ 3 ‑ 5 3 ] .Hence, V p ,=3KT,Vn,=3KT,V(πo +n i )=3K工学土走 。x andt h el i n e a r i z e dequationofmotioni s 市町生.!. = ‑enoE1‑ 3KT,~ 。t キ a x y n t h e s i so fawavefromana s s e m b l yo fi n d e p e n d e n to s c i l l a t o r s . FIGURE4 ‑ 3 S ~直圃』ー [ 4 ‑ 2 8 ] 4 . 4 恥 V· (εE) = 0 闘v・ yb ・忌降、。 守 HO タ件特に「ぞ ~ 臨港脳、 J y 宮 Byw r i t i n gt h el i n e a r i z e dPoisson ’s e q u a t i o nu s e di nt h ed e r i v a t i o no fs i m p l e p l a s m ao s c i l l a t i o n si nt h eform 4・4. C a l c u l a t et h ep l a s m af r e q u e n c yw i t ht h ei o nm o t i o n si n c l u d e d ,t h u sj u s t i f y ュ H i n t :i n c l u d et h et e r mn"i nPoisson ’s i n go u ra s s u m p t i o nt h a tt h ei o n sare 自 xed. ( e q u a t i o nandu s et h ei o ne q u a t i o n so fm o t i o nandc o n t m u i t y . ) 陰露、 達三 4 ‑ 3 .F o ras i m p l ep l a s m ao s c i l l a t i o nw i t hf i x e di o n sandas p a c e ‑ t i m eb e h a v i o r exp[i(kx ー wt)]. c a l c u l a t et h ep h a s e/ 5f o rφh E1,andv1i ft h ep h a s eo fn1i sz e r o . , ,and I l l u s t r a t et h er e l a t i v ep h a s e sbydrawings i n ew a v e sr e p r e s e n t i n gn , , φ ,, E v , :( a )a saf u n c t i o no fx ,( b )a saf u n c t i o noftfor 印/ k >0 ,and( c )a saf u n c t i o n oftf o rw/k<0 .N otet h a tt h et i m ep a t t e r n sc a nb eo b t a i n e db yt r a n s l a t i n gt h e xp a t t e r n si nt h ep r o p e rd i r e c t i o n ,a si ft h ewavewerep a s s i n gb yaf i x e do b s e r v e r . 4・2. y 留v ・ ,b と . ea s u PROBLEMS Plasmao s c i l l a t i o n sp r o p a g a t ei naf i n i t emediumb e c a u s eo f FIGURE4‑4 f r i n g i n gf i e l d s . 勾d ・ 1H 陥月 fa l lt h es p r i n g sa r ei d e n t i c a l ,eachb a l lw i l l e q u a l l yspacedi nal i n e .I ft h eb a l l sa r es t a r t e di nt h e o s c i l l a t ev e r t i c a l l yw i t ht h esamef r e q u e n c y .I properphasesr e l a t i v et oonea n o t h e r ,t h e ycanbemadetoformawave propagating i ne i t h e rd i r e c t i o n . The frequency w i l l be f i x e d by t h e s p r i n g s ,butt h ewavelengthcanbechosena r b i t r a r i l y .Thetwou n d i s t u r ュ bedb a l l sa tt h eendsw i l lnotbea f f e c t e d ,andt h ei n i t i a ld i s t u r b a n c edoes notp r o p a g a t e .E i t h e rt r a v e l i n gwavesorstandingwavescanbec r e a t e d , a si nt h ec a s eo fas t r e t c h e dr o p e . Waves on ar o p e , however, must on eighboringsegments. propagatebecauseeachsegmenti sconnectedt Thisanalogyi snotq u i t ea c c u r a t e ,becauseplasmao s c i l l a t i o n shave motionsi nt h ed i r e c t i o no fkr a t h e rthant r a n s v e r s et ok . However,a s longa se l e c t r o n sdonotc o l l i d ew i t hi o n sorw i t heacho t h e r ,theycan s t i l lbep i c t u r e da sindependento s c i l l a t o r smovingh o r i z o n t a l l y( i nF i g . h a textendp a s tt h eregion 4 ‑ 3 ) .Butwhataboutt h eelectric 自eld? Won'tt ofi n i t i a ld i s t u r b a n c eands e tneighboringl a y e r sofplasmai n t oo s c i l l a t i o n ? tw i l ln o t ,becauset h ee l e c t r i cf i e l dduet oequal Inoursimpl巴 example, i numberso fp o s i t i v eandn e g a t i v ei n f i n i t e ,planecharges h e e t si sz e r o . Inanyf i n i t es y s t e m ,plasmao s c i l l a t i o n sw i l lp r o p a g a t e .InF i g .4 ‑ 4 ,t h e p o s i t i v eandn e g a t i v e( s h a d e d )r e g i o n so faplaneplasmao s c i l l a t i o na r e confinedi nac y l i n d r i c a lt u b e .Thef r i n g i n ge l e c t r i cf i e l dc a u s e sacoupling o ft h ed i s t u r b a n c et oa d j a c e n tl a y e r s ,andt h eo s c i l l a t i o ndoesnots t a y l o c a l i z e d . Cha戸ter Fo1げ 8U 86 ナー ‑enoE1‑3KT,ikn1 [ 4 ‑ 2 9 ] E1andn 1a r es t i l lg i v e nbyE q s .[ 4 ‑ 2 3 ]and[ 4 ‑ 2 2 ] ,andwehave 同ovi = [eno (え) +3K吋ザVi /no/ 3KT . .9 ¥ ーιー+一一一- k' I \Eoηt m I 9 w‑v1=I ω 2 2 ; l . c2 2 = ωρ + 2k U 山 [ 4 ‑ 3 0 ] = wherev~h 2KT,/m.Thefrequencynowdependsonk ,andt h egroup v e l o c i t yi sf i n i t e : kd k 2wdw= ~v~h 2 一2 一一 2出一 φ 3 2出 一9 - 一ω 一一 u k 。 3 一一 h凶-’ bι ,必つa ug u -U [4・ 31] That"• i sa l w a y sl e s st h a nccane a s i l ybeseenfromagrapho fE q .[ 4 ‑ 3 0 ] . sap l o to ft h edis戸eγsion r e l a t i o nw(k)a sg i v e nbyE q .( 4 ‑ 3 0 ] . Figure4・5 i Atanyp o i n tP ont h i sc u r v e ,t h es l o p eo fal i n edrawnfromt h eo r i g i n g i v e st h ephasev e l o c i t yw / k .Thes l o p eo ft h ecurvea tPg i v e st h egroup w む2 ノ p / 丘、h / d ’ / v g k i s p e r s i o nr e l a t i o nf o re l e c t r o np l a s m aw a v e s(Bohm‑Grossw a v e s ) . FIGURE4‑5 D S c h e m a t i co ft h eLooney‑Browne x p e r i m e n tonplasmao s c i l l a t i o n s . FIGURE4‑6 Qd 畑山 -i間wnov 1 = v e l o c i t y .Thisi sc l e a r l ya l w a y sl e s sthan( 3 / 2 ) 1 1 2 v , h ,w h i c h ,i nourn o n r e l a ュ .Notet h a ta tl a r g ek( s m a l lλ ), informaュ t i v i s t i ct h e o r y ,i smuchl e s st h a nc t i o nt r a v e l se s s e n t i a l l ya tt h e thermal v e l o c i t y . At s m a l lk ( l a r g eλ ), informationt r a v e l smores l o w l ythanv , heventhoughUφis g r e a t e rthan U由・ This i sbecauset h ed e n s i t yg r a d i e n ti ss m a l la tl a r g eλ, and thermal motionsc a r r yv e r yl i t t l en e tmomentumi n t oa d j a c e n tl a y e r s . Thee x i s t e n c eo fplasmao s c i l l a t i o n sh a sbeenknowns i n c et h ed a y s o fLangmuiri nt h e1 9 2 0 s .I twasnotu n t i l1949t h a tBohmandGross workedoutad e t a i l e dt h e o r yt e l l i n ghowt h ewaveswouldpropagate and howt h e yc o u l dbee x c i t e d .A s i m p l ewayt oe x c i t eplasmawaves wouldbet oapplyano s c i l l a t i n gp o t e n t i a lt oag r i do ras e r i e so fg r i d s i nap l a s m a ;however,o s c i l l a t o r si nt h eGHzrangeweren o tg e n e r a l l y a v a i l a b l ei nt h o s ed a y s .I n s t e a d ,onehad t ou s eane l e c t r o nbeamt o ft h ee l e c t r o n si nt h ebeamwerebuncheds ot h a t e x c i t eplasmaw a v e s .I e n e r a t e t h e yp a s s e dbyanyf i x e dp o i n ta tafrequency ん, they wouldg ane l e c t r i cf i e l da tt h a tf r e q u e n c yande x c i t eplasmao s c i l l a t i o n s .I ti sn o t n e c e s s a r yt oformt h ee l e c t r o nbunchesbeforehand; oncet h eplasma o s c i l l a t i o n sa r i s e ,t h e yw i l lbuncht h ee l e c t r o n s ,andt h eo s c i l l a t i o n sw i l l growbyap o s i t i v efeedbackmechanism.Anexperimentt ot e s tt h i st h e o r y wasf i r s tperformedbyLooneyandBrowni n1 9 5 4 .Theirapparatusw a s キ e n t i r e l yc o n t a i n e di nag l a s sb u l babout1 0cmi ndiameter( F i g .4 ‑ 6 ) .A plasmaf i l l i n gt h eb u l bwasformedbyane l e c t r i c a ld i s c h a r g ebetween r e s s u r e( 3x 1 0 ‑ 3Torr) t h ecathodesKandananoder i n gA underalowp 81m Fouγ Notet h a ti nl i n e a r i z i n gwehaven e g l e c t e dt h etermsn1av1/atandn1E1 e r m .WithE q .[ 4 ‑ 2 0 ] ,E q .( 4 ‑ 2 8 ]becomes a sw e l la st h e(v1 ・ V)v1 t 山由 Z 1 mp 叫 88 C h a p t e r 90 DISCHARGECURRENT(MA) C h a p t e r Four 100 200 1 . 0 『,4 ’ / d 〆 〆 〆 { F 工り)U刊 NN e l e c t r o nbunchingwasa c c o m p l i s h e dn o ti nt h eplasmab u ti nt h eo s c i l l a t ュ i n gs h e a t h sa tt h eendso ft h eplasmacolumn.I nt h i se a r l ye x p e r i m e n t , onel e a r n e dt h a treproducingt h ec o n d i t i o n sassumedi nt h euniformュ plasmat h e o r yr e q u i r e sc o n s i d e r a b l es k i l l . A numbero fr e c e n te x p e r i m e n t shavev e r i f i e dt h eBohm‑Gross d i s p e r s i o nr e l a t i o n ,E q .( 4 ‑ 3 0 ] .w i t hp r e c i s i o n .Asanexampleo fmodern e x p e r i m e n t a lt e c h n i q u e , we show t h er e s u l t so fB a r r e t t ,J o n e s , and F r a n k l i n .F i g u r e4‑8i sas c h e m a t i co ft h e i ra p p a r a t u s .Thec y l i n d r i c a l columno fq u i e s c e n tplasmai sproducedi naQ‑machinebyt h e r m a l i o n i z a t i o no fCsatomsonh o tt u n g s t e f l 'p l a t e s( n o ts h o w n ) .A s t r o n g magneticf i e l dr e s t r i c t se l e c t r o n st omotionsa l o n gt h ec o l u m n .Thewaves 300 ノ 炉〈浮. . 8 〆 〆 〆 ノ F唱ρムー・ . 6 / 〆 〆 ・Aそρ,. . 4 〆 〆 9 1 WαU回 in Plas明白 〆 ザ〉・ 〆 . 2 〆 〆 〆 〆 " EXCITERPROBE ,, " 。 。 2 4 6 8 12 14x109 勺d m 白 pu n 10 q u a r eo ft h eo b s e r v e df r e q u e n c yv s .p l a s m ad e n s i t y ,whichi s FIGURE4 ‑ 7 S g e n e r a l l yp r o p o r t i o n a lt ot h ed i s c h a r g ec u r r e n t .Thei n s e tshows t h eo b s e r v e ds p a t i a ld i s t r i b u t i o no fo s c i l l a t i o ni n t e n s i t y ,i n d i c a t i n g t h ee x i s t e n c eo fad i f f e r e n ts t a n d i n gwavep a t t e r nf o re a c ho ft h e g r o u p so fe x p e r i m e n t a lp o i n t s .[ F r o mD .H .L o o n e ya n dS .C . h y s .R e v .9 3 ,965( 1 9 5 4 ) . ] B r o w n ,P DC BREAK o fmercuryv a p o r .Ane l e c t r o nbeamwasc r e a t e di nas i d earmc o n t a i n i n g an e g a t i v e l yb i a s e df i l a m e n t .Thee m i t t e de l e c t r o n swerea c c e l e r Q . t e dt o 200V ands h o ti n t ot h eplasmathroughas m a l lh o l e .A t h i n ,movable probew i r ec o n n e c t e dt oar a d i or e c e i v e rwas used t op i c k up t h e o s c i l l a t i o n s .F i g u r e4 ‑7showst h e i re x p e r i m e n t a lr e s u l t sf o rJ 2vs.disュ c h a r g ec u r r e n t ,whichi sg e n e r a l l yp r o p o r t i o n a lt odensity 目 The p o i n t s showal i n e a rdependence,i nroughagreementw i t hE q .( 4 ‑ 2 6 ] .D e v i ュ a t i o n sfromt h es t r a i g h tl i n ec o u l dbea t t r i b u t e dt ot h ek2v~h termi nE q . ( 4 ‑ 3 0 ] .H owever,n o ta l lf r e q u e n c i e swereo b s e r v e d ;k hadt obesuch t h a tani n t e g r a lnumbero fh a l fw a v e l e n g t h sf i talongt h eplasmacolumn. Thes t a n d i n gwave p a t t e r n sa r e showna tt h el e f to fF i g .4 ‑7 . The p r e d i c t e dt r a v e l i n gplasmawavesc o u l dn o tbes e e ni nt h i se x p e r i m e n t , p r o b a b l yb e c a u s et h ebeamwass ot h i nt h a tt h e r m a lmotionsc a r r i e d e l e c t r o n so u to ft h ebeam,t h u sd i s s i p a t i n gt h eo s c i l l a t i o ne n e r g y .The SIGNA し GENERATOR 10” 1200 MHz DC BREAK CRYSTAL MIXER 500kHz TUNED AMPLIFIER MODULATOR 500kHz CHART RECORDER S c h e m a t i co fa ne x p e r i m e n tt om e a s u r ep l a s m aw a v e s .[ F r o mP .J .B a r r e t t , FIGURE4 ‑ 8 .F r a n k l i n ,PlasmaP h ) キ s i c s1 0 ,9 1 1( 1 9 6 8 ) . ] H .G .J o n e s ,a n dR.N / . . . . . . . . . . . . . . . CZ っJM m 附m Ar Dzd 「 門司つ叫 1oi \PMハ 一一一一一一 Fouγ X q4 C h a p t e r nofλ 92 s F i g .4 ‑ 9g i v eameasuremento fk .Whent h eo s c i l l a t o rfrequencyw i v a r i e d ,ap l o to ft h ed i s p e r s i o ncurve( w / w p ) 2v s .k ai so b t a i n e d ,where ai st h er a d i u so ft h ecolumn( F i g .4 ‑ 1 0 ) .Thev a r i o u sc u r v e sa r el a b e l e d a c c o r d i n gt ot h ev a l u eo fw p a / v t t o o ,whichc orrespondst ot h ed i s p e r s i o nr e l a t i o nω = ωρ・ For f i n i t ev , h , t h ec u r v e scorrespond t ot h a to fF i g .4 ‑ 5 . Therei s goodagreement betweent h ee x p e r i m e n t a lp o i n t sandt h et h e o r e t i c a lc u r v e s .Thed e c r e a s e ts m a l lk ai st h ef i n i t e ‑ g e o m e t r ye f f e c tshowni nF i g .4 ‑ 4 .I nt h i s o fw a p a r t i c u l a re x p e r i m e n t ,t h a te f f e c tcanbee x p l a i n e d anotherw a y .To s a t i s f yt h eboundaryc o n d i t i o nimposedbyt h econductings h i e l d ,namely h ec o n d u c t o r ,t h eplasmawavesmustt r a v e la tana n g l e t h a tE =0ont t ot h emagneticf i e l d .D e s t r u c t i v ei n t e r f e r e n c ebetweenwavest r a v e l i n g w i t h an outward r a d i a lcomponento fk and t h o s et r a v e l i n ginward e n a b l e st h eboundaryc o n d i t i o nt obes a t i s f i e d .However,wavest r a v e l i n g n。= 4x108cmキ3 f = 170MHz λ = 1 ‑ 3cm ~= 1x107cmキ3 93 Wavesi n Plasm出 f=20MHz λ = 5 . 1cm 1 . 4 1 . 2 FIGURE4 ‑ 9 S p a t i a lv a r i a t i o no ft h ep e r t u r b e dd e n s i t yi nap l a s m aw a v e , a si n d i c a t e dbya ni n t e r f e r o m e t e r ,whichm u l t i p l i e st h e i n s t a n t a n e o u sd e n s i t ys i g n a l sfromtwop r o b e sandt a k e s t h et i m ea v e r a g e .Thei n t e r f e r o m e t e ri st u n e dt ot h ewave f r e q u e n c y ,whichv a r i e sw i t ht h ed e n s i t y .Thea p p a r e n t dampinga tlowd e n s i t i e si sc a u s e dbyn o i s ei nt h ep l a s m a . (FromB a r r e t t ,J o n e s ,andF r a n k l i n ,l o c .c i t . ] 1 . 0 ' ' ' o .. 8 3 、、、 N a r ee x c i t e dbyaw i r eprobed r i v e nbyano s c i l l a t o randar巴 detected by as e c o n d ,movablep r o b e .A m e t a ls h i e l dsurroundingt h eplasmapre幽 v e n t scommunicationbetweent h eprobesbyo r d i n a r ymicrowave( e l e c ュ t r o m a g n e t i cwave)p r o p a g a t i o n ,s i n c et h es h i e l dc o n s t i t u t e sawaveguide beyond c u t o f ff o rt h ef r e q u e n c yu s e d .The t r a v e l i n gwaveforms a r e t r a c e dbyi n t e r f e r o m e t r y :t h et r a n s m i t t e dandr e c e i v e ds i g n a l sa r ed e t e c ュ t e dbyac r y s t a lwhichg i v e sal a r g edcoutputwhent h es i g n a l sa r ei n phaseandz e r ooutputwhent h e ya r e90。 out o fp h a s e .Ther e s u l t i n g saf u n c t i o no fp o s i t i o nalongt h ecolumn. s i g n a li sshowni nF i g .4・9 a Synchronousd e t e c t i o ni susedt os u p p r e s st h en o i s el e v e l .Thee x c i t a t i o n s i g n a li schoppeda t500kHz,andt h er e c e i v e ds i g n a lshoulda l s obe modulateda t500kHz.Byd e t e c t i n go n l yt h e500‑kHzcomponento ft h e r e c e i v e ds i g n a l ,n o i s ea to t h e rf r e q u e n c i e si se l i m i n a t e d .Thet r a c e so f 3 . 6 . 4 . 2 。 。 2 4 6 8 10 1 2 1 4 1 6 1 ‑ 8 20 22 k a ‑ 1 0 Comparisono ft h emeasuredandc a l c u l a t e dd i s p e r s i o nc u r v e sf o re l e c t r o n FIGURE4 p l a s m aw a v e si nac y l i n d e ro fr a d i u sa .[ FromB a r r e t t ,J o n e s ,andF r a n k l i n , l o c .c i t . ] 一. . . . . . . . . . . . . . . 2 4 (4・33] L i n e a r i z i n gaboutas t a t i o n a r ye q u i l i b r i u mw i t huniformP oandp 0 ,we have B 一一一一』 γ戸。 ‑ z w p 0 v ,=一一- ikp, P o [ 4 ‑ 3 4 ] ‑iwp,+P o i kキV1 = 0 e [ 4 ‑ 3 5 ] wherewehaveagaintakenawavedependenceo ft h eform exp[ i ( kキr 一 wt)] FIGURE4 ‑ 1 1 W a v e f r o n t st r a v e l i n ga tana n g l et ot h em a g n e t i cf i e l da r es e p a r a t e d , i nt h ef i e l dd i r e c t i o n ,byad i s t a n c el a r g e rt h a nt h ew a v e l e n g t hλ. ForaplanewaYew i t hk=k去 and v=v圭, we f i n d ,upone l i m i n a t i n gp 1 , γPo., P o i k v 1 a tana n g l et oB havec r e s t sandtroughsseparatedbyad i s t a n c el a r g e r thanλ / 2 ( F i g .4・ 1 1 ) .S i n c et h ee l e c t r o n scanmoveonlyalongB ( i fB i s v e r yl a r g e ) ,t h e ya r es u b j e c tt ol e s sa c c e l e r a t i o n ,andt h efrequencyi s loweredbelowω合・ -zwρ0V1 =一一一- z舟ーで一一一 P o 2 i w '2γ·po wv ,=/(一- v, P o or PROBLEMS 4 ‑ 5 .E l e c t r o np l a s m aw a v e sa r ep r o p a g a t e di nau n i f o r mp l a s m aw i t hKT,= 1 0 0e V ,n=1 0 1 6m•, B =0 .I ft h ef r e q u e n c yfi sI .IGHz,w hati st h ew a v e l e n g t h tnc m? 4 ‑ 6 .( a )Computet h ee f f e c to fc o l l i s i o n a ldampingont h ep r o p a g a t i o no fL a n g ュ m u i rw a v e s( p l a s m ao s c i l l a t i o n s ) ,b ya d d i n gat e r m-mn阿 to t h ee l e c t r o ne q u a t i o n o fm o t i o nandr e d e r i v i n gt h ed i s p e r s i o nr e l a t i o nf o rT,= 0 . ( b )W r i t ea ne x p l i c i te x p r e s s i o nf o rIm( w )andshowt h a ti t ss i g ni n d i c a t e st h a t t h ewavei sdampedi nt i m e . ?=(で) / 2= (乎)二 c, [4司36] ,o fsoundwavesi nan e u t r a lgas 目 Thisi st h ee x p r e s s i o nf o rt h ev e l o c i t yc Thewavesa r ep r e s s u r ewavesprop昌gating fromonel a y e rtot h en e x t byc o l l i s i o n samongt h ea i rm o l e c u l e s .I naplasmaw i t hnon e u t r a l sand fewc o l l i s i o n s ,ananalogousphenomenono c c u r s .Thisi sc a l l e dani o n acoustic 即日ve, o r ,s i m p l y ,ani o nw a v e . 4.5 SOUNDWAVES Asani n t r o d u c t i o nt oi o nw a v e s ,l e tu sb r i e f l yreviewt h etheoryo fsound wavesi nordinarya i r .Neglectingv i s c o s i t y ,wecanw r i t et h eNav i e r ‑ S t o k e s e q u a t i o n( 3 ‑ 4 8 ) ,whichd e s c r i b e st h e s ew a v e s ,a s p [~+(v· 吋= ‑Vp= - ~Vp (4・ 32] ー--....』白,a・ー・,---・・- 問 -+V -( ρv) = 0 a t 「一一入 sec 出 問U δp z CMS Fou:γ zl 附 P Theequationo fc o n t i n u i t yi s Chapleγ 6m 94 ION 、VAVES I nt h eabsenceo fc o l l i s i o n s ,ordinarysoundwaveswouldnoto c c u r .I o n s can s t i l lt r a n s m i tv i b r a t i o n st o each o t h e r because o ft h e i rc h a r g e , however;anda c o u s t i cwavescanoccurthrought h eintermediaryo fan e l e c t r i cf i e l d .S i n c et h emotiono fm a s s i v ei o n sw i l lbei n v o l v e d ,t h e s e 4.6 =‑enV,P- γ;KT;Vn J [ 4 ‑ 3 7 ] k WehaveassumedE= -Vφand usedt h ee q u a t i o no fstate ・ andassumingp l a n ew a v e s ,wehave ‑iwMnov;i= -enoikφ1 一 γ,KT,ikn1 Linearizing 孔zυr = n =noexol¥丘.!... l=nnll +丘.!...+・..} KT,/ KT, J v¥ Thep e r t u r b a t i o ni nd e n s i t yo fe l e c t r o n s ,a n d ,t h e r e f o r e ,o fi o n s ,i sthen eφl [ 4 ‑ 3 9 ] n ,= ηn 一一一一 ‘ ~KT, Heret h en 0o fBoltzmann’s r e l a t i o na l s os t a n d sf o rt h ed e n s i t yi nt h e e キ q u i l i b r i u mp l a s m a ,i nwhichwecanchooseφ。= 0becausewehave assumedEo=0 .I nl i n e a r i z i n gE q .[ 4 ‑ 3 9 ] ,wehavedroppedt h eh i g h e r ュ ordert e r m si nt h eTaylorexpansiono ft h ee x p o n e n t i a l . Theo n l yo t h e re q u a t i o nneededi st h el i n e a r i z e di o ne q u a t i o no f c o n t i n u i t y .FromE q .(4司22], wehave iwn1= n 0 i k v ;i [4・ 40] I nE q .[ 4 ‑ 3 8 ] ,wemays u b s t i t u t ef o rφl andn1i ntermso fv i ifromE q s . b t a i n ( 4 ‑ 3 9 ]and(4・40] ando I KT. ¥n ・1 =I enoik -」+ γ,KT,ik l 」斗ーニ 、 en0 1 iαJ 山宮(子千) ~=(~(2=v, D i s p e r s i o nr e l a t i o nf o ri o n FIGURE4 ‑ 1 2 a c o u s t i cw a v e si nt h el i m i to f s m a l lDebyel e n g t h . [ 4 ‑ 3 8 ] Asf o rt h ee l e c t r o n s ,wemayassumem =0andapplyt h eargumento f S e c t i o n3 . 5 ,regardingmotionsalongB,t ot h ep r e s e n tc a s eo fB= 0 . Theb a l a n c eo ff o r c e sone l e c t r o n s ,t h e r e f o r e ,r e q u i r e s iwMη oV; 1 ,- Lat ea ”” Mnl 色+ ( v ;キ V ) v , l=叩E-Vp w [ 4 ‑ 4 1 ] o na c o u s t i cw a v e s ;v ,i st h esoundspeed Thisi st h ed i s p e r s i o nr e l a t i o nf o ri i nap l a s m a .S i n c et h ei o n ss u f f e rone‑dimensionalcompressionsi nt h e e ty ;=3h e r e .Thee l e c t r o n s p l a n eW昌ves wehaveassumed,wemays moves of a s tr e l a t i v et ot h e s ewavest h a tt h e yhavet i m et oe q u a l i z et h e i r temperaturee v e r y w h e r e ;t h e r e f o r e ,t h ee l e c t r o n sa r ei s o t h e r m a l ,and γ, = 1 .O t h e r w i s e ,af a c t o rγe wouldappeari nf r o n to fKT,i nE q .( 4 ‑ 4 1 ) . Thed i s p e r s i o nc u r v ef o ri o nwaves( F i g .4 ‑ 1 2 )h a safundamentally d i f f e r e n tc h a r a c t e rfromt h a tf o re l e c t r o nwaves( F i g .4 ‑ 5 ) .Plasmao s c i l l a ュ o n s t a n t ‑ f r e q u e n c yw a v e s ,w i t hac o r r e c t i o nduetothermal t i o n sa r eb a s i c a l l yc motions 目 Ion wa \’es a r eb a s i c a l l yc o n s t a n t ‑ v e l o c i t ywavesande x i s to n l ywhen t h e r ea r et h e r m a lm o t i o n s .Fori o nw a v e s ,t h egroupv e l o c i t yi se q u a lt o t h ephasev e l o c i t y .Ther e a s o n sf o rt h i sd i f f e r e n c ecanbes e e nfromt h e f o l l o w i n gd e s c r i p t i o no ft h ep h y s i c a lmechanismsi n v o l v e d .I ne l e c t r o n plasmao s c i l l a t i o n s ,t h eo t h e rs p e c i e s( n a m e l y ,i o n s )remainse s s e n t i a l l y f i x e d .I ni o na c o u s t i cw a v e s ,t h eo t h e rs p e c i e s( n a m e l y ,e l e c t r o n s )i sf a r fromf i x e d ;i nf a c t ,e l e c t r o n sa r ep u l l e dalongw i t ht h ei o n sandtendt o s h i e l doute l e c t r i cf i e l d sa r i s i n gfromt h ebunchingo fi o n s .However,t h i s s h i e l d i n gi sn o tp e r f e c tb e c a u s e ,a swesawi nS e c t i o n1 . 4 ,p o t e n t i a l so f e a koutbecauseo fe l e c t r o nthermalm o t i o n s . t h eordero fKT,/ecanl Whathappensi sa sf o l l o w s .Thei o n sformr e g i o n so fcompressionand r a r e f a c t i o n ,j u s ta si nano r d i n a r ysoundw a v e .Thecompressedr e g i o n s tend t oexpand i n t ot h er a r e f a c t i o n s ,f o rtwor e a s o n s .F i r s t ,t h ei o n thermalmotionss p r e a doutt h ei o n s ;t h i se f f e c tg i v e sr i s et ot h esecond . Second, t h ei o n bunchesa r e term i nt h es q u a r er o o to fE q . [4・41 ] p o s i t i v e l ychargedandtendt od i s p e r s eb e c a u s eo ft h er e s u l t i n ge l e c t r i c f i e l d .Thisf i e l di sl a r g e l ys h i e l d e doutbye l e c t r o n s ,ando n l yaf r a c t i o n , sa v a i l a b l et oa c tont h ei o nb u n c h e s .Thise f f e c t p r o p o r t i o n a lt oKT,,i g i v e sr i s et ot h ef i r s ttermi nt h esquarer o o to fE q .[ 4 ‑ 4 1 ] .Thei o n s o v e r s h o o tb e c a u s eo ft h e i ri n e r t i a ,andt h ecompressionsandr a r e f a c t i o n s a r er e g e n e r a t e dt oformaw a v e . ヴ初出 F o u r w i l lbel o w ‑ f r e q u e n c yo s c i l l a t i o n s ,andwecanu s et h eplasmaapproximaュ t i o no fS e c t i o n3 . 6 .Wet h e r e f o r eassumen; =叫= n anddonotu s e Poisson ’s e q u a t i o n .Thei o nf l u i de q u a t i o ni nt h eabsenceo famagnetic 白 eld i s ui aP山 z 恥P Chapleγ ,‘守 ! 96 98 Chα争/er Fou.γ ThesecondE庄ect mentionedabovel e a d st oac u r i o u sphenomenon. oz e r o ,i o nwavess t i l le x i s t .Thisdoesnothappeni na WhenKT;goest n e u t r a lg a s( E q .[ 4 ‑ 3 6 ] ) .Thea c o u s t i cv e l o c i t yi stheng i v e nby v ,= (KT./M)112 [4・ 42] Thisi st h esamea sweo b t a i n e dp r e v i o u s l y( E q .[ 4 ‑ 4 1 ) )e x c e p tf o rt h e ;= πe h a sg i v e nr i s et oanerroro f f a c t o r 1+k2λ~ - Ourassumptionn i n c eλD i sv e r ys m a l li nmostexperiments,t h e orderk2λ~ = (21TXo/λ )2. S plasmaapproximation i sv a l i df o ra l le x c e p tt h es h o r t e s twavelength 、、raves. Thisi so f t e nobservedi nl a b o r a t o r yp l a s m a s ,i nwhicht h ec o n d i t i o n Z < T, i sacommono c c u r r e n c e .Thesoundspeedv ,dependsonelectγon temperature( b e c a u s et h ee l e c t r i cf i e l di sp r o p o r t i o n a lt oi t )andonioπ mass( b e c a u s et h efluid ’S i n e r t i ai sp r o p o r t i o n a lt oi t ) . COMPARISONOFIONANDELECTRONWAVES 4.8 I fweconsidert h e s e short-wavele 時th wavesbyt a k i n gk2λ2 》 I, E q . )becomes [ 4 ‑ 47 一= Q [ 4 ‑ 4 5 ] 2dLJ 向φi(k2 +活)= 一一 I n s e r t i n gt h i si n t oE q .[ 4 ‑ 4 3 ) ,wehave η -E [ 4 ‑ 4 4 ) -ε eφ1 n . 1=一一一一向。 . . KT, ~ 一五ぬ Thee l e c t r o nd e n s i t yi sg i v e nbyt h el i n e a r i z e dBoltzmannr e l a t i o n[ 4・ 39): n 一。 n ,=n ,whileallowingE t obef i n i t e .Tos e ewhate r r o rwasengendered od i f f e rfrom叫 and uset h el i n e a r i z e d i nt h ep r o c e s s ,wenowa l l o wn; t P o i s s o ne q u a t i o n : ε0V·E1 = εok2φi =e(nil ー ηe i ) [ 4 ‑ 4 3 ] ’R ω I nderivingthev e l o c i t yo fi o nw a v e s ,weusedt h en e u t r a l i t yc o n d i t i o n 2 4 .7 VALIDITY OFTHEPLASMAAPPROXIMATION [ 4 . 4 9 ] Weh a v e ,f o rs i m p l i c i t y ,a l s otakent h el i m i tT ;• 0. HereQρis theion plasma f r e q u e n c y . For high f r e q u e n c i e s( s h o r tw a v e l e n g t h s )t h ei o n a c o u s t i cwave t u r n si n t o ac o n s t a n t ‑ f r e q u e n c ywave.There i st h u sa complementarybehaviorbetweene l e c t r o nplasmawavesandi o na c o u s t i c waves:t h eformera r eb a s i c a l l yc o n s t a n tf r e q u e n c y ,butbecomec o n s t a n t 、elocity a tl a r g ek ;t h el a t t e ra r eb a s i c a l l yc o n s t a n tv e l o c i t y ,butbecome .Thiscomparisoni sshowng r a p h i c a l l yi n c o n s t a n tfrequencya tl a r g ek F i g .4 ‑ 1 3 . Experimental v e r i f i c a t i o no ft h ee x i s t e n c eo fi o n waves was f i r s t accomplishedbyWong,M o t l e y ,andD ’Angelo. F i g u r e4‑14showst h e i r I ti snoa c c i d e n tt h a twehave a p p a r a t u s ,whichwasa g a i naQ司 machine. ( r e f e r r e dt oQ‑machiness oo f t e n ;c a r e f u lexperimentalcheckso fplasma €0φ1(k2λ~ + I)= enilλ2 Thei o nd e n s i t yi sg i v e nbyt h el i n e a r i z e di o nc o n t i n u i t yequation[ 4 ‑ 4 0 ) : ELECTRON k πs i= ‑ n0vil [4・46) ION w w αP I n s e r t i n gE q s .( 4 ‑ 4 5 )and[ 4 ‑ 4 6 ]i n t ot h ei o nequationo fmotion[4・38), wef i n d I " i k eλ~ ¥ =(ーニー一一ートτ + γ;KT,ik l 一旬1;1 ¥c o I+kAD Jw [ 4 ‑ 4 7 ] w2 = ~1 主~註!と五+ γ;KT;) M\l+k'A :', w /KT, k=口r Tτ子~-r M) ン / / ‘ I 3. , v 2 •th k [ 4 ‑ 4 8 ) 。 p 』一一一一一一一一一 / wp / ’‘/ lγ;KT;\ i 1 2 シ ケ ケ k Comparison o ft h ed i s p e r s i o nc u r v e sf o re l e c t r o nplasmawaves andi o n FIGURE4 ‑ 1 3 a c o u s t i cw a v e s . 99 W a v e siη P l a s m a s 司司,-目 子 " RECEIVER {X50) d=5.5cm .-~IYJV 4 . . 9 ELECTROSTATIC ELECTRONOSCILLATIONS PERPENDICULARTOB 円 ミ1 / ‑¥I ほ ¥ Upt onow,wehaveassumedB= 0 .Whenamagneticf i e l de x i s t s ,many moret y p e so fwavesa r ep o s s i b l e .Wes h a l lexamineo n l yt h es i m p l e s t c a s e s ,s t a r t i n gw i t hh i g h ‑ f r e q u e n c y ,e l e c t r o s t a t i c ,e l e c t r o no s c i l l a t i o n s 0 DRIVER RECEIVER (X50) 40 80 120 160 200 t(オsec) O s c i l l o g r a m so fs i g n a l sfromt h ed r i v e rand FIGURE4 ‑ 1 5 r e c e i v e rg r i d s ,s e p a r a t e dbyad i s t a n c ed ,s h o w ‑ i n gt h ed e l a yi n d i c a t i v eo fat r a v e l i n gw a v e . [FromWong,M o t l e y ,andD’Angelo, l o c .c i t . ] 、 propagatinga tr i g h ta n g l e stot h emagneticf i e l d .F i r s t ,weshouldd e f i n e t h etermsp e r p e n d i c u l a r ,p a r a l l e l ,l o n g i t u d i n a l ,transverse,ーlectrostatic, ande l e c t r o m a g n e t i c .P a r a l l e land 戸er世間diculaγwill beusedt odenote t h ed i r e c t i o no fkr e l a t i v et ot h eundisturbedmagnetic 日eld B 0 .L o n K i , ュ t u d i n a landt r a n s v e r s er e f e rt ot h ed i r e c t i o no fkr e l a t i v et ot h eo s c i l l a t i n g e l e c t r i cf i e l dE 1 .I ft h eo s c i l l a t i n gmagneticf i e l dB1i sz e r o ,t h ewavei s e l e c t r o s t a t i c ;o t h e r w i s e ,i ti se l e c t r o m a g n e t i c .Thel a s ttwos e t so ftermsa r e r e l a t e dbyMaxwell ’s e q u a t i o n 同出 o 町 D40 TO Fー一 X /, NEUTRAL BEAMOVEN FIGURE4・ 14 VラE 1= ‑Bi [ 4 ‑ 5 0 ] kXE1=wB1 [ 4 ‑ 5 1 ] o r Q ‑ m a c h i n ee x p e r i m e n tt od e t e c ti o nw a v e s .[ F r o mA .Y.Wong,R .W.M o t l e y ,a n d I fawavei sl o n g i t u d i n a l ,kxE 1v a n i s h e s ,andt h ewavei sa l s oe l e c t r o s t a t i c . I ft h ewavei st r a n s v e r s e ,B1i sf i n i t e ,andt h ewavei selectromagnetic・ N.D 一ーー~、 日 D‑RIVER 、, An 川加 附 P PヤN;t - d=3cm 0 .打開 t h e o r ywerep o s s i b l eo n l ya f t e rschemest omakeq u i e s c e n tplasmaswere d i s c o v e r e d . )Waveswerelaunchedandd e t e c t e dbyg r i d si n s e r t e di n t o t h ep l a s m a .F i g u r e4 ‑ 1 5showso s c i l l o s c o p et r a c e so ft h et r a n s m i t t e dand r e c e i v e ds i g n a l s .Fromt h ephases h i f t ,onecanf i n dt h ephasev e l o c i t y (samea sgroupv e l o c i t yi nt h i sc a s e ) .Thesephases h i f t sa r ep l o t t e da s f u n c t i o n so fd i s t a n c ei nF i g .4司 16 f o raplasmad e n s i t yo f3x 1 0 1 7m‑3 Thes l o p e so fsuchl i n e sg i v et h ephasev e l o c i t i e sp l o t t e di nF i g .4 ‑ 1 7f o r t h etwomおぽs andv a r i o u splasmad e n s i t i e sn0・ The c o n s t a n c yo fv ,w i t h wand 町民 demonstrated e x p e r i m e n t a l l y ,andt h etwos e t so fp o i n t sf o r K andCsp l a s m a sshowt h eproperdependenceonM. F o u r l 100 Chαpter 102 140 C h a p t e r Four z ノ 10 出 120 D./ にJ ~ 100 ミ > < ノ /品。〆 20 80 D .~D. ̲J w 0 ( / ' ) / D. / 60 。〆0 • ~- //ノ’ ~u w < / / i : , , 40 工 C l . . / 20 O〆 2 4 •./ キ~〆〆 6 8 FIGURE4 ‑ 1 6 E x p e r i m e n t a lmeasurementso fd e l a yv s .probes e p a r a t i o na tv a r i o u s f r e q u e n c i e so ft h ewavee x c i t e r .Thes l o p eo ft h el i n e sg i v e st h ep h a s e v e l o c i t y .[FromWong,M o t l e y ,andD’Angelo, l o c .c i t . ] 。v •• 5x105 m ̲ ̲ . , ; ̲ : ̲ =-e(E1 。t 4 十 v,, (ug\EU)事〉 竺工!. +noVキv,1= 0 2 企 企且 εoV xB o ) (4 ・52) キ E 1= ‑ e n . i ( 4 ‑ 5 4 ) Cs Wes h a l lc o n s i d e ro n l ylo咋itudinal wavesw i t hkJJE1 目 Without l o s so f x i st ol i ealongkandE 1 ,andt h eza x i s g e n e r a l i t y ,wecanchooset h exa ,=E ,=E ,=O,k=k圭, andE = E X . . toliealongB0(Fig.4‑18).T l i u s k ,=k Droppingt h es u b s c r i p t s 1andeands e p a r a t i n gE q . [4・52] i n t ocomュ p o n e n t s ,wehave ーァー合-D.·一句一一回一一 。 。 x ( 4 ‑ 5 3 ] a t K }号、-ー--i-一戸ーo一一’一一0。 Plasmαs I ti so fcoursep o s s i b l eforkt obea tana r b i t r a r ya n g l et oBoorE 1 ;then onewouldhaveamixtureo ft h ep r i n c i p a lmodespresentedh e r e . Comingbackt ot h ee l e c t r o no s c i l l a t i o n sperpendiculart oB 0 ,we s h a l lassumet h a tt h ei o n sa r et o omassivet omovea tt h ef r e q u e n c i e s i n v o l ¥ ' e dandformaf i x e d ,uniformbackgroundo fp o s i t i v ec h a r g e .We .Thee q u i l i b r i u m s h a l la l s on e g l e c tthermal motionsands e tKT,= 0 e r oE0and plasma,a su s u a l ,hasc o n s t a n tanduniformn0andB0andz Vo・ The motiono fe l e c t r o n si sthengovernedbyt h ef o l l o w i n gl i n e a r i z e d e q u a t i o n s : 1 0 12 14 16 18 PROBESEPARATION(cm) 3 1 0 3 Wavesi n Geometry o fal o n g i t u d i n a lp l a n e FIGURE4‑18 wavep r o p a g a t i n ga tr i g h ta n g l e st oB 0 . o , , o " "̲ , ••. ‑ 。 。 o " ' ー••"'e•yt{tf 川「 -V 『.,.......- 20 40 60 80 100 FREQUENCY(kHz) ‑zwmvx= ‑eE‑ev,B 。 FIGURE4‑17 Measuredphasev e l o c i t yo fi o nwavesi np o t a s s i u mandcesiump l a s ュ masa saf u n c t i o no ff r e q u e n c y .Thed i f f e r e n ts e t so fp o i n t sc o r r e s p o n d t od i f f e r e n tplasmad e n s i t i e s .[FromWong,M o t l e y ,andD’ Angelo, ‑zwmv,= l o c .c i t . ] -iw市民= O ( +ev,B0 ( 4 ‑ 5 5 ) ( 4 ‑ 5 6 ] 104 Chapteγ Fouγ S o l v i n gf o rv ,i nE q .[ 4 ‑ 5 6 ]ands u b s t i t u t i n gi n t oE q .[4・55], wehave ( 105 W a v e si n 8 同情Uχ = eE+eB。主主_()_ Vx Plasm山 ηzαJ eE/imw i 一 w, Iw [ 4 ‑ 5 7 ] ヘ\\\ E Vx =-;-一一一言ア一吉 Notet h a tVx becomesi n f i n i t ea tc y c l o t r o nr e s o n a n c e ,w =w"Thisi st o xandc o n t i n u o u s l y bee x p e c t e d ,s i n c et h ee l e c t r i cf i e l dchangess i g nw i t hv a c c e l e r a t e st h ee l e c t r o n s .[Thef l u i dands i n g l e ‑ p a r t i c l ee q u a t i o n sa r e r eboth n e g l e c t e d ;a l lt h e i d e n t i c a lwhen t h e( vキ V)vandVp termsa 4 ‑ 5 3 ] ,wehave p a r t i c l e smovet o g e t h e r . ]Fromt h el i n e a r i z e dformo fE q .( k n1 = η oVx v\ m [4・ 58] αJ M o t i o no fe l e c t r o n si na nupperh y b r i do s c i l l a t i o n . FIGURE4 ‑ 1 9 L i n e a r i z i n gE q .( 4 ‑ 5 4 ]andu s i n gt h el a s ttwor e s u l t s ,wehave k e EI w 九- 1 i k E 0 E= -e-no ァー l 1 -ーl α3 imw\ αI I (1 一点 E = ~E The e x i s t e n c eo ft h e upperh y b r i d frequency h a s been v e r i f i e d e x p e r i m e n t a l l ybymicrowavet r a n s m i s s i o na c r o s samagneticf i e l d .As t h eplasmad e n s i t yi sv a r i e d ,t h et r a n s m i s s i o nthrought h eplasmat a k e s adipa tt h ed e n s i t yt h a tmakeswh e q u a lt ot h ea p p l i e df r e q u e n c y .This i sb e c a u s et h eupperh y b r i do s c i l l a t i o n sa r ee x c i t e d ,andenergyi sa b ュ sorbedfromt h ebeam.FromE q .( 4 ‑ 6 0 ] ,wef i n dal i n e a rr e l a t i o n s h i p betweenw~ /w2 andt h ed e n s i t y : [4・ 59] Thed i s p e r s i o nr e l a t i o ni st h e r e f o r e lw2=w;+w;=w~I [4 ・ 60] 2 G》 ε , 2 Wp 一言= i -一言= Thef r e q u e n c ywhi sc a l l e dt h eu p p e rh y b r i df r e q u e n c y .E l e c t r o s t a t i ce l e c t r o n c r o s sB havet h i sf r e q u e n c y ,w h i l et h o s ea l o n gB a r et h eu s u a l wavesa e l o c i t yi sa g a i nz e r oa slong plasmao s c i l l a t i o n sw i t hw =w合・ The groupv a st h e r m a lmotionsa r en e g l e c t e d . Ap h y s i c a lp i c t u r eo ft h i so s c i l l a t i o ni sg i v e ni nF i g .4 ‑ 1 9 .E l e c t r o n s i nt h ep l a n ewaveformr e g i o n so fcompressionandr a r e f a c t i o n ,a si na plasmao s c i l l a t i o n .However,t h e r ei snowaB f i e l dperpendiculart ot h e m o t i o n ,andt h eLorentzf o r c et u r n st h et r a j e c t o r i e si n t oe l l i p s e s .There a r etwor e s t o r i n gf o r c e sa c t i n gont h ee l e c t r o n s :t h ee l e c t r o s t a t i cf i e l d and t h e Lorentz f o r c e . The i n c r e a s e dr e s t o r i n gf o r c e makes t h e f r e q u e n c yl a r g e rthant h a to faplasmao s c i l l a t i o n .Ast h emagneticf i e l d o e st oz e r oi nE q .(4・60], andoner e c o v e r saplasma g o e st oz e r o ,w,g o s c i l l a t i o n .Ast h eplasmad e n s i t yg o e st oz e r o ,wρgoes t oz e r o ,andone h a sas i m p l eLarmorg y r a t i o n ,s i n c et h ee l e c t r o s t a t i cf o r c e sv a n i s hw i t h d e n s i t y . , 1 ηe 2 一一一一宮 ωωε 。叩ω Thisl i n e a rr e l a t i o ni sf o l l o w e dbyt h ee x p e r i m e n t a lp o i n t sonF i g .4・ 20, 2' 2 wherewc lw i sR l o t t e da g a i n s tt h ed i s c h a r g ec u r r e n t ,whichi spropor‑ t i o n a lton. I fwenowc o n s i d e rpropagationa tana n g l e8t oB ,wew i l lg e ttwo p o s s i b l ew a v e s .Onei sl i k et h eplasmao s c i l l a t i o n ,andt h eo t h e ri sl i k e t h eupperhybrido s c i l l a t i o n ,butbothw i l lbemodifiedbyt h ea n g l eo f p r o p a g a t i o n .Thed e t a i l so ft h i sa r el e f ta sane x e r c i s e(Problem4 ‑ 8 ) . ,diagramf o rt h e s etwowaves F i g u r e4 ‑ 2 1showss c h e m a t i c a l l yt h ew ‑ k f o rf i x e dk .wherek x / k ,=tan8 .Becauseo ft h esymmetryo fE q .[ 4 ‑ 6 0 ] , t h ec a s ew ,>W p i st h esamea st h ec a s e wρ > w , with thes u b s c r i p t s "t h ewavet r a v e l sp a r a l l e lt oB 0 .Onewavei s i n t e r c h a n g e d .Forl a r g ek t h e rw a v e ,a tw=w"i sas p u r i o u s t h eplasmao s c i l l a t i o na tw=wρ , the o r o o ta tk , • co. Fors m a l lk"wehavet h es i t u a t i o no fk ム Bo d i s c u s s e di n 一ーー-・』』 十 106 C h a p t e r Four 1.0 1 0 7 むコ Wavesi n Plasm出 竺 h 9 ト\. ω wc>wp c ω 咽- POINTSOFMINIMUM TRANSMISSION . 7 . 6 w2 c 一 w2 . .5 。 iく z . 4 w . 3 むJ . 2 .\ 。 20 40 60 80 100 120 むJ h 一一ーーーーー--l ----ーーー-ー . 。 .>wc p む2 p 140 DISCHARGECURRENT(mA) FIGURE4 ‑ 2 0 R e s u l t so fanexperimentt od e t e c tt h ee x i s t e n c eo ft h eupperhybrid frequency by mapping t h ec o n d i t i o n sf o r maximum a b s o r p t i o n (minimumt r a n s m i s s i o n )o fmicrowaveenergys e n ta c r o s samagnetic 自eld. The 直eld a twhicht h i soccurs( e x p r e s s e da sw~/曲、 is p l o t t e d . a g a i n s td i s c h a r g ec u r r e n t{ p r o p o r t i o n a lt oplasmadensity)・[ From R r o c e e d i n g so ft h eSev四th I n t e r n a t i o n a lC o n f e r e n c eo nPhenomena S .Harp,P e l g r a d e ,1 9 6 5 ,J I ,294( 1 9 6 6 ) . ] i nI o n i z e dG a s e s .B 。 k z TheTrivelpiece‑Gould d i s p e r s i o nc u r v e s FIGURE4 ‑ 2 1 f o re l e c t r o s t a t i ce l e c t r o n waves i n acon・ ducting c y l i n d e rf i l l e d with a uniform plasmaandac o a x i a lmagneticf i e l d .[From A .W.T r i v e l p i e c eandR .W.Gould,] .A伶I. P h y s .3 0 ,1784( 1 9 5 9 ) . ] t h i ss e c t i o n . The lower branch v a n i s h e s , while the upper branch i r s t approaches the hybrid o s c i l l a t i o na t w = wh・ These curves were f c a l c u l a t e d by. T r i v e l p i e c e and Gould, who a l s ov e r i f i e d them e x p e r i ュ mentally( F i g .4 ‑ 2 2 ) .TheTrivelpiece‑Gouldexperimentwasdonei na ,int h i sc a s ei s c y l i n d r i c a lplasmacolumn;i tcanbeshownt h a tvaryingk equivalentt opropagatingplanewavesa tvariousanglestoBo ・ 4・ 7. F ort h eupperh y b r i do s c i l l a t i o n ,showt h a tt h ee l l i p t i c a lo r b i t s( F i g .4 ‑ 1 9 ) a r ea l w a y se l o n g a t e di nt h ed i r e c t i o no fk .( H i n t :Fromt h ee q u a t i o no fm o t i o n , deri 河 an e x p r e s s i o nf o rv . / v ,i nt e r m so fω/ωρ) 一一一一ー一ー--- PROBLEMS 『句”E 108 3 Z 且 Chapleγ 109 Bo W a v e si n P l a s m a s F o u r k,E x THEORY 2 ト 00o'o..,‘ FIGUREP 4 ‑ 8 『O旬、 EXPERIMENT ( a ) Showt h a tt h eansweri s w2(w2 ー w~ ) w wc +w;w;c o s 28=0 ( b )W r i t eo u tt h etwos o l u t i o n so ft h i sq u a d r a t i cf o rw 2 ,andshowt h a ti nt h e l i m i t sIJ • 0 andO • 7T/2, ourp r e v i o u sr e s u l t sa r er e c o v e r e d .Showt h a ti nt h e s e l i m i t s ,oneo ft h etwos o l u t i o n si sas p u r i o u sr o o tw i t hnop h y s i c a lm e a n i n g . o ( c ) Byc o m p l e t i n gt h es q u a r e ,showt h a tt h eabovee q u a t i o ni st h ee q u a t i o no f ane l l i p s e : o o ’’ ゲ’ O , ( y‑ 1 ) 2 x 2 1 一一τー+ τ= I a 『, io wherex 圭 cos I J ,y= 2w2,'w~. anda=wV2wεωρ・ ( d )P l o tt h ee l l i p s ef o rw,/w,=I,2 ,ando o . ( e )Showt h a ti fw ,>w , .t h el o w e rr o o tf o rw i sa l w a y sl e s st h a nw,for•any I }>O andt h eupperr o o ta l w a y sl i e sbetweenw,andw , ;andt h a ti fw,>w0t h el o w e r r o o tl i e sbeloww,w h i l et h eupperr o o ti sbetweenw,andωト 2 4 6 10 8 ELECTROSTATIC ION もVAVES PERPENDICULAR T O B kza FIGURE4 ‑ 2 2 Experimental v e r i f i c a t i o no ft h eT r i v e l p i e c e ‑ G o u l dc u r v e s , showingt h ee x i s t e n c eo fbackwardw a v e s ;t h a ti s ,waveswhose groupv e l o c i t y ,a si n d i c a t e dbyt h es l o p eo ft h ed i s p e r s i o n c u r v e ,i so p p o s i t ei nd i r e c t i o nt ot h ephasev e l o c i t y .[From T r i v e l p i e c eandG o u l d ,l o c .c i t . ] 4 ‑ 8 .F i n dt h ed i s p e r s i o nr e l a t i o nf o re l e c t r o s t a t i ce l e c t r o nwavesp r o p a g a t i n ga t ana r b i t r a r ya n g l e8 r e l a t i v et oB 0 .H i n t :Chooset h exa x i ss ot h a tkandEl i e i nt h ex‑zp l a n e( F i g .P 4 ‑ 8 ) .Then E.=E1sin8, E,=E,cos8, Eヲ= O ands i m i l a r l yf o r k .S o l v et h ee q u a t i o n so fmotionandc o n t i n u i t yandPoisson ’s e q u a t i o ni nt h eu s u a lwayw i t hn ouniformandV o=E o=0 . 育Ve n ext consider what happens t o the ion a c o u s t i cwave when k i s perpendiculart oB 0 .I ti stemptingt os e tkキB0e x a c t l yequalt oz e r o ,but t h i swouldleadt oar e s u l t( S e c t i o n4 . 1 1 )which,althoughmathematically c o r r e c t ,doesnotd e s c r i b ewhatu s u a l l yhappensi nr e a lplasmas.I n s t e a d , wes h a l ll e tkbea l m o s tperpendiculart oB 0 ;whatwemeanbv “ almost ” w i l lbemadec l e a rl a t e r .Wes h a l lassumetheu s u a li n f i n i t eplasmai n .For e q u i l i b r i u m ,withnoandB0constantanduniformandv 0= E0= 0 ,= O ;wes h a l lnotmissanyimportantE妊ects s i m p l i c i t y ,wes h a l lt a k eT becauseweknowt h a ta c o u s t i cwavess t i l le x i s ti fT ,= 0 .Wea l s oassume e l e c t r o s t a t i cwaves withkxE = 0 ,so t h a tE = -VφThe geometryi s showni nF i g .4・ 23. Theangle~7T ‑ I Ji stakent obes os m a l lt h a twemay 一ーーーー-』』 一一ーー一一J 勾ー一一ー ー 4.10 I 110 F o u r S o l v i n ga sb e f o r e ,wef i n d WAVEFRONTS Chapleγ Z 且 111 Vix = 品川 l ーさ) B。 W a v e si n I st h ei o nc y c l o t r o nf r e q u e n c y .Thei o ne q u a t i o no f whereflc= eBu/M i c o n t i n u i t yy i e l d s ,a su s u a l , kE k =n o‑v., 宵 ηz 1 ー -8 2 αJ n . i FIGURE4 ‑ 2 3 G eometryo fane l e c t r o s t a t i ci o nc y c l o t r o nwave p r o p a g a t i n gn e a r l ya tr i g h ta n g l e st oBo・ πo 1 x n ;v., =一一一u e k KT,n 0 k 一寸) w‑ Mw e n 0 w 民一 M -ev阻Bo Q ω -iwMvη = ’R [4 ・ 66] S i n c ewehavet a k e nKT;= 0 ,wec anw r i t et h i sa s I w2 二日~; [ 4 ‑ 6 7 ] Thisi st h ed i s p e r s i o nr e l a t i o nf o re l e c t r o s t a t i cioη cyclotron 山aves. Thep h y s i c a le x p l a n a t i o no ft h e s ewavesi sv e r ys i m i l a rt ot h a ti n ‑ 1 9f o rupperh y b r i dw a v e s .Thei o n sundergoana c o u s t i c ‑ t y p e F i g .4 o s c i l l a t i o n ,b日 t t h eLorentzf o r c ec o n s t i t u t e sanewr e s t o r i n gf o r c eg i Y i n g nE q .[ 4 ‑ 6 7 ] .Thea c o u s t i cd i s p e r s i o nr e l a t i o nw2= r i s etothen;termi k " v ;i sv a l i di ft h ee l e c t r o n sp r o v i d eDebyes h i e l d i n g .I nt h i sc a s e ,t h e y dos obyf l o w i n glongd i s t a n c e salongB 0 . E l e c t r o s t a t i ci o nc y c l o t r o nwavesweref i r s tobservedbyMotleyand D ’Angelo, a g a i ni n a Q‑machine ( F i g .4 ‑ 2 4 ) . Thewaves p ropagated r a d i a l l youtwarda c r o s st h emagneticf i e l dandweree x c i t e dbyac u r r e n t drawn along t h ea x i st o as m a l la u x i l i a r ye l e c t r o d e . The r e a s o nf o r e x c i t a t i o ni sr a t h e rc o m p l i c a t e dandw i l lnotbeg i v e nh e r e .F i g u r e4‑25 g i v e st h e i rr e s u l t sf o rt h ewavefrequencyv s . magneticf i e l d .I nt h i s [ 4 ‑ 6 1 ] Assumingplanewavespropagatingi nt h exd i r e c t i o nands e p a r a t i n g i n t ocomponents,wehave +ev;.,B 。 [4 ・ 65] (l z e r o ,o rs m a l lbutf i n i t e .Thee l e c t r o n shavesuchs m a l lLarmorr a d i i i r e c t i o nt op r e s e r v echargen e u t r a l i t y ; t h a tt h e ycannotmovei nt h exd a l lt h a tt h eE f i e l ddoesi s makethemd r i f tbackand f o r t hi nt h ey d i r e c t i o n .I fe i snote x a c t l y7 1 ' / 2 ,however,thee l e c t r o n scanmovealong oc a r r ychargefromn e g a t i v et o t h edashedl i n e( a l o n gB o )i nF i g .4‑23t p o s i t i v er e g i o n si nt h ewaveandc a r r youtDebyes h i e l d i n g .Thei o n s cannot do t h i se f f e c t i v e l yb e c a u s et h e i ri n e r t i ap r e v e n t s them from movingsuchJongd i s t a n c e si nawavep e r i o d ;t h i si swhywecann e g l e c t k ,f o ri o n s .Thec r i t i c a la n g l ex=針。 is p r o p o r t i o n a lt ot h er a t i oo f l e c t r o np a r a l l e lv e l o c i t i e s :x= (m/M)112( i nradians )・ For a n g l e s i o ntoe xlargerthanthis,thefollowingtreatmenti sv a l i d .Fora n g l e sxs m a l l e r . 1 1i sv a l i d . thant h i s ,t h et r e a t m e n to fS e c t i o n4 A f t e rt h i sl e n g t h yi n t r o d u c t i o n ,weproceedt ot h eb r i e fd e r i v a t i o n o ft h er e s u l t .Fort h ei o ne q u a t i o no fm o t i o n ,wehave ‑iwMvix=-eikφ1 eφI KT, Theplasmaapproximationn ;= n ,nowc l o s e st h es y s t e mo fe q u a t i o n s . 4 ‑ 6 4 ]and[4』65], wec anw r i t eE q .[ 4 ‑ 6 3 ]a s Witht h eh e l po fE q s .[ t a k eE=E andV =ik主 as f a ra st h eioηmotion i sc o n c e r n e d .Fort h e electγ0肌 however, i tmakesag r e a td e a lo fdifferer悶 whether か- ei s a t [ 4 ‑ 6 4 ] Assumingt h ee l e c t r o n sc a nmovea l o n gBob e c a u s eo ft h ef i n i t e n e s so f t h ea n g l ex .wecanusetheBoltzmannrelationforelectrons.Inlinearized form,t h i si s x M~ =-eVφ1 +ev;1ラ Bo [ 4 ‑ 6 3 ] [ 4 ‑ 6 2 ] ~‘ Plasm邸 ?「 112 C h a p t e r F o u r B 一一ー』 ~--::三三千戸 FIGURE4‑24 S c h e m a t i co faQ‑machinee x p e r i m e n tone l e c t r o s t a t i ci o nc y c l o t r o nw a v e s . .W.M o t l e yandN.D ’Angelo, P h y s .Ft似ゐ 6, 2 96( 1 9 6 3 ) . ] [ A f t e rR e q u a t i o no fm o t i o n ,E q .[3 ・62). I fwekeept h ee l e c t r o nmassf i n i t e ,t h i s h eVp,t e r m ; e q u a t i o ni sn o n t r i v i a leveni fweassumeτ = 0anddropt h e n c e ,wes h a l ldos oi nt h ei n t e r e s to fs i m p l i c i t y .Thei o ne q u a t i o no f motioni sunchangedfromE q .( 4 ‑ 6 3 ) : e k ! l ' . ¥‑I I U悶=プァφI い一 2) M α) \ αI I [ 4 ‑ 6 8 ] Bychanginget o‑ e ,Aftom,and! l ,t o‑w,i nE q .[4 田68], wecanw r i t e : downt h er e s u l to fs o l v i n gE q .( 3 ‑ 6 2 ]f o re l e c t r o n s ,w i t hT,= 0 U田=- ~φ,( 1 - ~rl . 3 [ 4 ‑ 6 9 ] Thee q u a t i o n so fc o n t i n u i t yg i v e 工予こι ← 内 J4 N k n , i= n0‑v,i k n , i= no‑v.i [ 4 ‑ 7 0 ] αJαJ Theplasmaapproximationη;= ηe thenr e q u i r e sv;1= t ' ,1・ Setting [ 4 ‑ 6 8 ]and( 4 ‑ 6 9 )e q u a lt oeacho t h e r ,wehave Eqs 目 1 -~) =一明( 1 -~) M( 川河) = m w~ +MD.~ = e叫十卦 2 4 6 8 10 B(kG) FIGURE4 ‑ 2 5 M e a s u r e m e n t so ff r e q u e n c yo fe l e c t r o s t a t i ci o nc y c l o t r o nw a v e sv s . m a g n e t i cf i e l d .[FromM o t l e yandD’Angelo, l o c .c i t . ] e x p e r i m e n t ,t h ek2v;1 同rm wass m a l lcomparedt ot h e!l~ ter瓜 and t h e measuredf r e q u e n c i e sl a yo n l ys l i g h t l yabove! l , . D . c W , 1 ‑ ( J )= (~,-:y/;;;.-:; l [ 4 ‑ 7 1 ] Thisi sc a l l e dt h e/oweγ hybrid f r e q u e n c y .I fwehadusedPoisson ’s e q u a t i o n i n s t e a do ft h eplasmaapproximation,wewouldhaveo b t a i n e d 一吋 l se x a c t l y7 r / 2 ,andt h ee l e c t r o n s Wenowc o n s i d e rwhathappenswhen(}i a r en o ta l l o w e dt op r e s e r v echargen e u t r a l i t ybyf l o w i n galongt h el i n e s e l a t i o n ,t h e yw i l lobeyt h ef u l l o ff o r c e .I n s t e a do fobeyingBoltzmann ’s r Mm l 叫 一 4.11 THELOWERHYBRID FREQUENCY 2~2 w2=~手-= [ 4 ‑ 7 l a ] Inl o w ‑ d e n s i t yplasmast h el a t t e rterma c t u a l l yd o m i n a t e s .Theplasma approximationi sn o tv a l i da tsuchhighf r e q u e n c i e s .Lowerh y b r i do s c i l l a ュ f ( }i sv e r yc l o s et o7 r / 2 . t i o n scanbeobservedo n l yi 113 W a v e si n Pl出現出 ?ー一一 114 Cha争ter Fouγ 4 . 1 2 ELECTROMAGNETIC WAVES WITH Bo=0 Nexti nt h eordero fc o m p l e x i t ycomewavesw i t hB1~ 0 .Thesea r e a d i owavest r a v e l i n g t r a n s v e r s ee l e c t r o m a g n e t i cwavesーlight wavesorr throughap l a s m a . Web e g i nw i t hab r i e fr e i v i e wo fl i g h twavesi na vacuum.Ther e l e v a n tMaxwelle q u a t i o n sa r e VXE1=‑B1 I fwec o n s i d e rl i g h twaveso rm i c r o w a v e s ,t h e s ew i l lbeo fsuch h i g h frequencyt h a tt h ei o n scanbec o n s i d e r e da sf i x e d .Thec u r r e n tj1t h e n comese n t i r e l yfrome l e c t r o nm o t i o n : Ji=‑ n o e v , i Fromt h el i n e a r i z e de l e c t r o ne q u a t i o no fm o t i o n ,wehave( f o rKT,=0 ) : 。v•• m -」ニ= [ 4 ‑ 7 2 ] 。t c2VxB1=E 1 c2Vx(VxB 1 )=V x 亘 1 =一丞 l [4・74] Againassumingp l a n e swavesv a r y i n ga sexp[i(kx ー wt)], wehave c 2 [ k ( kキ B i )‑k 2 B i ] w2B1= ‑c2kx( kラBi)=‑ [ 4 ‑ 7 5 ] S i n c ekキBi=‑iVキBi=0byanothero fMaxwell ’S e q u a t i o n s ,t h er e s u l t i s w2=fl k 2c2 [4・ 76] andci st h ephasev e l o c i t yw/ko fl i g h tw a v e s . ,E q .[4・72] i sunchanged,butwemustadd I naplasmaw i t hBo=0 oE q . [4・73] t oaccountf o rc u r r e n t sdue t o first・order atermji /εo t chargedp a r t i c l em o t i o n s : [ 4 ‑ 8 3 ] e E 1 V,i =で一一一 imw TL ( 4 ‑ 7 7 ] E, キ ( 4 ‑ 7 8 ] w h i l et h ec u r lo fE q .[ 4 ‑ 7 2 ]i s Vx(VラE i )=V(V.E i )‑V2Ei=‑ vxBi ( 4 ‑ 7 9 ] E l i m i n a t i n gV xBiandassuminganexp[ i( kキ r 一 wt)] d ependence,we have 2 -k(k·Ei)吋 2Ei =と吉ji +与Ei C ε oC (4・801 Byt r a n s v e r s ewaveswemeankキE i=0 ,s ot h i sbecomes ( w 2‑c 2 k 2 ) E i= -iwji /ε0 (4・ 81] 2 '2 [ 4 ‑ 8 5 ] Thisi st h ed i s p e r s i o nr e l a t i o nf o re l e c t r o m a g n e t i c! L ' a v e sp ropagating i naplasmaw i t hnodcmagneticf i e l d .Wes e et h a tt h evacuumr e l a t i o n [ 4 ‑ 7 6 ]i smodifiedbyaterm r e m i n i s c e n to fplasmao s c i l l a t i o n s .The phasev e l o c i t yo fal i g h twavei naplasmai sg r e a t e rthant h ev e l o c i t yo f l i g h t : w ! + > Pし at 2 ωρ + ck 一一 ε。 2= C ‘ ω 一一 1a j i cV xB,=一一一+ w ;isrecogr山able ontheright‑handside,andthe U Thet i m ed e r i v a t i v eo ft h i si s [ 4 ‑ 8 4 ] Thee x p r e s s i o nf o r r e s u l ti s ョ的子 - 2 2 " iw e E 1 n 0 e 2 (w ‑ck " ) E i=ーη oe ァ一一=一一 Ei ‘'o i官lWε onも JF + E Equation[ 4 ‑ 8 1 ]nowcanbew r i t t e n 2φ 一一 1LO ラ B fu 9h V -- - ‑eE [ 4 ‑ 7 3 ] s i n c ei navacuumj=0ande 0 オ . 0=c 2 Takingt h ec u r lo fE q .[ 4 ‑7 3 ] ands u b s t i t u t i n gi n t ot h et i m ed e r i v a t i v eo fE q .[ 4 ‑ 7 2 ] ,wehave 3 ( 4 ‑ 8 2 ] [ 4 ‑ 8 6 ] However,t h egroupv e l o c i t ycannotexceedt h ev e l o c i t yo fl i g h t .F1om 4 ‑ 8 5 ) ,wef i n d E q .( dw c 2 一=”=- dk vg Uφ [ 4 ‑ 8 7 ] s ot h a tVg i sl e s sthancwheneverUφis g r e a t e rthanc .Thed i s p e r s i o n r e l a t i o n[ 4 ‑ 8 5 ]i sshowni nF i g .4 ‑ 2 6 .Thisdiagramresemblest h a to fF i g . 4 ‑ 5f o rplasmaw a v e s ,butt h ed i s p e r s i o nr e l a t i o ni sr e a l l yq u i t edi任erent b e c a u s et h ea s y m p t o t i cv e l o c i t yci nF i g .4‑26i ss omuchl a r g e rthant h e , hi nF i g .4 ‑ 5 .Morei m p o r t a n t l y ,t h e r ei sad i f f e r e n c e t h e r m a lv e l o c i t yv i ndampingo ft h ew a v e s .Plasmawavesw i t hl a r g ek v , ha r eh i g h l ydamped, ar e s u l twes h a l lo b t a i nfromk i n e t i ct h e o r yi nChapter7 .E l e c t r o m a g n e t i c 115 W a v e sm P l a s m a s マーーー 116 EXPERIMENTALAPPLICATIONS 4.13 むJ Chapleγ Four Thephenomenono fc u t o f fs u g g e s t sane a s ywayt omeasureplasma d e n s i t y . A beamo fmicrowavesgeneratedbyak l y s t r o ni slaunched towardt h eplasmabyahornantenna( F i g .4 ‑ 2 7 ) .Thet r a n s m i t t e dbeam i sc o l l e c t e dbyanotherhornandi sd e t e c t e dbyac r y s t a l .Ast h efrequency o rt h e plasma d e n s i t yi sv a r i e d ,t h ed e t e c t e ds i g n a lw i l ld i s a p p e a r whenevert h ec o n d i t i o n[ 4 ‑ 8 8 ]i ss a t i s f i e dsomewherei nt h ep l a s m a .This procedureg i v e st h emaximumd e n s i t y .I ti snotac o n v e n i e n to rv e r s a t i l e schemeb e c a u s et h erangeo ff r e q u e n c i e sg e n e r a t e dbyas i n g l emicrowave g e n e r a t o ri sl i m i t e d . Aw i d e l yusedmethodo fd e n s i t ymeasurementr e l i e sont h ed i s p e r ュ s i o n ,o rv a r i a t i o no findexo fr e f r a c t i o n ,p r e d i c t e dbyE q .[ 4 ‑ 8 5 ] .The sd e f i n e da s indexo fr e f r a c t i o n i wp k FIGURE4・26 D i s p e r s i o nr e l a t i o nf o re l e c t r o m a g ュ n e t i cw a v e si nap l a s m aw i t hnoq c m a g n e t i cf i e l d . n 五 E c/vφ = w a v e s ,ont h eo t h e rhand,becomeo r d i n a r yl i g h twavesa tl a r g ek cand a r en o tdampedbyt h ep r e s e n c eo ft h eplasmdi nt h i sl i m i t . Ad i s p e r s i o nr e l a t i o nl i k eE q .[ 4 ‑ 8 5 ]e x h i b i t saphenomenonc a l l e d c u t o f f .I fones e n d samicrowavebeamw i t hag i v e nfrequencyw through ap l a s m a ,t h ewavelength2 7 T / ki nt h eplasmaw i l lt a k eon t h ev a l u e i sr a i s e d , p r e s c r i b e dbyE q .[ 4 ‑ 8 5 ] .Ast h eplasmad e n s i t y ,andhence k 2w i l ln e c e s s a r i l yd e c r e a s e ; andt h ewavelengthbecomesl o n g e rand l o n g e r .F i n a l l y ,ad e n s i t yw i l lbereachedsucht h a tk 2i sz e r o .Ford e n s i t i e s a t i s f i e df o ranyr e a lk ,andt h e l a r g e rthant h i s ,Eq 目[ 4司85] cannotbes wavecannotp r o p a g a t e .Thisc u t o f fc o n d i t i o no c c u r sa tac r i t i c a ld e n s i t y n ,s ucht h a tw =wp;namely(fromE q .[4 ” 25]) w ! , η, 2I 2 = mE0w/ e [ 4 ‑ 8 8 1 I fn i st o ol a r g eo rw t o os m a l l ,ane l e c t r o m a g n e t i cwavecannotp a s s s through a p l a s m a . When t h i s happens, E q .[ 4 ‑ 8 5 ]t e l l su st h a tk i i m a g i n a r y : ck=(w2 ー w!)1;2=ilw!-w2l1;2 e -柑 o=lkl-1 = ア~ττ72 (w;-w ‘ ) “ [ 4 ‑ 9 1 ] Thisc l e a r l yv a r i e sw i t hw , anda plasmai s ad i s p e r s i v e medium. A microwavei n t e r f e r o m e t e remployingt h esamep h y s i c a lp r i n c i p l e sa st h e Michelsoni n t e r f e r o m e t e ri susedt omeasured e n s i t y( F i g .4 ‑ 2 8 ) .The s i g n a lfromak l y s t r o ni ss p l i ti n t otwop a t h s .P a r to ft h es i g n a lg o e st o t h e rp a r ti ss e n tthrough t h ed e t e c t o rthroughthe “ reference leg. ” The o t h eplasmaw i t hhorna n t e n n a s . Thed e t e c t o rrespondst ot h e mean s q u a r eo ft h esumo ft h ea m p l i t u d e so ft h etwor e c e i v e dsignals ・ These s i g n a l sa r ea d j u s t e dt obee q u a li namplitudeand180。 out o fphasei n h ea t t e n u a t o randphases h i f t e r ,s ot h a tt h e t h ea b s e n c eo fp l a s m a byt d e t e c t o routputi sz e r o .Whent h eplasmai sturnedo n ,t h ephaseo ft h e s i g n a li nt h eplasmal e gi schangeda st h ewavelengthi n c r e a s e s( F i g . 4 ‑ 2 9 ) .Thed e t e c t o rthen g i v e s af i n i t eoutputs i g n a l . Ast h ed e n s i t y i n c r e a s e s ,t h ed e t e c t o routputg o e sthroughamaximumandaminimum e n s i t yi nt h e e v e r yt i m et h ephases h i f tchangesby360。. Theaveraged [4・ 89] S i n c et h ewaveh a sas p a t i a ldependencee x p ( i k x ) ,i tw i l lbee x p o n e n t i a l l y a t t e n u a t e di fki si m a g i n a r y .Thes k i ndepth8i sfounda sf o l l o w s : eikx = e ‑ l k l x= ck/w I KLYSTRON 仁二ご--1i·1i1·1·i1 ータ二ゴ DETECTOR I [4・ 90] Formostl a b o r a t o r yp l a s m a s ,t h ec u t o f ffrequencyl i e si nt h emicrowave r a n g e . Microwavemeasuremento fplasmad e n s i t ybyt h ecuto鉦 s i g n a l . of t h et r a n s m i t t e d FIGURE4 ‑ 2 7 1 1 7 W a v e si n Pia町民国 / 1 1 8 plasmai sfoundfromt h enumbero fsuchf r i n g es h i f t s .A c t u a l l y ,one u s u a l l yu s e sahighenoughfrequencyt h a tt h ef r i n g es h i f ti skepts m a l l . Thent h ed e n s i t yi sl i n e a r l yp r o p o r t i o n a lt ot h ef r i n g es h i f t(Problem 4・ 13 )・ The s e n s i t i v i t yo ft h i stechniquea tlowd e n s i t i e si sl i m i t e dt ot h e s t a b i l i t y .o ft h er e f e r e n c el e ga g a i n s tv i b r a t i o n sandthermale x p a n s i o n . C o r r e c t 1 0 n smusta l s obemadef o ra t t e n u a t i o nduet oc o l l i s i o n sandf o r d i f f r a c t i o nandr e f r a c t i o nbyt h ef i n i t e ‑ s i z e dp l a s m a . ’ The f~ct t h a tt h eindexo fr e f r a c t i o ni sl e s sthanu n i t yf o raplasma ~~s somei町es叫 cons叩ences. A convexplasmal e n s( F i g .4 ‑ 3 0 )i s 1 v e r g e n tr a t h e rthanc o n v e r g e n t .ThisE征ect i simportanti nt h el a s e r ュ s o l e n o i d proposalf o ral i n e a rf u s i o nr e a c t o r .A plasmahundredso f meterslongi sconfinedbyas t r o n gmagneticf i e l dandheatedbya b s o r p ュ t i o no fC02l a s e rr a d i a t i o n( F i g .4 ‑ 3 1) .I ft h eplasmah a sanormald e n s i t v p r o f i l e(maximumont h eaxi札 it behavesl i k ean e g a t i v el e n sa吋叩 t h el a s e rbeamt od i v e r g ei n t ot h ew a l l s .I fani n v e r t e dd e n s i t yp r o f i l e (minimumont h ea x i s )canbec r e a t e d ,however,t h el e n se f f e c tbecomes conv~rgi昭 and t h er a d i a t i o ni sfocusedandtrappedbyt h ep l a s m a . Themvertedp r o f i l ecanbeproducedbysqueezingt h eplasmaw i t ha p u l s e dc o i lsurroundingi t ,o ri tcanbeproducedbyt h el a s e rbeami t s e l f . As 中e beamh e a t st h ep l a s m a ,t h ela附 expands, d e c r e a s i n gt h edens町 a tt h ec e n t e ro ft h e beam. The C02 l a s e ro p e r a t e s atλ = 1 0 . 6,um, Cha戸/er Four 1 1 9 Wavesin P l as川副 DETECTOR OUTPUT 1 CUTOFF DENSITY WAVEPATTERN I NPLASMA Theo b s e r v e ds i g n a l fromani n t e r f e r o m e t e r( r i g h t )a s plasmad e n s i t yi s FIGURE4‑29 i n c r e a s e d ,andt h ec o r r e s p o n d i n gwavep a t t e r n si nt h eplasma( l e f t ) . WAVEGUIDE r--REFERENCE しEG ー| ATTENUATOR Aplasmal e n sh a su n u s u a lo p t i c a lp r o p e r ‑ FIGURE4 ‑ 3 0 t i e s ,s i n c et h ei n d e xo fr e f r a c t i o ni sl e s s t h a nu n i t y . DETECTOR PLASMA FIGURE4・28 Amicrowavei n t e r f e r o m e t e rf o rplasmad e n s i t ym e a s u r e m e n t . LASER Aplasmac o n f i n e di nal o n g ,l i n e a rs o l e n o i dw i l lt r a pt h eC02l a s e rl i g h tu s e d FIGURE4 ‑ 3 1 t oh e a ti to n l yi ft h ep l a s m ah a sad e n s i t yminimumona x i s .Thevacuum chamberh a sbeeno m i t t e df o rc l a r i t y . 一 120 121 correspondingt oafrequency C h a p t e r Four f=一=で?で~て;;:= 3x108 λ10.6 x1 0 ‑ 0 Wavesi n P l a s m a s ' 2.8Xl0 且 Hz Thec r i t i c a ld e n s i t yi s ,fromEq.[4・88], n ,=前向( 27rf〕2/e2=l02sm-s However,becauseoft h elongpathl e n g t h si n v o l v e d ,ther e f r a c t i o ne f f e c t s a r eimportantevena td e n s i t i e sof 1 0 2 2m‑3. Thefocusinge f f e c to fa hollowplasmahasbeenshowne x p e r i m e n t a l l y . Perhapst h eb e s tknowne f f e c to ftheplasmac u t o f fi st h ea p p l i c a t i o n t o shortwave radio communication. When a radio wave reaches an a l t i t u d ei nt h eionospherewheretheplasmad e n s i t yi ss u f f i c i e n t l yh i g h , t h ewavei sr e f l e c t e d( F i g .4 ‑ 3 2 ) ,makingi tp o s s i b l et osends i g n a l saround t h ee a r t h .I fwet aket h emaximumd e n s i t yt obe 1 0 1 2m‑3thec r i t i c a l c f .E q.[ 4 ‑ 2 6 ] ) .Tocommunicate frequencyi soft h eorderof10MHz( withspacev e h i c l e s ,i ti snecessaryt ousefrequenciesabovet h i si norder t op e n e t r a t et h eionosphere.However,duringreentryo faspacev e h i c l e , aplasmai sgeneratedbyt h ei n t e n s eheatoff r i c t i o n .Thisc a u s e saplasma c u t o f f ,r e s u l t i n gi nacommunicationsblackoutduringreentry( F i g .4 ‑ 3 2 ) . PROBLEMS 4 ‑ 9 .A s p a c ec a p s u l emakingar e e n t r yi n t ot h ee a r t h ' satmospheres u f f e r sa c o m m u n i c a t i o n sb l a c k o u tb e c a u s eaplasmai sg e n e r a t e dbyt h es h o c kwavei n f r o n to ft h ec a p s u l e .I ft h er a d i oo p e r a t e sa taf r e q u e n c yo f300MHz,whati s t h eminimump l a s m ad e n s i t yduringt h eb l a c k o u t ? ‑ 3 2 E x a g g e r a t e dv i e wo ft h eeartl内 iono_sphere, i l l u s t r a t i n gt h e FIGURE4 e f f e c to fplasmaonr a d i ocommunications. 4・は I nap o t a s s i u mQ‑machinep l a s m a ,af r a c t i o nK o ft h ee l e c t r o n scan 円 r e p l a c e db yn e g a t i v eC li o n s .Thep l a s m at h e nh a snoK+i o n s ,KnoC「 ions, and ( J‑K) n oe l e c t r o n sp e rm3 F i n dt h ec r i t i c a lv a l u eo fnowhichw i l lc u to f fa3‑cm w a v e l e n g t hmicrowavebeami fK =0 . 6 . 4 ‑ 1 3 .An8‑nimmicrowavei n t e r f e r o m e t e ri su s e donani n f i n i t ep l a n e ‑ p a r a l l e l p l a s m as l a b8cmt h i c k( F i g .P 4 ‑ 1 3 ) . ft h eplasmad e n s i t yi su n i f o r m ,andap h a s es h i f to fI I I 0f r i n g ei so b s e r v e d , ( a )I h i f t . ) whati st h ed e n s i t y ?( N o t e :Onef r i n g ec o r r e s p o n d st oa360。 phase s ( b ) Showt h a ti fr h ep h a s es h i f ti ss m a l l ,i ti sp r o p o r t i o n a lt ot h ed e n s i t y . 4 ‑ 1 0 . HannesA l f v e n ,t h ef i r s tp l a s m ap h y s i c i s tt ob eawardedt h eNobelp r i z e , h a ss u g g e s t e dt h a tp e r h a p st h ep r i m o r d i a lu n i v e r s ewass y m m e t r i cbetween m a t t e randa n t i m a t t e r .Supposet h eu n i v e r s ewasa tonet i m eauniformm i x ュ t u r eo fp r o t o n s ,a n t i p r o t o n s ,e l e c t r o n s ,andp o s i t r o n s ,e a c hs p e c i e sh a v i n ga d e n s i t yn 0 . ( a )Worko u tt h ed i s p e r s i o nr e l a t i o nf o rh i g h ‑ f r e q u e n c ye l e c t r o m a g n e t i cw a v e s i nt h i sp l a s m a .Youmayn e g l e c tc o l l i s i o n s ,a n n i h i l a t i o n s ,andt h e r m a le f f e c t s . 8mm ( b )Worko u tt h ed i s p e r s i o nr e l a t i o nf o ri o nw a v e s ,u s i n gPoisson ’S e q u a t i o n . Youmayn e g l e c tT‘( but n o tT , )anda ssumet h a ta l ll e p t o n sf o l l o wt h eBoltzmann r e l a t i o n . •• Bern 4 ‑ 1 1 .F o re l e c t r o m a g n e t i cw a v e s ,showt h a tt h ei n d e xo fr e f r a c t i o ni se q u a lt o t h es q u a r er o o to ft h ea p p r o p r i a t eplasmad i e l e c t r i cc o n s t a n t( c f .Problem4 ‑ 4 ) . FIGUREP4‑13 一一一ーι一一一一一←ーー 一 マ一一 122 Chai骨leγ F o u r 4.14 ELECTROMAGNETICWAVES PERPENDICULART OBo シくk We nowc o n s i d e rt h e propagation o fe l e c t r o m a g n e t i cwaveswhen a magneticf i e l di sp r e s e n t Wet r e a tf i r s tt h ec a s eo fperpendicularpropa‑ fwet a k et r a n s v e r s ew a v e s ,w i t hk ム E 1 .t h e r ea r es t i l l g a t i o n ,k 上 Bo. I twoc h o i c e s :E1canbep a r a l l e lt oB0o rperpendiculart oBo( F i g .4 ‑ 3 3 ) . 123 W a v e si n P l a s m a s I I Bo 4.14.1 OrdinaryWave,E1 I fE1i sp a r a l l e lt oB 0 ,wemayt a k eBo=B0ま, E1 =E1z.andk=k 圭. I n ar e a lexperiment,t h i sgeometryi sapproximatedbyabeamo fm i c r o ‑ wavesi n c i d e n tonaplasmacolumnw i t ht h enarrowdimensiono ft h e waveguidei nl i n ew i t hBo( F i g .4 ‑ 3 4 ) . 4蜘81]: Thewaveequationf o rt h i sc a s ei ss t i l lg i v e nbyE q .[ (w2‑c 2 k 2 ) E 1= -iwji/εo = in0ewv.i /ε。 [ 4 ‑ 9 2 ] n l yt h ecomponentv , z .Thisi sg i v e nbyt h e S i n c eE1=E1z,weneedo equationo fmotion ma v , J a t=‑eE, [ 4 ‑ 9 3 ] B0 S i n c et h i si st h esamea st h ee q u a t i o nf o rB0=0 ,t h er e s u l ti st h esame a swehadp r e v i o u s l yf o rB0=0 : I w2=w;+c 2 k 2 I Ano r d i n a r ywavel a u n c h e dfromawaveguidea n t e n n at o w a r d FIGURE4・34 am a g n e t i z e dplasmac o l u m n . [4・94] Thisw a v e ,w i t hE 1 I I B 0 ,i sc a l l e d the 。γdinar)' wave ・ The terminology “ ordinary ” and “ extraordinary ” is takenfromc r y s t a lo p t i c s ;however, t h etermshavebeeninterchanged 目 In plasmap h y s i c s ,i tmakesmore s e n s et ol e tthe “ ordinary” wave bet h eonet h a ti snota f f e c t e dbyt h e magnetic 白eld. S t r i c tanalogyw i t hc r y s t a lo p t i c swouldhぉe r e q u i r e d c a l l i n gt h i st h e“ extraordinary ” wave. ZI E 1I IB。 同ァ~ ExtraordinaryWave,E1 y 上 Bo I fE ,i sperpendiculart oB 0 ,t h ee l e c t r o nmotionw i l lbea仔ected byB o . andt h ed i s p e r s i o nr e l a t i o nw i l lbechanged.Tot r e a tt h i sc a s e ,onewould betemptedt ot a k eE1=E1yandk=k 去( Fig. 4 ‑ 3 3 ) .However,i tt u r n s outt h a twavesw i t hE1 ム Bo tendt obee l l i p t i c a l l yp o l a r i z e di n s t e a do f planep o l a r i z e d .Thati s ,a ssuchawavepropagatesi n t oap l a s m a ,i t d e v e l o p sacomponentE xa l o n gk ,t h u sbecomingp a r t l yl o n g i t u d i n a land p a r t l yt r a n s v e r s e .Tot r e a tt h i smodep r o p e r l y ,wemusta l l o wE 1t ohave k x FIGURE4 ‑ 3 3 Geometryf o re l e c t r o m a g n e t i cw a v e sp r o p a ‑ g a t i n ga tr i g h ta n g l e st oBo・ 一一一一一一 一一一」ー • 4.14.2 T"" ηzα) \ I\ αJ ( w 2‑c 2 k 2 ) E ,= ‑ ~竺ι (叫竺 Exll Eo E , 作1α) Introducingt h ed e f i n i t i o no fwρ, y E y (l) ¥ we αJ ノ 1 - ~r1 ノ 1αJ [ 4 ‑ 1 0 0 ] ノ mayw r i t et h i ss e ta s \〓 ll 寸ー ω;トーか 0 [ 2{ ( l ) x 、 αJ ノ αJ (@ ( 4 ‑ 1 0 1 ] [(ω仁川)(1- ~) -w!]E, 一 i~竺~Ex= 0 FIGURE4 ‑ 3 5 The E ‑ v e c t o ro f an e x t r a o r d i n a r y wave i s e l l i p t i c a l l yp o l a r i z e d .ThecomponentsE.and Eヲ oscillate 90ーo u to fp h a s e ,s ot h a tt h et o t a l e l e c t r i cf i e l dv e c t o rE1h a sat i pt h a tmovesi n ane l l i p s eoncei ne a c hwavep e r i o d . 、 W I W ⑤⑤ Thesea r etwosimultaneouse q u a t i o n sf o rExandEヲ which a r ecompatible a n i s h e s : o n l yi ft h edeterminanto ft h ecoe 伍cients v rB l = (4 ・ 102] C D bothxandycomponents( F i g .4 ‑ 3 5 ) : E 1=Ex 去十 E,y [4・95] S i n c et h ec o e f f i c i e n tA i sCt,2 一 w ~.where whi st h eupperhybridfreque町y definedbyE q .[ 4 ‑ 6 0 ] ,t h ec o n d i t i o nA D=BCcanbew r i t t e n Thel i n e a r i z e de l e c t r o nequationo fmotion( w i t hKT,= O )i snow ‑1mwve1=‑e(E+v e 1ラ B o ) (w2 ー w~ ) I w2‑w~ [4 司96] L r en o n t r i v i a l ;t h e ya r e Onlyt h exandycomponentsa 、 ~= ωω 作1αJ ( 4 ‑ 9 7 ] v ,=二!!_ ( E ,‑V x B o ) ηJU) αI IJ ¥ W I 2 [ 4 ‑ 1 0 3 ] 2 一 w, Thiscanbes i m p l i f i e dbyafewa l g e b r a i cm a n i p u l a t i o n s .Replacingt h e f i r s t ~ ont h er i g h t ‑ h a n ds i d eby ート ω; andm u l t i p l y i n gthroughby 2 2 • ω 一 wh, w enave w w ; c 2 k 2 , w!(w2-w~ )+(w;w~/ぷ) 7-1 ー(w2 ー w;)(w 2 ー (l) ~) Thes u b s c r i p t s1andehavebeens u p p r e s s e d .S o l v i n gf o rv .andv ,a s u s u a l ,we 五 nd ' w!w2 ( w2 ー w~ ) +w;w; ‑キ wキ 2(w 2一 w,2)(w 2一 wh) 2 222 2 22 2 ' (l) ρω (ω ー w ,) ー ω バω 一 w,) • 2 2 2 2 2 -ー一一 I [ 4 ‑ 9 8 ] 円=ヰ(一叫十三ι)( 1-告) ω Thewaveequationi sg i v e nbyE q .[4・80], wherewemustnowkeept h e l o n g i t u d i n a ltermkキ E1=k E x : 2旦2 (ω 一 w,)(w 2 一 (l) h) 2 2 2 f l C , W p W 一 ωρ ーすーー~~ 1 一一万一寸一一ーす ( l ) ( w 2‑c 2 k 2 ) E 1+c2kEχk = ‑iwji/Eo= inowev,i/ε0 ー竺引 l=l~竺) c 2 k 2 w2 一 (l)~ ー[(w!w)w)2/(w2 ー w~ )] ‑ i e V x=一一(Ex+ v , B o ) ぃヰ(-iEx ーす吋( 1 一手) ‑c 2 k 2 ll [ 4 ‑ 9 9 ] 一一」ーー一一← v φωω 一 (l)h [ 4 ‑ 1 0 4 ] 回 ε。 ua 。 iwnoe er w, 、 I W 戸、 w'Ex=一一」一一- l i E x+」 E, ) ll-ーヲl phJ m ・ Separatingt h i si n t oxandycomponentsandu s i n gE q .[ 4 ‑ 9 8 ] ,wehave 陥m z 目配 m 124 C h a p t e r F o u r 1 2 6 Cha1争t肝 F o u r Thisi st h ed i s p e r s i o nr e l a t i o nf o rt h eextraordinaηwave. I ti sane l e c ュ tromagnetic w a v e ,p a r t l yt r a n s v e r s e and p a r t l yl o n g i t u d i n a l , which i t hE 1p e r p e n d i c u l a rt oBo ・ propagatesp e r p e n d i c u l a rt oB0w 2 (1 -~) 1 2 7 αJ c ‑ W a v e si n P l a s m a s 9 αJ 2 α3 仇 α), w αp I 一一三=土」 w2 平 ww, = w!= 0 4.15 CUTOFFS ANDRESONANCES The d i s p e r s i o nr e l a t i o nf o rt h ee x t r a o r d i n a r y wave i sc o n s i d e r a b l y morec o m p l i c a t e dthananywehavemetupt onow.Toa n a l y z ewhati t means,i ti su s e f u lt od e f i n et h etermsc u t o f fandr e s o n a n c e .A c u t o f fo c c u r s i naplasmawhent h eindexo fr e f r a c t i o ng o e st oz e r o ;t h a ti s ,whent h e k / w .Aγesonance o c c u r swhen wavelengthbecomesi n f i n i t e ,s i n c e五= c h a ti s ,whent h ewavelength t h eindexo fr e f r a c t i o nbecomesin白 nite; t becomesz e r o .Asawavep r o p a g a t e sthroughar e g i o ni nwhichwvand w, a r ec h a n g i n g ,i tmayencountercuto圧s andr e s o n a n c e s .A wavei s g e n e r a l l yr e f l e c t e da tac u t o f fandabsorbeda tar e s o n a n c e . q u a l Theresonanceo ft h ee x t r a o r d i n a r ywavei sfoundbys e t t i n gke toi n f i n i t yi nE q .(4 ” 10 4 ] .Foranyf i n i t ew,k • oo i m p l i e sw • Wh, SOt h a t aresonanceo c c u r sa tap o i n ti nt h eplasmawhere 2 2' 2 2 W h = W 合十 w, = w [ 4 ‑ 1 0 5 ] Thisi se a s i l yr e c o g n i z e da st h ed i s p e r s i o nr e l a t i o nf o re l e c t r o s t a t i cwaves E q .[ 4 ‑ 6 0 ] ) .Asawaveo fg i v e nw approachest h e propagatinga c r o s sB0( resonancep o i n t ,bothi t sphasevelocity 昌nd i t sgroupv e l o c i t yapproach z e r o ,andt h ewaveenergyi sconvertedi n t oupperhybrido s c i l l a t i o n s . Thee x t r a o r d i n a r ywavei sp a r t l ye l e c t r o m a g n e t i candp a r t l ye l e c t r o s t a t i c ; h a ta tresonancet h i swavel o s e s i tcane a s i l ybeshown(Problem4‑14)t i t se l e c t r o m a g n e t i cc h a r a c t e randbecomesane l e c t r o s t a t i co s c i l l a t i o n . Thec u t o f f so ft h ee x t r a o r d i n a r ywavea r efoundbys e t t i n gke q u a l 4・ 104]. D i v i d i n gbyw2 wecanw r i t et h er e s u l t i n t oz e r oi nE q .[ e q u a t i o nf o rω 且s f o l l o w s : [4・ 107] Eacho ft h etwos i g n sw i l lg i v ead i f f e r e n tcuto 圧 frequency; wes h a l lc a l l o o t so ft h etwoq u a d r a t i c sa r e t h e s eW R andwL・ The r WR = 占[w, +(w~ +4w!)11空] W L = ~(一w, +( w ;+4w!J1β] [ 4 ‑ 1 0 8 ] Wehavet a k e nt h ep l u ss i g ni nf r o n to ft h es q u a r er o o ti neachc a s e sa l w a y sp o s i t i v e ; waves becausewea r eu s i n gt h ec o n v e n t i o nt h a tw i i r e c t i o nw i l lbed e s c r i b e dbyn e g a t i v ek .Thec u t o f f goingi nt h e‑x d r ec a l l e dt h e right・hand andl e f t ‑ h a n dc u t o f f s , f r e q u e n c i e sW R andwL a r e s p e c t i v e l y ,f o rr e a s o n swhichw i l lbecomec l e a ri nt h en e x ts e c t i o n . Thecuto 圧 and r e s o n a n c ef r e q u e n c i e sd i v i d et h ed i s p e r s i o ndiagram i n t or e g i o n so fpropagationandnonpropagation.I n s t e a do ft h eu s u a l w ‑kd iagram,i ti smoree n l i g h t e n i n gt og i v eap l o to fphasev e l o c i t y v e r s u sf r e q u e n c y ;o r ,t ob ep r e c i s e ,ap l o to fw2/c2k2= 1 /五 2 v s .w ( F i g . ,i sf i x e d ,andawave 4 ‑ 3 6 ) .Toi n t e r p r e tt h i sd i a g r a m ,imaginet h a tw v~ 2 c w ; , 。 2 w, 1 I=;f1 ー [w~/(w2 ‑ w ! ) J [ 4 ‑ 1 0 6 ] A fewt r i c k ya l g e b r a i cs t e p sw i l ly i e l das i m p l ee x p r e s s i o nf o rw: 2 2 Wp w, I 一一言一一一言=一言 ω 一 Wp I 2 W 2 ,2 w。 WcfW 一一言=一一一一一言一一一 w I‑ ( wp/w ) Thed i s p e r s i o no ft h ee x t r a o r d i n a r yw a v e ,a ss e e nfromt h eb e h a v i o ro ft h e FIGURE4 ‑ 3 6 p h a s ev e l o c i t yw i t hf r e q u e n c y .Thewaved o e sn o tp r o p a g a t ei nt h es h a d e d r e g i o n s . ァー一 0 WAVE 128 Cha争leγ Fouγ Thewaveequation[ 4 ‑ 9 9 ]f o rt h ee x t r a o r d i n a r ywavecans t i l lbeused i fwes i m p l ychangekfromk 圭 to k ま From E q .[ 4 ‑ 1 0 0 ] ,t h ecomponents a r en口、v 2 (ぷ- c2k2)E,= w; 2(ι _ zw , サ I‑w,/w w ( 4 ‑ 1 1 0 ] v~ 2 c ~ 2(E,+~w, 斗 I‑w,/w w (w2‑c 2 k 2 ) E ,= 。 む)-ー- Usingt h ea b b r e v i a t i o n 2 色》 p [ 4 ‑ 1 1 1 ] 日三 l 一(ω;目/ω 。三) FIGURE4 ‑ 3 7 As i m i l a rd i s p e r s i o nd i a g r a mf o rt h eo r d i n a r yw a v e . wecanw r i t et h ecouplede q u a t i o n sf o rE,andEヲ ( w 2‑c 2 k 2‑a)E,+iα w,E, ss e n ti n t oap l a s ! T ¥ , afromt h eo u t s i d e .Ast h e w i t haf i x e dfrequencyw i waveencountersr e g i o n so fi n c r e a s i n gd e n s i t y ,t h ef r e q u e n c i e swL, w和 w h ,andW R a l li n c r e a s e ,movingt ot h er i g h ti nt h ediagram.Thisi st h e r a d u a l l y samea si ft h ed e n s i t yweref i x e dandt h efrequencyw wereg tl a r g ew beingd e c r e a s e d .Takingt h el a t t e rp o i n to fv i e w ,wes e eth且t a ( o rlowd e n s i t y ) ,t h ep h a s e キv e l o c i t yapproachest h ev e l o c i t yo fl i g h t .As t h ewavet r a v e l sf u r t h e r ,vφincreases u n t i lt h er i g h t ‑ h a n dc u t o f fw =W R i se n c o u n t e r e d .There,vφbecomes i n f i n i t e .Betweent h ew = wR and w = wh l a y e r s ,w2.jk2i sn e g a t i v e ,andt h e r ei snopropagationp o s s i b l e . Atw = wh, t h e r ei sar e s o n a n c e ,anduφgoes t oz e r o .Betweenw = wh andw = WL,propagationi sa g a i np o s s i b l e .Int h i sr e g i o n ,t h ewavet r a v e l s e i t h e rf a s t e ro rs l o w e rthancdependingonwhetherw i ss m a l l e ro r ' p . FromE q . [4・ 104], i ti sc l e a rt h a ta tw = wp. t h ewave l a r g e rthanw t r a v e l sa tt h ev e l o c i t yc .Forω く wL, t h e r ei sanotherr e g i o no fnonpropaュ g a t i o n .Thee x t r a o r d i n a r ywave,t h e r e f o r e ,h a stwor e g i o n so fpropagaュ t i o ns e p a r a t e dbyas t o pband. Bywayo fcomparison,weshowi nF i g .4‑37t h esames o r to fdiagram f o rt h eo r d i n a r yw a v e .Thisd i s p e r s i o nrεlation h a so n l yonec u t o f fand nor e s o n a n c e s . ( 4 ‑ 1 1 2 ] 2 22 .w, (w ‑ck ‑a) E ,‑za‑ E,=0 α3 S e t t i n gt h edeterminanto ft h ec o e f f i c i e n t st oz e r o ,wehave ( w 2‑c 2 k 2‑a ) 2=(awc/w)2 [ 4 ‑ 1 1 3 ] w2-c2k2 一 α =土αwc/w ( 4 ‑ 1 1 4 ] Thus ぷ- c2k2= α( 1 土計= 2 ω:/ヨ( 1 土計 1‑(w, w ) l 土 (wc/w) 2 =Wp[I+(w,/w)][l ー (w,/w)] 2 αJp I 芋 (wc/w) ( 4 ‑ 1 1 5 ] The 平 sign i n d i c a t e st h a tt h e r ea r etwop o s s i b l es o l u t i o n st oE q .[4 ” 1 1 2 ] h a tcanpropagatealongB 0 .The correspondingt otwodi 百erent wavest d i s p e r s i o nr e l a t i o n sa r e c 2 k 2 , w;/w2 ω 乙白 l 一 (w,/w) 一一 4.16 ELECTROMAGNETICWAVES PARALLELTOBo x i sanda l l o wE 1t ohavebotht r a n s v e r s e Nowwel e tkl i ealongt h exa componentsEχand Eィ E 1= Eχ去 + E,y =0 αJ .~2 k=kZ as ‑2 2 '2 cf l ' 」」 [ 4 ‑ 1 1 6 ] (Lw a , キ e ) (4 ・ 117] 2 ,2 w ρ/ ω " =‑;2=1‑l+(wJw) ( 4 ‑ 1 0 9 ] (Rw a v e ) 129 i n P l a s m a s Wαves 130 z Chapleγ Fouγ j¥/LWAVE 2 v ゆ 131 W a v e si n P l a s m a s ! 2 c y o~ 、、w/2 I wL 、 ER 、 、| x ¥ ! W R w -ー__,・ー l I I FIGURE4 ‑ 3 8 Geometryo fr i g h t ‑andl e f t ‑ h a n d e dc i r c u l a r l y p o l a r i z e dw a v e sp r o p a g a t i n ga l o n gB 0 . T~ev_~/c2 v (vUc 之く 0) h a v en o tbeens h a d e d ,s i n c et h e ya r e.di宜erent f o rt h etwow a v e s . E L e L u r noutt obec i r c u l a r l yp o l a r i z e d ,t h ed e s i g n a t i o n s TheR andL wavest R andL meaning,respectively, γight-hand ciγcu laγ polarizatioηand l e f t ュ ‑ 1 7 ) .Thegeometryi sshowni nF i g . handcirculaγ po laγization (Problem4 4 ‑ 3 8 .Thee l e c t r i cf i e l dv e c t o rf o rt h eR waver o t a t e sc l o c k w i s ei nt i m e a v e .S i n c e a sviewedalongt h ed i r e c t i o no fB 0 ,andv i c ev e r s af o rt h eL w E q s .( 4 ‑ 1 1 6 ]and[4・ 1 1 7 ]dependo n l yonk" ,t h ed i r e c t i o no fr o t a t i o no f t h eEv e c t o ri sindependento ft h es i g no fk ;t h ep o l a r i z a t i o ni st h esame f o rwavespropagatingi nt h eo p p o s i t ed i r e c t i o n .Tosummarize:The p r i n c i p a le l e c t r o m a g n e t i cwavespropagatinga l o n gB0a r ear i g h t ‑ h a n d ( R )andal e f t ‑ h a n d( L )c i r c u l a r l yp o l a r i z e dwave;t h ep r i n c i p a lwaves propagatinga c r o s sBoa r eap l a n e ‑ p o l a r i z e dwave(0・wave) andanellipti・ c a l l yp o l a r i z e dwave(X司wave). Wen e x tc o n s i d e rt h ec u t o f f sandr e s o n a n c e so ft h eR andLw a v e s . Fort h eRwave,kbecomesi n f i n i t eatw=w , ;t h ewavei stheni nresonance i r e c t i o no fr o t a t i o no f w i t ht h ec y c l o t r o nmotiono ft h eelectrons 目 The d t h ep l a n eo fp o l a r i z a t i o ni st h esamea st h ed i r e c t i o no fg y r a t i o no f e l e c t r o n s ;t h ewave l o s e si t senergyi nc o n t i n u o u s l ya c c e l e r a t i n gt h e a v e ,ont h eo t h e rhand,does e l e c t r o n s ,andi tcannotp r o p a g a t e .TheL w nothaveac y c l o t r o nresonancew i t ht h ee l e c t r o n sbecausei tr o t a t e si n h eL wavedoes t h eo p p o s i t es e n s e .Asi se a s i l yseenfromE q .[4・ 117], t fwehadincludedi o nmotionsi n nothavearesonancef o rp o s i t i v ew .I ourt r e a t m e n t ,t h eL wavewouldhavebeenfoundtohavearesonance l "s i n c ei twouldthenr o t a t ew i t ht h ei o ng y r a t i o n . a tw = f Thec u t o f f sa r eo b t a i n e dbys e t t i n gk= 0i nE q s .[ 4司 1 1 6 ]and[ 4 ‑ 1 1 7 ] . Wetheno b t a i nt h esamee q u a t i o n sa swehadf o rt h ecuto 百s o ft h eX wave( E q .[4・ 107]). Thust h ec u t o f ff r e q u e n c i e sa r et h esamea sb e f o r e . TheR w a v e ,w i t ht h eminuss i g ni nE q s .[4・ 1 1 6 ]and(4・ I 0 7 ] ,h a st h e i v e nbyE q .(4・ 108]; t h eL wave,w i t ht h e h i g h e rc u t o f ffrequencyW R g st h ereasonf o rt h e p l u ss i g n ,h a st h elowercuto狂 frequency wL・ This i r e v i o u s l y .Thed i s p e r s i o ndiagramf o rt h eR n o t a t i o nωι wL chosenp andL wavesi sshowni nFig目 4-39. TheL waveh a sas t o pbanda tlow f r e q u e n c i e s ;i tbehavesl i k et h e0 wavee x c e p tt h a tt h ec u t o f fo c c u r sa t wLi n s t e a do fwp・ The R waveh a sas t o pb且nd betweenwRandw"b u t , .Thewave t h e r ei sasecondbando fp r o p a g a t i o n ,w i t huφ く c, beloww h i s t l e rmode andi so fextreme i nt h i slow‑frequencyr e g i o ni sc a l l e dt h ew importancei nt h es t u d yo fi o n o s p h e r i cphenomena. 。 EXPERIMENTAL CONSEQUENCES 4.17 TheWhistlerMode 4 . 1 7 . 1 E a r l yi n v e s t i g a t o r so fr a d i oe m i s s i o n s from t h e ionosphere were rewarded by v a r i o u sw h i s t l i n gsounds i nt h e audiofrequency r a n g e . ‑ 4 0showsaspectrogramo ft h efrequencyr e c e i v e da saf u n c t i o n F i g u r e4 .. ~・ 』ー 「 山由 0‑ 2 。 3 Diagramshowinghoww h i s t l e r sa r e FIGURE4 ‑ 4 1 c r e a t e d .Thec h a n n e l sA ,B ,andC r e f e rt otiιe s i g n a l ss omarkedi nF i g . 4 ‑ 4 0 . t( s e c ) c t u a ls p e c t r o g r a m so fw h i s t l e rs i g n a l s ,showingt h ec u r ュ FIGURE4 ‑ 4 0 A v a t u r ec a u s e dbyt h el o w ‑ f r e q u e n c ybrancho ft h eR‑wave d i s p e r s i o nr e l a t i o n( F i g .4 ‑ 3 9 ) .Ate a c ht i m e, tt h er e c e i v e r r a p i d l ys c a n st h ef r e q u e n c yr a n g ebetween0and2 0kHz, t r a c i n gav e r t i c a ll i n e .Ther e c o r d e rmakesas p o twhose d a r k n e s si sp r o p o r t i o n a lt ot h ei n t e n s i t yo ft h es i g n a la t e a c hf r e q u e n c y .Thedownwardmotiono ft h ed a r ks p o t w i t ht i m et h e ni n d i c a t e sad e s c e n d i n gg l i d et o n e .[ C o u r t e s y o fD .L .C a r p e n t e r , ] .Geo世hys. R e s .7 1 ,693( 1 9 6 6 ) . ] o ft i m e .Therei st y p i c a l l yas e r i e so fdescendingg l i d et o n e s ,whichcan beheardoveraloudspeaker.Thisphenomenoni se a s i l yexplainedi n i g h t n i n g termso ft h ed i s p e r s i o ncharactensucso ft h eR wave.Whenal f l a s ho c c u r si nt h eSouthernHemisphere,r a d i on o i s eo fa l lf r e q u e n c i e s i sg e n e r a t e d .Amongt h ewavesgeneratedi nt h eplasmao ft h eionosphere r a v e l i n galongtheearth’s magnetic andmagnetospherea r eR wavest f i e l d .Thesewavesa r eguidedbyt h ef i e l dl i n e sand a r ed e t e c t e dby o b s e r v e r si nCanada.However,d i f f e r e n tf r e q u e n c i e sa r r i v ea td i f f e r e n t h ephasev e l o c i t y t i m e s .FromF i g .4 ‑ 3 9 ,i tcanbeseent h a tf o rω く w,/2, t tcana l s obeshown(Problem i n c r e a s e sw i t hfrequencv(Problem4・ 19). I 4 ‑ 2 0 )t h a tt h egroupv e l o c i t yi n c r e a s e sw i t hfrequency.Thust h elow f r e q u e n c i e sa r r i v el a t e r ,g i v i n gr i s et ot h e descending t o n e .S e v e r a l w h i s t l e scanbeproducedbyasmglel i g h t n i n gf l a s hbecauseo fpropagaュ t i o nalongd i f f e r e n tt u b e so ff o r c eA,B,C ( F i g .4・41). Sincet h ewaves h e ymusthavef r e q u e n c i e slowerthant h el o w e s tg y r o ュ haveω く w" t h ew h i s t l e s frequencyalongt h etubeo ff o r c e ,about100kHz. ’ Either t l i ed i r e c t l yi nt h eaudiorangeort h e ycane a s i l ybeconvertedi n t oaudio s i g n a l sbyheterodyning. F a r a d a yr o t a t i o no ft h ep l a n eo fp o l a r i z a t i o no fa ne l e c ュ FIGURE4 ‑ 4 2 t r o m a g n e t i cwavet r a v e l i n ga l o n gB0・ FaradayRotation 4.17.2 Ap l a n e ‑ p o l a r i z e dwaves e n talongamagnetic 員eld i naplasmaw i l lsu百er ar o t a t i o no fi t splaneo fp o l a r i z a t i o n( F i g .4 ‑ 4 2 ) .Thiscanbeunderstood nphasev e l o c i t yo ft h eR andL w a v e s .From i ntermso ft h edi圧erence i ,t h eR wavet r a v e l sf a s t e rthant h e F i g .4 ‑ 3 9 ,i ti sc l e a rt h a tf o rl a r g ew L wave.Considertheplane‑polarizedwavet obet h esumo fanR wave F i g .4 ‑ 4 3 ) . Bothwaves a r e ,, o fc o u r s e ,a tt h e same and anL wave ( f r e q u e n c y .AfterN c y c l e s ,t h eELandERv e c t o r sw i l lreturnt ot h e i r i n i t i a lp o s i t i o n s .Aftert r a v e r s i n gag i v e nd i s t a n c e d ,however,t h eR and . . . . . . . . . . . . . . . 。3nU c 3nm 陥月 (Nヱ〉一)ヤ F由『 1j 20 ー 132 Chapleγ 司,・・ーー P r o v et h a tt h ee x t r a o r d i n a r ywavei sp u r e l ye l e c t r o s t a t i ca tr e s o n a n c e . H i n t :E x p r e s st h er a t i oE,/Eて as af u n c t i o no fw ands e tw e q u a lt ow , . 4・ 14. l a n e ‑ p o l a r i z e dwavea st h esumo fl e f t ‑andr i g h t ‑ FIGURE4 ‑ 4 3 Ap 4・ 15. P r o v et h a tt h ec r i t i c a lp o i n t sonF i g .4 ‑ 3 6a r ec o r r e c t l yo r d e r e d ;n a m e l y , thatwL く w , く w, く WR目 ( 4 ‑ 1 6 . Showt h a tt h eX‑wavegroupv e l o c i t yv a n i s h e sa tcuto百s andr e s o n a n c e s . Youmayn e g l e c ti o nm o t i o n s Bo 4・ 17. P r o v et h a tt h eR andL w a v e キ sa r er i g h t ‑andl e f t ‑ c i r c u l a r l yp o l a r i z e da s f o l l o w s : a nb ew r i t t e ni nt h eform ( a ) Showt h a tt h es i m u l t a n e o u se q u a t i o n sf o rE,andE,c F(w)(E,‑i E , )= 0 , f t e rt r a v e r s i n gt h ep l a s m a ,t h eL wavei sadvancedi nphase FIGURE4 ‑ 4 4 A L wavesw i l lhaveundergonead i f f e r e n tnumbero fc y c l e s ,s i n c ethey requireadi 旺erent amounto ftimet ocoverthed i s t a n c e .SincetheL wavet r a v e l s mores l o w l y ,i tw i l l have undergoneN + εcycles a t the p o s i t i o nwheretheR wavehasundergoneN c y c l e s .Thev e c t o r sthen havet h ep o s i t i o n sshowni nF i g .4 ‑ 4 4 .Theplaneo fp o l a r i z a t i o ni sseen t ohaver o t a t e d .A measuremento ft h i sr o t a t i o nbymeanso famicrowave horncanbeusedt og i v eavalueo fw and,hence,o fthed e n s i t y(Problem 4 ‑ 2 2 ) .Thee f f e c to fFaradayr o t a t i o nhasbeenv e r i f i e dexperimentally, buti ti snota su s e f u lamethodo fd e n s i t ymeasurementa smicrowave i n t e r f e r o m e t r y ,becausea c c e s sa ttheendso faplasmacolumni su s u a l i y di伍cult, andb ecausethee f f e c ti ssmallu n l e s sthed e n s i t yi ss ohight h a t r e f r a c t i o nbecomesaproblem. Whenpowerfulpulsedl a s e r sareusedt oproduceadenseplasma byvaporizingas o l i dt a r g e t ,magneticf i e l d so fmegagaussi n t e n s i t i e sare sometimesspontaneouslygenerated.ThesehavebeendetectedbyFara司 dayr o t a t i o nusingl a s e rl i g h to fhigherfrequencythanthemainbeam. Ini n t e r s t e l l a rs p a c e ,thepathl e n g t h sares olongt h a tFaradayr o t a t i o n ! G(w)(E,+i E , )= 0 whereF(w)=0f o rt h eR waveandG(w)=0f o rt h eL w a v e . ( b ) FortheRwave,C(w);CO;andthereforeE,= iEヲ Recalling t h ee x p o n e n t i a l t i m edependenceo fE ,showt h a tEthenr o t a t e si nt h ee l e c t r o ng y r a t i o nd i r e c t i o n . Confirmt h a tEr o t a t e si nt h eo p p o s i t ed i r e c t i o nf o rt h eL w a v e . ( c )Fort h eR w a v e ,drawt h eh e l i c e st r a c e db yt h et i po ft h eEv e c t o rm s p a c e ,>0and(ii)たく 0. : ‑ ‑ ! o t et h a tt h er o t a t i o no fEisi nt h e a tag i v e nt i m ef o r( i )k samed i r e c t i o ni nb o t hi n s t a n c e si fones t a y sa taf i x e dp o s i t i o nandw a t c h e st h e h e l i xp a s sb y . 4・ 18. L e f t ‑ h a n dc i r c u l a r l yp o l a r i z e d wavesa r ep r o p a g a t e da l o n gauniform magnetic 自eld B= B ozi n t oaplasmaw i t hd e n s i t yi n c r e a s i n gw i t hz .Atwhat . 8GHzandBo=0 . 3T? d e n s i t yi sc u t o f fr e a c h e di ff= 2 4 ‑ 1 9 .Showt h a tt h ew h i s t l e rmodeh a smaximump h a s ev e l o c i t ya tw = wJ2and t h a tt h i smaximumi sl e s st h a nt h ev e l o c i t yo fl i g h t . 4 ‑ 2 0 .Showt h a tt h egroupv e l o c i t yo ft h ew h i s t l e rmodei sp r o p o r t i o n a ltow 凹 i fw < w, andε 》 l 4 ‑ 2 1 .Showt h a tt h e r ei snoFaradayr o t a t i o ni nap o s i t r o n i u mplasma( e q u a l numberso fp o s i t r o n sande l e c t r o n s ) . 4 ‑ 2 2 .F a r a d a yr o t a t i o no fan8‑mm‑wavelengthmicrowavebeami nauniform plasmai na0 . 1 ‑ Tmagnetic 五eld i smeasured.Thep l a n eo fp o l a r i z a t i o ni sfound r a v e r s i n gIm o fp l a s m a .Whati st h edensity:コ t ob er o t a t e d90。 after t PROBLEMS phJη 日 Four 3um i s importantevena tverylowd e n s i t i e s . Thise在ect hasbeen usedt o e x p l a i n the p o l a r i z a t i o no f microwave r a d i a t i o n generated by maser a c t i o ni ncloudso fO HorH20moleculesduringtheformationo fnew s t a r s . Bo 肌川町口 ( ]山由 134 Cha{lteγ 司v’- 4 ‑ 2 4 .I nsomel a s e r ‑ f u s i o ne x p e r i m e n t si nwhichap l a s m ai sc r e a t e dbyap u l s e o f 1.06・µ.m l i g h ti m p i n g i n gonas o l i dt a r g e t ,v e r yl a r g em a g n e t i cf i e l d sa r e g e n e r a t e dbyt h e r m o e l e c t r i cc u r r e n t s .Thesef i e l d sc a nbemeasuredb yF a r a d a y r o t a t i o no ff r e q u e n c y ‑ d o u b l e dl i g h t(λ。= 0 . 5 3オ .m )d e r i v e dfromt h esamel a s e r . I fB = 1 0 0' t ,n = 1 0 2 7m ‑ 3 ,andt h ep a t hl e n g t hi nt h ep l a s m ai s30オ.m,what i st h eF a r a d a yr o t a t i o na n g l ei nd e g r e e s ?(Assumek l l B . ) y v B E ,. i1 4 ‑ 2 5 . Amicrowavei n t e r f e r o m e t e remployingt h eo r d i n a r ywavec a n n o tb eu s e d a b o v et h ec u t o f fd e n s i t yn , . To measure h i g h e rd e n s i t i e s , one c a nu s et h e e x t r a o r d i n a r yw a v e . ( a )W r i t eanexpressio日 for 4.18 Geometry o f an A l f v e n wave p r o p a g a t i n g FIGURE4 ‑ 4 5 a l o n gB 0 . p r e , キ i o u s l yi nE q .[ 4 ‑ 6 3 ] . Forcompleteness,wei n c l u d eheret h ecomュ r i t t e ne x p l i c i t l yb e f o r e : ponentUη, which wasnotw n:\¥ te ’I HYDROMAGNETIC 、VAVES i 九=一一い一一言 l M w¥ The l a s tp a r to f our survey o f fundamental plasma waves concerns low‑frequencyi o no s c i l l a t i o n si nt h epresenceo famagneticf i e l d .Oft h e manymodesp o s s i b l e ,wes h a l lt r e a tonlyt w o :t h ehydromagneticwave a v e ,andthemagnetosonicwave.TheAlfvenwave alongB 0 ,orAlfv正n w oB o ;and i nplanegeometryhaskalongB 0 ;E1andhperpendiculart B1andv 1perpendiculart obothB0andE1( F i g .4 ‑ 4 5 ) .FromMaxwell ’s equationweh a v e ,a su s u a l( E q .[ 4 ‑ 8 0 ] ) , 9αJ 空・ ZαJ V xV xE1= ‑k(kキ E i )+k"E1= τE1 +一言 j I ι (4・ ll8] 巴 Oむ S i n c ek=k ZandE1=E1xbyassumption,onlythexcomponentoft h i s equationi sn o n t r i v i a l .Thecurrentj 1nowhasc o n t r i b u t i o n sfromboth i o n s and e l e c t r o n s ,s i n c e we a r ec o n s i d e r i n g low frequenci巴s. Thex componento fEq.[4 ” 118] becomes ε。(w2 ‑c2k2)E1= -iwη 0e(v;, ‑v , . ) [4・ 119] Thermal motionsa r enotimportantf o rt h i swave; we mayt h e r e f o r e u s et h es o l u t i o no ft h ei o n equation ofmotionwith T ,= 0 obtained 1 x t h ec u t o f fd e n s i t yn"f o rt h eX w a v e . ( b ) Onav ! / c 2v s .w d i a g r a m ,showt h eb r a n c ho ft h eX‑waved i s p e r s i o nr e l a t i o n onwhichs u c hani n t e r f e r o m e t e rwouldw o r k . 1’ e w n ,( ' (4・ 120] } < , I J‑ D~\ 町=;\石互い --;;:;; I‑ 1 : , . Thecorrespondings o l u t i o nt ot h ee l e c t r o nequationo fmotioni sfound e, n,→ー w" andthent a k i n gt h el i m i tω ?》 w2: byletti昭 M → m, e • - ie αJ 2 v , .=一一ーーす E1 → 0 mα) w , [ 4 ‑ 1 2 1 ] v ew ,w2F E1 ,=一一ー一方,,. ι1 =一τァ m w w, 150 Int h i sl i m i t ,t h eLarmorg y r a t i o n so ft h ee l e c t r o n sa r en e g l e c t e d ,and t h ee l e c t r o n s havesimplyanExB d r i f ti nt h eyd i r e c t i o n .I n s e r t i n g t h e s es o l u t i o n si n t oE q .[ 4 ‑ 1 1 9 ] ,weo b t a i n E o ( w 2‑c2k2)E1= -iwnoe 与( M《β \ l - ~f1E1 I [ 4 ‑ 1 2 2 ] l<> Theycomponentso fVi a r eneededonlyf o rt h ep h y s i c a lp i c t u r et obe E q . givenl a t e r . Usingt h ed e f i n i t i o no ft h ei o nplasmafrequencyDp( 回 whereλ 。 is t h ef r e e ‑ s p a c ew a v e l e n g t handL t h ep a t hl e n g t hi nt h ep l a s m a . Assumew2 》 ω ;, ω? 円 Jm ’ E BtaEE JO zl P a O RU --’ ,L } (= 1 . 5X [Q IIλgJ B(z)n,(z)dz Lk Fouγ 附 z Showt h a tt h eF a r a d a yr o t a t i o na n g l e ,i nd e g r e e s ,o fal i n e a r l yp o l a r i z e d t r a n s v e r s ewavep r o p a g a t i n ga l o n gBoi sg i v e nb y 4・23. 日開m 136 Cha世ter 一『-------一← [ 4 ‑ 4 9 ] ) ,weh ave ,,I1 29 0 ‘、 一一 P帥 pb ’ 。4 9 h ω 9 h F o u r 崎市町 138 Cha戸teγ g i v e nby ~2 2 •, 2 2n o e 111 2P 2 2 ,2 2llp ? . =一ω てごτ =一ω 一一一ーτTτ ==一 一一τ w ‑c/ 。; 2 ε 0M e·Br, 2 c w 2 c 11 = 了τ石五五百= 1+(pµ,。/ B'f,)c2 c c ( 4 ‑ 1 2 4 ) f o r /LR= I 一一一一一一寸7吉一一寸7吉 k 何R/LR) ' εI<. Ex=( w / k ) B , ( 4 ‑ 1 2 8 ] As we have seen p r e v i o u s l y ,E i s much l a r g e r than u n i t yf o r most r i t t e napproximatelya s l a b o r a t o r yp l a s m a s ,andE q .[4・ 124) canbew 一μ O で}, B 一ω AV 一一 一一 U ω 一k Thes m a l lcomponentB , .whenaddedt oB 0 ,g i v e st h el i n e so ff o r c ea h ep o i n tshown, s i n u s o i d a lr i p p l e ,showne x a g g e r a t e di nF i g .4‑46.Att B,i si nt h ep o s i t i v eyd i r e c t i o n ,s o ,accordingt oE q .[4・ 128), E xi si nt h e i r e c t i o ni fw/ki si nt h ezd i r e c t i o n .Thee l e c t r i cf i e l dExg i v e s p o s i t i v exd r i f ti nt h en e g a t i v eyd i r e c t i o n .S i n c ewehave t h eplasmaanE 1ラBod bothi o n sande l e c t r o n sw i l lhavet h esamed r i f t t a k e nt h el i m i tw2 < v , .accordingt oE q s .[4‑120)and[4‑121).Thus,t h ef l u i dmovesupand i r e c t i o n ,a sp r e v i o u s l yi n d i c a t e di nF i g .4 ‑ 4 5 .Themagni・ downi ntheyd tudeo ft h i sv e l o c i t yi sI E . IB01.Sincetheripplei nt h ef i e l di smovingby a tt h ephasev e l o c i t yw / k ,t h el i n eo ff o r c ei sa l s omovingdownwarda t e l o c i t yo ft h el i n eo f t h ep o i n ti n d i c a t e di nF i g .4‑46.Thedownwardv w / k ) I B , /B 0 I ,w h i c h ,a c c o r d i n gt oE q .[4司 128), i sj u s te q u a lt ot h e f o r c ei s( f l u i dv e l o c i t y! E x !B 0 I .Thus,t h ef l u i dandt h ef i e l dl i n e so s c i l l a t et o g e t h e r ω ザ the particles 叫ere s t u c kt ot h el i n e s .Thel i n e so ff o r c ea c ta si ft h e y weremass‑loadeds t r i n g sundert e n s i o n , andanAlfvenwavecanbe regardeda st h epropagatingd i s t u r b a n c eo c c u r r i n gwhent h es t r i n g sa r e p l u c k e d .Thisconcepto fplasmaf r o z e nt ol i n e so ff o r c eandmoving w i t hthemi sau s e f u lonef o runderstandingmanylow‑frequencyplasma phenomena.I tcanbeshownt h a tt h i sn o t i o ni sana c c u r a t eonea slong a st h e r ei snoe l e c t r i cf i e l da l o n gB . I tremainsf o ru st os e ewhats u s t a i n st h ee l e c t r i cf i e l dExwhichwe a u s e sthem presupposedwast h e r e .AsE 1f l u c t u a t e s ,t h eions ’ inertia c n;, εoBo whereρis t h emassd e n s i t yn0M.Thisansweri snos u r p r i s e ,s i n c et h e denominatorcanber e c o g n i z e da st h er e l a t i v ed i e l e c t r i cc o n s t a n tf o r 3 ‑ 2 8 ) ) .E quation [4・ 124) low‑frequency p e r p e n d i c u l a r motions ( E q .[ s i m p l yg i v e st h ephasev e l o c i t yf o rane l e c t r o m a g n e t i cwavei nad i e l e c t r i c medium: αJ vxE,=‑Bi ( 4 ‑ 1 2 3 ) Wemustnowmaket h ef u r t h e rassumptionw2 < n;; hydromagnetic waveshavef r e q u e n c i e sw e l lbelowi o nc y c l o t r o nr e s o n a n c e .I nt h i sl i m i t , E q .[4‑123)becomes 139 ( 4 ‑ 1 2 5 ] Thesehydromagneticwavest r a v e lalongB0a tac o n s t a n tv e l o c i t yVA, c a l l e dt h eA l f v e nv e l o c i t y : 五一…示-| [ 4 ‑ 1 2 6 ) Thisi sac h a r a c t e r i s t i cv e l o c i t ya twhichp e r t u r b a t i o n so ft h el i n e so ff o r c e r i t t e n t r a v e l .Thed i e l e c t r i cc o n s t a n to fE q .(3‑28)cannowbew εR = ε/ε。= 1+(c2/v~ ) B0 x , . / [4圃 127] Notet h a tvA i ss m a l lf o rw e l l ‑ d e v e l o p e dplasmasw i t ha p p r e c i a b l ed e n s i t y , andt h e r e f o r eεR i sl a r g e . Tounderstandwhathappensp h y s i c a l l yi nanAlfvenwave,r e c a l l t h a tt h i si sane l e c t r o m a g n e t i cwavew i t haf l u c t u a t i n gmagneticf i e l dB1 E 1̲ , . . . l l . 82 1= E1xB / R e l a t i o namongt h eo s c i l l a t i n gq u a n t i t i e si na nA l f v e nwaveandt h e( e x a g g e r ュ FIGURE4‑46 a t e d )d i s t o r t i o no ft h el i n e so ff o r c e . W a v e si n P l a s m a s 司‘’F・・- 140 141 C h a p t e r Wavesi n Fouγ Plasm山 FIGURE4 ‑ 4 7 Geometry o f at o r s i o n a l( o rs h e a r ) A l f v e nwavei nac y l i n d r i c a lc o l u m n . 5 Q4 Jo 8 a u フh 0u 白耐 qu ρ8 OA 町 4 o f 6x1 0 7 d〉 D U U) ( 山田E\ nt h e t ol a gbehindt h ee l e c t r o n s ,andt h e r ei sap o l a r i z a t i o nd r i f tvp i d i r e c t i o no fE 1 .Thisd r i f tV;xi sg i v e nbyE q .(4・ 120] andc a u s e sac u r r e n t l o wi nt h ex d i r e c t i o n .Ther e s u l t i n gj iラBof o r c eont h ef l u i di s j 1tof i r e c t i o nandi s9 0 ーouto fphasew i t ht h ev e l o c i t yv 1 .Thisf o r c e i ntheyd p e r p e t u a t e st h eo s c i l l a t i o ni nt h esamewaya si nanyo s c i l l a t o rwheret h e f o r c ei souto fphasew i t ht h ev e l o c i t y .I ti s ,o fc o u r s e ,a l w a y st h ei o n i n e r t i at h a tc a u s e sano v e r s h o o tandas u s t a i n e do s c i l l a t i o n , buti na plasma t h e momentum i st r a n s f e r r e di nac o m p l i c a t e d way v i at h e e l e c t r o m a g n e t i cf o r c e s . I namorer e a l i s t i cgeometryf o re x p e r i m e n t s ,E 1wouldbei nt h e ‑ 4 7 ) .Themotion r a d i a ld i r e c t i o nandv 1i nt h ea z i m u t h a ld i r e c t i o n( F i g .4 n o ft h eplasmai stheni n c o m p r e s s i b l e .Thisi st h er e a s o nt h eVptermi t h ee q u a t i o no fmotioncouldbe n e g l e c t e d . This mode i sc a l l e dt h e torsioη al Alfvin 山ave. I twas f i r s t produced i nl i q u i d mercury by B . L e h n e r t . Alfvenwavesi naplasmaweref i r s tgeneratedandd e t e c t e dbyA l l e n , B a k e r ,P y l e , and Wilcoxa tB e r k e l e y ,C a l i f o r n i a , and byJ e p h c o t ti n Englandi n1 9 5 9 .Theworkwasdonei nahydrogenplasmac r e a t e di n l e c t r o d e sa l i g n e dalongamagnetic a “ slow pinch ” discharge betweentwoe ‑ 4 8 ) .Dischargeo fas l o wc a p a c i t o rbankA c r e a t e dt h ep l a s m a . f i e l d( F i g .4 ot h em e t a lw a l l ,wasthenf i r e dt oc r e a t e Thef a s tc a p a c i t o rB,connectedt ane l e c t r i cf i e l dEip e r p e n d i c u l a rt oB 0 .Ther i n g i n go ft h ec a p a c i t o r generatedawave,whichwasd e t e c t e d ,w i t hana p p r o p r i a t et i m ed e l a y , .F igure4 ‑ 4 9shows measurements o f phase v e l o c i t yv s . by probes P magneticf i e l d ,demonstratingt h el i n e a rdependencep r e d i c t e dbyE q . ( 4 ‑ 1 2 6 ] . S c h e m a t i co fa ne x p e r i m e n tt od e t e c tA l f v e nw a v e s .[FromJ .~f. W i l c o x , FIGURE4 ‑ 4 8 F .I .B o l e y ,andA .W.D e S i l v a ,P h y s .F l u i d s3 ,1 5( 1 9 6 0 ) . ] 。 。 4 8 12 16 20 8。( kG) ‑ 4 9 Measuredp h a s ev e l o c i t yo fA l f v e nw a v e sv s .m a g n e t i cf i e l d .[FromW i l c o x , FIGURE4 B o l e y ,andD e S i l v a ,t o e .c i t . ] Thisexperimentwasad i f f i c u l to n e ,b e c a u s eal a r g emagneticf i e l d oovercomedamping.Withl a r g eB 0 ,VA, andhence o f1Twasneededt t h ew a v e l e n g t h ,becomeuncomfortablyl a r g eu n l e s st h ed e n s i t yi sh i g h . ta l . ,ad e n s i t yo f6ラ 1 0 2 1m‑3wasusedt o I nt h eexperimento fWilcoxe a c h i e v ealowAlfvenspeedo f2 . 8ラ 1 0 5m / s e c .Notet h a ti ti snotp o s s i b l e 寝震予 1 4 2 C h a p t e r Fouγ t oi n c r e a s ep byusingah e a v i e ratom.Thefrequencyw =k vA i sproporュ t i o n a lt oM ‑112,whilet h ec y c l o t r o nfrequencyf l "i sp r o p o r t i o n a lt oM‑1. / n ,i sp r o p o r t i o n a lt oM 1 1 2 .Withh e a v i e ratoms Therefore,t h er a t i ow i ti snotp o s s i b l eto 叫お Thee q u a t i o no fc o n t i n u i t yy i e l d s n 1 143 W a v e si n k [ 4 ‑ 1 3 2 ] --=一- v,, π。 α3 s ot h a tE q .[ 4 ‑ 1 3 1 ]becomes U同=一一一- v. Bn + ーτ , . Mw 日" w< [ 4 ‑ 1 3 3 ] v. り 問一 M 可Vith M t h i sbecomes v;,( ト A )= 一旦~v目 ( 4 ‑ 1 3 4 ] α3 Mπ 。一一= a t t h ea b b r e v i a t i o n AR 一ぷ OV;1 もγith A F i n a l l y ,wec o n s i d e rlow‑frequencye l e c t r o m a g n e t i cwavespropagating a c r o s sB o .Againwemayt a k eBo=B0zandE 1=£1 圭, but wenowl e t k=kチ( Fig. 4 ‑ 5 0 ) .Nowwes e et h a tt h eE1ラB0d r i f t sl i ealongk ,s ot h a t t h eplasmaw i l lbecompressedandr e l e a s e di nt h ecourseo ft h eo s c i l l a ュ t i o n .I ti sn e c e s s a r y ,t h e r e f o r e ,t okeept h eVptermi nt h ee q u a t i o no f motion.Fort h ei o n s ,wehave '. k2γiKT; i e 4.19 MAGNETOSONIC WAVES e n o ( E 1+Vi1 × Bo)一 γ;KT;Vn, (4・ 129] Combiningt h i sw i t hE q .[ 4 ‑ 1 3 0 ] ,wehave i n ,I i f ) , ¥ ourc h o i c eo fE 1andk ,t h i sbecomes MW U悶= τ与一 (Eχ + v;,Bo) [ 4 ‑ 1 3 1 ] W \ αJ I ( 4 ‑ 1 3 5 ] ••(I 一山)=日 1‑A Mw ( 4 ‑ 1 3 0 ] ルfα3 ie 白 k y、KTi 札、 =一一 (- v,.B0) 十一ーでアー JI;,氏。 w M no , Vix =てτ- E. +一一よ l 一一一)( 1-A )「 U悶 Thisi st h eo n l ycomponento fv ;1wes h a l ln e e d ,s i n c et h eo n l yn o n t r i v i a l o ft h ewavee q u a t i o n[ 4 ‑ 8 1 ]i s 仁omponent ε0(w2 ‑c 2 k 2 ) E .= -iwη0e(v;, ‑v , . ) z [4・ 136] Too b t a i nU口’ we needo n l yto maket h ea p p r o p r i a t echangesi nE q . [ 4 ‑ 1 3 5 ]andt a k et h el i m i to fs m a l le l e c t r o nm a s s ,s ot h a tw2 《 w~ and w2 < k2v;h,: i e w2{ . k2γ,KT,\ 【 ik 2γ,KT, 【 1 一一苛一一一一 u:,一歩一ーーーτ 一一一一-!:, 守 . mww;¥ ω ゐ間 I ‑ wBo e ‑ v. .=一一一一一一百ー I ( 4 ‑ 1 3 7 ] y P u t t i n gt h el a s tt h r e ee q u a t i o n st o g e t h e rwehave k 9 x FIGURE4 ‑ 5 0 Geometry o f am a g n e t o s o n i c wave p r o p a g a t i n ga tr i g h ta n g l e st oB0・ 9 o ri e I 1 A ¥ ε。( w' ‑ c ' k ' ) E ,= -ituηoel-E.I • • ) L M t u \1-A ー(fl.~ / w")/ +ik2ぜ γ,KT, ~_l 一一一 wB0 eM ‑ J ( 4 ‑ 1 3 8 ] Pl邸明白 写事竺 145 s - 市山一 M Y一 ¥ - K一 H, g +一 M βqv A ノ - K一 、 e Plasm出 T一 9 o of γl KT,¥ I o 。剤-KT\ ザ- c " k " (1+七ァγ )+オ( w"‑k" 竺ー)= O b ’民 n : l V l γ一 一一 VA 2 '" 9 一一 k2c2γ,KT, 2 (w -ck )= ーポ ω (ト A )+ 一γ てア Wavesi n 2S U zR ω 9h Bo= 0ork I I B o : け z- F、 rι v γ, e、 u o t u ( t a t nU t e f e u a Aυ 。! 伺H n;, Wes h a l la g a i nassumew2 < s ot h a t1‑ Acanben e g l e c t e dr e l a t i v e t o!l~/w2. Witht h eh e l po ft h edefinit問1s o f! l pandvA ,wehave 叫 Fouγ ri 144 Cha争teγ ; ( A c o u s t i cw a v e s ) [ 4 ‑ 1 4 5 ] [ 4 ‑ 1 3 9 ] w2= n~ k ム Bo: I ( E l e c t r o s t a t t c1 0 0 4 ‑ 1 4 6 ] c l o t r o nw a v e s ) [ +k 2 v ' f C) S i n c e 。;/!l~ = c 2/v~ o r [4・ 140] E q .[ 4 ‑ 1 3 9 ]becomes W て l +~)= c2k2(1 +叫 γぷT,) =c2 \凡1VA VA } \凡/ [ 4 ‑ 1 4 1 ] Electroπ 即日 ves ( L o w e rh y b r i d 2 , . . . = W t = H,W, OS口 llations) w !+k2c2 cRα); 7す = c k k ム Bo, E1 I IBo: ーす= 1 一号 2' 2 2v s 十 UA [4・ 142] 十 UA 2 , 2 R 白J 2 2 h ωωω Thisi st h ed i s p e r s i o nr e l a t i o nf o rt h emagnetosoη ic wave propagating perpendiculart oB 0 .I ti sana c o u s t i cwavei nwhicht h ecompressions andr a r e f a c t i o n sa 1 eproducednotbymotionsalongE ,butbyEラB d r i f t sa c r o s sE .Int h el i m i tB0• O,vA • 0, t h emagnetosonicwavet u r n s o na c o u s t i cwave. In t h el i m i tKT • 0, v , • 0, t h e i n t oan ordin且ry i p r e s s u r eg r a d i e n tf o r c e sv a n i s h ,andt h ewavebecomesamodi自ed Alfven wave.Thephasev e l o c i t yo ft h emagnetosonicmodei salmosta l w a y s ;f o rt h i sr e a s o n ,i ti so f t e nc a l l e dsimplythe “ fast ” hydro” l a r g e rthanvA magnetICwave. k 上 Bo: 2 2 2 U p p e rh y b r i d 2 ( = W p +W , = W h o s c i l l a t i o n s ) 1 2 '2 Wp/W 7-1 一戸<;;;:M c 2 k 2 α) ; : ; 2 I αJ 1+(w,/w) w Ioπ 山aves t.\wa、 e) [ 4 ‑ 1 5 0 ] (R w a v e ) ( w h i s t l e rm o d e ) [ 4 ‑ 1 5 1 ] (Lw a v e ) [ 4 ‑ 1 5 2 ] ( e l e c t r o m a g n e t i c ) Bo=0 : None W 2=(?.VA ' 22 ( A l f v e nwa 、 e) [ 4 ‑ 1 5 3 ] 。。 k 上 B ,》: ( e l e c t r o s t a t i c ) W [ 4 ‑ 1 4 9 ] 一 Wh 一-r= 1 一一一」L一一一 4 . 2 0 SUMMARY OFELEMENTARYPLASMAWAVES ( P l a s m aoscilla <ions) 2 '2 C / ? . ̲ kI I B o : k l l B o : Bo= 0ork I I B o : w2=w !+ ~k2v (0w a v e ) 2 "'白)n k.LB0.E1 よ Bo :ーす= 1--i 寸一ーす Electron 叩aves [4・ 148] αJαJ ーす一--;;- C ( L i g h twa 、 es) 2 9. 9 2 w [ 4 ‑ 1 4 7 ] ( e l e c t r o m a g n e t i c ) w2= Bo=0 ・ wherev ,i st h ea c o u s t i cs p e e d .F i n a l l y ,wehave 2 竺ー= ,2:1!.£土主主 k 2 " c2+v 4 ‑ 1 5 4 ] ( M a g n e t o s o n i cw a v e ) [ Thiss e to fd i s p e r s i o nr e l a t i o n si sag r e a t l ys i m p l i f i e donecovering o n l yt h ep r i n c i p a ld i r e c t i o n so fp r o p a g a t i o n .N o n e t h e l e s s ,i ti sav e r y u s e f u ls e to f equations t o have i n mind a s a frame o fr e f e r e n c e so f t e np o s s i b l et o f o rd i s c u s s i n gmorecomplicatedwavem o t i o n s .・It i [ 4 ‑ 1 4 3 ] [ 4 ‑ 1 4 4 ] 一」 understandacomplexs i t u a t i o na sam o d i f i c a t i o nors u p e r p o s i t i o no ft h e s e b a s i cmodeso fo s c i l l a t i o n . M/m ( Rmω 146 C h a p t e r F o u r o 1 4 7 W a v e si n P l as相田 4 . 2 1 THECMA DIAGRAM Qx ROO ( o * L 山〉 伶 υ3 。」ω一 Lυ 一ト ω20《2Z03 \ Whenpropagationo c c u r sa tananglet ot h emagneticf i e l d ,t h ephase v e l o c i t i e schangewitha n g l e .Someo ft h emodesl i s t e dabovew i t hk1Bo andk J .Bochangec o n t i n u o u s l yi n t oeacho t h e r ;othermodessimply sg r e a t l y disappeara tac r i t i c a la n g l e .Thiscomplicateds t a t eo fa百airs i c l a r i f i e dbyt h eClemmow‑Mullaly‑Allis(CMA)diagram,s onamedf o r i t sc o ‑ i n v e n t o r sbyT.H.S t i x .Suchadiagrami sshowni nF i g .4 ‑ 5 1 .The ,= T ,= 0 . CMAdiagrami sv a l i d ,however,onlyf o rc o l dp l a s m a s ,withT Extensiont of i n i t etemperaturesi n t r o d u c e ss omuchcomplexityt h a tt h e diagrami snolongeru s e f u l . Figure4 ‑ 5 1i sap l o to fw c / wv s .w ; / w 2or,equivalently,aplotof ,anye xperimental magneticf i e l dv s .d e n s i t y .Forag i v e nfrequencyw ,i sdenotedbyap o i n tont h eg r a p h . s i t u a t i o nc h a r a c t e r i z e dbyωρand w Thet o t a lspacei sd i v i d e di n t os e c t i o n sbyt h ev a r i o u sc u t o f f sandr e s o n ュ anceswehaveencountered.Fori n s t a n c e ,t h ee x t r a o r d i n a r ywavec u t o f f a tw2= w ;+w !i saq u a d r a t i cr e l a t i o nbetweenw c l wandw ! / w 2 ;the r e s u l t i n gparabolacanberecognizedonF i g .4 ‑ 5 1a st h ecurvel a b e l e d “ upper hybridresonance. ” These cutoffandresonancecurvesseparate r e g i o n so fpropagationandnonpropagationf o rt h ev a r i o u sw a v e s .The s e t so fwavest h a tcane x i s ti nt h ed i f f e r e n tr e g i o n sw i l lt h e r e f o r ebe di百erent. Thes m a l ldiagrami neachregioni n d i c a t e snotonlywhichwaves a r ep r e s e n tbuta l s ohowt h ephasev e l o c i t yv a r i e sq u a l i t a t i v e l yw i t ha n g l e . Themagneticf i e l di simaginedt obev e r t i c a lont h ediagram.Thed i s t a n c e fromt h ec e n t e rt oanyp o i n tonane l l i p s eorf i g u r e ‑ e i g h ta tanangle( } t ot h ev e r t i c a li sp r o p o r t i o n a lt ot h ephasev e l o c i t ya tt h a ta n g l ew i t h r e s p e c tt ot h emagnetic f i e l d . Fori n s t a n c e ,i nt h et r i a n g u l a rr e g i o n markedwithan*onF i g .4 ‑ 5 1 ,wes e et h a tt h eL wavebecomest h eX wavea s( }v a r i e sfromz e r ot o' T T " / 2 .TheR wavehasav e l o c i t ys m a l l e r td i s a p p e a r sa s ( }v a r i e sfromzerot o' T T " / 2 .I tdoes thant h eL wave,andi e g i o n ,andt h e0 nott u r ni n t ot h e0 wave,becausew2 く w! in 出at r wavedoesnote x i s t . Theupperr e g i o n so ft h eCMAdiagramcorrespondto’ ω 《 w,.The low司frequency i o nwavesa r efoundh e r e .S i n c ethermalv e l o c i t i e shave beenn e g l e c t e dont h i sdiagram,t h ee l e c t r o s t a t i cionwavesdonotappear; theypropagateonlyi nwarmp l a s m a s .Onecanregardt h eCMAdiagram 。 。 2 イ / w2 ORDENSITY A Clemmow‑Mullaly‑Allisdiagramf o rclassi晶cation o fwavesi nac o l d FIGURE4 ‑ 5 1 p l a s m a . 一~・』』 事官 148 4 ‑ 3 1 .. At hree‑componentplasmah a sad e n s i t ynoo fe l e c t r o n s ,( I‑e ) n oo fi o n s V f , ,and 制。 of i o n so fmassM白,. L e tT 1 1= T , 2=0 ,T ,> "0 o fmass: a sa “ plasma pond”: A pebble dropped i n each region w i l l send out r i p p l e swithshapesl i k etheonesshown. Cha戸ter Four 149 Wavesi n Pl山間山 ( a )D e r i v ead i s p e r s i o nr e l a t i o nf o re l e c t r o s t a t i ci o nc y c l o t r o nw a v e s . ( b ) Findas i m p l ee x p r e s s i o nf o rw2whenεis s m a l l . PROBLEMS 4 ‑ 2 6 . A hydrogend i s c h a r g ei na1-T 白eld ( c )E v a l u a t et h ewavef r e q u e n c i e sf o rac a s ewhenεis n o ts m a l l :a50‑50%D‑T m i x t u r ea tKT,=1 0keV,Bu=5T,andk=Icm 1 . producesad e n s i t yo f1 0 1 6m‑3 ? ( a ) Whati st h eA l f v e nspeedvA ForaLangmuirplasmao s c i l l a t i o n ,showt h a tt h et i m e ‑ a v e r a g e de l e c t r o n k i n e t i cenergyperm3i se q u a lt ot h ee l e c t r i cf i e l denergyd e n s i t y長。(£2). 4・32. ( b ) SupposevAhadcomeo utg r e a t e rthanc .Doest h i smeant h a tAlfvenwaves t r a v e lf a s t e rt h a nt h espeedo flight:コ 4 ‑ 3 3 . ForanAlfvenw a v e ,showt h a tt h etime-avera耳ed i o nk i n e t i cenergyp e r m"i se q u a lt ot h emagneticwaveenergy(Bi)/2µ0・ C a l c u l a t et h e Alfven speed i n ar e g i o no ft h e magnetosphere where . 6 7ラ 1 0 ‑ 2 1k g . B= 1 0RT, η = 108m•, and M =M H= 1 4・27. 4 ‑ 3 4 .F i g u r eP4‑34showsaf a r ‑ i n f r a r e dl a s e ro p e r a t i n gatλ = 337オm.When Bo=0 ,t h i sr a d i a t i o ne a s i l yp e n e t r a t e st h eplasmawheneverωρis l e s st h a nw , orn<叫= 1 0 2 2m ‑ 3 .However,b e c a u s eo ft h el o n gp a t hl e n g t h ,t h ed e f o c u s i n g e旺ect o ft h eplasma( c f .F i g .4 ‑ 3 0 )s p o i l st h eo p t i c a lc a v i t y ,andt h ed e n s i t yi s lim町d b yt h ec o n d i t i o n sw !<印 2, whereε 《 l Intheinterestofincreasing s t h el i m i t i n gd e n s i t y ,andhencet h el a s e routputpower,amagneticf i e l dBoi a d d e d . 4 ‑ 2 8 . Supposeyou have c r e a t e d al a b o r a t o r y plasmaw i t hn = 1 0 1 5m‑3 and B =1 0 ‑ 2T.Youc o n n e c ta160‑MHzs i g n a lg e n e r a t o rt oaprobei n s e r t e di n t o t h ep l a s m a . ( a ) DrawaCMAdiagramandi n d i c a t et h er e g i o ni nwhicht h eexperimenti s l o c a t e d . ( b ) Whate l e c t r o m a g n e t i cwavesmightbee x c i t e dandpropagatedi nt h eplasma:コ ( a ) If€ i sunchanged,showt h a tt h el i m i t i n gd e n s i t yc a nb ei n c r e a s e di fl e f t ‑ h a n d c i r c u l a r l yp o l a r i z e dwavesa r epropagated 目 4 ‑ 2 9 .Supposeyouw i s ht od e s i g nanexperimenti nwhichs t a n d i n gt o r s i o n a l Alfvenwavesa r eg e n e r a t e di nac y l i n d r i c a lplasmacolumn,s ot h a tt h es t a n d i n g waveh a smaximumamplitudea tt h emidp l a n eandnodesa tt h ee n d s .Tos a t i s f y t h ec o n d i t i o nω 《 n" youmak巳 w = 0.10,・ ( b )I fni st obed o u b l e d ,howl a r g ed o e sB0havet obeコ ( a )I fyouc o u l dc r e a t eahydrogenplasmaw i t hη = 1 0 1 9m ‑ : iandB = IT,how longd o e st h ecolumnhavet ob e ? 図 図 図 Bo ー一・ー- 図 ( b )I fyout r i e dt odot h i sw i t ha0 . 3T Q‑machine,i nwhicht h es i n g l ycharged o n gwould Csi o n shaveana t o m i cweight1 3 3andad e n s i t yη = 1018m•, how l t h eplasmahavet ob e ?H i n t :F i g u r eoutt h es c a l i n gf a c t o r sanduset h er e s u l t o fp a r t( a ) . + ( a )I ft h ei n t e r s t e l l a rmagneticf i e l di sn e g l i g i b l eandw2 > w;, showt h a t DISCHARGEPULSER 図 354hv rfLfJ Z 4 一d where ん is 図 図 ト一一/ CONCAVEMIRROR t h eplasmaf r e q u e n c yandxi st h ed i s t a n c eo ft h ep u l s a r . ( b )I ft h ea v e r a g ee l e c t r o nd e n s i t yi ns p a c ei s2ラ l 0 5m 図 : iPLASMAii~i~\\ifff)} 4 ‑ 3 0 .A p u l s a re m i t sabroadspectrumo fe l e c t r o m a g n e t i cr a d i a t i o n ,whichi s d e t e c t e dw i t har e c e i v e rtunedt ot h eneighborhoodoff=80MHz.Becauseo f t h ed i s p e r s i o ni ngroupv e l o c i l ycausedbyt h ei n t e r s t e l l a rp l a s m a ,t h eo b s e r v e d f / d t=‑5MHz/sec. f r e q u e n c yduringe a c hp u l s ed r i f t sa tar a t eg i v e nbyd -xc 図 FLATMIRRORWITH OUTPUTCOUPLINGHOLE PLASTICWINDOW 3 ,howf a rawayi st h e Schematico fapulsedHCNl a s e r . FIGUREP4‑34 p u l s a r ?( lparsec=3X 1 0 1 6m . ) ̲L̲ マ- 150 Cha1争leγ Fouγ : ( c )Showt h a tt h eplasmai saf o c u s i n gl e n sf o rt h ew h i s t l e rmode. ( d ) Canoneu s et h ew h i s t l e rmodeandt h e r e f o r egot omuchhi 百her y 4 ‑ 3 5 . UseMaxwell ’s e q u a t i o n sandt h ee l e c t r o ne q u a t i o no fmotiont od e r i v e t h ed i s p e r s i o nr e l a t i o nf o rl i g h twavespropagatingthroughau n i f o r m ,unmagュ l e c t r o nt e m ュ n e t i z e d ,c o l l i s i o n l e s s ,i s o t h e r m a lplasmaw i t hdensityηand 自nite e , .(Ignorei o nm o t i o n s . ) p e r a t u r eT Plas:抽出 ’-. 4 ‑ 3 6 . Prove t h a tt r a n s v e r s ewaves a r eu n a f f e c t e d by t h eVp term whenever kXBo=0 ,eveni fi o nmotioni si n c l u d e d . 4 ‑ 3 7 . Considert h edampingo fano r d i n a r ywavec a u s e dbyac o n s t a n tc o l l i s i o n l e c t r o n sandi o n s . frequency1betweene ( a ) Showt h a tt h ed i s p e r s i o nr e l a t i o ni s c 2 k 2 " 1 w< ( a ) < 0 よ’ z ヂI! (JJ ρ w(w+ iv) x 1, showt h a tt h edamping V 42 ( b ) Forwavesdampedi nt i m e( kr e a l )when11/w rateγ = Im( w )i sa p p r o x i m a t e l y 151 W a v e siη densities コ 一2 γ 一一 ( a )t h ewaveguidei so r i e n t e ds ot h a tE 1i si nt h eid i r e c t i o n ; ( b )t h ewaveguidei so r i e n t e ds ot h a tE 1i si ntheyd i r e c t i o n . ( c ) Forwavesdampedi ns p a c e(wr e a l )when11/w ) ‑ 1i sa p p r o x i m a t e l y d i s t a n c e8=(Imk < 1, showt h a tt h ea t t e n u a t i o n 4 ‑ 4 1 .. ‑ ¥U >Id plasmai scomposedo fpositi可e i o n so fchargeZ eandmassM+and negati、e i o n so fcharge‑eandmassM .I nt h ee q u i l i b r i u ms t a t e ,t h e r ei sno magnetico re l e c t r i cf i e l dandnov e l o c i t y ;andt h er e s p e c t i v ed e n s i t i e sa r en o + andno‑=Z n o + Derivet h ed i s p e r s i o nr e l a u o nf o rp l a n eelectromagneucw a v e s . 8 = 詰( 1 ーさ) 1 / 2 I th a sbeenproposedt ob u i l das o l a rpowers t a t i o ni ns p a c ew i t hhuge st r a n s m i t t e d p a n e l so fs o l a rc e l l sc o l l e c t i n gs u n l i g h t24hoursaday司 The poweri t oe a r t hi na30‑cm‑wavelengthmicrowavebeam.Wew i s ht oe s t i m a t ehowmuch o ft h epoweri sl o s ti nh e a t i n gupt h ei o n o s p h e r e .Treatingt h el a t t e ra saweakly i o n i z e dg a sw i t hc o n s t a n te l e c t r o n ‑ n e u t r a lc o l l i s i o nf r e q u e n c y ,whatf r a c t i o no f ,= 1 0 1 1m ‑ " . t h e beam power i sl o s ti nt r a v e r s i n g lOOkm o f plasma w i t hn 川= 1 0 1 6m ".and 日= 1 01 4m 3 / s e c ? 4・38. 4 ‑ 4 2 . Ionw a ¥ ' e Sa r eg e n e r a t e di nag a s ‑ d i s c h a r g eplasmai nam i x t u r eo fargon andheliumg a s e s .Theplasmah a st h ef o l l o w i n gc o n s t i t u e n t s : ( a )E l e c t r o n so fd e n s i t yn0andtemperatureKT,; ( b ) Argoni o n so fd e n s i t ynA,massMA,charge+ Z e ,andtemperatureO ;and e ,andtemperature0 . ( c ) Hei o n so fd e n s i t ynH,massMH,charge+ 4 ‑ 3 9 .TheAppleton‑Hartreed i s p e r s i o nr e l a t i o nf o rh i g h ‑ f r e q u e n c ye l e c t r o m a g ュ ot h emagneticf i e l di s n e t i cw a ¥ ' e sp r o p a g a t i n ga tana n g l e0t c2k2 冒 一=ー w" ‘ 2w;(l ー w;Jw2) D e r i v ean e x p r e s s i o nf o rt h e phasev e l o c i t yo ft h ewavesu s i n gal i n e a r i z e d , o n e ‑ d i m e n s i o n a lt h e o r yw i t ht h e plasma approximation and t h e Boltzmann r e l a t 1 0 nf o re l e c t r o n s . 2w ヨ(1 ー w;Jw2 ) ー w; s i n 2e 土 w,[w; s i n 40+4w2(1 ー w;Jw2)2 cosヨ 0]1/2 D i s c u s st h ecuto圧s andr e s o n a n c e so ft h i sequation 目 Which a r eindependento fO? 4 ‑ 4 0 . Microwavesw i t hf r e e ‑ s p a c ewavelengthA oe q u a lt o1cma r es e n tthrough aplasmas l a b1 0cmt h i c ki nwhicht h ed e n s i t yandmagneticf i e l da r euniform and g i v e n by n0=2.8Xl018m‑3 and B0=1.07T. C a l c u l a t et h e number o f n s i d et h es l a bi f( s e eF i g .P 4 ‑ 4 0 ) wavelengthsi 4 ‑ 4 3 .I n a remote p a r to ft h eu n i v e r s e ,t h e r ee x i s t s a plasma c o n s i s t i n go f p o s i t r o n sandf u l l ys t r i p p e dantifermiumn u c l e io fcharge‑ Z e ,whereZ=1 0 0 . From t h ee q u a t i o n so fm o t i o n ,c o n t i n u i t y , and P o i s s o n ,d e r i v e ad i s p e r s i o n r e l a t i o nf o rplasmao s c i l l a t i o n si nt h i sp l a s m a .i n c l u d i n gi o nm o t i o n s .De日 ne t h e ,B 。= 0 ,anda l lo t h e rs i m p l i f y i n g plasmaf r e q u e n c i e s .YoumayassumeKT=0 i n i t i a lc o n d i t i o n s . 一一ー一ームー一一一一一~ FIGURE P4‑40 司””- 1 5 2 4 ‑ 4 7 . Byi n t r o d u c i n gag r a d i e n ti nB o ,i ti sp o s s i b l et omaket h eupperh y b r i d resonancea c c e s s i b l et oanX waves e n ti nfromt h eo u t s i d eo ft h eplasma( c f . precedingp r o b l e m ) . 4 ‑ 4 4 .I n t e l l i g e n tl i f eonap l a n e ti nt h eCrabnebulat r i e st ocommunicatew i t h u sp r i m i t i v ec r e a t u r e sont h ee a r t h .Wer e c e i v er a d i os i g n a l si nt h eIO純一 109 Hz r a n g e ,b u tt h espectrums t o p sa b r u p t l ya t120MHz.Fromo p t i c a lmeasurements, i ti sp o s s i b l et op l a c eanupperl i m i to f36G ont h emagneticf i e l di nt h evi口nity o ft h ep a r e n ts t a r .I ft h es t a ri sl o c a t e di nanHI!r e g i o n( o n ewhichc o n t a i n s i o n i z e dh y d r o g e n ) ,andi ft h er a d i os i g n a l sa r ea f f e c t e dbysomes o r to fcuto庇 i nt h eplasmat h e r e ,whati sar e a s o n a b l el o w e rl i m i tto t h e plasmad e n s i t y ? ( Igauss=10-• T.) C h a p t e r F o u r s .w;/w2diagramt h ep a t ht a k e nbyt h ew a v e ,showing ( a ) DrawonanwJw v howthew"c u t o f fi sa v o i d e d . ( b ) Showt h a tt h er e q u i r e dchangei nB。 upperh y b r i dl a y e ri s 4 ‑ 4 5 .A s p a c es h i pi smovingthrought h eionosphereo fJ u p i t e ra taspeedo f 100k m / s e c ,p a r a l l e lt ot h e1 0 ‑ 5 ‑ Tmagneticf i e l d .I ft h emotioni ss u p e r s o n i c ( v>v , ) ,i o na c o u s t i cshockwaveswouldbeg e n e r a t e d .I f ,i na d d i t i o n ,t h emotion i ss u p e r ‑ A l f v e n i c(v>" " ) ,magneticshockwaveswoulda l s obee x c i t e d .Instnト mentsonboardi n d i c a t et h eformerb u tn o tt h el a t t e r .Findl i m i t st ot h eplasma d e n s i t yande l e c t r o ntemperatureandi n d i c a t ewhethert h e s ea r euppero rl o w e r l i m i t s . Assumet h a tt h eatmosphereo fJ u p i t e rc o n t a i n sc o l d ,s i n g l ycharged m o l e c u l a ri o n so fH 2 ,He,CH4,C02,andNH4w i t hana v e r a g eatomicweight o f1 0 . between t h eplasmas u r f a c eandt h e tlB0=B0w!/2w~ 4 ‑ 4 8 . Ac e r t a i nplasmawaveh a st h ed i s p e r s i o nr e l a t i o n c 2 k 2 ‑2 α,. 一一一= I 2 αJ 9 ω si n c i d e n tonaplasmafromt h e 4 ‑ 4 6 . Ane x t r a o r d i n a r ywavew i t hf r e q u e n c yw i h eupper o u t s i d e .Thev a r i a t i o no ft h er i g h t ‑ h a n dc u t o f ff r e q u e n c yw. andt i t hr a d i u sa r ea sshown.Therei sane v a n e s c e n t h y b r i dr e s o n a n c efrequencywhw l a y e ri nwhicht h ewavecannotp r o p a g a t e .I ft h ed e n s i t yg r a d i e n ta tt h ep o i n t sg i v e nbyJ a n /a r l= η/γ0, showthatthedistanced betweenthe wherew=w, i w =w.andwhp o i n t si sa p p r o x i m a t e l yd=(wJw)r0・ w2(w, ‑ f l , ) 2 < 一 W,lL , 十 ー- o . . ‑ w ; 一 w"+w,!l, where w2=w!+ f l ! . Write e x p l i c i te x p r e s s i o n sf o rt h er e s o n a n c e and cuto百 f r e q u e n c i e s( o rf o rt h es q u a r e st h e r e o f ) ,whenε = m/M 《 1. 4 ‑ 4 9 .The e x t r a o r d i n a r y wave w i t hi o n motions i n c l u d e dh a st h ef o l l o w i n g d i s p e r s i o nr e l a t i o n : c 2 k 2 w ; n; 一一一一一 w2 • w2 ー w~ w2-fl~ (竺」L一生~)' w w2 w~ w 叫 2-n; w : n : Iw 2 ‑ " ; ; ; ; w2‑n; ( a ) Showt h a tt h i si si d e n t i c a lt ot h ee q u a t i o ni nt h ep r e v i o u sproblem 目(Warning: t h i sproblemmaybehazardoust oyourmentalh e a l t h . ) αJ ( b )I fw 1andwLa r et h el o w e rh y b r i dandl e f t ‑ h a n dc u t o f ff r e q u e n c i e so ft h i s w a v e ,showt h a tt h eo r d e r i n g!1,壬 w, 壬 wL i sa l w a y so b e y e d . e s u l t sandt h eknownphasev e l o c i t yi nt h eω → 0 l i m i t ,drawa ( c ) Usin 戸 these r Ic2vs ,印 plot showingtheregionsofpropagationandevanescence. キ q u a l i t a t i v ev! 4 ‑ 5 0 . Wew i s htodol o w e r ‑ h y b r i dh e a t i n go fahydrogenplasmacolumnw i t h ωρ = Oatγ = a andωρ =占w, a tt h ec e n t e r ,i naumformmagnetic 且eld. Theantenna l a u n c h e sanX wavew i t hk 1 1=0 . 。 FIGUREP4‑46 守 一一」ι一一一一一一 1 5 3 W山田 m Plas明白 事 154 C h a p t e r F01げ ( a ) Drawaq u a l i t a t i v ep l o to fw"n"wL,andw1 v s .r a d i u s .T h i sgraphs h o u l d ft h e s e n o tb et os c a l e ,b u ti ts h o u l dshowc o r r e c t l yt h eγ·elative magnitudeso f r e q u e n c i e sa tt h eedgeandc e n t e ro ft h ep l a s m a . ChapterF i v e ( h )E s t i m a t et h et h i c k n e s so ft h ee v a n e s c e n tl a y e rb e t w e e nw1andwL( c f .p r e v i o u s p r o b l e m )i ft h er ff r e q u e n c yw i ss e te q u a lt ow1a tt h ec e n t e r . DIFFUSIONAND R E S I S T I V I T Y ( c )R e p e a t( a )and( b )f o rwρ ( max)=2w。 a nddrawac o n c l u s i o na b o u tt h i sa n t e n n a d e s i g n . 4 ‑ 5 1 .Thee l e c t r o m a g n e t i ci o nc y c l o t r o nwave( S t i xw a v e )i ssometimesu s e df o r r a d i o f r e q u e n c yh e a t i n go ff u s i o np l a s m a s .D e r i v et h ed i s p e r s i o nr e l a t i o na s f o l l o w s : ( a )D e r i v eawavee q u a t i o ni nt h eformo fE q .( 4 ‑ 1 1 8 ]b u tw i t hd i s p l a c e m e n t c u r r e n tn e g l e c t e d . ft h i se q u a t i o nassumingk ,=0 ,k 2=k ;+k ; , ( b )W r i t et h exandycomponentso andk , k , E ,=0 . ( c )Toe v a l u a t ej 1= η0e(v, ‑v , ) ,d e r i v et h ei o ne q u i v a l e n to fE q .( 4 ‑ 9 8 ]t oo b t a i n makeal o w ‑ f r e q u e n c ya p p r o x i m a t i o ns ot h a tv ,i ss i m p l yt h eEラ Bd r i f t . Vυto ( d )I n s e r tt h er e s u l to f( c )i n t o( b )t oo b t a i nt w os i m u l t a n e o u shomogeneous , .u s i n gt h ede自 nition f o rnρin E q .( 4 ‑ 4 9 ] . e q u a t i o n sf o rEτand E DIFFUSIONAND MOBILITYINWEAKLY IONIZED GASES 5 . 1 o w e s to r d e ri nn;t oo b t a i n ( e )S e tt h ed e t e r m i n a n tt oz e r oands o l v etol 2 Thei n f i n i t e ,homogeneousplasmasassumedi nt h epre 、ious chapterf o r t h ee q u i l i b r i u mc o n d i t i o n sa r e ,o fc o u r s e ,h i g h l yi d e a l i z e d .Anyr e a l i s t i c plasmaw i l lhavead e n s i t yg r a d i e n t ,andt h eplasmaw i l ltendt od i f f u s e towardr e g i o n so flowd e n s i t y .Thec e n t r a lproblemi nc o n t r o l l e dt h e r ュ monuclearr e a c t i o n si st oimpedet h er a t eo fd i f f u s i o nbyusingamagnetic f i e l d . Before t a c k l i n gt h e magnetic f i e l d problem, however, we s h a l l c o n s i d e rt h ec a s eo fd i f f u s i o ni nt h eabsenceo fmagneticf i e l d s .A f u r t h e r s i m p l i f i c a t i o nr e s u l t si fweassumet h a tt h eplasmai sweaklyi o n i z e d ,s o t h a tchargep a r t i c l e sc o l l i d ep r i m a r i l ywithn e u t r a l atomsr a t h e rthan w i t honea n o t h e r .Thec a s eo faf u l l yi o n i z e dplasmai sdeferredt oa l a t e rs e c t i o n ,s i n c ei tr e s u l t si nanonlinearequationf o rwhicht h e r ea r e fewsimplei l l u s t r a t i v es o l u t i o n s .Inanyc a s e ,p a r t i a l l yi o n i z e dg a s e sa r e n o tr a r e : High‑pressure a r c s and i o n o s p h e r i c plasmas f a l li n t ot h i s c a t e g o r y ,andmosto ft h ee a r l yworkong a sd i s c h a r g e si m キ o l v e df r a c t i o n a l i o n i z a t i o n sbetween 1 0 3 and 1 0 6, whenc o l l i s i o n swithn e u t r a latoms 且re d ominant. The p i c t u r e ,t h e n ,i so f a nonuniform d i s t r i b u t i o no fi o n s and ‑ 1 ) .Astheplasma e l e c t r o n si nadensebackgroundo fn e u t r a l s( F i g .5 spreadsouta sar e s u l to fp r e s s u r e ‑ g r a d i e n tande l e c t r i cf i e l df o r c e s ,t h e i n d i v i d u a lp a r t i c l e sundergoarandomw a l k ,c o l l i d i n gf r e q u e n t l yw i t h t h en e u t r a l atoms.Webegin w i t h ab r i e f reviewo fd e f i n i t i o n sfrom 且tomic t h e o r y . n ;(I I¥l' = ぽr i l+-;;-f ーで+←i | ー L c "¥ k ; k ワJ よ 1 5 5 comesw i t h i nt h ea r e ablockedbyt h eatom,t h eele仁tron l o s e sa l lo fi t s momentum.Thenumbero fatomsi nt h es l a bi s 156 Chapteγ 。 F i v e 一~\ n"Ad x 。 Thef r a c t i o no ft h es l a bblockedbyatomsi s 。 n"Aσ dx/A = ηnσ dx 。 。 I faf l u xro fe l e c t r o n si si n c i d e n tont h es l a b ,t h ef l u xemergingont h e others i d ei s 。 。 0 0 0 ~ r ’= f(l-n ,.σ dx) ' ‑ ' Thust h echangeo ffw i t hd i s t a n c ei s FIGURE! > ‑ 1 D i f f u s i o no fg a sa t o m s by random c o l l i s i o n s . df/dx= -n ,,σr or r=foe h町三 fo e 吋/λm 5 . 1 . 1 CollisionParameters When ane l e c t r o n ,s a y ,c o l l i d e sw i t h an e u t r a latom,i tmayl o s eany f r a c t i o no fi t si n i t i a lmomentum,dependingont h ea n g l ea twhichi t rebounds.Inahead‑onc o l l i s i o nw i t hah田vy atom,t h ee l e c t r o ncan l o s et w i c ei t si n i t i a lmomentum,s i n c ei t sv e l o c i t yr e v e r s e ss i g na f t e rt h e c o l l i s i o n .Thep r o b a b i l i t yo fmomentuml o s scanbeexpressedi nterms o ft h ee q u i v a l e n tc r o s ss e c t i o nσthat t h eatomswouldhavei ft h e ywere p e r f e c ta b s o r b e r so fmomentum. h i c k n e s s I nF i g .5 ‑ 2 ,e l e c t r o n sa r ei n c i d e n tuponas l a bo fa r e aA andt dxc ontaining""n e u t r a latomsperm 3 .Theatomsa r eimaginedt obe opaques p h e r e so fc r o s s ‑ s e c t i o n a lareaσ, that i s ,e v e r ytimeane l e c t r o n [ 5 ‑ 1 ] h ef l u xwouldbedecreasedt ol / eo fi t si n i t i a lv a l u e . Inadistanceλ "" t Theq u a n t i t yλm i st h emean/1γee p a t hf o rc o l l i s i o n s : | λm = l/n,,a‑I [ 5 ‑ 2 ] A f t e rt r a v e l i n gadistanceλm• ap a r t i c l ew i l lhavehadagoodp r o b a b i l i t y o fmakingacollision ‘ The meant i m ebetweenc o l l i s i o n s ,f o rp a r t i c l e so f v e l o c i t yv ,i sg i v e nby r = λm/v andt h emeanfrequencyo fc o l l i s i o n si s T‑l = V /λm ・一一ーーーベーー = η,.(TV [ 5 ‑ 3 ] I f we now a verage over p a r t i c l e so fa l lv e l o c i t i e sv i n a Maxwellian d i s t r i b u t i o n ,wehavewhati sg e n e r a l l yc a l l e dt h ec o l l i s i o nfrequencyv : • l / = 1lnCTV 一← .一一--- .一一ーー- [ 5 ‑ 4 ] D i f f u s i o nParameters 5 . 1 . 2 Thef l u i dequationo fmotioni n c l u d i n gc o l l i s i o n si s ,f o ranys p e c i e s , mn[ご+ (v· 叶=叫 - Vp-mnvv mnTi= l l u s t r a t i o no ft h ede宣nition o fc r o s ss e c t i o n . FIGURE5 ‑ 2 I 上 [ 5 ‑ 5 ] 1 5 7 D i f f u s i o nand R e s i s t i v i t y 喝事 158 Cha戸ter F i v e wherea g a i n the 士 indicates t h es i g no ft h ec h a r g e . Theaveraging p r o c e s susedt ocomputevissucha stomakeEq.[ 5 ‑ 5 ]c o r r e c t ;weneed notbeconcernedw i t ht h ed e t a i l so ft h i scomputation.Theq u a n t i t yv must,however,beassumedtobeac o n s t a n ti norderf o rE q .[ 5 ‑ 5 ]t obe v / a t= 0 .I fv i s u s e f u l . We s h a l lc o n s i d e ras t e a d ys t a t ei n which a u f f i c i e n t l yl a r g e ) ,af l u i delementw i l lnotmove s u f f i c i e n t l ys m a l l( o rvs nac o l l i s i o nt i m e ,andt h ec o n v e c t i v e i n t or e g i o n so fdi 征erent EandVpi d e r i v a t i v ed v / d tw i l la l s ov a n i s h .S e t t i n gt h el e f t ‑ h a n ds i d eo fE q .[ 5 ‑ 5 ] t oz e r o ,weh a v e ,f o rani s o t h e r m a lp l a s m a , v= 一日一一一『一、、、 Thisequationmerelye x p r e s s e st h ef a c tth且t d i f f u s i o ni sarandom‑walk p r o c e s s ,i nwhichan e tf l u xfromdenser e g i o n st ol e s sdenser e g i o n s o c c u r ssimplybecausemorep a r t i c l e ss t a r ti nt h edenser e g i o n .This 自 ux i so b v i o u s l yp r o p o r t i o n a ltot h eg r a d i e n to ft h ed e n s i t y .Inp l a s m a s ,F i c k ' s lawi s notn e c e s s a r i l yobeyed. Becauseo ft h ep o s s i b i l i t yo forganized motions(plasmaw a v e s ) ,aplasmamayspreadouti namannerwhichi s 口 ot t r u l yrandom. ___!__(土enE-KTVn) DECAY OF A PLASMABYDIFFUSION 5 . 2 mnv [ 5 ‑ 6 ] KTVn =土一- E 一一一一一 ηiv ηw n AmbipolarDiffusion 5 . 2 .l Wenowc o n s i d e rhowaplasmac r e a t e di nac o n t a i n e rdecaysbyd i f f u s i o n t ot h ewalls 目 Once i o n sande l e c t r o n sreacht h ew a l l ,t h e yrecombine t h e r e .Thed e n s i t yneart h ew a l l ,t h e r e f o r e ,i se s s e n t i a l l yz e r o .Thef l u i d e q u a t i o n so fmotionandc o n t i n u i t ygovernt h eplasmab e h a v i o r ;buti f t h edecayi ss l o w ,weneedonlykeept h etimed e r i v a t i v ei nt h ec o n t i n u i t y e q u a t i o n .Thet i m ed e r i v a t i v ei nt h eequationo fmotion,E q .[5 ・5], w i l l sl a r g e .Wet h u shave ben e g l i g i b l ei ft h ec o l l i s i o nfrequencyvi Thec o e f f i c i e n t sabovea r ec a l l e dt h em o b i l i t yandt h ed i f f u s i o nc o e f f i c i e n t : lオ = lql 川 Mobilityβ coefficientβ ID= KT/mv I D i f f u s i o n 一 一軒v 一 E 一 D 一 μ 7v 一 [ 5 ‑ 1 0 ] れ一n 一一+ 一一」』← D 一μ [ 5 ‑ 1 1 ] D 一μ F i e I r=オ,nE‑D,Vn=一µ,nE-D, Vn E I = ‑DVn 一一 [ 5 ‑ 9 ] F i c k ' sla叫 of di 妊usion i sas p e c i a lc a s eo ft h i s ,occurringwhene i t h e r E= 0ort h ep a r t i c l e sa r euncharged,s othatオ= 0 :・ I r [ 5 ‑ 1 2 ] w i t hr ig i v e nbyE q .[ 5 ‑ 1 0 ] .I ti sc l e a rt h a ti fr ,andr ,werenote q u a l , ft h eplasma i s much as e r i o u schargeimbalancewouldsoon a r i s e .I l a r g e rthanaDebyel e n g t h ,i tmustbeq u a s i n e u t r a l ; and onewould e x p e c tt h a tt h er a t e so fdi 圧usion o fi o n sande l e c t r o n swouldsomehow a d j u s tthemselvess ot h a tt h etwos p e c i e sl e a v ea tt h esamer a t e .How t h i shappensi se a s yt os e e .Thee l e c t r o n s ,beingl i g h t e r , havehigher e a v et h eplasmafirst 目 A p o s i t i v echarge thermalv e l o c i t i e sandtendtol i sl e f tbehind,andane l e c t r i cf i e l di ss e tupo fsuchap o l a r i t ya st or e t a r d t h el o s so fe l e c t r o n sanda c c e l e r a t et h el o s so fi o n s .TherequiredEf i e l d ,=f .FromEq.[ 5 ‑ 1 0 ] ,wecanw r i t e i sfoundbys e t t i n gr ,= f Witht h ehelpo ft h e s ed e f i n i t i o n s ,t h ef l u xr io ft h ej t hs p e c i e scanb号 、vritten 円U l.u=lqlD/叶 + r v a一。 Thesew i l lbedi 圧erent f o reachs p e c i e s . Notet h a tD i s measuredi n r econnectedbyt h eE i n s t e i n m 2 / s e c .Thet r a n s p o r tcoe伍cients オandD a r e l a t i o n : [ 5 ‑ 1 3 ] [ 5 ‑ 1 4 ] 159 Diffusion 仰d R e s i s t i v i t y r 160 Thecommonf l u xri stheng i v e nby s e 目 -? -- ‑ T , T=T > e 打d 、 d2S d x 2 1 D r ' " ' S= Acos~市+ B sin -ーとち ( D r ) ( D r ) (5・ 18] (5・27] Wewoulde x p e c tt h ed e n s i t yt oben e a r l yz e r oa tt h ew a l l s( F i g .5 ‑ 3 )and nb e t w e e n .Thes i m p l e s ts o l u t i o ni st h a tw i t h t oh且ve oneormorepeaksi as i n g l emaximum.Bysymmetry,wecanr e j e c tt h eodd( s i n e )termi n Eq 目[ 5 2 7 ) .Theboundaryc o n d i t i o n sS= 0a tx =土L thenr e q u i r e s [ 5 ‑ 1 9 ] Thee 圧ect o ft h eambipolare l e c t r i cf i e l di st oenhancet h edi圧usion o f i o n sbyaf a c t o ro ft w o ,butt h edi釘usion r a t eo ft h etwos p e c i e st o g e t h e r i sp r i m a r i l yc o n t r o l l e dbyt h es l o w e rs p e c i e s . or r =(およ i naSlab n( r , t )= T ( t ) S ( r ) [ 5 ‑ 2 6 ] w i t ht h es o l u t i o n 1i Thedi百usion equation ( 5 ‑ 1 7 ]cane a s i l ybes o l v e dbyt h emethodo f s e p a r a t i o no fvariables. 市Ve l e t (5・ 25] I ns l a bgeometry,t h i sbecomes ForT,= T ; ,wehave Da= 2D, [ 5 ‑ 2 4 ] 一肋 円u 、 ( 5 ‑ 1 7 ] =D,+ 壬 D, </γ Thes p a t i a lp a r tSobeyst h ee q u a t i o n I ft h i si sc o n s t a n t ,E q .( 5 ‑ 1 2 ] Themagnitudeo fDacanbee s t i m a t e di fwetakeµ. ,》 /Li 目 That t h i s i st r u ecanbeseenfromE q .[ 5 ‑7 ] .S i n c evi sp r o p o r t i o n a lt ot h ethermal v e l o c i t y , which i sp r o p o r t i o n a lt om 112, オ .i sp r o p o r t i o n a lt o m 112 Equations[ 5 ‑ 1 6 ]and( 5 ‑ 9 ]theng i v e Da=D;+笠 D, オ . , (5 ・ 23] w i t ht h es o l u t i o n ( 5 ‑ 1 6 ] a n / a t= DaV2n Di鉦usion T d t l coefficient. (5・ 22] dT v c a l l e dt h e ambipolardiffusioη becomess i m p l y +オ.,D, / L i+/Le [5 ・ 21] S i n c et h el e f ts i d ei saf u n c t i o no ft i m ea l o n eandt h er i g h ts i d eaf u n c t i o n o fs p a c ea l o n e ,t h e ymustbothbee q u a lt ot h esamec o n s t a n t ,whichwe s h a l lc a l l-1/r・ The f u n c t i o nT t h e nobeyst h ee q u a t i o n [ 5 ‑ 1 5 ] Thisi sFick ’ s laww i t hanewd i f f u s i o nc o e f f i c i e n t D. 一 µ.;D, 一S vn D一 μ一μ 一 - +一+ Z μ一 D 一μ e ー一 vn / L i+/Le t 一T µ.,D, 一 µ.;D , 一 µ.,D , 一 µ.,D,_ c u dvS ‑D,Vη =比」一一一ニ Vn 目 /Li + /Le T DD 一一一、\ 一一一一 D,‑D, sl F i v e 汀一d- 汀一 d whereuponE q .( 5 ‑ 1 7 ] ,w i t ht h es u b s c r i p tonDaunderstood,becomes Cha戸ter (5・ 28] CombiningE q s .(5・20], [ 5 ‑ 2 4 ] ,( 5 ‑ 2 7 ] ,and[ 5 ‑ 2 8 ] ,wehave ! π = ( 5 ‑ 2 0 ] l -ti• 7TX noe キ cos‑ 2L [5司 29] 161 D i f f u s i o nand R e s i s t i v i t y F 163 162 D i f f u s i o nand R e s i s t i v i t y Chae争ter Fi叩 一→一一、、、 x ーし x ーし 。 。 +し ‑ 4 Decay o fa ni n i t i a l l y nonuniform FIGURE5 p l a s m a ,s h o w i n gt h er a p i dd i s a p p e a r ュ a n c eo ft h eh i g h e r ‑ o r d e rd i f f u s i o n m o d e s . +L e n s i t yo fap l a s m aa tv a r i o u s FIGURE5 ‑ 3 D t i m e sa si td e c a y sbyd i f f u s i o n t ot h ew a l l s . ands i m i l a r l yf o rt h es i n et e r m s .Thust h edecayt i m ec o n s t a n tf o rt h e I t hmodei sg i v e nby Thisi sc a l l e dt h elowestdiffusionmode.Thed e n s i t yd i s t r i b u t i o ni sac o s i n e , andt h epeakd e n s i t yd e c a y se x p o n e n t i a l l yw i t ht i m e .Thet i m ec o n s t a n t T i n c r e a s e sw i t hL andv a r i e si n v e r s e l yw i t hD,a sonewoulde x p e c t . Therea r e ,o fc o u r s e ,h i g h e rd i f f u s i o nmodesw i t hmorethanone p e a k .Supposet h ei n i t i a ld e n s i t yd i s t r i b u t i o ni sa sshownbyt h et o pc u r v e i nF i g .5 ‑ 4 .Suchana r b i t r a r yd i s t r i b u t i o ncanbeexpandedi naF o u r i e r s e r i e s : f~ ( l+討すX ̲., . m ' 1 T x ¥ n=n 0 ¥~ a 1c o s-τ一十士 Om smτ-; 「 n u q u 一針 [ 5 ‑ 3 2 ] + l -;=吋(1 +託] 一γ ’ 1A - γ S u b s t i t u t i n gt h i si n t ot h ed i f f u s i o ne q u a t i o n[ 5 ‑ 1 7 ] ,we s e et h a teach c o s i n etermy i e l d sar e l a t i o no ft h eform + 必一 lU (5 ・ 31] 2 ¥ Thes p a t i a lp a r to ft h edi 圧usion e q u a t i o n ,E q .[ 5 ‑ 2 5 ] ,r e a d s ,i nc y l i n d r i c a l geometry, d 一d ‑t/T . 2 . 3 D i f f u s i o ni naCylinder 5 qu一2 (l +~)= [ 5 ‑ 3 3 ] Thef i n e ‑ g r a i n e ds t r u c t u r eo ft h ed e n s i t yd i s t r i b u t i o n ,correspondingt o l a r g e Inumbers, d e c a y sf a s t e r ,w i t h as m a l l e rt i m ec o n s t a n tT1. The plasmadecayw i l lproceeda si n d i c a t e di nF i g .5 ‑ 4 .F i r s t ,t h ef i n es t r u c t u r e w i l lbewashedoutbydi 飢ision. Thent h el o w e s td i f f u s i o nmode,t h e i l lber e a c h e d .F i n a l l y ,t h epeak s i m p l ec o s i n ed i s t r i b u t i o no fF i g .5 ・3, w h i l et h eplasmad e n s i t yp r o f i l er e t a i n st h e d e n s i t yc o n t i n u e stodecayw sames h a p e . Wehavechosent h ei n d i c e ss ot h a tt h eboundaryc o n d i t i o na tx =土L i s a u t o m a t i c a l l ys a t i s f i e d . To t r e a tt h et i m e dependence, we can t r ya s o l u t i o no ft h eform /山 1 2I 一 D L(l 十王) 7TJ (5 ・ 30] η = n仲 e ‑tJ 'cos 一了+ ~bme ’ msinTJ L T1 =I 一一一了一| ( 5 ‑ 3 4 ] Thisdi 圧ers fromE q .[ 5 ‑ 2 6 ]byt h ea d d i t i o no ft h emiddlet e r m ,which merely a c c o u n t sf o rt h echangei nc o o r d i n a t e s .Theneedf o rt h ee x t r a fas l i c eo fplasmai n( A )i smoved termi si l l u s t r a t e dsimplyi nF i g .5・ 5. I l l o w e dt oe xpand, t h ed e n s i t ywould toward l a r g e rx withoutbeinga -ム←一一一一 ?「 164 o fi n f i n i t es e r i e sandmaybefoundi nmathematicalt a b l e s .U n f o r t u n a t e l y , B e s s e lf u n c t i o n sa r en o ty e tfoundi nhandc a l c u l a t o r s . To s a t i s f yt h e boundary c o n d i t i o n η = 0 atγ = a , we must s e t a / ( D r ) 1 1 2e q u a lt ot h ef i r s tz e r oo f] 0 ;n amely,2 . 4 .Thisy i e l d st h edecay t i m ec o n s t a n tr .Theplasmaa g a i nd e c a y se x p o n e n t i a l l y ,s i n c et h etemュ p o r a lp a r to ft h ed i f f u s i o ne q u a t i o n ,E q .[ 5 ‑ 2 3 ] ,i sunchanged.Wehave n ac y l i n d e r . Higher d i f f u s i o n d e s c r i b e dt h el o w e s t di 任usion mode i modes,w i t hmorethanonemaximumi nt h ec y l i n d e r ,w i l lbeg i v e ni n termso fB e s s e lfu ロctions o fhighero r d e r ,i nd i r e c ta n a l o g yt ot h ec a s e o fs l a bgeometry. Cha;争ter F i v e x A FIGURE5ふ B o faplasmas l a bi nr e c t i l i n e a randc y l i n d r i c a lg e o m e t r y ,i l l u s t r a t i n gt h e d i f f e r e n c eb e t w e e nac o s i n eandaB e s s e lf u n c t i o n . Motion remainc o n s t a n t .Ont h eo t h e rhand,i fas h e l lo fplasmai n( B )i smoved towardl a r g e rγwith t h es h e l lt h i c k n e s skeptc o n s t a n t ,t h ed e n s i t ywould n e c e s s a r i l yd e c r e a s ea sl / r .C o n s e q u e n t l y ,onewoulde x p e c tt h esol山on t oE q .[ 5 ‑ 3 4 ]t obel i k eadampedc o s i n e( F i g .5・6). Thisf u n c t i o ni sc a l l e d e s s e lf u n c t i o no fo r d e rzeγo, andE q .[ 5 ‑ 3 4 ]i sc a l l e dBessel’ s e q u a t i o n( o f aB orderz e r o ) .I n s t e a do ft h esymbolc o s ,i ti sg i v e nt h esymbol] o .The f u n c t i o nJo (γ/[Dr]112) i sas o l u t i o nt oE q .( 5 ‑ 3 4 ] ,j u s ta sc o s[ x / ( D r ) 1 n ]i s as o l u t i o nt oE q .( 5 ‑ 2 6 ] .Bothc o sk xand]o(kγ ) a r ee x p r e s s i b l ei nt e r m s STEADYSTATESOLUTIONS 5 . 3 I nmanye x p e r i m e n t s ,aplasmai smaintainedi nas t e a d ys t a t ebyc o n ュ t i n u o u si o n i z a t i o no ri n j e c t i o no fplasmat oo f f s e tt h el o s s e s .Toc a l c u l a t e t h ed e n s i t yp r o f i l ei nt h i sc a s e ,wemustaddas o u r c etermt ot h ee q u a t i o n o fc o n t i n u i t y : 生- DV2η = a t Q(r) ( 5 ‑ 3 5 ] Thes i g ni schosens ot h a twhenQ i sp o s i t i v e ,i tr e p r e s e n t sas o u r c e n / a t .I ns t e a d ys t a t e ,wes e tan / δt = 0 and andc o n t r i b u t e st op o s i t i v ea a r el e f tw i t haP o i s s o n ‑ t y p ee q u a t i o nf o rn ( r ) . ConstantI o n i z a t i o nFunction 5 . 3 . 1 I nmanyweaklyi o n i z e dg a s e s ,i o n i z a t i o ni sproducedbye n e r g e t i ce l e c ュ t r o n si nt h et a i lo ft h eMaxwelliand i s t r i b u t i o n .I nt h i sc a s e ,t h es o u r c e termQ i sp r o p o r t i o n a lt ot h ee l e c t r o nd e n s i t yn .S e t t i n gQ = Z n ,where Zi sthe “ 10nization function ,” we have V2n=ー(Z/D)n 。 k r FIGURE5 ‑ 6 TheB e s s e lf u n c t i o no fo r d e rz e r o . ( 5 ‑ 3 6 ] Thisi st h esamee q u a t i o na st h a tf o rS ,E q .[ 5 ‑ 2 5 ]. . C o n s e q u e n t l y ,t h e d e n s i t yp r o f i l ei sac o s i n eo rB e s s e lf u n c t i o n ,a si nt h ec a s eo fadecaying p l a s m a ,o n l yi nt h i sc a s et h ed e n s i t yremainsc o n s t a n t .Theplasmai s o s s e sbywhateverh e a ts o u r c ekeepst h e maintaineda g a i n s tdi百usion l e l e c t r o ntemperaturea ti t sc o n s t a n tv a l u eandbyas m a l li n f l u xo fn e u t r a l atomst or e p l e n i s ht h o s et h a ta r ei o n i z e d . 165 D i f f u s i o na n d R e s i s t i v i t y 腎 EE 1 6 6 Cha世ter F i v e 5 . 3 . 2 PlaneSource 1 6 7 Wen e x tc o n s i d e rwhatp r o f i l ewouldbeobtainedi ns l a bgeometryi f .Suchasourcemightb e , t h e r ei sal o c a l i z e ds o u r c eont h eplanex= 0 f o ri n s t a n c e ,as l i t ‑ c o l l i m a t e dbeamo fu l t r a v i o l e tl i g h tstrongenought o i o n i z et h en e u t r a lg a s .Thes t e a d ys t a t ed i f f u s i o nequationi sthen , 2 一一~\ r、 主主=ー笠 8(0) d x " D i f f u s i o na n d R e s i s t i v i t y D [ 5 ‑ 3 7 ) Excepta tx= 0 ,t h ed e n s i t ymusts a t i s f ya 2 n / a x 2= 0 .Thiso b v i o u s l yh a s t h es o l u t i o n( F i g .5 ‑7 ) …中与) a [5・ 38) F i n a l l y ,wec o n s i d e rac y l i n d r i c a lplasmaw i t hasourcel o c a t e dont h e a x i s .Suchas o u r c em i g h t ,f o ri n s t a n c e ,beabeamo fe n e r g e t i ce l e c t r o n s ,t h ed e n s i t ymust producingi o n i z a t i o nalongt h ea x i s .Exceptatγ = 0 s a t i s f y ;ま(r わ= O Thed e n s i t ybecomesi n f i n i t ea tr= 0 ( F i g .5 ‑ 8 ) ;i ti sn o tp o s s i b l et o determinet h ed e n s i t yneart h ea x i sa c c u r a t e l ywithoutc o n s i d e r i n gt h e f i n i t ewidtho ft h es o u r c e . RECOMBINATION 5 . 4 [5・ 39) Thes o l u t i o nt h a tv a n i s h e sa tr= ai s η = π。 ln (a / γ ) [ 5 ‑ 4 0 ) Whenani o nandane l e c t r o nc o l l i d e ,p a r t i c u l a r l ya tlowrelative 、,elocity, t h e yhaveaf i n i t ep r o b a b i l i t yo frecombiningi n t oan e u t r a latom.To c o n s e r v emomentum,at h i r dbodymustbep r e s e n t .I ft h i st h i r dbody a d i a t i v er e c o m b i n a t i o n .I fi ti s i sane m i t t e dphoton,t h ep r o c e s si sc a l l e dr ap a r t i c l e ,t h ep r o c e s si sc a l l e dt h r e e ‑ b o d yr e c o m b i n a t i o n .Thel o s so fplasma byrecombinationcanber e p r e s e n t e dbyan e g a t i v es o u r c etermi nt h e e q u a t i o no fc o n t i n u i t y .I ti sc l e a rt h a tt h i stermw i l lbep r o p o r t i o n a lt o n , n ;= n2.I nt h eabsenceo ft h ed i f f u s i o nt e r m s ,t h ee q u a t i o no fc o n t i n u i t y thenbecomes 。η / at= x ーし 。 +し r i a n g u l a rd e n s i t yp r o f i l e FIGURE5 ‑ 7 Thet r e s u l t i n gfromap l a n es o u r c e underd i f f u s i o n . a The l o g a r i t h m i c d e n s i t y p r o f i l e FIGURE5‑8 r e s u l t i n gfromal i n es o u r c eunder d i f f u s i o n . Theplasmah a sal i n e a rp r o f i l e .Thed i s c o n t i n u i t yi ns l o p ea tt h es o u r c e i sc h a r a c t e r i s t i co fS 司function s o u r c e s . 5 . 3 . 3 LineSource 。 an ヨ [5 ・ 41) Thec o n s t a n to fp r o p o r t i o n a l i t yαis c a l l e dt h erecomb初日tion c o e f f i c i e n t andh a su n i t so fm 3 / s e c .Equation( 5 ‑ 4 1 ]i san o n l i n e a requationf o rη. Thismeanst h a tt h es t r a i g h t f o r w a r dmethodf o rs a t i s f y i n gi n i t i a land boundaryc o n d i t i o n sbyl i n e a rs u p e r p o s i t i o no fs o l u t i o n si sn o ta v a i l a b l e . F o r t u n a t e l y ,E q .( 5 . 4 1 ]i s such as i m p l en o n l i n e a requation t h a tt h e 一司r-一一← 168 s o l u t i o ncanbefoundbyi n s p e c t i o n .I ti s Chapteγ 1 F i v e r"/O\'I<、 0 whereπ0(r) i st h ei n i t i a ld e n s i t yd i s t r i b u t i o n .I ti se a s i l yv e r i f i e dt h a tt h i s s a t i s f i e sE q .[ 5 ‑ 4 1 ] .A f t e rt h ed e n s i t yh a sf a l l e nf a rbelowi t si n i t i a lv a l u e , i tdecays 阿ci世roeαlly witht i m e : na : :1 /日t 0 0 。 。 。 。 。 er‑ ~ U 』 ‑ ‑ 0 0 0 0 。 。 B 0 』 0 ‑ 1 0 Ac h a r g e dp a r t i c l ei nam a g n e t i cf i e l dw i l lg y r a t ea b o u t FIGURE5 t h esamel i n eo ff o r c eu n t i li tmakesac o l l i s i o n . r e c o m b i n a t i o n ,whichi sp r o p o r t i o n a lton2,i sdominant,andt h ed e n s i t y d e c a y sr e c i p r o c a l l y .A f t e rt h ed e n s i t yh a sreachedalowv a l u e ,d i f f u s i o n becomesdominant,andt h edecayi st h e n c e f o r t he x p o n e n t i a l . ¥ \ . 5 DIFFUSIONACROSS A MAGNETIC FIELD 5 ‑ , Ther a t eo fplasmal o s sbyd i f f u s i o ncanbedecreasedbyamagnetic f i e l d ;t h i si st h eproblemo fconfinementi nc o n t r o l l e df u s i o nr e s e a r c h . Considerau ' e a k l yi o n i z e dp lasmai namagnetic 白eld ( F i g .5 ‑ 1 0 ) .Charged p a r t i c l e sw i l lmovealongB byd i f f u s i o nandm o b i l i t yaccordingt oE q . [ 5 ‑ 1 0 ] ,s i n c eB doesn o ta f f e c tmotioni nt h ep a r a l l e ld i r e c t i o n .Thuswe h a v e ,f o reachs p e c i e s , \\も、 z -円。 η 一 「 O D η μ E \ 一一 \、。 士 r iz aE) U 戸』 (円 \、£、h ( 5 ‑ 4 4 ] \九 \、\\ 1 0 8 I ft h e r e were no c o l l i s i o n s ,p a r t i c l e s would n o td i f f u s ea ta l li nt h e y r a t eaboutt h esameュ perpendiculardirection‑theywouldcontinuetog l i n eo ff o r c e .Therea r e ,o fc o u r s e ,p a r t i c l ed r i f t sa c r o s sB becauseo f e l e c t r i cf i e l d so rg r a d i e n t si nB ,butt h e s ecanbearrangedt obep a r a l l e l t ot h ew a l l s .Fori n s t a n c e ,i nap e r f e c t l ysymmetricc y l i n d e r( F i g .5 ‑ 1 1 ) , t h eg r a d i e n t sa r ea l li nt h er a d i a ld i r e c t i o n ,s ot h a tt h eguidingc e n t e r d r i f t sa r ei nt h eazimuthald i r e c t i o n .Thed r i f t swouldthenbeh a r m l e s s . Whent h e r ea r ec o l l i s i o n s ,p a r t i c l e smigratea c r o s sB to t h ew a l l s alongt h eg r a d i e n t s .Theydot h i sbyarandom‑walkp r o c e s s( F i g .5 ‑ 1 2 ) . Whenani o n ,s a y ,c o l l i d e sw i t han e u t r a latom,t h ei o nl e a v e st h ec o l l i s i o n i r e c t i o n .I tc o n t i n u e st og y r a t eaboutt h emagュ t r a v e l i n gi nadi ぽerent d n e t i cf i e l di nt h esamed i r e c t i o n ,buti t sphaseo fg y r a t i o ni schanged d i s c o n t i n u o u s l y .(TheLarmorr a d i u smaya l s ochange,butl e tu ssuppose t h a tt h ei o ndoesnotg a i norl o s eenergyont h ea v e r a g e . ) \口、。,0 .口、 。 3 2 4 1 6 9 D i f f u s i o nand R e s i s t i v i t y -一・・・ [ 5 ‑ 4 3 ] Thisi safundamentallyd i f f e r e n tbehaviorfromt h ec a s eo fd i f f u s i o n , i nwhicht h etimev a r i a t i o ni se x p o n e n t i a l . Figure5θshows t h er e s u l t so fmeasurementso ft h ed e n s i t ydecay i nt h ea f t e r g l o wo faweaklyi o n i z e dH p l a s m a .Whent h ed e n s i t yi sh i g h , 、、- 0 。 o 0 0 VVVf ( 5 ‑ 4 2 ] -一一一=一一一一+ αt η ( r,I ) π。( r) 1 0 9 o 。 0 1 5 t(msec) e n s i t ydecayc u r v e so faw e a k l yi o n i z e dplasmaunderr e c o m b i n a t i o nand FIGURE5‑9 D d i f f u s i o n .[FromS .C .Brown,BasicDatao fPlasmaP h y s i c s ,J ohnW i l e yandS o n s , NewY o r k ,1 9 5 9 . ) ム 一ー司噂田園ー一一一 170 C h a p t e r Wehavea g a i nassumedt h a tt h eplasmai si s o t h e r m a landt h a t1i sl a r g e enoughf o rt h edvj ̲ /d ttermt oben e g l i g i b l e .Thexandycomponentsa r e F叩e 戸 dn -KT ー土問v.B ' ax [ 5 ‑ 4 6 ] ρb Bx u n 平 y , η 一 句。一円。 T η E 06 士 ヲ 一一 η U v n K /B m n 1 1 v ,=土enE. Usingt h ed e f i n i t i o n sofオ.andD,wehave U U 平 η一 aτd y D 一π 一一 「 F μ 士 川町v一 品、ν一 土 π 一x qO 一角。 D 一η EX μ 土 U m e t r i cp l a s m acolumnc i on o tl e a dt o l o s s e s . 一一 vx FIGURE5 ‑ 1 1 P a r t i c l ed r i f t si nac y l i n d r i c a l l ysymュ [ 5 ‑ 4 7 ] S u b s t i t u t i n gf o rv . ,wemays o l v ef o r円: a n 2 2 D δη2 2E , 2 2K T1 v,(l+w,r }= 土µEヲ一一一一 w,r 土 w,r 一一一一 J B 托 ay eB η ax [ 5 ‑ 4 8 ] wherer= ν - I S i m i l a r l y ,Vx i sg i v e nby v , ( l+w;r)=土 µE, a n a n D 2 2E , 2 2K T1 一一一 + w,r 一平 ω ♂一一一一 π ax B ‘ eB η ay [5・ 49] Thel a s ttwotermso ft h e s ee q u a t i o n sc o n t a i nt h eExB anddiamagnetic d r i f t s : E. E, v E ,= ‑ B VEx =玉 FIGURE5 ‑ 1 2 D i f f u s i o no fg y r a t i n gpaト K T1a n t i d e sb yc o l l i s i o n sw i t h n e u t r a la t o m s . U 口γ =平一ーー一一- ~- d t [5 ・ 50] ~ eB na x The f i r s ttwo termscanbes i m p l i f i e dbyd e f i n i n gt h ep e r p e n d i c u l a r m o b i l i t yandd i f f u s i o nc o e f f i c i e n t s : Theguidingc e n t e r ,t h e r e f o r e ,s h i f t sp o s i t i o ni nac o l l i s i o nandundergoes arandomw a l k .Thep a r t i c l e sw i l lr F f f u s ei nt h ed i r e c t i o no p p o s i t eVn. Thes t e pl e n g t hi nt h erandomwalki snolongerλm. a si nmagnetic-field自 f r e ed i f f u s i o n ,buth a si n s t e a dt h emagnitudeo ft h eLarmorr a d i u sγL· D i f f u s i o na c r o s sB cant h e r e f o r ebesloweddownbyd e c r e a s i n gr L ;t h a t i s ,byi n c r e a s i n gB . Tos e ehowt h i scomesa b o u t ,wew r i t et h eperpendicularcomponent o ft h ef l u i de q u a t i o no fmotionf o re i t h e rs p e c i e sa sf o l l o w s : mn 企土=土問(E +v j ̲X B)‑KTVn‑mn11v= 0 eB η ay K T1a n U 同=土ー一一一一一 D ~,=~ l+ui;r" μ μ ム=一一一一τ一言 i 十 w,r [5 ・ 51] Witht h eh e l po fE q s .(5・50] and( 5 ‑ 5 1 ] ,wec anw r i t eE q s .( 5 ‑ 4 8 ]and ( 5 ‑ 4 9 ]a s V [ 5 ‑ 4 5 ] V E +V o Vム=土μ ムE-D ム一一+了ーで寸アす7 η1 +(〆/ ω ;) よ』 [ 5 ‑ 5 2 ] 171 D i f f u s i o nand R e s i s t i v i t y T 172 C h a p t e r F i v e W,'T = wjv= オ , B""Am /γL 2 2 Int h el i m i tw,'T > 1, wehave D KT 1 KTv ム- 2 2‑ 2 -一一ー mv 白J , ' T l \ 2γE r E A ご !と B a ss t r a i g h t f o r w a r da si nt h e B = 0c a s e . Considert h ep a r t i c l ef l u x e s perpendiculart oB ( F i g .5‑13).O r d i n a r i l y ,s i n c er, ょ is s m a l l e rthanr , j ̲ , at r a n s v e r s ee l e c t r i cf i e l dwouldbes e tups oa st oa i de l e c t r o nd i f f u s i o n h i selectric 自 eld canbes h o r t ‑ c i r c u i t e d andr e t a r di o ndi 庄usion. However,t byan imbalance o ft h ef l u x e sa l o n gB . Thati s ,t h en e g a t i v e charge r e s u l t i n gfromI, ムく r, ム can bed i s s i p a t e dbye l e c t r o n sescapingalong t h ef i e l dl i n e s . Although t h et o t a ld i f f u s i o n must be ambipolar, t h e perpendicularp a r to ft h el o s s e sneedn o tbea m b i p o l a r .Thei o n scan di ぽuse o utp r i m a r i l yr a d i a l l y ,w h i l et h ee l e c t r o n sd i f f u s eoutp r i m a r i l y alongB .Whetherorn o tt h i si nf a c thappensdependsont h ep a r t i c u l a r e x p e r i m e n t .I ns h o r tplasmacolumnsw i t ht h ef i e l dl i n e st e r m i n a t i n gon conductingp l a t e s ,onewoulde x p e c tt h eambipolare l e c t r i cf i e l dt obe s h o r t ‑ c i r c u i t e do u t .Eachs p e c i e sthend i f f u s e sr a d i a l l ya tad i f f e r e n tr a t e . I nl o n g ,t h i nplasmacolumnst e r m i n a t e dbyi n s u l a t i n gp l a t e s ,onewould e x p e c tt h er a d i a ldi 圧usion t obeambipolarbecauseescapealongB i s arduous. M a t h e m a t i c a l l y ,t h eproblemi st os o l v es i m u l t a n e o u s l yt h ee q u a t i o n s 5 ‑ 1 2 ]f o ri o n sande l e c t r o n s .I ti sn o tt h ef l u x e sr ibutt h e o fc o n t i n u i t y[ d i v e r g e n c e sV キr i whichmustbes e te q u a lt oeacho t h e r .S e p a r a t i n g V キr ii n t operpendicularandp a r a l l e lcomponents,wehave ( 5 ‑ 5 3 1 ( 5 ‑ 5 4 ] Thisform,t h esquareo fal e n g t hoverat i m e ,showst h a td i f f u s i o ni sa r i t t e n random‑walkp r o c e s sw i t has t e pl e n g t hλm· Equation[5・ 54] canbew KTv I 1 i n 一一昔』 P a r a l l e landp e r p e n d i c u l a rp a r t i c l ef l u x e si nam a g n e t i cf i e l d . FIGURE5‑13 mα>, ム=一τ ~百出 ~ν ~ー ηzαJ ' v , h ' T 、 Di ! f u s i o na n d R e s i s t i v i t y 且 el 1en 一一一一一画』 Comparingw i t hE q .[ 5 ‑ 8 ] ,wes e et h a tt h er o l eo ft h ec o l l i s i o nfrequency 1 1h a sbeenr e v e r s e d .I ndi狂usion p a r a l l e lt oB ,D i sp r o p o r t i o n a lt o1 1‑i . s i n c ec o l l i s i o n sr e t a r dt h em o t i o n .Indi 旺usion perpendiculart oB ,D ム i sp r o p o r t i o n a lt o11,s i n c ec o l l i s i o n sa r eneededf o rcross司自eld m i g r a t i o n . Thedependenceonm h a sa l s obeenr e v e r s e d .Keepingi nmindt h a t1 1 l/2 ‑l/2 1/2 i sp r o p o r t i o n a lt om ,wes e et h a tD e x :m ,w h i l eDム CX:m p a r a l l e ld i f f u s i o n ,e l e c t r o n smovef a s t e rthani o n sbecauseo ft h e i rhigher thermalv e l o c i t y ;i nperpendiculard i f f u s i o n ,e l e c t r o n se s c a p emores l o w l y becauseo ft h e i rs m a l l e rLarmorr a d i u s . Disregardingnume1i c a lf a c t o r so forderu n i t y ,wemayw r i t eE q . [ 5 ‑ 8 ]a s D = KT/mv ~ ll~h'T ~ λ ~/'T (5・ 55] D 173 1i1 皐ゎ From t h i s ,i ti se v i d e n tt h a tt h e perpendicularv e l o c i t yo fe i t h e r s p e c i e si scomposedo ftw0p a r t s .F i r s t ,t h e r ea r eu s u a lvEandv0d r i f t s μψendiculaγto t h eg r a d i e n t si np o t e n t i a landd e n s i t y .Thesed r i f t sa r e slowed down byc o l l i s i o n sw i t h 町utrals; t h edrag f a c t o r 1+(112/ w ; ) becomesu n i t ywhenv • 0. Second,t h e r ea r et h em o b i l i t yandd i f f u s i o n ot h eg r a d i e n t si np o t e n t i a landd e n s i t y .Thesed r i f t shave d r i f t spaγallel t t h esameforma si nt h eB = 0c a s e ,butt h ec o e f f i c i e n t sオ , andD a r e reducedbyt h ef a c t o r1+w;'T2 Theproductw,'Ti sanimportantq u a n t i t yi nmagneticc o n f i n e m e n t . Whenw;'T2 < 1, t h emagneticf i e l dh a sl i t t l ee恥ct ond i f f u s i o n .When ωγ 》 1, t h emagneticfield 叫nificantly r e t a r d st h er a t eo fd i f f u s i o n a s i l ybev e r i f i e d : a c r o s sB .Thef o l l o w i n ga l t e r n a t i v eformsf o rw,'T cane V 札= Vム· (オ,,1‑nEJ̲‑D;J̲'17n ) 寸 (µ,,nE, ‑D,~) (5・ 57] v‑ r ,=帆(一µ,ej_nEJ_ ‑Del̲Vn)+手 l一µ,,1ι - n,~) ¥ d I ( 5 ‑ 5 6 1 。Z Thisshowst h a tperpendiculard i f f u s i o ni sarandom‑walkp r o c e s sw i t h as t e pl e n g t hrL叱 rather thanλm・ Thee q u a t i o nr e s u l t i n gfroms e t t i n gVキI ;= Vキ r ,cannoteasilybes己 par­ a t e di n t oone‑dimensionale q u a t i o n s .F u r t l : e r m o r e ,t h eanswerdepends s e n s i t i v e l yont h eboundaryc o n d i t i o n sa tt h eendso ft h ef i e l dl i n e s . U n l e s st h e plasmai ss olongt h a tp a r a l l e ld i f f u s i o ncanben e g l e c t e d a l t o g e t h e r ,t h e r ei s no s i m p l e answer t ot h e problem o f ambipolar di百usion a c r o s samagneticf i e l d . 5 . 5 . 1 AmbipolarD i f f u s i o na c r o s sB Becauset h ed i f f u s i o na n d ,m o b i l i t ycoe伍cients a r ea n i s o t r o p i ci nt h e presenceo famagneticf i e l d ,t h eproblemo fambipolardi 圧usion i sn o t ーム ? 174 5 . 5 . 2 ExperimentalChecks Chαpte r F i v e Whetherorn o tamagneticf i e l dreducest r a n s v e r s ed i f f u s i o ni na c c o r d ュ ancew i t hE q .[ 5 ‑ 5 1 ]becamet h es u b j e c to fnumerousi n v e s t i g a t i o n s .The f i r s texperimentperformedi natubelongenought h a tdi百usion t ot h e endsc o u l dben e g l e c t e dwast h a to fLehnertandHohi nSweden.They usedaheliump o s i t i v ecolumnabout1cmi ndiameterand3 . 5m long ( F i g .5 ‑ 1 4 ) .Insuchap l a s m a ,t h ee l e c t r o n sa r ec o n t i n u o u s l yl o s tbyr a d i a l d i f f u s i o nt ot h ew a l l sanda r er e p l e n i s h e dbyi o n i z a t i o no ft h en e u t r a l g a sbyt h ee l e c t r o n si nt h et a i lo ft h ev e l o c i t yd i s t r i b u t i o n .Thesef a s t e l e c t r o n s ,i nt u r n ,a r er e p l e n i s h e dbya c c e l e r a t i o ni nt h el o n g i t u d i n a l e l e c t r i cf i e l d .Consequently,onewoulde x p e c tE,toberoughlyproporュ t i o n a lt ot h er a t eo ft r a n s v e r s edi 狂usion. Twoprobess e ti nt h ew a l lo f t h ed i s c h a r g etubewereusedt omeasureE,a sB wasv a r i e d .Ther a t i o B )t oE,( 0 )i sshowna saf u n c t i o no fB i nF i g .5 ‑ 1 5 .AtlowB f i e l d s , o fE,( t h ee x p e r i m e n t a lp o i n t sf o l l o wc l o s e l yt h ep r e d i c t e dc u r v e ,c a l c u l a t e don t h eb a s i so fE q .(5帽 52]. Atac r i t i c a lf i e l dB,o fabout0 . 2T,however,t h e e x p e r i m e n t a lp o i n t sdepartedfromt h e o r yand,i nf a c t ,showedanincγ-ease o fd i f f u s i o nw i t hB.Thec r i t i c a lf i e l dB,i n c r e a s e dw i t hp r e s s u r e ,s u g g e s t ュ i n gt h a tac r i t i c a lv a l u eo fw1r wasi n v o l v e dandt h a tsomethingwent wrongw i t ht h e“ classical” theory o fd i f f u s i o nwhenw , rwast o ol a r g e . Thet r o u b l ewassoonfoundbyKadomtsevandNedospasovi nt h e U . S . S . R .Theset h e o r i s t sd i s c o v e r e dt h a tani n s t a b i l i t yshoulddevelopa t highmagneticf i e l d s ;t h a ti s ,aplasmawavewouldbee x c i t e dbyt h eE, f i e l d ,andt h a tt h i swavewouldc a u s eenhancedr a d i a ll o s s e s .Thet h e o r y , .Thew ave,i nt h eformo fah e l i c a l c o r r e c t l yp r e d i c t e dt h ev a l u eo fB d i s t o r t i o no ft h eplasmacolumn,wasl a t e rseend i r e c t l yi nane x p e r i r p e n t byA l l e n ,P a u l i k a s ,andP y l ea tB e r k e l e y .Thish e l i c a li n s t a b i l i t yo ft h e p o s i t i v ecolumnwast h ef i r s ti n s t a n c ei nwhich“ anomalous diffusion ” a c r o s smagneticf i e l d swasd e f i n i t i v e l ye x p l a i n e d ,butt h ee x p l a n a t i o nwas 1 . 0 ~-,...~ 175 " t』 D i f f u s i o nand R e s i s t i v i t y / : ! , . . 1ぇ・ . 0.8 ト 1' 、 ー \\ 0 . 4 0 . 2 。 。 0 . 2 0 . 4 0 . 6 B( T ) Then o r m a l i z e dl o n g i t u d i n a le l e c t r i cf i e l dmeasured FIGURE5 ‑ 1 5 a saf u n c t i o no fB a ttwod i f f e r e n tp r e s s u r e s .T h e o r e t i ュ c a lc u r v e sa r eshownf o rc o m p a r i s o n .[FromF .C .Hoh andB .L e h n e r t ,P h y s .F l u i d s3 ,6 0 0( 1 9 6 0 ) . ) a p p l i c a b l eo n l ytoweaklyi o n i z e dg a s e s .I nt h ef u l l yi o n i z e dplasmaso f f u s i o nr e s e a r c h , anomalous d i f f u s i o n proved to be a much tougher problemtos o l v e . PROBES CATHODE 5 ‑ 1 .Thee l e c t r o nn e u t r a lc o l l i s i o nc r o s ss e c t i o nf o r2 ‑ e Ve l e c t r o n si nHei sa b o u t PROBLEMS 6 r . a g ,w herea o=0.53 × 10-• cmi st h er a d i u so fthe 自 rst Bohro rb i to ft h e f h y d r o g e na t o m .A p o s i t i v ecolumnw i t hnom a g n e t i cf i e l dh a sp= ITorro He( a troomt e m p e r a t u r e )andKT,= 2e V . ANODE nm 2 / s e c ,a s s u m i n g that ( a )Compute t h ee l e c t r o nd i f f u s i o n co品目nt i a v e r a g e do v e rt h ev e l o c i t yd i s t r i b u t i o ni se q u a ltoσu f o r2・e Ve l e c t r o n s . B -一一揖』 FIGUREι14 TheLehnert‑Hohe x p e r i m e n tt oc h e c kt h ee f f e c to fam a g n e t i cf i e l don d i f f u s i o ni naw e a k l yi o n i z e dg a s . 日 ( b )I ft h ec u r r e n td e n s i t ya l o n gcolumni s2kA/m2andt h ep l a s m ad e n s i t yi s 1 0 1 6m ‑ 3 ,whati st h ee l e c t r i cf i e l da l o n gt h ecolumn? ___..,,』 1 7 7 、 D i f f u s i o nand ‘、. ,, e Resisliviり i Aw e a k l yi o n i z e dp l a s m ai sc r e a t e di nac u b i c a laluminumboxo fl e n g t hL one a c hs i d e .I td e c a y sbya m b i p o l a rdi 百us ion 目 5・3. 、 Thep l a s m ad e c a y sb yb o t hd i f f u s i o nandr e c o m b i n a t i o n .I fL = 0 . 0 3m,D = 0 . 4m2/ s e c ,anda = 1 0 15m3/ s e c ,a twhatd e n s i t yw i l lt h er a t eo fl o s sbyd i f f u s i o n bee q u a lt ot h er a t eo fl o s sbyr e c o m b i n a t i o n ? / 、 一L 壬 x 三 L 4F η (x) = π。 cos (πx/2L ) 〆 5 ‑ 2 . Aw e a k l yi o n i z e dp l a s m as l a bi np l a n eg e o m e t r yh a sad e n s i t yd i s t r i b u t i o n ナー lil-i- 176 C h a p t e r F i v e ( a )W r i t eane x p r e s s i o nf o rt h ed e n s i t yd i s t r i b u t i o ni nt h el o w e s td i f f u s i o nmode. ¥ ( b )D e f i n ewhatyoumeanb yt h ed e c a yt i m ec o n s t a n tandcomputei ti fD.= 1 0 ‑ 3m 2 / s e c • I \ / 。 B 、、/ “・・・・・” S h i f to fg u i d i n gc e n t e r so ftwol i k ep a r t i c l e s FIGURE 5 ‑ 1 6 makinga9 0 ーc o l l i s i o n . 5 ‑ 4 . Al o n g ,c y l i n d r i c a lp o s i t i v ecolumnh a sB = 0 . 2T .KT;= 0 . 1eV,ando t h e r p a r a m e t e r st h esamea si nP r o b l e m5 ‑ 1 .Thed e n s i t yp r o f i l ei s n (γ)= ηofo (γ/[D1']112) w i t ht h eboundarycond山onη = 0atγ = α = Ic m .N o t e :J 0 ( z )= 0a tz= 2 . 4 . twoguidingc e n t e r sremaini nt h esamep l a c e s .Ther e s u l ti st h esam巴 a si naglancingc o l l i s i o n ,i nwhicht h et r a j e c t o r i e sa r ehardlyd i s t u r b e d . Theworstt h a tcanhappeni sa9 0 ーc o l l i s i o n ,i nwhicht h ev e l o c i t i e sa r e changed9 0 ーi nd i r e c t i o n .Theo r b i t sa f t e rc o l l i s i o nw i l lthenbet h edashed c i r c l e s ,and t h eguidingc e n t e r sw i l l haves h i f t e d . However,i ti sc l e a r fmass ” of t h etwoguidingc e n t e r sremainss t a t i o n a r y . t h a tt h e“ center o o l l i s i o n sb e t w e e nl i k ep a r t i c l e sg i v er i s et ov e r yl i t t l ediffusioη Fort h i sr e a s o n ,c Thiss i t u a t i o ni st obec o n t r a s t e dwitht h ec a s eo fi o n sc o l l i d i n gw i t h n e u t r a l atoms. In t h a tc a s e ,t h ef i n a lv e l o c i t yo ft h en e u t r a li so f no t si n i t i a lp o s i t i o n .Int h e concern,andt h ei o nrandom 句walks awayfromi c a s eo fi o n ‑ i o nc o l l i s i o n s ,however,t h e r ei sad e t a i l e dbalancei neach c o l l i s i o n ;f o reachi o nt h a tmovesoutward,t h e r ei sanothert h a tmoves inwarda sar e s u l toft h ec o l l i s i o n . Whentwop a r t i c l e so fo p p o s i t echargec o l l i d e ,however,t h es i t u a t i o n a s ei snowt h e180。 collision, i se n t i r e l yd i f f e r e n t( F i g .ふ 17). Theworstc i nwhicht h ep a r t i c l e semergewitht h e i rv e l o c i t i e sr e v e r s e d .S i n c ethey mustcontinuet og y r a t eaboutt h el i n e soff o r c ei nt h epropers e n s e , both guidingc e n t e r sw i l l move i nt h e same d i r e c t i o n . [Joηlike-particle c o l l i s i o n sg i v er i s et od i f f u s i o n .Thep h y s i c a lp i c t u r ei ssomewhatdi圧erent f o ri o n sande l e c t r o n sbecauseo ft h ed i s p a r i t yi nm a s s .Thee l e c t r o n s bounce o f ft h en e a r l ys t a t i o n a r yi o n s and random‑walk i nt h eu s u a l f a s h i o n .Thei o n sa r es l i g h t l yj o s t l e di neachc o l l i s i o nandmoveabout a sar e s u l to ffrequentbombardmentbye l e c t r o n s .Nonetheless,because o ft h ec o n s e r v a t i o nofmomentumi neachc o l l i s i o n ,t h er a t e so fd i f f u s i o n a r et h esamef o ri o n sande l e c t r o n s ,a swes h a l lshow. ( a )Showt h a tt h eamb i p o l a rd i f f u s i o nc o e f f i c i e n tt ob eu s e da b o v ec a nb ea p p r o x i ュ matedbyD"" ( b )N e g l e c t i n gr e c o m b i n a t i o nandl o s s e sfromt h ee n d so ft h ec o l u m n ,compute t h ec o n f i n e m e n tume1 ' . 5 ‑ 5 .F o rt h ed e n s i t ypro日 le o fF i g .5田7, d e r i v eane x p r e s s i o nf o rt h ep e a kd e n s i t y n0i nt e r m so ft h es o u r c es t r e n g t hQ andt h eo t h e rp a r a m e t e r so ft h ep r o b l e m . ( H i n t :E司uate t h es o u r c ep e rm2t ot h ep a r t i c l ef l u xt ot h ew a l l sp e rm 2 . } 5 ‑ 6 . Youdoar e c o m b i n a t i o ne x p e r i m e n ti naw e a k l yi o n i z e dg a si nwhicht h e mainl o s smechanismi sr e c o m b i n a t i o n .Youc r e a t eap l a s m ao fd e n s i t y1 0 2 0m 3 byasuddenb u r s to fu l t r a v i o l e tr a d i a t i o nando b s e r v et h a tt h ed e n s i t yd e c a y s t oh a l fi t si n i t i a lv a l u ei n1 0m s e c . Whati st h ev a l u eo ft h er e c o m b i n a t i o n c o e f f i c i e n ta?G i v eu n i t s . 5.6 COLLISIONSINFULLY IONIZED PLASMAS Whent h eplasmai scomposedo fi o n sande l e c t r o n sa l o n e ,a l lc o l l i s i o n s a r eCoulombc o l l i s i o n sbetweenchargedp a r t i c l e s .However,t h e r ei sa d i s t i n c td i f f e r e n c ebetween( a )c o l l i s i o n sbetweenl i k ep a r t i c l e s( i o n ‑ i o n ore l e c t r o n ‑ e l e c t r o nc o l l i s i o n s )and( b )c o l l i s i o n sbetweenu n l i k ep a r t i c l e s ( i o n ‑ e l e c t r o nore l e c t r o n ‑ i o nc o l l i s i o n s ) .Considertwoi d e n t i c a lp a r t i c l e s fi ti sahead‑onc o l l i s i o n ,t h ep a r t i c l e semergewith c o l l i d i n g(Fig. ふ 16). I t h e i rv e l o c i t i e sr e v e r s e d ;t h e ysimplyinterchanget h e i ro r b i t s ,andt h e よ』 \\ γ「一一 1 7 8 Wecanw r i t eP , .i ntermso ft h ec o l l i s i o nfrequencyi nt h eu s u a l mannerキ Chαpter F i v e P , ,=叩n(v; ‑ v , } v , ; ,ダー ands i m i l a r l yf o rP ; , .S i n c et h ec o l l i s i o n sa r eCoulombc o l l i s i o n s ,one would e x p e c tP , ; to bep r o p o r t i o n a lt ot h e Coulombf o r c e , whichi s p r o p o r t i o n a lt oe 2( f o rs i n g l ychargedi o n s ) .Furthermore,P , .mustbe ,andt ot h ed e n s i t yo fs c a t t e r i n g p r o p o r t i o n a lt ot h ed e n s i t yo fe l e c t r o n sn c e n t e r sn ; ,w h i c h ,o fc o u r s e ,i se q u a lton,. F i n a l l y ,P , ;shouldbeproporュ t i o n a lt ot h er e l a t i v ev e l o c i t yo ft h etwof l u i d s . On p h y s i c a lgrounds, t h e n ,wecanw r i t eP , ;a s \\ / t ) ' ¥ , γ 、、、 ,' .、. I キ , l I /’ \\、、--/ \ / \ / P , ;= ηe2n2(v;-v,} whereηis ac o n s t a n to fp r o p o r t i o n a l i t y .Comparingt h i sw i t hE q .[ 5 ‑ 6 0 ] , wes e et h a t 、ー-- h i f to fg u i d i n gc e n t e r so f two FIGURE5‑17 S o p p o s i t e l yc h a r g e dp a r t i c l e smakュ i n ga180。 collision. [5 ・ 62] 5 . 6 . 1 PlasmaResistivity Theconstantηis t h especi五c r e s i s t i v i t yo ft h ep l a s m a ;t h a tt h i sj i b e sw i t h t h eu s u a lmeaningo fr e s i s t i v i t yw i l lbecomec l e a rs h o r t l y . fc h a r g e d ‑ p a r t i c l e Thef l u i de q u a t i o n so fmotioni n c l u d i n gt h eE征ects o c o l l i s i o n smaybew r i t t e na sf o l l o w s(cf 目 Eq. [3 ・47]): . 6 . 2 Mechanicso fCoulombC o l l i s i o n s 5 M : i~ = en(E+v;× B) ‑V p;‑Vキ' I T ;+P. d t d t [ 5 ‑ 6 1 ] 。 B \ ‘ / η 生= [ 5 ‑ 6 0 ] Whenane l e c t r o nc o l l i d e sw i t han e u t r a latom,nof o r c ei sf e l tu n t i lt h e h eatom on t h es c a l eo fatomicd i m e n s i o n s ;t h e e l e c t r o ni sc l o s e to t c o l l i s i o n sa r el i k eb i l l i a r d ‑ b a l lc o l l i s i o n s .Whenane l e c t r o nc o l l i d e sw i t h ani o n ,t h ee l e c t r o ni sg r a d u a l l yd e f l e c t e dbyt h elong田range Coulomb f i e l do ft h ei o n .N o n e t h e l e s s ,onecand e r i v eane f f e c t i v ec r o s ss e c t i o n f o rt h i s kind o fc o l l i s i o n .I tw i l ls u f f i c ef o rour purposes t og i v e an order‑of‑magnitudee s t i m a t eo ft h ec r o s ss e c t i o n .InFig. ふ 18, ane l e c t r o n .I nt h eabsenceo fCoulomb o fv e l o c i t yvapproachesaf i x e di o no fchargee f o r c e s ,t h ee l e c t r o nwouldhavead i s t a n c eo fc l o s e s tapproachr 0 ,c a l l e d nt h epresenceo faCoulomba t t r a c t i o n ,t h ee l e c t r o n t h eimpactparameteγ. I w i l lbed e f l e c t e dbyana n g l ex .whichi sr e l a t e dtoγ0・ The Coulombf o r c e i s [ 5 ‑ 5 8 ] ‑en(E+v ,xB) Vp,‑V キ ' I T , +P , , 一ゲ’ 一4 一- o 一刑 」』 e [ 5 ‑ 5 9 ] 2 一一 P ; .= -P目 F ThetermsP ; ,andP , ;r e p r e s e n t ,r e s p e c t i v e l y ,t h emomentumg a i no f t h ei o nf l u i dcausedbyc o l l i s i o n sw i t he l e c t r o n s ,andv i c ev e r s a .The s t r e s st e n s o rP ;h且s beens p l i ti n t ot h ei s o t r o p i cp a r tP ;andtheanisotropic v i s c o s i t ytensor 官1・ Like-particle c o l l i s i o n s ,whichg i v er i s et os t r e s s e s i n c et h e s ec o l l i s i o n s w i t h i neachf l u i di n d i v i d u a l l y ,a r ec o n t a i n e di nτr;. S don o tg i v er i s et omuchd i f f u s i o n ,wes h a l li g n o r et h etermsv ・甘i· As f o rt h etermsP , ;andP ; . ,whichr e p r e s e n tt h ef r i c t i o nbetweent h etwo f l u i d s ,t h ec o n s e r v a t i o no fmomentumr e q u i r e s [ 5 ‑ 6 3 ] 1 7 9 D i f f u s i o nand R e s i s t i v i t y ず「 180 C h a p t e r F i v e ~, Equation( 5 ‑7 0 ]i st h er e s i s t i v i t ybasedonl a r g e ‑ a n g l ec o l l i s i o n salone ・ I np r a c t i c e ,becauseo ft h el o n grangeo ft h eCoulombf o r c e ,small ” angle c o l l i s i o n sa r emuchmoref r e q u e n t ,andt h ec u m u l a t i v ee f f e c to fmany fl a r g e ‑ a n g l e s m a l l ‑ a n g l ed e f l e c t i o n st u r n so u tt obel a r g e rthant h ee圧ect o u l t i p l i e d c o l l i s i o n s .I twasshownbyS p i t z e rt h a tE q .(5句70] shouldbem byaf a c t o rl nA : 181 D i f f u s i o nand R e s i s t i v i t y 21 / 2 η = ‑ " " ' " I nA ( 5 ‑ 7 1 ] (4π·ea)"(KT,)"'" where Thisf a c t o rr e p r e s e n t st h emaximumimpactp a r a m e t e r ,i nu n i t sofγ0 a s g i v e n by E q .[ 5 ‑ 6 6 ] , averaged over a Maxwellian d i s t r i b u t i o n . The maximumimpactparameteri st a k e nt obeλD becauseDebyes h i e l d i n g s u p p r e s s e st h eCoulombf i e l da tl a r g e rd i s t a n c e s .AlthoughA depends onnandKT,,i t sl o g a r i t h mi si n s e n s i t i v et ot h ee x a c tv a l u e so ft h eplasma p a r a m e t e r s .T y p i c a lv a l u e so fl nA a r eg i v e nb e l o w . Thisf o r c ei sf e l tduringt h et i m et h ee l e c t r o ni si nt h ev i c i n i t yo ft h e i o n ;t h i st i m ei sroughly T zγ。/ v ( 5 ‑ 7 2 ] A = λn /γ。 FIGURE5 ‑ 1 8 O r b i to fa ne l e c t r o nmakingaCoulombc o l l i s i o nw i t ha ni o n . [ 5 ‑ 6 4 1 Thechangei nt h eelectron’s momentumi st h e r e f o r eapproximately 2 t l ( m v )=fFTI z 一三一一 ’ 4m',> rov [ 5 ‑ 6 5 ] KT,(e¥') n(m 3 ) I nA IO" IO" 9 . 1 1 0 . 2 1 3 .7 1 6 . 0 6 . 8 l 0 . 2 Wewisht oe s t i m a t et h ec r o s ss e c t i o nf o rl a r g e ‑ a n g l ec o l l i s i o n s ,i nwhich x~ 90ー.Fora90。 collision, thechangeinmvi so ft h eordero fmvi t s e l f . Thus ム(mv )= 叩U 呈 e2/4wε0r0v, r0=e2/47rεomv2 9 1 0 0 I O " I O " (5・ 66] Thec r o s ss e c t i o ni sthen ' 2 2 4 σ = πr0=e4/167rεom v 1 0 2 ' 1 0 2 7 I ti se v i d e n tt h a tl nAv a r i e so n l yaf a c t o ro ftwoa st h eplasmaparameters rangeo v e r manyo r d e r so fmagnitude. Formostp u r p o s e s ,i tw i l lbe s u f f i c i e n t l ya c c u r a t et ol e tl nA =I 0r e g a r d l e s so ft h et y p eo fplasma i n v o l v e d . [ 5 ‑ 6 7 ] Thec o l l i s i o nfrequencyi s ,t h e r e f o r e , ν"= η回= ne4/16m; ~m2v3 I O ' " ( 5 ‑ 6 8 ] andt h er e s i s t i v i t yi s 作E e2 η =一一吉"" =一一一言一一吉 ηe 167rε omv ( Q ‑ m a c h i n e ) ( l a bp l a s m a ) ( t y p i c a lt o r u s ) ( f u s i o nr e a c t o r ) ( l a s e rp l a s m a ) P h y s i c a lMeaningofη [ 5 ‑ 6 9 ] L e tu ssupposet h a tane l e c t r i cf i e l dE e x i s t si naplasmaandt h a tt h e c u r r e n tt h a ti td r i v e si sa l lc a r r i e dbyt h ee l e c t r o n s ,whicha r emuchmore ,s ot h a tV キP ,=0 .Then, mobilethant h ei o n s .L e tB =0andKT,= 0 i ns t e a d ys t a t e ,t h ee l e c t r o ne q u a t i o no fmotion[ 5 ‑ 5 8 ]r e d u c e st o ForaMaxwelliand i s t r i b u t i o no fe l e c t r o n s ,wemayr e p l a c ev2byKT,/m f o rourorder‑of‑magnitudee s t i m a t e : 2 1 / 2 T r em [ 5 ‑ 7 0 ] η ""'(47rt:o)2(KT,)312 enE= P , . 」』 ( 5 ‑ 7 3 1 5 . 6 . 3 マF← 182 C h a p t e r F i v e S i n c ej= eη (v, ‑v , ) ,E q .( 5 ‑ 6 1 )canbew r i t t e n P目= ηeπj (5・74] 一\ s ot h a tE q .[ 5 ‑ 7 3 )becomes E = ηj ( 5 ‑ 7 5 ] Thisi ss i m p l yOhm’s l a w ,andt h econstantηis j u s tt h es p e c i f i cr e s i s t i v i t y . l a s m a ,a sg i v e nbyE q .[ 5 ‑ 7 1 )o rE q .( 5 ‑ 6 9 ) , Thee x p r e s s i o nf o rηin ap h a ss e v e r a lf e a t u r e swhichshouldbep o i n t e do u t . fd e n s i t y( e x c e p tf o r ( A )I nE q .( 5 ‑ 7 1 ) ,wes e et h a tηis iηdepend叩t o ) .T hisi sar a t h e rs u r p r i s i n gr e s u l t ,s i n c e t h eweakdependencei nI nA i tmeanst h a ti faf i e l dE i sa p p l i e dt oap l a s m a ,t h ec u r r e n tj ,as 耳iven byE q .( 5 ‑ 7 5 ) ,i sindependento ft h enumbero fchargec a r r i e r s .The r e a s o ni st h a talthoughji n c r e a s e sw i t hη" t h ef r i c t i o n a ldraga g a i n s tt h e ; .S i n c e同= n ; ,t h e s etwoe f f e c t sc a n c e l .Thisc a n c e l l a ュ i o n si n c r e a s e sw i t hn t i o ncanbes e e ni nE q s .( 5 ‑ 6 8 )and[ 5 ‑ 6 9 ) .Thec o l l i s i o nfrequencyv , ;i s a n c e l souti nη. Af u l l yi o n i z e d indeedp r o p o r t i o n a lt o n ,butt h ef a c t o rnc o n i z e donei nt h i sr e s p e c t . plasmabehavesq u i t edi 征erently fromaweaklyi n e v . ,v ,=一 ,u,E, s ot h a tj= I naweaklyi o n i z e dp l a s m a ,wehavej= ‑ n e , u , E .S i n c e, u ,dependso n l yont h ed e n s i t yo fn e u t r a l s ,t h ec u r r e n ti s . p r o p o r t i o n a lt ot h eplasmad e n s i t yn ‑3/2 ( B )E quation( 5 ‑ 7 1 )showsthatηis p r o p o r t i o n a lt o(KT,) .Asa plasmai sh e a t e d ,t h eCoulombc r o s ss e c t i o nd e c r e a s e s ,andt h er e s i s t i v i t y dropsr a t h e rr a p i d l yw i t hi n c r e a s i n gt e m p e r a t u r e .Plasmasa tthermonuュ c l e a rtemperatures( t e n so fk eV)a r ee s s e n t i a l l yc o l l i s i o n l e s s ;t h i si st h e r e a s o ns omucht h e o r e t i c a lr e s e a r c hi sdoneonc o l l i s i o n l e s sp l a s m a s .Of c o u r s e ,t h e r emusta l w a y sbesomec o l l i s i o n s ;o t h e r w i s e ,t h e r ewouldn o t be 且ny f u s i o nr e a c t i o n se i t h e r .Ane a s ywayt oh e a taplasmai ss i m p l y t op a s sac u r r e n tthroughi t .TheI2R( o rj2η ) l o s s e sthent u r nupa san i n c r e a s ei ne l e c t r o nt e m p e r a t u r e . This i sc a l l e do h m i c heating・ The ( K T , ) ‑ 3 1 2dependenceofη, however, d oesnota l l o wt h i smethodt obe usedupt othermonucleart e m p e r a t u r e s .Theplasmabecomessucha goodconductora ttemperaturesabove 1keVt h a tohmich e a t i n gi sa v e r ys l o wp r o c e s si nt h a tr a n g e . ( C )Equation(5 ” 68) showst h a tv , ;v a r i e sa sv ‑ 3 .Thef a s te l e c t r o n s i nt h et a i lo ft h ev e l o c i t yd i s t r i b u t i o n makev e r yfew collisions 目 The c u r r e n ti st h e r e f o r ec a r r i e dmainlybyt h e s ee l e c t r o n sr a t h e rthanbyt h e b u l ko ft h ee l e c t r o n si nt h emainbodyo ft h ed i s t r i b u t i o n .Thes t r o n g a sanotheri n t e r e s t i n gconsequence. I fane l e c t r i c dependenceonv h f i e l di ssuddenlya p p l i e dt oap l a s m a ,aphenomenonknowna se l e c t r o n γuηa叫ay c ano c c u r .A fewe l e c t r o n swhichhappent obemovingf a s ti n \ t h ed i r e c t i o no f Ewhent h ef i e l di sa p p l i e dw i l lhaveg a i n e ds omuch energyb e f o r eencounteringani o nt h a tt h e ycanmakeo n l yag l a n c i n g c o l l i s i o n .Thisa l l o w sthemt op i c kupmoreenergyfromt h eelectric 五eld andd e c r e a s et h e i rc o l l i s i o nc r o s ss e c t i o n even f u r t h e r .I fE i sl a r g e enough,t h ec r o s ss e c t i o nf a l l ss of a s tt h a tt h e s erunawaye l e c t r o n snever makeac o l l i s i o n .Theyformana c c e l e r a t e de l e c t r o nbeamdetachedfrom t h emainbodyo ft h ed i s t r i b u t i o n . NumericalValuesofη E x a c tcomputationsofηwhich t a k ei n t oaccountt h ei o nr e c o i li neach c o l l i s i o nanda r ep r o p e r l yaveragedovert h ee l e c t r o nd i s t r i b u t i o nwere f i r s tg i v e nbyS p i t z e r .Thef o l l o w i n gr e s u l tf o rhydrogeni ssometimes c a l l e dt h eS p i t z e rr e s i s t i v i t y : , ZlnA 1 (eV) 川= 5.2 × 10ーコーす72,一一一 ohm-m [ふ76] HereZi st h ei o nchargenumber,whichwehavet a k e nt obe1e l s e w h e r e i nt h i sb o o k .S i n c et h edependenceonM i sweak,t h e s ev a l u e scana l s o beusedf o rotl町 gases. Thes u b s c r i p t1meanst h a tt h i sv a l u eofηis t o e r p e n d i c u l a rt oB,one beusedf o rmotionsp a r a l l e lt oB.Formotionsp shoulduseη ょ gi 、 en by η ょ= 2.0ηH ( 5 ‑ 7 7 ] Thisdoesn o tmeant h a tconduct川 ty alongB i so n l ytwot i m e sb e t t e r .A f a c t o rlil< e w;T2s t i thancond叩iv町 across B a c c o u n t .Thef a c t o r2 . 0comesfromadi 百erence i nw e i g h t i n go ft h e v a r i o u sV巴 locities i nt h ee l e c t r o nd i s t r i b u t i o n .I np e r p e n d i c u l a rm o t i o n s , m a l lLarmorr a d i i ,c o n t r i b u t emoret o t h es l o we l e c t r o n s ,whichh おe s t h er e s i s t i ¥ ' i t ythani np a r a l l e lm o t i o n s . q .[ 5 ‑ 7 6 )y i e l d s ForKT,= 100eV,E η = 5x1 0 ‑ 7ohm‑m Thisi st obecomparedw i t hv a r i o u sm e t a l l i cc o n d u c t o r s : copper ...........η = 2x1 0 8ohm‑m 0 ‑ 7ohm‑m s t a i n l e s ss t e e l........ η = 7x1 mercury ............η = 10‑6ohm‑m A 100‑eVp l a s m a ,t h e r e f o r e ,h a sac o n d u c t i v i t yl i k et h a to fs t a i n l e s ss t e e l . ム』 183 D i f f u s i o na n d R e s i s t i v i t y 5 . 6 . 4 ?「 184 5 . 7 THESINGLE‑FLUIDMHDEQUATIONS f o rt h et o t a lp r e s s u r e .Witht h eh e l po fE q s .[ 5 ‑ 7 8 ] ‑ [ 5 ‑ 8 0 ] ,E q .[ 5 ‑ 8 3 ]can bew r i t t e ns i m p l y Cha世teγ z ‘’ M+m j=e ( n ; v ; n , v , )=n e ( v ;‑v , ) I S [5・ 78] Mmn~ 何 v,) =川 [5・ 79] + MV丸一(M+m)P,. [5・ 80] [ 5 ‑ 8 1 ] 間n ~ =‑en(E+v ,XB )‑Vp,+削 g+ P , ; [5・ 82] : V t m n aIi¥ っ- at \~)= epE ー(品I+m)1問 j-m V p,+M'Vp, 。t 。t ¥ 1 v ;+mv,+M(v,‑v;)+m(v;‑v,) mv;+ i ' W v ,=1 =f!_v-(M 一間)よ ηηe +p, [ 5 ‑ 8 8 ] D i v i d i n gE q .[ 5 ‑ 8 7 ]bye p ,wenowh ave E+v × B 一 ηj 1 fM刑n a (j¥ l =‑ : ‑ 1: . . : . : . : . : ̲‑ ( ‑) +(M 一明)j xB+m Vp,‑M Vp,I eoL e a t¥nI I Thea / a ttermcanbeneglectedi ns l o wm o t i o n s ,wherei n e r t i a l( i . e . , c y c l o t r o nf r e q u e n c y )e f f e c t sa r eunimportant.I nt h el i m i tm /M • 0, Eq. [ 5 ‑ 8 9 ]thenbecomes [5・83] Thee l e c t r i cf i e l dh a sc a n c e l l e do u t ,a shavet h ec o l l i s i o ntermsP , ;=‑ P . , . Wehaveintroducedt h en o t a t i o n 戸 = p; [ 5 ‑ 8 7 ] Thel a s ttermcanbes i m p l i f i e da sf o l l o w s : Fors i m p l i c i t y ,wehaven e g l e c t e dt h ev i s c o s i t ytensorτ , as wed i dearlier 目 Thisn e g l e c tdoesnoti n c u rmuche r r o ri ft h eLannorr a d i u si smuch s m a l l e rthant h es c a l el e n g t hoverwhicht h ev a r i o u sq u a n t i t i e sc h a n g e . Wehavea l s on e g l e c t e dt h e( vキ V)vtermsbecauset h ed e r i v a t i o nwould be u n n e c e s s a r i l yc o m p l i c a t e do t h e r w i s e . This s i m p l i f i c a t i o ni s more di伍cult t oj u s t i f y .Toa v o i dal e n g t h yd i s c u s s i o n ,wes h a l ls i m p l ys a yt h a t v i sassumedt obes os m a l lt h a tt h i sq u a d r a t i ctermi sn e g l i g i b l e . WenowaddE q s .[ 5 ‑ 8 1 ]and[ 5 ‑ 8 2 ] ,o b t a i n i n g η~ (Mv;+mv,)=en(v;-v,)× B ‑Vp+n(M+m)g [ 5 ‑ 8 6 ] Witht h eh e l po fEqs ・[ 5-78], [ 5 ‑ 8 0 ] ,and[ 5 ‑ 6 1 ] ,t h i sbecomes +en(mv;+i v f v , )xB Mn~ = en(E+v,XB)‑Vp,+M:時十 P;, [ 5 ‑ 8 5 ] Thisi st h es i n g l e ‑ f l u i de q u a t i o no fmotiond e s c r i b i n gt h emassf l o w .The electric 白eld d oesn o tappeare x p l i c i t l yb e c a u s et h ef l u i di sn e u t r a l .The t h r e ebodyf o r c e sont h er i g h t ‑ h a n ds i d ea r ee x a c t l ywhatonewould havee x p e c t e d . Al e s so b v i o u se q u a t i o ni so b t a i n e d byt a k i n g ad i f f e 1e n tl i n e a r combinationo ft h et w o ‑ f l u i de q u a t i o n s .L e tu sm u l t i p l yE q .[ 5 ‑ 8 1 ]bym andE q .[ 5 ‑ 8 2 ]byM ands u b t r a c tt h el a t t e rfromt h ef o r m e r .Ther e s u l t I nt h ee q u a t i o no fm o t i o n ,wes h a l laddatermMngf o rag r a v i t a t i o n a l f o r c e .Thistermcanbeusedt or e p r e s e n tanynonelectromagneticf o r c e h ep l a s m a .Thei o nande l e c t r o ne q u a t i o n scanbew r i t t e n a p p l i e dtot 。t σb p 、‘・ R e s i s t i v i t y + n F Mv;+mv, V 三一(n,Mv,+ η,mv,)=一一」一一一一よ ム V- ""n(M+m) ., Ed V + η,m - ラ p=n;M - o B h eproblemo fdi狂usion i naf u l l yi o n i z e dp l a s m a . Wenowcometo t n、elocities v ,‑v , , S i n c et h ed i s s i p a t i v etermP , ;c o n t a i n st h edi百erence i i ti ss i m p l e rt oworkw i t hal i n e a rcombinationo ft h ei o nande l e c t r o n e q u a t i o n ssucht h a tv ;‑v ,i st h eunknownr a t h e rthanv ,o rv ,s e p a r a t e l y . Upt onow,wehaveregardedaplasmaa scomposedo ftwointerpenetraト i n gf l u i d s .Thel i n e a rcombinationwea r egoingtochoosew i l ld e s c r i b e t h eplasmaa sas i n g l ef l u i d ,l i k el i ' q u i dmercury,w i t hamassd e n s i t yp andane l e c t r i c a lc o n d u c t i v i t yI/ri ・ These a r et h ee q u a t i o n so fmagnetohyュ drodynamics(MHD). Foraq u a s i n e u t r a lplasmaw i t hs i n g l ychargedi o n s ,wecand e f i n et h e massd e n s i t yp ,massv e l o c i t yv ,andc u r r e n td e n s i t yja sf o l l o w s : M一ud F i v e E+vXB = ηj +土( j xB‑Vp,) e n [5・ 84] 」」 185 Diffi山ion aηd [ 5 ‑ 9 0 ] τ 186 Chapleγ F i v e whichi st h eo r d i n a r yOhm’s l a w .Thep e r p e n d i c u l a rcomponenti sfound byt a k i n gt h ec r o s s ‑ p r o d u c tw i t hB : Thisi sourseconde q u a t i o n ,c a l l e dt h eg e n e r a l i z e dOhm'sl a w .I td e s c r i b e s t h ee l e c t r i c a lp r o p e r t i e so ft h econductingf l u i d .ThejxBtermi sc a l l e d a l lcurγ四t t e r m .I to f t e nhappenst h a tt h i sandt h el a s tterma r e t h eH sthens i m p l y s m a l lenought oben e g l e c t e d ;Ohm ’s lawi 一、\ \ ExB+(vム x B )× B = η ょj xB = η ょ Vp ExB-vょB2 = η ょ Vp E+vXB = ηj [5 ・91] EXB 明 Vム=ー了一一吉町 E q u a t i o n so fc o n t i n u i t yf o rmassp andchargeσare e a s i l yo b t a i n e d from t h e sum and d i f f e r e n c eo ft h ei o n and e l e c t r o ne q u a t i o n so f c o n t i n u i t y .Thes e to fMHDe q u a t i o n si sthena sf o l l o w s : b -一γ ペパυ 一角付 υ hF 一一 a t [5 ・ 97] Thef l u xa s s o c i a t e dw i t hdi百usion i s rη .cn(KT, +KT,) ー 。σ ー+ V·j=O U [5司 92] L一B [ 5 ‑ 9 1 ] =0 [5品l e l o c i t yi nt h ed i r e c t i o no f‑Vp.Fori n s t a n c e ,i nan termi st h edi 庄usion v axisymmetricc y l i n d r i c a l plasmai nwhichE andV戸 are i nt h er a d i a l d i r e c t i o n ,wewouldhave , a 一一 a t B The 自 rst t ermi sj u s tt h eExBd r i f to fboths p e c i e st o g e t h e r .Thesecond U ー+ v ・(pv) nδ E+vxB = ηj a p r a o - g h o AY V B ・- X 一一 n v 加一M + B ょ = n vょ= ‑ [5 ・93] B2 vn [ 5 ‑ 9 8 ] Thish a st h eformo fFick’s l a w ,E q .[ 5 ‑ 1 1 ] ,w i t ht h ed i f f u s i o nc o e f f i c i e n t Togetherw i t hMaxwell ’s e q u a t i o n s ,t h i ss e ti so f t e nusedt od e s c r i b et h e e q u i l i b r i u ms t a t eo ft h ep l a s m a .I tcana l s obeusedt od e r i v eplasma w a v e s ,buti ti sc o n s i d e r a b l yl e s sa c c u r a t ethant h et w o ‑ f l u i de q u a t i o n s wehavebeenu s i n g .Forproblemsi n v o l v i n gr e s i s t i v i t y ,t h es i m p l i c i t yo f t h eMHDe q u a t i o n soutweighst h e i rd i s a d v a n t a g e s .The:VfHDe q u a t i o n s havebeenusede x t e n s i v e l ybya s t r o p h y s i c i s t sworkingi ncosmice l e c t r o d y ュ n a m i c s ,byhydrodynamicistsworkingonMHDenergyc o n v e r s i o n ,and byf u s i o nt h e o r i s t sworkingw i t hc o m p l i c a t e dmagneticg e o m e t r i e s . 5.8 DIFFUSIONINFULLYIONIZED PLASMAS 5 ‑ 8 5 ]and[ 5 ‑ 9 1 ]f o ras t e a d ys t a t eplasma I nt h eabsenceo fg r a v i t y ,E q s .[ become jxB = Vp E+vxB = ηj [ 5 ‑ 9 4 ] [ 5 ‑ 9 5 ] Thep a r a l l e lcomponento ft h el a t t e re q u a t i o ni ss i m p l y E u= η11i11 一一一一」』』ー一一~一 Dη ムn"i.KT よ =ー B2 [5 ・ 99] Thisi st h eso-called “ classical ” diffusion c o e f f i c i e n tfor 旦 fully i o n i z e dg a s . r o p o r t i o n a lt oI /B2, j u s ta si nt h ec a s eo fweakly Notet h a tDム is p i f f u s i o nand i o n i z e dg a s e s .Thisdependencei s キc h a r a c t e r i s t i co fcl且ssical d canultim 呂tely bet r a c e dbackt ot h erandom-wall< process w i t has t e p l e n g t hrL・ Equation [ 5 ‑ 9 9 ] ,h owever,d i f f e r sfromE q .[ 5 ‑ 5 4 ]f o rap a r t i a l l y naf u l l y i o n i z e dg a si nt h r e ee s s e n t i a lw a y s .F i r s t ,D ょ is not α canstαnt i i o n i z e dg a s ;i ti sp r o p o r t i o n a lt o n .T hisi sb e c a u s et h ed e n s i t yo fs c a t t e r i n g c e n t e r si snotf i x e dbyt h en e u t r a latomd e n s i t ybuti st h eplasmad e n s i t y r o p o r t i o n a lt o(KT )• 12. Dム decreases w i t h i t s e l f .Second,s i n c eηis p i n c r e a s i n gtemperaturei naf u l l yi o n i z e dg a s .Theo p p o s i t ei st r u ei na p a r t i a l l yi o n i z e dg a s .Ther e a s o nf o rt h ed i f f e r e n c ei st h ev e l o c i t ydepenュ dence o ft h e Coulomb c r o s ss e c t i o n .T h i r d ,d i f f u s i o ni sa u t o m a t i c a l l y amb妙。 lar i n af u l l yi o n i z e dg a s( a slonga sl i k e ‑ p a r t i c l ec o l l i s i o n sa r e q .[ 5 ‑ 9 9 ]i st h ec o e f f i c i e n tf o rt h ee n t i r ef l u i d ; no n e g l e c t e d ) . Dょ in E ambipolare l e c t r i cf i e l da r i s e s ,becauseboths p e c i e sd i f f u s ea tt h esame r a t e .Thisi saconsequenceo ft h ec o n s e r v a t i o no fmomentumi ni o n ‑ 一一一一一 187 D i f f u s i o na n d R e s i s t i v i t y ーー『噂,,- 188 C h a p t e r F i v e where‑1/ri st h es e p a r a t i o nc o n s t a n t .Thes p a t i a lp a r to ft h i se q u a t i o n i sd i f f i c u l tt os o l v e ,butt h etemporalp a r ti st h esamee q u a t i o nt h a twe encounteredi nr e c o m b i n a t i o n ,E q .[ 5 ‑ 4 1 ] .Thes o l u t i o n ,t h e r e f o r e ,i s e l e c t r o nc o l l i s i o n s .Thisp o i n ti ssomewhatc l e a r e ri fonesu s e st h et w o ュ f l u i de q u a t i o n s( s e eProblem5 ‑ 1 5 ) . F i n a l l y ,wew i s ht op o i n toutt h a ttheγe i snotγαn.meγse m o b i l i t yi na f u l l yi o n i z e dg a s .Equation[ 5 ‑ 9 6 ]f o rVム contains nocomponentalong fat r a n s v e r s eE f i e l di sa p p l i e dt oauniform E whichdependsonE .I p l a s m a ,boths p e c i e sd r i f tt o g e t h e rw i t ht h eExB v e l o c i t y .S i n c et h e r e i snor e l a t i v ed r i f tbetweent h etwos p e c i e s ,t h e ydonotc o l l i d e ,andt h e r e i snod r i f ti nt h ed i r e c t i o no fE .Ofc o u r s e ,t h e r ea r ec o l l i s i o n sduet o thermalm o t i o n s ,andt h i ss i m p l er e s u l ti so n l yanapproximateo n e .I t comesfromourn e g l e c to f( a )l i k e ‑ p a r t i c l ec o l l i s i o n s ,( b )t h ee l e c t r o n m a s s ,and( c )t h el a s ttwotermsi nOhm ’s l a w ,E q .( 5 ‑ 9 0 ] . 1 1 t T To T -ー=一一+- 189 D i f f u s i o nand R e s i s t i v i t y (5 ・ 104] Atl a r g et i m e st ,t h ed e n s i t yd e c a y sa sl / t ,a si nt h ec a s eo fr e c o m b i n a t i o n . Thisr e c i p r o c a ldecayi swhatwouldbeexpectedo faf u l l yi o n i z e dplasma d i f f u s i n gc l a s s i c a l l y .Thee x p o n e n t i a ldecayo faweaklyi o n i z e dg a si sa d i s t i n c t l yd i f f e r e n tb e h a v i o r . Time” Independent S o l u t i o n s 5 . 9 . 2 q u a t i o ncanbes o l v e ds i m p l y . Therei sonec a s ei nwhicht h edi妊usion e Imaginealongplasmacolumn( F i g .5 ‑ 1 9 )w i t has o u r c eont h ea x i swhich e c o m b i ュ m a i n t a i n sas t e a d ys t a t ea splasmai sl o s tbyr a d L i ldi 圧usion andr nation 目 The d e n s i t yp r o f i l eo u t s i d et h es o u r c er e g i o nw i l lbedetermined byt h ec o m p e t i t i o nbetweend i f f u s i o nandr e c o m b i n a t i o n .Thed e n s i t y fallo 百 distance w i l lbes h o r ti fdi百usion i ss m a l landrecombin亘tion i s l a r g e ,andw i l lbelongi nt h eo p p o s i t ec a s e .I nt h er e g i o no u t s i d et h e s o u r c e ,t h ee q u a t i o no fc o n t i n u i t yi s 5 . 9 SOLUTIONSOFTHEDIFFUSIONEQUATION S i n c eDょ is n o tac o n s t a n ti naf u l l yi o n i z e dg a s ,l e tu sde 自 ne aq u a n t i t y Aw hichi sc o n s t a n t : ( 5 ‑ 1 0 0 ] A EηKT/B2 Wehaveassumedt h a tK TandB a r euniform,andt h a tt h edependence ofηon n t hrought h el nA f a c t o rcanbei g n o r e d .Fort h ec a s eT ,= T , . wethenhave Dム= 2nA ‑AV2n2=-aη (5 ・ 101] a s i l ybes o l v e d .I nc y l i n d r i c a l Thise q u a t i o ni sl i n e a ri nn2andc証n e g e o m e t r y ,t h es o l u t i o ni saB e s s e lf u n c t i o n .I np l a n egeometry,E q .[ 5 ‑ 1 0 5 ] r e a d s Thee q u a t i o no fc o n t i n u i t y[ 5 ‑ 9 2 ]cannowbew r i t t e n 。η / at= Vキ(D ょ Vn) = A V キ( 2 nVn) 3η / at= A V 2n2 。2 ηα 2 (5 ・ 102] ←斗/|! \ 5 . 9 . 1 TimeDependence I fwes e p a r a t et h ev a r i a b l e sbyl e t t i n g T ( t ) S ( r ) wecanw r i t eE q .[ 5 ‑ 1 0 2 ]a s 1 dT A 一τ 一一= T' d t o o ‑ v キ s キ= s 1 ‑ 。 。 ( 5 ‑ 1 0 6 ] 五す = An Thisi san o n l i n e a re q u a t i o nf o rn ,f o rwhicht h e r ea r ev e r yfews i m p l e s o l u t i o n s . η = ( 5 ‑ 1 0 5 ] ( 5 ‑ 1 0 3 ] 8 -ー』 .-..-.‑‑ . . . .-・ ... ..... . ’.・・.-.・.・.-.エ.・ ..・.・・.・ .. . . -. ・. .・ . .・ー ・二. ..・ ・ ・ .・ゐ ・ν ・.・イム・:-.・ •••••••• .... ・・...目・・・・・・ ・..目・...・ ・・ ・・・・・・. ・ -ー.-・.. .--・・・ .・.・ ・・ ..一.- ・.・-・・.+ ー. D i f f u s i o no faf u l l yi o n i z e dc y l i n d r i c a lplasmaa c r o s sam a g n e t i cf i e l d . FIGURE5 ‑ 1 9 T ~ーー ーー『明司.,田-ー一一 190 w i t ht h es o l u t i o n Cha,骨teγ η2 = n~ e xp[一 (a/A)112 x ] F i v e [ 5 ‑ 1 0 7 ] •~ Thes c a l ed i s t a n c ei s l=(A /臼) 1 / 2 ( 5 ‑ 1 0 8 ] N S i n c eA changesw i t hmagneticf i e l dwhile 臼 remains c o n s t a n t ,t h echange i t hB c o n s t i t u t e sachecko fc l a s s i c a ldi 釘usion. Thisexperiment o flw wasa c t u a l l yt r i e donaQ‑machine,whichp r o v i d e saf u l l yi o n i z e dp l a s m a . r i f t sl e a d i n gt o U n f o r t u n a t e l y ,t h ep r e s e n c eo f asymmetric EラB d anothert y p eo floss‑byconvection‑madet h eexperimenti n c o n c l u s i v e . F i n a l l y ,wewisht op o i n toutas c a l i n glawwhichi sa p p l i c a b l et oany f u l l yi o n i z e ds t e a d ys t a t eplasmamaintainedbyac o n s t a n ts o u r c eQ i n i e l d .Thee q u a t i o no fc o n t i n u i t ythenr e a d s auniformB f A \72η2 = γ1KT\72(n2/B2)=Q nR 2D8an/aγ2Dsη / R R2 =•n 2Ds ( 5 ‑ 1 1 2 ] Theq u a n t i t yT si so f t e nc a l l e dt h eBohmt i m e . Perhapst h emoste x t e n s i v es e r i e so fexperimen 凶 verifying t h eBohm formulawasdoneonah a l f ‑ d o z e nd e v i c e sc a l l e ds t e l l a r a t o r sa tP r i n c e t o n . As t e l l a r a t o ri sat o r o i d a l magneticc o n t a i n e rw i t ht h el i n e so ff o r c e t w i s t e ds oa st oaverageoutt h egrad‑B andc u r v a t u r ed r i f t sd e s c r i b e d i nS e c t i o n2 . 3 .F i g u r e5 ‑ 2 0showsac o m p i l a t i o no fd a t at a k e no v e ra decadeonmanyd i f f e r e n tt y p e so fd i s c h a r g e si nt h eModelCS t e l l a r a t o r . Themeasuredv a l u e so frl i enearal i n erepresenti 口g t h eBohmt i m e T s .C l o s eadherencet oBohmd i f f u s i o nwouldhaves e r i o u sconsequences f o rt h ec o n t r o l l e df u s i o n program. Equation [ 5 ‑ 1 1 1 ] shows t h a tDs i n c r e a s e s ,r a t h e r than d e c r e a s e s ,w i t ht e m p e r a t u r e , and though i t d e c r e a s e sw i t hB ,i td e c r e a s e smores l o w l ythane x p e c t e d .I na b s o l u t e sa l s omuchl a r g e rt h a nDムー For i n s t a n c e ,f o ral 0 0 ‑ eV magnitude,Dsi plasmai n1‑Tf i e l d ,wehave [5・ 109] l( 1 0 2 ) ( 1 . 6ラ 1 0 1行ワ 1 9 =6.25m"/sec ( 1 . 6x IO -'ョ) (1) =‑ 1 6 Althought h et h e o r yo fd i f f u s i o nv i aCoulombc o l l i s i o n shadbeenknown f o ralongt i m e ,l a b o r a t o r yv e r i f i c a t i o no ft h e1/B2dependenceo fDム i naf u l l yi o n i z e dplasmaeludeda l lexperimentersu n t i lt h e1 9 6 0 s .I n sB‑1,r a t h e rthanB ‑ 2 ,and a l m o s ta l lp r e v i o u se x p e r i m e n t s ,Dム scaled a t h edecayo fplasmaswasfoundt obee x p o n e n t i a l ,r a t h e rt h a nr e c i p r o c a l , a rl a r g e rthan w i t ht i m e .Furthermore,t h ea b s o l u t ev a l u eo fDム was f t h a tg i v e nbyE q .[ 5 ‑ 9 9 ) .Thisanomalouslypoormagneticconfinement was f i r s t noted i n 1946 by Bohm, Burhop, and M a s s e y , who were developingamagnetica r cf o ru s ei nuraniumi s o t o p es e p a r a t i o n .Bohm gavet h es e m i e m p i r i c a lformula ~ nR γ =一一一一一一一=一一一一一= 5.10 BOHM DIFFUSIONANDNEOCLASSICALDIFFUSION R 2 f , whereN i st h et o t a lnumbero fi o n ‑ e l e c t r o np a i r si nt h ep l a s m a .With t h ef l u xrγgiven byFick’s l a wandBohm’s f o r m u l a ,wehave ( 5 ‑ 1 1 0 ] ~ ηR dN/dt I ' , 2 7 T R L Onemighthaveexpectedt h ee q u i l i b r i u md e n s i t yn t os c a l ea sB 2 ,s i n c e Dょに B 2 ;butonemustremembert h a tDム is i t s e l fp r o p o r t i o n a lt on . D, KT ,= ' =1‑ ‑ ~ 1 6 eB n-rrR2L r =-一一一一=一一一一一一一=一一一 S i n c enandB occuro n l yi nt h ecombinationn /B,thedensityprofile schanged,andt h ed e n s i t yi t s e l fw i l li n c r e a s e w i l lremainunchangeda sB i l i n e a r l yw i t hB: n o : : . B \ Thisformulawasobeyedi nas u r p r i s i n gnumbero fd i f f e r e n te x p e r i ュ i f f u s i o n .S i n c eDni s m e n t s .D i f f u s i o nf o l l o w i n gt h i sl a wi sc a l l e dBohmd independento fd e n s i t y ,t h edecayi se x p o n e n t i a lw i t ht i m e .Thet i m e e n g t hLcanbee s t i m a t e d c o n s t a n ti nac y l i n d r i c a lcolumno fr a d i u sRandl a sf o l l o w s : I ft h ed e n s i t yi s1 0 1 9m •, the c l a s s i c a ld i f f u s i o ncoe伍cient i s D. 2nK乃ム(2)(101 行( l 0 2 ) ( ;. 6ラ 1 01 9 ) • =一一一 ‑ B" o r ×( 3.3)(5.2 × I0-5)(10) ( 1 0 0 ) 3 1 2 = ( 1 . 0 6ラ ! 0 3 ) ( 5 . 2xI 0 ‑ 7 )= 5 . 4 9ラ I 0 ‑ 4m2/sec Thedisagreementi sfouro r d e r so fmagnitude. S e v e r a le x p l a n a t i o n shavebeenproposedf o rBohmd i f f u s i o n .F i r s t , t h e r ei st h ep o s s i b i l i t yo f magnetic f i e l de r r o r s .I nt h ec o m p l i c a t e d [5 ・ 111] __....,,,,』 191 D i f f u s i o nand R e s i s t i v i t y 『司司司F’F 1 9 2 100 Cha戸leγ F i v e ' o ALKALI PLASMA (DATANORMALIZEDTO 1 2 . 3KG,5 . 0cmRADIUS) 一、 、 \ nunu (U由国E )ト盟主トトZ凶三凶ZEzoυ fromu n s t a b l eplasmaw a v e s .I ft h e s ef l u c t u a t i n gf i e l d sa r erandom,t h e ExB d r i f t sc o n s t i t u t eac o l l i s i o n l e s srandom‑walkp r o c e s s .Eveni ft h e o s c i l l a t i n gf i e l di sapures i n ewave,i tcanl e a dt oenhancedl o s s e sb e c a u s e t h ephaseo ft h eExB d r i f tcanbesucht h a tt h ed r i f ti sa l w a y soutward whenevert h ef l u c t u a t i o ni nd e n s i t yi sp o s i t i v e . Onemayregard t h i s s i t u a t i o na samovingc o n v e c t i v ec e l lp a t t e r n .F l u c t u a t i n ge l e c t r i cf i e l d s nmanyc a s e s , a r eo f t e nobservedwhent h e r ei sanomalousdi 狂usion, buti i tcanbeshownt h a tt h ef i e l d sa r en o tr e s p o n s i b l ef o ra l lo ft h el o s s e s . A l lt h r e eanomalousl o s smechanismsmaybep r e s e n ta tt h esamet i m e i nexperimentsonf u l l yi o n i z e dp l a s m a s . Thes c a l i n go fDsw i t hKT,andB cane a s i l ybeshownt obet h e n a t u r a lonewhenevert h el o s s e sa r ecausedbyExBd r i f t s ,e i t h e rs t a t i o n ュ r i f t a r yo ro s c i l l a t i n g .L e tt h ee s c a p ef l u xbep r o p o r t i o n a lt ot h eEラ B d v e l o c i t y : rム= nv ょに ηE/B ( 5 ‑ 1 1 3 ] Becauseo fDebyes h i e l d i n g ,t h emaximump o t e n t i a li nt h eplasmai s g i v e nby eφmax=KT, 0 . 1 0 . 1 I fR i sac h a r a c t e r i s t i cs c a l el e n g t ho ft h eplasma( o ft h eordero fi t s r a d i u s ) ,t h emaximume l e c t r i cf i e l di st h e n 1 . 0 10 E ~ー~- - φm出~ KT m a x R eR 100 Kに/ B ( a r b .u n i t s ) FIGURE5 ・ 20 [ 5 ‑ 1 1 4 ] ( 5 ‑ 1 1 5 ] Summaryo fcon員nement t i m emeasurementst a k e nonv a r i o u st y p e so fd i s ュ c h a r g e si nt h eModelCS t e l l a r a t o r ,showinga d h e r e n c et ot h eBohmd i f f u s i o n .Grove,P r i n c e t o nU n i v e r s i t yP l a s m aP h y s i c sL a b o r a t o r y , l a w .[ C o u r t e s yo fD .J s p o n s o r e db yt h eU . S .A t o m i cE n e r g yC o m m i s s i o n . ] Thisl e a d st oaf l u xFム g e o m e t r i e susedi nf u s i o nr e s e a r c h ,i ti snota l w a y sc l e a rt h a tt h el i n e s o ff o r c ee i t h e rc l o s eupont h e m s e l v e so revens t a yw i t h i nt h echamber 目 S i n c et h emeanf r e ep a t h sa r es ol o n g ,o n l yas l i g h tasymmetryi nt h e magneticc o i ls t r u c t u r ew i l le n a b l ee l e c t r o n st owanderoutt ot h ew a l l s w i t h o u tmakingc o l l i s i o n s .Theambipolare l e c t r i cf i e l dw i l lthenp u l lt h e i o n sout Second,t h e r ei st h ep o s s i b i l i t yo fasymmetrice l e c t r i cf i e l d s . Thesecana r i s efromo b s t a c l e si n s e r t e di n t ot h ep l a s m a , fromasymュ m e t r i e si nt h evacuumchamber,o rfromasymmetriesi nt h ewayt h e plasmai sc r e a t e do rh e a t e d .ThedcExBd r i f t sthenneednotbep a r a l l e l t ot h ew a l l s ,andi o n sande l e c t r o n scanbec a r r i e dt o g e t h e rt ot h ew a l l s byExBc o n v e c t i o n .Thed r i f tp a t t e r n s ,c a l l e dconvectivec e l l s ,h avebeen o b s e r v e d .F i n a l l y ,t h e r ei st h ep o s s i b i l i t yo fo s c i l l a t i n ge l e c t r i cf i e l d sa r i s i n g where y i s some f r a c t i o nl e s s than u n i t y . Thus t h ef a c tt h a tDs i s snos u r p r i s e .Thevalueγ =古 has not h e o r e t i c a l p r o p o r t i o n a lt oKT,/eBi j u s t i f i c a t i o nbuti sane m p i r i c a lnumbera g r e e i n gw i t hmostexperiments t ow i t h i naf a c t o ro ftwoo rt h r e e . Recentexperimentsont o r o i d a ld e v i c e shavea c h i e v e dconfinement t i m e so forder l O O T B .Thiswasaccomplishedbyc a r e f u l l ye l i m i n a t i n g o s c i l l a t i o n sanda s y m m e t r i e s .However,i nt o r o i d a ld e v i c e s ,o t h e re征ects occurwhichenhancec o l l i s i o n a ld i f f u s i o n .F i g u r e5 ‑ 2 1showsat o r u sw i t h h e l i c a ll i n e so ff o r c e .Thet w i s ti sneededt oe l i m i n a t et h eu n i d i r e c t i o n a l grad司B a ndc u r v a t u r ed r i f t s .Asap a r t i c l ef o l l o w sal i n eo ff o r c e ,i ts e e s B l neart h ei n s i d ew a l lo ft h et o r u sandas m a l l e rI B l neart h e al a r g e rI o u t s i d ew a l l .Somep a r t i c l e sa r etrappedbyt h emagneticmirrore f f e c t given by nKT. R eB ムー γ 一一一二 z ’ KT. Vn= ‑DB' V n γ ー----' キeB ‑ ( 5 ‑ 1 1 6 ] 1 9 3 D i f f u s i o nand R e s i s t i v i t y 一一ーー司帽圃..........--一一一一一 194 c u r r e n t salongB .Thet h e o r e t i c a lcurvef o rn e o c l a s s i c a l di 庇usion has beenobservedexperimentallybyOhkawaa tLaJ o l l a ,C a l i f o r n i a . C h a p t e r F i v e 5・7. Showt h a tt h emeanf r e epathλ” for e l e c t r o n ‑ i o nc o l l i s i o n si sp r o p o r t i o n a l t o r ; . FIGURE5 ‑ 2 1 Abananao r b i to fap a r t i c l ec o n f i n e di nt h et w i s t e dmagneticf i e l do f at o r o i d a lconfinementd e v i c e .The“ orbit” is r e a l l yt h el o c u so fp o i n t s a twhicht h ep a r t i c l ec r o s s e st h ep l a n eo ft h ep a p e r . ,‑BANANADIFFUSION . / i ! REGION PROBLEMS 5 ‑ 9 . Supposet h eplasmai naf u s i o nr e a c t o ri si nt h es h a p eo fac y l i n d e r1 . 2m i nd i a m e t e rand1 0 0m l o n g .The5‑Tm a g n e t i cf i e l di suniforme x c e p tf o rs h o r t m i r r o rr e g i o n sa tt h ee n d s ,whichwemayn e g l e c t .Otherp a r a m e t e r sa r eKT,= 20k e V ,KT,=1 0k e V ,andn= 1 0 2 1m‑3(atγ = 0 ) .Thed e n s i t yp r o f i l ei sfound e x p e r i m e n t a l l yt obea p p r o x i m a t e l ya ss k e t c h e di nF i g .P 5 ‑ 9 . a l c u l a t eDょ ( a ) Assumingc l a s s i c a ldi町usion, c DIFFUSION h et o t a lnumbero fi o n ‑ e l e c t r o np a i r sl e a v i n gt h ec e n t r a l ( b )C a l c u l a t edN/dt,t r e g i o nr a d i a l l yp e rs e c o n d . at r= 0 . 5m. 〆 〆 』 F 』 F D1 Resisti叫ty 5 ‑ 8 . ATokamaki sat o r o i d a lplasmac o n t a i n e ri nw h i c hac u r r e n ti sd r i v e ni n t h ef u l l yi o n i z e dp l a s m abyanelectric 日eld a p p l i e da l o n gB ( F i g .P 5 ‑ 8 ) .How r i v eat o t a lc u r r e n to f200kAi naplasmaw i t h manyV/mmustb ea p p l i e dtod KT,= 5 00eVandac r o s ss e c t i o n a la r e ao f7 5cm勺 MODIFIED r ! PLATEAU I CLASSICAL 195 D i f f u s i o nand dF dF dF dF v FIGURE5 ‑ 2 2 B e h a v i o ro ft h en e o c l a s s i c a ld i f f u s i o nc o e f f i c i e n tw i t h c o l l i s i o nfrequencyv . FIGUREP 5 ‑ 8 anddonotc i r c u l a t ea l lthewayaroundt h et o r u s .Theguidingc e n t e r s o ft h e s etrappedp a r t i c l e st r a c eoutbanana‑shapedo r b i t sa stheymake s u c c e s s i v ep a s s e sthroughagivenc r o s ss e c t i o n( F i g .5 ‑ 2 1 ) .Asap a r t i c l e makes c o l l i s i o n s ,i tbecomes trappedand untrapped s u c c e s s i v e l yand goesfromonebananao r b i tt oanother.Therandom‑walks t e plength i s therefore t h e width of t h e banana o r b i tr a t h e r than γL· and t h e “classical” di 百usion c o e f f i c i e n ti si n c r e a s e d . This i sc a l l e dn e o c l a s s i c a l diffusioη. Thedependenceo fDム on v i sshown i nF i g .5 ‑ 2 2 . In the regiono fs m a l lv ,bananad i f f u s i o ni sl a r g e rthanc l a s s i c a ld i f f u s i o n .In t h eregionofl a r g ev ,therei sc l a s s i c a ld i f f u s i o n ,buti ti smodifiedby n 50 I 0 50 r(cm) FIGUREP 5 ‑ 9 一一ー咽司’-一一 1 9 6 C ? a P t e r F i v e ( c )E s t i m a t et h econfinementt i m e . , .b y . , . =‑N/(dN/dt).N o t e :aroughe s t i m a t e i sa l lth旦t canbee x p e c t e di nt h i st y p eo fproblem.Thep r o f i l eh a so b v i o u s l y beena f f e c t e dbyp r o c e s s e so t h e rt h a nc l a s s i c a ldi 百usion. 1 9 7 D i f f u s i o nand 一、 R e s i s t i v i t y \ 5 ‑ 1 0 .E s t i m a t et h ec l a s s i c a ld i f f u s i o nt i m eo faplasmac y l i n d e r1 0cmi nr a d i u s , 0 2 1m ",KT,=KT,= 1 0keV,B =5T. w i t hn= 1 5 ‑ 1 1 .Ac y l i n d r i c a lplasmacolumnh a sad e n s i t ydistributio日 B η = η。( I ー γ2 Iα2) FIGURE P5‑14 wherea= 1 0cmandη。= 1019m3 I fKI二= 100eV,KT,=0 ,andt h ea x i a l magneticf i e l dBui s IT,whati st h er a t i obetweent h eBohmandt h ec l a s s i c a l e r p e n d i c u l a rt oBo? d i f f u s i o ncoe伍cients p ( a ) Fromt h e0componentso ft h e s ee q u a t i o n s ,showthat""=v , , 5 ‑ 1 2 . A weakly i o n i z e d plasma c a ns t i l l be governed byS p i t z e rr e s i s t i v i t yi f V,; 》 ν,,,, w herev州 is t h ee l e c t r o nn e u t r a lc o l l i s i o nf r e q u e n c y . Herea 1esome d a t af o rt h ee l e c t r o n ‑ n e u t r a lmomentumt r a n s f e rc r o s ssecuon 民。 in s q u a r e angstroms(λ2): 」=2eV E=lOeV Helium Argon 6 . 3 2 . 5 ( b ) Fromt h ercomponents,showt h a tU仰 = VF.+ Vn;(j=, ie ) . , ,showingt h a ti td o e sn o tdependon」,. ( c ) Findane x p r e s s i o nf o rv 5 ‑ 1 6 . Uset h es i n g l e ‑ f l u i dMHDe q u a t i o no fmotionandt h emassc o n t i n u i t y e q u a t i o nt oc a l c u l a t et h ephasev e l o c i t yo fani o na c o u s t i cwave111anunmagnet勾 i z e d ,uniformplasmaw i t hT,》 T,・ 4 . 1 1 3 . 8 C a l c u l a t et h er e s i s t i v edampingo fA l f v e nwavesbyd e r i v i n gt h ed i s p e r s i o n q u a t i o n s[ 5 ‑ 8 5 ]and[ 5 ‑ 9l ]andM a x w e l l ' se q u a t i o n s r e l a t i o nfromt h esin 宵le-fluid e p . [ 4 ‑ 7 2 ]and[ 4 ‑ 7 7 ] .L i n e a r i z eandn e g l e c tg r a v i t y ,d i s p l a c e m e n tc u r r e n t .andV 5・ 17 Fors i n g l yi o n i z e dHeandA p l a s m a sw i t hKT,=2and1 0eV( 4c a s e s ) ,e s t i m a t e ; )a twhichv , ,=丸山 assuming t h a tt h ev a l u e t h ef r a c t i o n a li o n i z a t i o n [ =nJ (π。+ n ' V ( T , )c a nb ec r u d e l yapproximatedbyσ (£) 1 v i ( 」 ) ,whereE =KT,.( H i n t : o fO , . , ,u s eE q .[ 7 ‑ 1 1 ] ;f o rv , ; ,u s eE q s .[ 5 ‑ 6 2 ]and[ 5 ‑ 7 6 ] . Forv ( a ) Showt h a t 手= c2ε 5 ‑ 1 3 . Theplasmai nat o r o i d a ls t e l l a r a t o ri so h m i c a l l yh e a t e dbyac u r r e n ta l o n g Bo f1 0 5A/m2 Thed e n s i t yi suniforma t1 1=1 0 1 9m‑"andd o e sn o tc h a n g e . o e st ot h ee l e c t r o n s .C a l c u l a t et h em <e o fi n c r e a s eo fKT,i n TheJ o u l eh e a t吋2 g 0eV. eV/オseca tt h et i m ewhenKT,= 1 ( b )F i n dane x p l i c i te x p r e s s i o nf o rIm( k )whenw i sr e a landηis s m a ' l l I fac y l i n d r i c a lplasmadi 征uses a tt h eBohmr a t e ,c a l c u l a t et h es t e a d ys t a t e r a d i a ld e n s i t ypro 自 le n(r),i g n o r i n gt h ef a c tt h a ti tmayb eu n s t a b l e .Assumet h a t : >a ndh a sav a l u en0atγ = To t h ed e n s i t yi sz e r oatγ = a 5・ 18. I na0 ‑ p i n c h ,al a r g ecurre 口 t i sd i s c h a r g e dthroughao n e ‑ t u r nc o i l .The r i s i n gmagnetic f i e l di n s i d et h ec o i li n d u c e s as u r f a c ec u r r e n ti nt h eh i g h l y conductingp l a s m a .Thes u r f a c ec u r r e n ti so p p o s i t ei nd i r e c t i o nt ot h ec o i lc u r r e n t andhencek e e p st h emagneticf i e l douto ft h ep l a s m a .Themagneticf i e l dp r e s s u r e betweent h ec o i landt h eplasmat h e ncompressest h ep l a s m a .Thisc a nwork o n l yi ft h emagneticf i e l ddoesn o tp e n e t r a t ei n t ot h eplasmaduringt h ep u l s e . Usingt h eS p i t z e rr e s i s t i v i t y ,e s t i m a t et h emaximump u l s el e n g t hf o rahydrogen 0 ‑ p i n c hwhosei n i t i a lc o n d i t i o n sa r eKT,= 1 0eV,n = 1 0 2 2m•, r =2cm,i ft h e f i e l di st op e n e t r a t eo n l yl / 1 0o ft h ewayt ot h ea x i s . 5・ 14. 5 ‑ 1 9 . Ac y l i n d r i c a lcolumno fplasmai nauniformmagneticf i e l dB =B).c a r r i e s , z ,where i sauniいector p a r a l l e lt ot h ea x i so f auniformc u r r e n td e n s i t yj=j t h ec y l i n d e r . z ( a )C a l c u l a t et h emagneticf i e l dB ( r )producedb yt h i splasmac u r r e n t . . ,=Oi n ( b )W r i t eane x p r e s s i o nf o rt h egrad‑Bd r i f to fachargedp a r t i c l ew i t hォ . ,j . ,r ,v , ,q ,andm .Youmayassumet h a tthe 日eld c a l c u l a t e di n( a ) t e r m so fB i ss m a l lcomparedt oB,( b u tn o tz e r o ) . 5 ‑ 1 5 . Considerana x i s y m m e t r i cc y l i n d r i c a lplasmaw i t hE=E J : ,B =B z ,and Vム= V丸=ね世/ aγIf wen e g l e c tt h e( v V)vt e r m ,whichi stantamountt on e g l e c t ュ i n gt h ec e n t r i f u g a lf o r c e ,t h es t e a d ys t a t et w o ‑ f l u i d~quations canbew r i t t e ni n ( c )I ft h eplasmah a se l e c t r i c a lr e s i s t i v i t y ,t h e r ei sa l s oane l e c t r i cf i e l dE=E) . C a l c u l a t et h ea z ; m u t h a le l e c t r o nd r i f tduet othi店員eld, t a k i ' ¥ gi n t oaccountt h e h e l i c i t yo ft h eB 自eld t h eform en(E+v,xB)‑Vp, e2η2η ( v, ‑v,)=0 ( d ) Drawadiagramshowingt h ed i r e c t i o no ft h ed r i f t si n( b )and( c )f o rb o t h i o n sande l e c t r o n si nt h e( r ,0)p l a n e . en(E+v,× B) ‑V p ,+e2n2η ( v; ‑v , )=0 一--- τ C h a p t e rS i x E込UILIBRIUM ANDSTABILITY INTRODUCTION 6 . 1 I fwel o o konlya tt h emotionso fi n d i v i d u a lp a r t i c l e s .i twouldbee a s y t od e s i g namagneticf i e l dwhichw i l lc o n f i n eac o l l i s i o n l e s sp l a s m a .We needonlymakes u r et h a tt h el i n e so ff o r c edon o th i tt h evacuumw a l l andarranget h esymmetryo ft h esystemi nsuchawayt h a ta l lt h ep a r t i c l e , B ,ands of o r t ha r ep a r a l l e lt ot h ew a l l s .Fromamacroscopic d r i f t sV」, v l a s m aw i l lbe f l u i dv i e w p o i n t ,however,i ti sn o te a s yt os e ewhetherap confinedi namagneticf i e l ddesignedt oc o n t a i ni n d i v i d u a lp a r t i c l e s .No matterhowt h eexternal 自elds a r ea r r a n g e d ,t h eplasmacangenerate i n t e r n a lf i e l d swhicha百ect i t sm o t i o n .Fori n s t a n c e ,chargebunchingcan c r e a t eE f i e l d swhichcanc a u s eExB d r i f t st ot h e\、•all. Currentsi nt h e plasmacangenerateBf i e l d swhichc a u s egrad‑Bd r i f t soutward vVecana r b i t r a r i l yd i v i d et h eproblemo fconfinementi n t otwop a r t s : t h eproblemo fe q u i l i b r i u mandt h eproblemo fs t a b i l i t y .Thed i f f e r e n c e between e q u i l i b r i u m and s t a b i l i t yi sb e s ti l l u s t r a t e d bya mechanical a n a l o g y .Figure6 ‑ 1showsv a r i o u sc a s e so famarbler e s t i n gonahard s u r f a c e .Anequilibrumi sas t a t ei nwhicha l lt h ef o r c e sa r eb a l a n c e d ,s o t h a tatime‑independents o l u t i o ni sp o s s i b l e .Thee q u i l i b r i u mi ss t a b l e oru n s t a b l eaccordingt owhethers m a l lp e r t u r b a t i o n sa r edampedo r a m p l i f i e d .Inc a s e( F ) ,t h emarblei si nas t a b l ee q u i l i b r i u ma slonga si t i sn o tpushedt o of a r .Oncei ti smovedbeyondat h r e s h o l d ,i ti si nan u n s t a b l es t a t e .Thisi sc a l l e dan “ explosive i n s t a b i l i t y . "Inc a s e( G ) ,t h e marblei si nanu n s t a b l es t a t e ,buti tcannotmakev e r yl a r g ee x c u r s i o n s . 一__..』 1 9 9 『?「 Suchani n s t a b i l i t yi sn o tv e r ydangerousi ft h en o n l i n e a rl i m i tto t h e amplitudeo ft h e motioni ss m a l l .Thes i t u a t i o nw i t h aplasma is ,。f c o u r s e ,muchmorec o m p l i c a t e dthanwhati ss e e ni nF i g .6 ‑ 1 ;t oa c h i e v e e q u i l i b r i u mr e q u i r e sb a l a n c i n gt h ef o r c e soneachf l u i de l e m e n t .Oft h e twop r o b l e m s ,e q u i l i b r i u mands t a b i l i t y ,t h el a t t e ri se a s i e rt ot r e a t .One can l i n e a r i z et h ee q u a t i o n so f motion f o rs m a l ld e v i a t i o n s from an nt h ec a s eo f e q u i l i b r i u ms t a t e .Wethenhavel i n e a re q u a t i o n s ,jt国 as i plasmaw a v e s .Thee q u i l i b r i u mproblem,ont h eo t h e rhand,i san o n l i n e a r problem l i k et h a to fd i f f u s i o n .I ncomplexmagneticg e o m e t r i e s ,t h e c a l c u l a t i o no fe q u i l i b r i ai sat e d i o u sp r o c e s s . 200 Chapleγ ~ S i x 。 努~ A B c NOEQUILIBRIUM NEUTRALLYSTABLE (METASTABLE) EQUILIBRIUM HYDROMAGNETIC EQUILIBRIUM 6 . 2 Although t h eg e n e r a l problemo fe q u i l i b r i u mi cc o m p l i c a t e d ,s e v e r a l p h y s i c a lc o n c e p t sa r ee a s i l ygleanedfromt h eMHDe q u a t i o n s . Fora s t e a d ys t a t ew i t ha / a t=0andg=0 ,t h eplasmamusts a t i s f y(cf 目 Eq. [5・ 85]) Vp= jxB 。 STABLEEQUILIBRIUM E [6・ l] and VxB=/.l 。j UNSTABLEEQUILIBRIUM [ 6 ‑ 2 1 Fromt h esimplee q u a t i o n[6匂 I], wecana l r e a d ymakes e v e r a lo b s e r v a ュ t 1 0 n s . 6 ‑ 1 ]s t a t e st h a tt h e r ei sab a l a n c eo ff o r c e sbetween ( A ) Equ 旦 tion [ t h ep r e s s u r e ‑ g r a d i e n tf o r c eandt h eLorentzf o r c e .Howdoest h i scome abouθConsider ac y l i n d r i c a lplasmaw i t hV戸 directed towardt h ea x i s ( F i g .6 ‑ 2 ) .Toc o u n t e r a c tt h eoutwardf o r c eo fe x p a n s i o n ,t h e r emustbe an a z i m u t h a lc u r r e n ti nt h ed i r e c t i o nshown.Themagnitudeo ft h e 6 ‑ 1 ] r e q u i r e dc u r r e n tcanbefoundbyt a k i n gt h ec r o s sproducto fE q .[ w i t hB : BxVp BxVn F G j j ̲=ヲ「 =( KT; +KT,) ヲ「 EQUILIBRIUMWITHLINEAR STABILITYANDNONLINEAR INSTABILITY EQUILIBRIUMWITH LINEAR INSTABI し ITY ANDNONLINEAR Thisi sj u s tt h ediamagneticc u r r e n tfoundp r e v i o u s l yi nE q .( 3 ‑ 6 9 ] !From as i n g l e ‑ p a r t i c l ev i e w p o i n t ,t h e diamagnetic c u r r e n ta r i s e s from t h e Larmorg y r a t i o nv e l o c i t i e so ft h ep a r t i c l e s ,whichdonota v e r a g et oz e r o whent h e r ei sad e n s i t yg r a d i e n t . FromanMHDf l u i dv i e w p o i n t ,t h e o r c ea c r o s sB ;t h er e s u l t i n g diamagneticc u r r e n ti sgeneratedbyt h eVpf c u r r e n ti sj u s ts u f f i c i e n tt ob a l a n c et h ef o r c e soneachelemento ff l u i d ands t o pt h em o t i o n . STABI し ITY FIGURE6 ‑ 1 M e c h a n i c a la n a l o g yo fv a r i o u st y p e so fe q u l i b r i u m . -晶』』 [ 6 ‑ 3 ] 2 0 1 E q u i l i b r i u m andS t a b i l i t y 審 202 203 C h a p t e r S i x Equilibγium andS t a b i l i t y ーー一ーー・4・h / 甲ーーー一一’ー- E x p a n s i o no faplasmas t r e a m i n gi n t oam i r r o r . FIGURE6 ‑ 4 ( C ) Considert h ecomponento fE q .[ 6 ‑ 1 ]alongB .I ts a y st h a t FIGURE6 ‑ 2 ThejxBf o r c eo ft h ed i a m a g n e t i ccuト r e n tb a l a n c e st h ep r e s s u r e ‑ g r a d i e n t f o r c ei ns t e a d ys t a t e . 。世/ as= o ( 6 ‑ 4 ] wheresi st h ec o o r d i n a t ealongal i n eo ff o r c e .Forc o n s t a n tKT,t h i s meanst h a ti nhydromagnetice q u i l i b r i u mt h ed e n s i t yi sc o n s t a n talong al i n eo ff o r c e .Atf i r s ts i g h t ,i tseemst h a tt h i sc o n c l u s i o nmustbei n e r r o r .F o r ,c o n s i d e raplasmai n j e c t e di n t oamagneticmirror( F i g .6 ‑ 4 ) . Ast h eplasmastreamst h r o u g h ,f o l l o w i n gt h el i n e so ff o r c e ,i texpands andthenc o n t r a c t s ;andt h ed e n s i t yi sc l e a r l ynotc o n s t a n talongal i n e o ff o r c e .However,t h i ss i t u a t i o ndoesr i o ts a t i s f yt h ec o n d i t i o n so fas t a t i c e q u i l i b r i u m .The( vキ V)vt e r m ,whichwen e g l e c t e dalongt h ew a y ,does n o tv a n i s hh e r e .Wemustc o n s i d e ras t a t i cplasmaw i t hv= 0 .Int h a t c a s e ,p a r t i c l e sa r etrappedi nt h em i r r o r ,andt h e r ea r emorep a r t i c l e s trappedneart h emidplanethanneart h eendsbecauset h emirrorr a t i o i sl a r g e rthere ・ This e 狂ect j u s tcompensatesf o rt h el a r g e rc r o s ss e c t i o n a tt h emidplane,andt h en e tr e s u l ti st h a tt h ed e n s i t yi sc o n s t a n talong al i n eo ff o r c e . b v i o u s l yt e l l su st h a tjandB a r eeachperpenュ ( B )Equation(6・ l] o p .Thisi snotat r i v i a lstatementwhenonec o n s i d e r st h a tt h e d i c u l a rt oV geometrymaybev e r yc o m p l i c a t e d .Imagineat o r o i d a lplasmai nwhich t h e r ei sasmoothr a d i a ld e n s i t yg r a d i e n ts ot h a tt h es u r f a c e so fc o n s t a n t )a r en e s t e dt o r i( F i g .6 ‑ 3 ) .S i n c ejandBare d e n s i t y( a c t u a l l y ,c o n s t a n tp p ,theymustl i eon t h es u r f a c e so fc o n s t a n tp . In perpendiculart oV g e n e r a l ,t h el i n e so ff o r c eando fcurrentmaybet w i s t e dt h i swayand t h a t ,butt h e ymustnotc r o s st h ec o n s t a n t ‑ ps u r f a c e s . THE CONCEPT OFβ6.3 Wenows u b s t i t u t eE q .[ 6 ‑ 2 ]i n t oEq.( 6 ‑ 1 ]t oo b t a i n Vp=オ01(VxB)xB =オ01((BキV)B - ~VB2] [6・5] v(戸+毛)=去(B·V)B ( 6 ‑ 6 ] o r FIGURE6・3 Inmanyi n t e r e s t i n gc a s e s ,sucha sas t r a i g h tc y l i n d e rwitha x i a lf i e l d , t h eright‑hands i d ev a n i s h e s ;B doesnotvaryalongB.I nmanyo t h e r Botht h ejandBv e c t o r sl i eonc o n s t a n t ‑ p r e s s u r es u r f a c e s . 」ム 『『- 204 i nt h ed e f i n i t i o nofβHigh-βplasmas a r ecommoni nspaceandMHD energyconversionr e s e a r c h .Fusionr e a c t o r sw i l lhavet ohave( 3w e l li n %i nordert obee c o n o m i c a l ,s i n c et h eenergyproducedi s e x c e s so f1 h i l et h ec o s to ft h emagneticc o n t a i n e ri n c r e a s e s proportionalt on2, w withsomepowero fB . Inp r i n c i p l e ,onecanhaveaβ = 1plasmai nwhicht h ediamagnetic current generates a f i e l de x a c t l yequaland o p p o s i t et oane x t e r n a l l y generateduniformf i e l d .Therea r ethentwor e g i o n s :aregiono fplasma withoutf i e l d ,andaregiono ff i e l dwithoutp l a s m a .I ft h eexternal 白eld l i n e sa r es t r a i g h t ,t h i se q u i l i b r i u mwouldl i k e l ybeu n s t a b l e ,s i n c ei ti s l i k eablobofj e l l yheldt o g e t h e rw i t hs t r e t c h e drubberbands.I tremains ft h i st y p ecaneverbea c h i e v e d .In t obeseenwhetheraβ =-l plasmao some magneticc o n f i g u r a t i o n s ,t h evacuumf i e l d hasan u l li n s i d et h e n f i n i t et h e r e .Thishappens, plasma;t h el o c a lv a l u eofβwould thenbei f o ri n s t a n c e ,whenf i e l d sa r ea p p l i e do n l yneart h es u r f a c eo fal a r g e h er a t i oofmaximump a r t i c l e plasma.I ti sthencustomaryt odefineβas t pressuret omaximummagneticp r e s s u r e ;i nt h i ss e n s e ,i ti snotp o s s i b l e f o ram a g n e t i c a l l yconfinedplasmat ohaveβ > 1 . Cha骨Uγ S i x /〆 FIGURE ふ5 Inafinite・βplasma, t h ed i a m a g n e t i ccu町ent s i g n i f i c a n t l yd e c r e a s e st h em a g n e t i cf i e l d , k e e p i n gt h esumo ft h emagneticandp a r t i c l e p r e s s u r e sac o n s t a n t . 205 E q u i l i b r i u m αnd Stαbility n a 一一 e o n o c h u A + ピ一恥 6 ‑ 6 ]thens a y st h a t c a s e s ,t h eright‑hands i d ei ss m a l l . Equat 即1 ( DIFFUSION OF MAGNETIC FIELD INTO A PLASMA 6.4 [ 6 ‑ 7 ] na s t r o p h y s i c si st h ed i f f u s i o no famagnetic A problemwhichoften 旦rises i f i e l di n t oaplasma.I ft h e r ei saboundarybetweenaregionw i t hplasma butnof i e l dandaregionwithf i e l dbutnoplasma( F i g .6 ‑ 6 ) ,t h er e g i o n s w i l ls t a yseparatedi ft h eplasmah a snor e s i s t i v i t y ,f o rt h esamereason t h a tf l u xcannotp e n e t r a t easuperconductor.Anyemft h a tt h emoving l i n e so ff o r c egeneratew i l lc r e a t ean i n f i n i t ec u 1r e n t ,and t h i si sn o t p o s s i b l e .Ast h eplasmamovesaround,t h e r e f o r e ,i tpushest h el i n e so f Sine右 B 2/ 2 オ , 0i st h e magneticf i e l dp r e s s u r e ,t h esumoft h ep a r t i c l e p r e s s u r eandt h emagneticf i e l dp r e s s u r ei sac o n s t a n t .Inaplasmawith ad e n s i t yg r a d i e n t( F i g .6 ‑ 5 ) ,t h emagneticf i e l dmustbelowwheret h e d e n s i t yi sh i g h ,andv i c ev e r s a .Thedecreaseoft h emagneticf i e l di n s i d e t h eplasmai sc a u s e d ,o fc o u r s e ,byt h ediamagneticc u r r e n t .Thes i z eof si n d i c a t e dbyt h er a t i oo ft h etwotermsi nE q . t h ediamagneticE庇ect i (6・7]. T hisr a t i oi su s u a l l ydenotedbyβ : β =主手- P a r t i c l epressure B/ 2 オ , 0 Magneticf i e l dpressure B ONLY [6・8] e ①①①①①①♂ g Gら@①①①① 2 Upt onowwehavei m p l i c i t l yconsideredlow”βplasmas, i nwhichβis between1 0 ‑ 3and1 0 ‑ 6 .Thediamagnetice f f e c t ,t h e r e f o r e ,i sverys m a l l . nt h etreatment Thisi st h ereasonwecouldassumeauniformf i e l dBoi o fplasmaw a v e s .Ifβis l o w ,i tdoesnotmatterwhethert h edenominator o fE q .( 6 ‑ 8 ]i sevaluatedwitht h evacuumf i e l dort h ef i e l di nt h epresence i g h ,t h el o c a lv a l u eofB canbeg r e a t l yreducedby o fp l a s m a .Ifβis h t h ep l a s m a .Int h a tc a s e ,i ti scustomaryt ouset h evacuumv a l u eo fB PLASMAONLY a n FIGURE6‑6 I nap e r f e c t l yc o n d u c t i n gp l a s m a ,r e g i o n so fplasmaandmagnetic 員eld c bes e p a r a t e dbyas h a r pb o u n d a r y .C u r r e n t sont h es u r f a c ee x c l u d et h ef i e l d fromt h ep l a s m a . -ι』 206 C h a p t e r 5は f o r c eand can bendand t w i s tthem.This maybe the reason f o rt h e f i l a m e n t a r ys t r u c t u r eo ftheg a si nt h eCrabn e b u l a .I ftheresisti、·ity i s f i n i t e ,however,theplasmacanmovethroughthef i e l dandv i c ev e r s a . fthemotionsare Thisd i f f u s i o nt a k e sac e r t a i namounto ftime ,旦nd i slowenough,thel i n e so ff o r c eneednotbed i s t o r t e dbythegasmotions. Thedi 百usion t imei se a s i l yc a l c u l a t e dfromtheequations( c f .Eq.[ 5 ‑ 9 1 ] ) V ラE =‑ B [ 6 ‑ 9 ] Fors i m p l i c i t y ,l e tusassumet h a tt h eplasmai sa trest a r emovingi n t oi t .Thenv= 0 ,andwehave 呂 nd = ‑VXηj aBηη9 -=一- v ×( Vx B)=一一[ V(V キ B)‑' i i ' " B ] µ, 。 μ。 [6 開 11] [ 6 ‑ 1 2 ] S i n c eV キB = 0 ,weo b t a i nad i f f u s i o nequationo fthetypeencountered i nChapter5 : aBη ョ ー= ‑'V"B a t [6・ 13] µ, 。 Thiscan bes o l v e d bythes e p a r a t i o no fv a r i a b l e s ,a su s u a l . Togeta roughe s t i m a t e ,l e tu st a k eL t obethes c a l elengtho fthes p a t i a l、 ar i a t i o n o fB .Thenwehave 。Bηn a t 、 Fτ = η白色~二=主= 2 匂 [ 6 ‑ 1 8 ] .Thusri se s s e n t i a l l ythetimei tt a k e sf o rthe 白eld energyt obed i s s i p a t e d i n t oJouleh e a t . thef i e l dl i n e s Sinceji sgivenbyEq.[6” 2], t h i sbecomes a t 一「 207 E q u i l i b r i u m andStabili匂 [ 6 ‑ 1 0 ] E+vXB = ηj 。B/at fromMaxwell ’s equationwithdisplacementcurrentn e g l e c t e d ,theenergy d i s s i p a t i o ni s [6 ・ 14] 戸子 D B =Boe 土t/T [6 ・ 15] where r= /.L 。L 2 /η [ 6 ‑ 1 6 ] 6・ 1. S upposet h a ta ne l e c t r o m a g n e t i ci n s t a b i l i t yl i m i t sβto (m/M)'12i naD‑D r e a c t o r .L e tt h em a g n e t i cf i e l db el i m i t e dt o20T b yt h es t r e n g t ho fm a t e r i a l s . I fKT,=KT,=2 0keV ,自 nd t h emaximump l a s m ad e n s i t yt h a tc a nb ec o n t a i n e d . I nl a s e r ‑ f u s i o ne x p e r i m e n t s ,a b s o r p t i o no fl a s e rl i g h tont h es u r f a c eo fa 0 2 7m̲,andt e m p e r a t u r eT,= T ‘, = 1 0 4eV p e l l e tc r e a t e sap l a s m ao fd e n S i t yn= I T h e r m o e l e c t r i cc u r r e n t sc a nc a u s espontaneousm a g n e t i cf i e l d sa sh i g ha sI O 'T . 6・2. nt h i sp l a s m a ,andh e n c ee l e c t r o n motioni ss e v e r e l y ( a )Showt h a tw,T,; > I i a f f e c t e db yt h em a g n e t i cf i e l d . ( h )Showthatβ 》 I, s ot h a tm a g n e t i cf i e l d sc a n n o te f f e c t i v e h キc o n f i n et h ep l a s m a ( c ) Howdo t h e plasmaand f i e l d moves ot h a tt h es e e m i n g l yc o n t r a d i c t o r y c o n d i t i o n s( a )and( b )c a nb o t hb esatis 自 ed コ Ac y l i n d r i c a lplasmacolumno fr a d i u sac o n t a i n sac o a x i a lmagnetic B=B 0 zandh a sap r e s s u r ep r o f i l e 6・3. 自eld p=p , ,c o s 2(m/2a) ( a )C a l c u l a t et h emaximumv a l u eof 戸。 ( b )U s i n gt h i sv a l u eo fp 0 ,c a l c u l a t et h ed i a m a g n e t i cc u r r e n tj ( r )and< he t o t a l f i e l dB ( r ) ( c ) Showj ( r ) ,B ( r ) ,andp ( r )onag r a p h . Z X B V 1 0 ・ 一一 μ B 一L This i st h ec h a r a c t e r i s t i c time f o r magnetic f i e l d penetration i n t oa plasma. Thetimer cana l s obei n t e r p r e t e da sthetimef o ra n n i h i l a t i o nof i n e s move through the plasma, the the magnetic f i e l d . As the 自eld l inducedc u r r e n t scauseohmicheatingo ft h eplasma.Thisenergycomes fromtheenergyoft h ef i e l d .Theenergyl o s tperm3i natimeri sη•/r. S i n c e [ 6 ‑ 1 7 ] ( d )I ft h ec y l i n d e ri sb e n ti n t oat o r u sw i t ht h el i n e so ff o r c ec l o s i n gupon t h e m s e l v e sa f t e ras i n g l et u r n ,t h i se q u i l i b r i u m ,i nwhicht h em a c r o s c o p i cf o r c e s a r eeverywhereb a l a n c e d ,i so b v i o u s l yd i s t u r b e d .I si tp o s s i b l et or e d i s t r i b u t et h e ns u c hawayt h a tt h ee q u i l i b r i u mi srestored コ p r e s s u r ep(r,。) i 6 ‑ 4 .C o n s i d e ra ni n f i n i t e ,s t r a i g h tc y l i n d e ro fplasmaw i t has q u a r ed e n s i t ypro品 le c r e a t e di nauniform 抗 eld 80( F i g .P 6 ‑ 4 ) .Showt h a tB v a n i s h e sont h ea x i si f β = I ,b yp r o c e e d i n ga sf o l l o w s . ( a ) Usingt h eMHDequations ,自 nd j "i ns t e a d ys t a t ef o rK T =c o n s t a n t PROBLEMS γ 208 209 Cha戸leγ S i x ~ E q u i l i b r i u m andS t a b i l i t y 、 v VOLTAGE INDUCED 「一一一一一一一ー一一「 I I n 0 B=B0OUTSIDEPLASMA n ( r )I n レー a 0 FIGUREP G ‑ 4 n t e g r a t eo v e rt h ea r e ao ft h el o o p ( h )U s i n gVラ B=IL。j andStokes’ theorem, i shownt oo b t a i n 「 00 a n / a r B山一 B。= μ。2.KTI 一二- dr ん B (γ) FIGUREPふ5 6 ‑ 5 .Ad i a m a g n e t i cl o o pi sad e v i c eu s e dt omeasurep l a s m ap r e s s u r eb yd e t e c t i n g t h ed i a m a g n e t i ce f f e c t( F i g .P 6 ‑ S ) .Ast h ep l a s m ai sc r e a t e d ,t h ed i a m a g n e t i c c u r r e n ti n c r e a s e s ,B d e c r e a s e si n s i d et h ep l a s m a ,andthe 日 uxφenclosed b yt h e l o o pd e c r e a s e s ,i n d u c i n gav o l t a g e ,w h i c hi st h e nt i m e ‑ i n t e g r a t e db ya nRCc i r c u i t ( F i g .P 6 ‑ 5 ) . ( a )Showt h a t I Vdt= N ~φ =- NI B dキ dS t -一事』 B削= B , ~u ( c )Dot h ei n t e g r a lb yn o t i n gt h a tan/aγis a8 ‑ f u n c t i o n ,s ot h a tB( r )a tr= ai s 0 . t h ea v e r a g eb e t w e e nB白 and B 'loop t -一唱』 vi 人 = Bd B ‑Bu ' ( b )Uset h et e c h n i q u eo ft h ep r e v i o u sp r o b l e mt of i n dB d ( r ) .b u tnowa s s u m e n( r )= lluexp[ー( r/r0)2]. Todot h ei n t e g r a l , assumeβ 《 I, s ot h a tB c a nb e a p p r o x i m a t e db yB。 in t h eime百ral. ( c )Showt h a tJ Vd t= ~N1TT6βB0, w i t hf 3d e f i n e da si nE q .[ 6 ‑ 8 ] . 6 . 5 CLASSIFICATIONOFINSTABILITIES I nt h etreatmento fplasmaw a v e s ,weassumedanunperturbeds t a t e whichwasoneo fp e r f e c tthermodynamice q u i l i b r i u m :Thep a r t i c l e sh a < l Maxwellian v e l o c i t yd i s t r i b u t i o n s ,and t h ed e n s i t yand magneticf i e l d wereuniform.Insuchas t a t eo fh i g h e s te n t r o p y ,t h e r ei snof r e eenergy x c i t ew a v e s ,andwehadt oc o n s i d e rwavest h a tweree x c i t e d a v a i l a b l etoe by e x t e r n a l means 目 We now c o n s i d e rs t a t e st h a ta r e not i np e r f e c t thermodynamice q u i l i b r i u m , although t h e ya r ei ne q u i l i b r i u mi nt h e s e n s et h a ta l lf o r c e sa r ei nb a l a n c eandatime‑independents o l u t i o ni s p o s s i b l e . The f r e e energy which i sa v a i l a b l e can cause w a ¥ キ e st o be n s t a b i l i t yi s s e l f ‑ e x c i t e d ;t h ee q u i l i b r i u mi sthenanu n s t a b l eone 目 An i a l w a y samotionwhichd e c r e a s e st h ef r e eenergyandb r i n g st h eplasm丘 c l o s e rt ot r u ethermodynamice q u i l i b r i u m . I n s t a b i l i t i e smaybec l a s s i f i e daccordingt ot h et y p eo ff r e eenergy a v a i l a b l et od r i v ethem.Therea r efourmainc a t e g o r i e s . I . Streaming instαbilities. In t h i sc a s e ,e i t h e ra beamo fe n e r g e t i c p a r t i c l e st r a v e l sthrought h ep l a s m a ,o rac u r r e n ti sd 1i v e nthrought h e plasmas ot h a tt h ed i f f e r e n ts p e c i e shaved r i f t srelati、E t oone2 n o t h e r . Thed r i f tenergyi susedt oe x c i t ew a v e s ,ando s c i l l a t i o nenergyi sgained a tt h eexpenseo ft h ed r i f tenergyi nt h eunperturbeds t a t e . 2 . Rayleigh-Tayloγ instabilities. I nt h i sc a s e ,t h eplasmahasad e n s i t y g r a d i e n to rasharpboundary,s ot h a ti ti sn o tuniform.I na d d i t i o n ,an e x t e r n a l ,nonelectromagneticf o r c ei sa p p l i e dt ot h ep l a s m a .I ti st h i s f o r c ewhichd r i v e st h ei n s t a b i l i t y .Ananalogyi sa v a i l a b l ei nt h eexample o fani n v e r t e dg l a s so fwater( F i g .6 ‑7 ) .Althought h eplanei n t e r f a c e 「Fー 210 C h a p t e r S i x i nmirrorm a c h i n e s ,wherep a r t i c l e sa r el o s tbyd i f f u s i o ni nv e l o c i t ys p a c e i n t ot h el o s sc o n e . ー、\ TもVO-STREAM INSTABILITY 6 . 6 Asas i m p l eexampleo fastreamingi n s t a b i l i t y ,c o n s i d e rauniformplasma i nwhich t h ei o n sa r es t a t i o n a r yand t h ee l e c t r o n shaveav e l o c i t yv 0 r e l a t i v et ot h ei o n s .Thati s ,t h eo b s e r v e ri si naframemovingw i t ht h e “ stream ” of i o n s .L e tt h eplasmabec o l d(KT,=KT,=0 ) ,andl e tt h e r e benomagneticf i e l d( B o=0 ) .Thel i n e a r i z e de q u a t i o n so fmotiona r e then . ‑a v..ー ル1no 一一一= e n o . t . , FIGURE6 ‑ 7 HydrodynamicR a y l e i g h ‑ T a y l o ri n s t a b i l i t yo f ah e a v yf l u i d s u p p o r t e db yal i g h to n e . 。t betweent h ew a t e randa i ri si nas t a t eo fe q u i l i b r i u mi nt h a tt h eweight o ft h ewateri ssupportedbyt h ea i rp r e s s u r e ,i ti sanu n s t a b l ee q u i l i b r i u m . Anyr i p p l ei nt h es u r f a c ew i l ltendt ogrowa tt h eexpenseo fp o t e n t i a l energyi nt h eg r a v i t a t i o n a lf i e l d .Thishappenswheneveraheavyf l u i d i ssupportedbyal i g h tf l u i d ,a si sもveil knowni nhydrodynamics. 3 . Univeγ'Sal i n s t a b i l i t i e s . Evenwhent h e r ea r enoo b v i o u sd r i v i n g f o r c e ssucha sane l e c t r i co rag r a v i t a t i o n a lf i e l d ,aplasmai sn o ti np e r f e c t thermodyn昌mic e q u i l i b r i u ma slonga si ti sc o n f i n e d .Theplasmap r e s s u r e t e n d st omaket h eplasmaexpand,andt h eexpansionenergycand r i v e ani n s t a b i l i t y .Thist y p eo ff r e eenergyi sa l w a y sp r e s e n ti nanyf i n i t e plぉma, a ndt h er e s u l t i n gwavesa r ec a l l e du n i v e r s a li n s t a b i l i t i e s . 4 .K i n e t i ci n s t a b i l i t i e s .I nf l u i dt h e o r yt h ev e l o c i t yd i s t r i b u t i o n sa r e assumedt obeM a x w e l l i a n .I ft h ed i s t r i b u t i o n sa r ei nf a c tnotM a x w e l l i a n , t h e r ei sad e v i a t i o nfromthermodynamice q u i l i b r i u m ;andi n s t a b i l i t i e s canbed r i v e dbyt h ea n i s o t r o p yo ft h ev e l o c i t yd i s t r i b u t i o n .Fori n s t a n c e , i fT 1 1and Tょ are d1釘erent, an i n s t a b i l i t yc a l l e dt h e modified H a r r i s i n s t a b i l i t ycana r i s e .I nmirrord e v i c e s ,t h e r ei sad e f i c i to fp a r t i c l e sw i t h l a r g ev11/v ム because o ft h el o s sc o n e ;t h i sa n i s o t r o p yg i v e sr i s et oa “ loss conei n s t a b i l i t y .” I nt h es u c c e e d i n gs e c t i o n s ,wes h a l lg i v eas i m p l eexampleo feach o ft h e s et y p e so fi n s t a b i l i t i e s .Thei n s t a b i l i t i e sd r i v e nbya n i s o t r o p ycannot bed e s c r i b e dbyf l u i dt h e o r yandad e t a i l e dt r e a t m e n to fthemi sbeyond t h es c o p eo ft h i sb o o k . Nota l li n s t a b i l i t i e sa r ee q u a l l ydangerousf o rplasmac o n f i n e m e n t . n s t a n c e , cannota f f e c tt h e Ah i g h ‑ f r e q u e n c yi n s t a b i l i t y near w炉 for i motiono fheavyi o n s .Low‑frequencyi n s t a b i l i t i e sw i t hω 《 n" however, canc a u s eanomalousambipolarl o s s e sv i aExB d司fts. Ins帥ilities w i t h w" " i l cdonote f f i c i e n t l yt r a n s p o r tp a r t i c l e sa c r o s sB buta r edangerous [6・ 19] e 白昼 mη。[~よ+同 V川J =‑en0E1 [6・ 20] Theterm( v . iキ V ) v oi nE q .( 6 ‑ 2 0 )h a sbeendroppedbecauseweassume V ot obeu n i f o r m . The (v0 ・ V)v1 termdoes notappeari nE q .( 6 ‑ 1 9 ) b e c a u s ewehavet a k e nv , o=0 .Wel o o kf o re l e c t r o s t a t i cwaveso ft h eform ' ' k x wo圭[6・21] E 1= Ee where 走 is t h ed i r e c t i o no fv oandk .E q u a t i o n s( 6 ‑ 1 9 )and[ 6 ‑ 2 0 )become • ‑ ‑iwMn0v,1=問。E1 mn0(‑iw+i k v 0 ) v . i= -eη0E1 le Vi ]= τナ E呈[6・22] JVJW i e E呈 m w ‑rw0 V,i =一ーーー一一一7一一 [ 6 ‑ 2 3 ] Thev e l o c i t i e sv ; 1a r ei nt h ex d i r e c t i o n ,andwemayomitt h es u b s c r i p t x .Thei o ne q u a t i o no fc o n t i n u i t yy i e l d s δηE 1 一一+ πoV·v,1=0 i l l k ien ,』 n , 1 = ‑ n 0 V i 1 = : . : . : . : . ; : E w A1w [6・24] Notet h a tt h eo t h e rtermsi nV キ(nv ; )v a n i s hbecauseVn0=v 0 ,= 0 .The e l e c t r o ne q u a t i o no fc o n t i n u i t yi s i l n . , ‑ ‑ ‑ ' ‑ ' ‑+n0VキV . i+(v0 ・ V)πd =0 a t (‑iw+i k v 0 ) n . i+i k n 0 v . i=0 kno ‑k v o i e k n o m(w‑k v 0 ) π.i =十一寸- v.i =一一_____:_::__一言 E 一. . . . . . . . . ・・ーーー [6・25] [ 6 ‑ 2 6 ] [ 6 ‑ 2 7 ] 211 E q u i l i b r i u m andS t a b i l i t y 212 Cha1争leγ Si:χ S i n c et h eu n s t a b l ewavesa r ehigh‑frequencyplasmao s c i l l a t i o n s ,wem a : ; q u a t i o n : n o tu s et h eplasmaapproximationbutmustu s ePoisson ’ s e εoV キ E,= e ( n ; i‑n , . ) [6・28] ikεoE = e(ien0kE)I_!_τ +一一J一「1 LMtu ・ m(w ‑kvo>"J [ 6 ‑ 2 9 ] 苓 早 213 E q u i l i b r i u m andS t a b i l i t y . . 一一~\ Thed i s p e r s i o nr e l a t i o ni sfoundupond i v i d i n gbyikE0E: J I ,,,2rm/ゲ+ 1 ' L w" (w‑kvon 一一一一 。 [6・30] y 。 Letu ss e ei fo s c i l l a t i o n sw i t hr e a lka r es t a b l eo ru n s t a b l e . Upon m u l t i p l y i n gthroughbyt h ecommondenominator,onewouldo b t a i na f o u r t h ‑ o r d e re q u a t i o nf o r " ' キI fa l lt h er o o t sw ia r er e a l ,eachr o o twould i n d i c a t eap o s s i b l eo s c i l l a t i o n x 一一ー』 Thef u n c t i o nF(x,y )i nt h et w o ‑ s t r e a mi n s t a b i l i t y ,whent h eplasmai s FIGURE6 ‑ 8 s t a b l e . ' ; n x E ,= EeiCkx " I fsomeo ft h er o o t sa r ecomplex,t h e yw i l loccuri ncomplexc o n j u g a t e p a i r s .Lett h e s ecomplexr o o t sbew r i t t e n tu;= α;+ zγ1 [6・31] whereaandγare Re(t u )andI m ( t u) ,r e s p e c t i v e l y .Thet i m edependence i snowg i v e nby E ,= Ee''kx αρe 叩圭 。 [ 6 ‑ 3 2 ] 。 P o s i t i v eIm(tu)i n d i c a t e sane x p o n e n t i a l l ygrowingwave;n e g a t i v eIm(w) i n d i c a t e sadampedw a v e .S i n c et h er o o t s" ' ioccuri nc o n j u g a t ep a i r s , oneo ft h e s ew i l la l w a y sbeu n s t a b l eu n l e s sa l lt h er o o t sa r er e a l .The dampedr o o t sa r en o ts e l f ‑ e x c i t e danda r enoto fi n t e r e s t . n a l y z e dw i t h o u ta c t u a l l y The d i s p e r s i o nr e l a t i o n [6・30] can be a s o l v i n gt h ef o u r t h ‑ o r d e re q u a t i o n .L e tu sd e f i n e =tu/tup x =kvo/tu ρ y 1 =----;;ー+一一一寸呈 F(x,ァ) X白 (x ‑y)" , X 一一一一国』 Thef u n c t i o nF(x,y )i nt h et w o ‑ s t r e a mi n s t a b i l i t y ,whent h eplasma FIGURE6‑9 i su n s t a b l e . [ 6 ‑ 3 3 ] s m a l l e rv a l u eo fy ,t h egraphwouldl o o ka sshowni nF i g .6‑9.Nowt h e r e a r eo n l ytwoi n t e r s e c t i o n sa n d ,t h e r e f o r e ,o n l ytwor e a lr o o t s .Theo t h e r twor o o t smustb ecomplex,andoneo fthemmustcorrespondt oan u n s t a b l ew a v e .Thus,f o rsu 伍ciently s m a l lk v 0 ,t h eplasmai su n s t a b l e . 0 ,t h e plasma i sa l w a y su n s t a b l et ol o n g ‑ w a v e l e n g t h For any g i v e nv o s c i l l a t i o n s .Themaximumgrowthr a t ep r e d i c t e dbyE q .(6句30] i s ,f o r [ 6 ‑ 3 4 ] m/M < 1, ThenE q .[ 6 ‑ 3 0 ]becomes l m/M y Foranyg i v e nv a l u eo fy ,wec anp l o tF(x,y )a saf u n c t i o no fx .T his F i g .6 ‑ 8 ) .Thei n t e r s e c ュ f u n c t i o nw i l lhaves i n g u l a r i t i e sa tx= 0andx= y( )= 1g i v et h ev a l u e so fxs a t i s f y i n g t i o n so ft h i scurvew i t ht h el i n eF(x,y t h ed i s p e r s i o nr e l a t i o n .I nt h e example o fF i g .6 ‑ 8 ,t h e r ea r e four fwechoosea i n t e r s e c t i o n s ,s ot h e r ea r efourr e a lr o o t swi・ However, i 一一一~』ーー Im !主1 =I~) [ 6 ‑ 3 5 ] \ αJp ノ、i’とE ノ S i n c eas m a l lv a l u eo fkv0i sr e q u i r e df o ri n s t a b i l i t y ,onecans a yt h a t ,v0h a st obesu伍ciently s m a l lf o ri n s t a b i l i t y .Thisdoesn o t f o rag i v e nk makemuchp h y s i c a ls e n s e ,s i n c ev0i st h es o u r c eo fenergyd r i v i n gt h e 214 C h a p t e r S i x i n s t a b i l i t y .Thedi伍culty comesfromouruseoft h ef l u i de q u a t i o n s .Any r e a lplasmahasaf i n i t etemperature,andthermale f f e c t sshouldbetaken i n t oaccountbyak i n e t i c ‑ t h e o r yt r e a t m e n t .A phenomenon knowna s , h ,andnoi n s t a b i l ュ Landaudamping(Chapter7 )w i l lthenoccurf o rv 0 v i t yi sp r e d i c t e di fv 0i st o os m a l l . This“ Buneman” instability, a si ti ssometimesc a l l e d ,hast h ef o l l o w ュ i n gp h y s i c a le x p l a n a t i o n .Then a t u r a l frequencyofo s c i l l a t i o n si nt h e h en a t u r a lfrequencyofo s c i l l a t i o n si nt h ei o n e l e c t r o nf l u i di swp,andt h eDopplers h i f toft h eω。 oscilla­ f l u i di s.Op=(m/M)112wp・ Because oft t i o n si nt h emovinge l e c t r o nf l u i d ,t h e s etwof r e q u e n c i e scanc o i n c i d ei n a st h eproperv a l u e .Thed e n s i t yf l u c t u a t i o n s t h el a b o r a t o r yframei fkvoh o fi o n sande l e c t r o n scanthens a t i s f yPoisson ’s e q u a t i o n .Moreover,t h e e l e c t r o no s c i l l a t i o n scanbeshownt ohavenegativee n e r g y .Thati st os a y , t h et o t a lk i n e t i cenergyoft h ee l e c t r o n si sl e s swhen t h eo s c i l l a t i o ni s p r e s e n tthanwhen i ti sa b s e n t . In t h eundisturbedbeam, t h ek i n e t i c 3 ・ 1 energyperm r s2mη0v0. Whent h e r ei sano s c i l l a t i o n ,t h ek i n e t i cenergy h i si saveragedovers p a c e ,i tt u r n sout i s~m(n0+n1)(v0+v1)2. Whent ft h ephaser e l a t i o nbetweenn1andv1 t obel e s sthani市町vf, becauseo requiredbyt h eequationofc o n t i n u i t y .Consequently,t h ee l e c t r o no s c i l l a ュ t i o n shaven e g a t i v ee n e r g y ,andt h ei o no s c i l l a t i o n shavep o s i t i v ee n e r g y . BothwaYes can growt o g e t h e rw h i l e keepingt h et o t a lenergyoft h e systemc o n s t a n t .Ani n s t a b i l i t yo ft h i st y p ei susedi nk l y s t r o n st ogenerate microwaYes.V e l o c i t ymodulationduet oE1c a u s e st h ee l e c t r o n st oform bunches 目 As t h e s ebunchesp a s sthroughamicrowaver e s o n a t o r ,t h e y h en a t u r a lmodeso ft h eresonatorandproduce canbemadet oexιite t microwavepower. ー ' " PROBLEMS E q u i l i h r i u m andS t a b i l i t y L e tt w oc o l d ,c o u n t e r s t r e a m i n gi o nAu 凶 have d e n s i t i e s4 1 1 0andv e l o c i t i e s i namagnetic 自eld B 0 zandac o l dn e u t r a l i z i n gelectron 日 uid. Thef i e l dBo i ss t r o n genough<O c o n f i n ee l e c t r o n sb u tn o ts t r o n genought oa f f e c ti o no r b i t s . 6・9. 土 v.,y ( a )O b t a i nt h ef o l l o w i n gd i s p e r s i o nr e l a t i o nf o re l e c t r o s t a t i cw a v e sp r o p a g a t i n g nt h ef r e q u e n c yr a n g en~ くく w " 《 w~ : i nthe 土子 direction i n~ n~ w~ 一一一一二ーです+一一一一-"--ーで= --f+l 2 ( w-kvo)ζ2(w +kvo)ζω ; ( b )C a l c u l a t et h ed i s p e r s i o nw(k), g r o w t hr a t ey(k), and t h er a n g eo fwave numberso ft h eu n s t a b l ew a v e s . THE “ GRAVITATIONAL” INSTABILITY 6.7 I nap l a s m a ,aRayleigh‑Taylori n s t a b i l i t ycanoccurbecauset h emagnetic f i e l da c t sa sal i g h tf l u i dsupportingaheavyf l u i d( t h ep l a s m a ) .Incurved magneticf i e l d s ,t h ec e n t r i f u g a lf o r c eont h eplasmaduet op a r t i c l emotion alongt h ecurYedl i n e so ff o r c ea c t sa sanequivalent “gra、itational ” force ・ Tot r e a tt h es i m p l e s tc a s e ,c o n s i d e raplasmaboundaryl y i n gi nt h ey ‑ z p l a n e( F i g .6 ‑ 1 0 ) .Lett h e r ebead e n s i t yg r a d i e n tVn0i nt h e‑xd i r e c t i o n i r e c t i o n .Wemayl e tKT;=KT,=O andag r a , キ i t a t i o n a lf i e l dgint h exd f o rs i m p l i c i t yandt r e a tt h elow-βcase, i nwhichB0i suniform.Int h e e q u i l i b r i u ms t a t e ,t h ei o n sobeyt h eequation 命Vfn0(vり・ V)vo = e nvoラ Bo+1'vfηog D e r i , キ et h ed i s p e r s i o nr e l a t i o nf o rat w o ‑ s t r e a mi n s t a b i l i t yo c c u r r i n gwhen t h e r ea r et w oc o l de l e c t r o ns t r e a m sw i t he q u a lando p p o s i t ev 0i nabackground o ff i x e di o n s .Eachs t r e a mh a sad e n s i t y~n.,. 6・6.(a) t ~n0 ( b )C a l c u l a t et h emaximumgrowthr a t e . 6 ‑ 7 .A p l a s m ac o n s i s t so ft w ou n i f o r ms t r e a m so fp r o t o n sw i t hv e l o c i t i e s+vox e s p e c t i v ed e n s i t i e s? . n oand} n 0 .Therei san e u t r a l i z i n ge l e c t r o n and-vo去, and r .A l ls p e c i e sa r ec o l d ,andt h e r ei sno f l u i dw i t hd e n s i t yn 0andw i t hV o ,= 0 m a g n e t i cf i e l d .D e r i v ead i s p e r s i o nr e l a t i o nf o rs t r e a m i n gi n s t a b i l i t i e si nt h i s s y s t e m . PLASMA -ー- v ̲ ( 6 ‑ 3 6 1 。 B 会%タ%。%タ%タ%ィシ'.///~タ%タ%タ%ク:»χ VACUUM e l o c i t yui ss h o ti n t oac o l dp l a s m a 6 ‑ 8 .Ac o l de l e c t r o nbeamo fd e n s i t y8n0andv o fd e n s i t y' " 'a tr e s t . l x 7 Aplasmas u r f a c es u b j e c tt oag r a v i t a t i o n a li n s t a b i l i t y . FIGURE6 ‑ 1 0 , . ~ 一一一 2 1 5 ( a )D e r i ¥ ' ead i s p e r s i o nr e l a t i o nf o rt h eh i g h ‑ f r e q u e n c ybeam‑plasmai n s t a b i l i t y t h a te n s u e s . sd i f f i c u l tt oc a l c u l a t e ,b u tonec a nmakea ( b )Themaximumgrowthrateγm i ya n a l o g yw i t ht h ee l e c t r o n ‑ i o nBunemani n s t a b i l i t y . r e a s o n a b l eg u e s si f8 < l b U s i n gt h er e s u l tg i ¥ ' e nw i t h o u tp r o o fi nE q .[ 6 ‑ 3 5 ] ,g i v ea ne x p r e s s i o nf o rγ'" in <erms o f8 . 一一一 『司司”- i 218 219 E q u i l i b r i u m andS t a b i l i t y / 日unu h ア oω ‘、 U一 UηA 斗 IJ 一 + 二 Qω ,,ll I 町 Aソ t 一 O 一 LM c 一一η 一恥 ,町一 U向 ’ 、 ωω U + Lm ωrh一九 S u b s t i t u t i n gt h i si n t oE q .[ 6 ‑ 4 8 ] ,wehave ω C h a p t e r S i x [ 6 ‑ 5 0 ] w(w‑k v o )= -voD.,η ;,/ no [6・51] S u b s t i t u t i n gf o rv0fromE q .[6” 37], weo b t a i naq u a d r a t i ce q u a t i o nf o rω・ w2‑kvow-g (η ;,; n o )=0 [ 6 ‑ 5 2 ] Thes o l u t i o n sa r e w =~kv0 土 [~k2vi +g (吋/ηo)]112 [ 6 ‑ 5 3 ] Therei si n s t a b i l i t yi fw i scomplex;t h a ti s ,i f -g川/η。> ア k 2 v 5 [ 6 ‑ 5 4 ] A “ flute ” instability. Fromt h i s ,wes e et h a ti n s t a b i l i t yr e q u i r e sg andn;,/n0t ohaveo p p o s i t e s i g n .Thisi sj u s tt h es t a t e m e n tt h a tt h el i g h tf l u i di ssupportingt h eheavy sr e a landt h eplasmai ss t a b l e .S i n c egcanbeused f l u i d ;o t h e r w i s e ,w i t omodelt h ee f f e c t so fmagneticf i e l dc u r v a t u r e ,wes e efromt h i st h a t s t a b i l i t ydependsont h es i g no ft h ec u r v a t u r e .C o n f i g u r a t i o n sw i t hf i e l d l i n e sbendingi ntowardt h eplasmatendt obes t a b i l i z i n g ,andv i c ev e r s a . m a l lk( l o n gw a v e l e n g t h ) ,t h egrowthr a t ei sg i v e nby Forsu伍ciently s ド長雨プ山i''2 resemblef l u t e sw i t has l i g h th e l i c a lt w i s t( F i g .6 ‑ 1 3 ) .I fwee n l a r g et h e c r o s ss e c t i o ne n c l o s e dbyt h eboxi nF i g .6 ‑ 1 3ands t r a i g h t e ni touti n t o C a r t e s i a ngeometry,i twouldappeara si nF i g .6 ‑ 1 4 .Theo n l yd r i v i n g V n o (we assume f o r c ef o rt h ei n s t a b i l i t yi st h ep r e s s u r eg r a d i e n tK T' K T =c o n s t a n t ,f o rs i m p l i c i t y ) .I nt h i sc a s e ,t h ez e r o t h ‑ o r d e rd r i f t s( f o r Eu=0 )a r e I Ther e a lp a r to fw i s~kv0・ Since v0i sani o nveloci恥 this i salow-freq田町y o s c i l l a t i o n ,a sp r e v i o u s l yassumed. Thisi n s t a b i l i t y ,whichh a sk ム B0, i ssometimesc a l l e da"flute” ins ta噌 b i l i t yf o rt h ef o l l o w i n gr e a s o n .I nac y l i n d e r ,t h ewavest r a v e li nt h eB d i r e c t i o ni ft h ef o r c e sa r ei nt h erd i r e c t i o n .Thes u r f a c e so fc o n s t a n t d e n s i t ythenresemblef l u t e dGreekcolumns( F i g .6-12 )ー KT;n~ , V ; o=Vo ;=一τ:-- y en0no [ 6 ‑ 5 6 ] KT,n b , V , o=Vo,=一一τァ一一 y [ 6 ‑ 5 7 ] eno η。 Fromoure x p e r i e n c ew i t ht h ef l u t ei n s t a b i l i t y ,we mighte x p e c td r i f t rVo,・ We s h a l lshow wavest ohaveaphasev e l o c i t yo ft h eordero fVo; o sapproximatelye q u a lt ov 0 , . t h a tw/k,i S i n c ed r i f twaveshavef i n i t ek "e l e c t r o n scanf l o walongBotoe s t a b l i s h athermodynamice q u i l i b r i u mamongt h e m s e l v e s( c f .d i s c u s s i o no fS e c ュ i l lthenobeyt h eBoltzmannr e l a t i o n( S e c t i o n3 . 5 ) : t i o n4.10 )目 They w 6 . 8 RESISTIVEDRIFTWAVES n 1 / n o= eφ 1/KT, As i m p l eexampleo fau n i v e r s a li n s t a b i l i t yi st h er e s i s t i v ed r i f tw a v e .In c o n t r a s tt og r a v i t a t i o n a lf l u t emodes,d r i f twaveshaveas m a l lbutf i n i t e componento fk alongB 0 . The c o n s t a n td e n s i t ys u r f a c e s ,t h e r e f o r e , [ 6 ‑ 5 8 ] Atp o i n tA i nF i g .6 ‑ 1 4t h ed e n s i t yi sl a r g e rthani nequilibrium , ηI i s sp o s i t i v e .S i m i l a r l y ,a tp o i n tB ,n1andφi a r e p o s i t i v e ,andthereforeφl i n e g a t i v e .Thed i f f e r e n c ei np o t e n t i a lmeanst h e r ei s キane l e c t r i cf i e l dE 1 一..--..・ー FIGURE6 ‑ 1 2 216 I fgi sac o n s t a n t ,Vow i l lbea l s o ;and(v0 ・ V)vo v a n i s h e s .Takingt h ec r o s s producto fE q .( 6 ‑ 3 6 ]w i t hB 0 ,wef i n d ,a si nS e c t i o n2 . 2 , Cha戸leγ S i x M gラBo , Notet h a tgh a sc a n c e l l e do u t .Informationregardingg ,however,i ss t i l l c o n t a i n e di nv 0 .Forp e r t u r b a t i o n so ft h eformexp[ i(ky ー wt)], wehave 1 Jf(w‑k v 0 ) v 1= i e ( E 1+v 1X Bο) g• vo=-;B下=一石; Y [ 6 ‑ 3 7 ] Thee l e c t r o n shaveano p p o s i t ed r i f twhichcanben e g l e c t e di nt h el i m i t m/M • 0. Therei snodiamagneticd r i f tbecauseK T =0 ,andnoEaxBo d r i f tbecauseE0= 0 . I far i p p l eshoulddevelopi nt h ei n t e r f a c ea st h er e s u l to frandom thermalf l u c t u a t i o n s ,t h ed r i f tv 0w i l lc a u s et h er i p p l et ogrow( F i g .6 ‑ 1 1 ) . Thed r i f to fi o n sc a u s e sacharget ob u i l dupont h es i d e so ft h er i p p l e , andane l e c t r i cf i e l dd e v e l o p swhichchangess i g na soneg o e sfromc r e s t t otroughi nt h ep e r t u r b a t i o n .AscanbeseenfromF i g .6 ‑ 1 1 ,t h eE 1ラBo d r i f ti sa l w a y supwardi nt h o s er e g i o n swheret h es u r f a c eh a smoved upward,anddownwardwherei th a smoveddownward.Ther i p p l egrows a sar e s u l to ft h e s ep r o p e r l yphasedE 1xBod r i f t s . Tof i n dt h egrowthr a t e ,wecanperformt h eu s u a ll i n e a r i z e dwave a n a l y s i sf o rwavespropagatingi ntheyd i r e c t i o n :k= k タ The perturbed i o nequationo fmotioni s M(n0 + ηillLa 主(vo +v 1 )+( v o+v1)・ V(vo +vi)I t I = e (η。+ ni ) [ E 1+( v o+v1 )× Bo] +M(no+n1 ) g n ;サ(w‑ kvo)2 Af(n0+ni)(v0 ・ V)vo = e (目。+ ηilvo X Bo+M(no+n1 ) 冨[6・39] S u b t r a c t i n gt h i sfromE q .[ 6 ‑ 3 8 ]andn e g l e c t i n gsecond‑ordert e r m s ,we have [6・40] [6・42] t h es o l u t i o ni s E, vx =一- Bo w ‑kvoE, v = -z 一一一一一ーー η!l, Bo [6 ” 43] Thel a t t e rq u a n t i t yi st h ep o l a r i z a t i o nd r i f ti nt h ei o nframe.Thec o r r e s ュ pondingq u a n t i t yf o re l e c t r o n sv a n i s h e si nt h el i m i tm/1\lf • 0. Fort h e e l e c t r o n s ,wet h e r e f o r ehave v"=E,/B0 v , ,=0 [ 6 ‑ 4 4 ] Theperturbede q u a t i o no fc o n t i n u i t yf o ri o n si s a n , a t Wenowm u l t i p l yE q .(6・36] by1+(π 1/n0) too b t a i n Mno[守+何· V)v1]= eno(E1+い Bo) Thisi st h esamea sE q .( 4 ‑ 9 6 ]e x c e p tt h a tw i sr e p l a c e dbyw ‑k v 0 ,and e l e c t r o nq u a n t i t i e sa r er e p l a c e dbyi o nq u a n t i t i e s .Thes o l u t i o n ,t h e r e f o r e , i sg i v e nbyE q .( 4 ‑ 9 8 ]w i t ht h ea p p r o p r i a t ec h a n g e s .ForE,= 0and 一一+ [6司38] [ 6 ‑ 4 1 ] V (nova)+(vυ·V)n1 +(v1 ・ V)n0 十 n1V· vυ +noV V 1+V キ( n 1 v 1 )= 0 [ 6 ‑ 4 5 ] Thezeroth” order termv a n i s h e ss i n c ev 0i sperpendiculartoVn0,and t h en1V キv 0termv a n i s h e si fv 0i sc o n s t a n t .Thef i r s t ‑ o r d e re q u a t i o ni s , t h e r e f o r e , ‑iwn1+ikv0n1+v悶η~ +ikn0v;,= 0 [ 6 ‑ 4 6 ] wherenb=c i n 0 /a x .Theelectronsfollowasimplerequation,sincev , 0=O andu町= 0 : -zwn1 十 V.xnb = Q [ 6 ‑ 4 7 ] Notet h a twehaveusedt h eplasmaapproximationandhaveassumed n ;1= n ,Iキ T hisi sp o s s i b l ebecauset h eu n s t a b l ewavesa r eo flowf r e q u e n ュ c i e s( t h i scanbej u s t i f i e dap o s t e r i o r i ) .E q u a t i o n s[ 6 ‑ 4 3 ]and( 6 ‑ 4 6 ]y i e l d E旬ー w ‑kvn E.屯 (w‑k v o ) n 1+z 」川 + ikn0 -一一」ーよ= 0 Bo ! l , Bo [ 6 ‑ 4 8 ] E q u a t i o n s[ 6 ‑ 4 4 ]and( 6 ‑ 4 7 ]y i e l d ~.,《 FIGURE6‑11 wn1+i 云ム πo=U Do ι. iwn, 云.z. =-,よ Doπ 。 [ 6 ‑ 4 9 ] 217 E q u i l i b r i u m andS t a b i l i t y 寸- DENSE FIGURE 6・ 13 LESSDENSE Geometryo fad r i f ti n s t a b i l i t yi nac y l i n d e r .Ther e g i o n i nt h er e c t a n g l ei sshowni nd e t a i li nF i g .6 ‑ 1 4 . ーーーー相』 x .J u s ta si nt h ec a s eo ft h ef l u t ei n s t a b i l i t y ,E 1c a u s e sa betweenA andB ,xBo/B~ i nt h exd i r e c t i o n .Ast h ewavep a s s e sb y ,t r a v e l i n g d r i f tv ,=E i r e c t i o n ,ano b s e r v e ra tp o i n tA w i l ls e en1andφ1 o s c i l l a t i n g i nt h eyd i nt i m e .Thed r i f tv ,w i l la l s oo s c i l l a t ei nt i m e ,a n c ii nf a c ti ti sv 1which c a u s e st h ed e n s i t yt oo s c i l l a t e .S i n c et h e r ei sag r a d i e n tVn0i nt h e‑x d i r e c t i o n ,t h ed r i f tv 1wiUb r i n gplasmao fdi 圧erent d e n s i t yt oaf i x e d r i f tw a v e ,t h e r e f o r e ,h a samotionsucht h a tt h ef l u i d o b s e r v e rA.A d movesbackandf o r t hi nt h exdirection 旦! though t h ewavet r a v e l si nt h e yd i r e c t i o n . Tobemoreq u a n t i t a t i v e ,t h emagnitudeo fv 1 xi sg i v e nby Vtx=E,/B 。= ‑ik,「1/Bo P h y s i c a lmechanismo fad r i f tw a v e . FIGURE6 ‑ 1 4 h ed e n s i t yo f o f our p r e v i o u sa s s u m p t i o n . The di百erence between t i v e sac o r r e c t i o nt oE q . guidingc e n t e r sandt h ed e n s i t yo fp a r t i c l e sn1g [ 6 ‑ 6 0 ]whichi sh i g h e rorderandmayben e g l e c t e dh e r e . UsingE q s . r i t eE q .[ 6 ‑ 6 0 ]a s [ 6 ‑ 5 9 ]and[6 ” 58], wecanw ik,φI . Bo . eφl KT, ~ ~ [ 6 ‑ 6 1 ] Thuswehave ( 6 ‑ 5 9 ] w Wes h a l lassumevIχdoes notv a r yw i t hxandt h a tk ,i smuchl e s sthan k , ;t h a ti s ,t h ef l u i do s c i l l a t e si n c o m p r e s s i b l yi nt h exd i r e c t i o n .Consider nowt h enumbero fguidingc e n t e r sbroughti n t oIm3a taf i x e dp o i n t A ;i ti so b v i o u s l y a n , / a t= ‑ v , x a n o / a x , -iwη1 =ーー一- n,,=-iw 一一一- n,, KT,n ;> ー-=一一ーー一一一= k , eB0 η。 V n , ( 6 ‑ 6 2 ] r i f tv e l o c i t y Thesew a v e s ,t h e r e f o r e ,t r a v e lw i t ht h eelectγon diamagneticd st h ev e l o c i t yi nt h ey ,o ra z i m u t h a l , anda r ec a l l e ddrift 山aves. Thisi d i r e c t i o n .I na d d i t i o n ,t h e r ei sacomponento fkint h ezd i r e c t i o n .For r e a s o n sn o tg i v e nh e r e ,t h i scomponentmusts a t i s f yt h ec o n d i t i o n s [ 6 ‑ 6 0 ] Thisi sj u s tt h ee q u a t i o no fc o n t i n u i t yf o rguidingc e n t e r s ,w h i c h ,o f c o u r s e ,don o thaveaf l u i dd r i f tv n .Thetermn oV キ v 1v a n i s h e sbecause k, < k, 一一ームー v,h ; < w/k , < Vtt [ 6 ‑ 6 3 ] カ / 9 - u 川市 //〆 /./ // 4F ー‘ 町 + lm 2 官 Ju q B Z ① B。 2一肌仙 i 1I 5 C h a p t e r S i x /イノ //ル 220 224 Chai争/er S i x congregatea tA andupward‑movingonesa tB.Ther e s u l t i n gc u r r e n t s h e e t sj= ‑enov,a r ephasede x a c t l yr i g h tt ogenerateaBf i e l do ft h eshape assumed,andt h ep e r t u r b a t i o ng r o w s .Thought h eg e n e r a lc a s er e q u i r e sa ,= v , h ,V x= v ,= 0c anbec a l c u l a t e d k i n e t i ct r e a t m e n t ,t h el i m i t i n gc a s ev v e r ysimplyfromt h i sp h y s i c a lp i c t u r e ,y i e l d i n gagrowthrateγ = W p V , h / C . / C h a p t e rS e v e n I < I N E T I CTHEO悶F THE MEANING OF/ ( v ) 7 . 1 Thef l u i dt h e o r ywehavebeenusings of a ri st h es i m p l e s td e s c r i p t i o n o fap l a s m a ;i ti sindeedf o r t u n a t et h a tt h i sapproximationi ss u f f i c i e n t l y a c c u r a t et od e s c r i b et h em a j o r i t yo fo b s e r ¥ ' e dphenomena 目 There a r e somephenomena,however,f o rwhichaf l u i dtreatmenti si n a d e q u a t e . ( v )f o r Fort h e s e ,weneedt oc o n s i d e rt h ev e l o c i t yd i s t r i b u t i o nf u n c t i o nf e a c hs p e c i e s ;t h i st r e a t m e n ti sc a l l e dk i n e t i ct h e o r y .Inf l u i dt h e o r y ,t h e dependentv a r i a b l e sa r ef u n c t i o n so fo n l yfourindependentv a r i a b l e s : x ,y ,z ,and. tThisi sp o s s i b l ebecauset h ev e l o c i t yd i s t r i b u t i o no feach s p e c i e si sassumedt obeMaxwellianeverywhereandcant h e r e f o r ebe .S i n c ec o l ュ u n i q u e l ys p e c i f i e dbyo n l yonenumber,t h etemperatureT l i s i o n scanber a r ei nhigh‑temperaturep l a s m a s ,d e v i a t i o n sfromthermal e q u i l i b r i u mcanbemaintainedf o rr e l a t i v e l ylongt i m e s .Asanexample, i ( v x )and ん( vx) i naone‑dimensional c o n s i d e rtwov e l o c i t yd i s t r i b u t i o n sf system ( F i g .7 ‑ 1 ) . These twod i s t r i b u t i o n sw i l lhaYee n t i r e l ydi 庄erent b e h a v i o r s ,b u ta slonga st h ea r e a sundert h ec u r v e sa r et h esame ,日 uid t h e o r ydoesnotd i s t i n g u i s hbetweenthem. Thed e n s i t yi saf u n c t i o no ffours c a l a rv a r i a b l e s :n = n(r,t ) .When wec o n s i d e rv e l o c i t yd i s t r i b u t i o n s ,wehavesevenindependentv a r i a b l e s : f=f ( r ,v ,t ) .Byf ( r ,v ,t ) ,wemeant h a tt h enumbero fp a r t i c l e sperm3 a tp o s i t i o nrandtimetw i t hv e l o c i t ycomponentsbet、veen V xandV x+d v x , ,+d v , ,andv ,andv ,+d v ,i s v ,andv f ( x ,y ,z ,V x ,v , .v , ,t )d v xd v ,d v , ーム 225 『司”- 222 Chα争leγ S i x Tos e ewhyd r i f twavesa r eu n s t a b l e ,onemustr e a l i z et h a tv1 ,i snot , /B0fortheions.Therearecorrectionsduetothepolarization q u i t eE d r i f t ,E q .[ 2 ‑ 6 6 ] ,andt h enonuniformE d r i f t ,E q .[ 2 ‑ 5 9 ] .Ther e s u l to f a gbehind t h e s ed r i f t si salwayst omaket h ep o t e n t i a ld i s t r i b u t i o nφl l t h ed e n s i t ydistributionηi (Problem4 ‑ 1 ) .Thisphases h i f tc a u s e sv 1t o beoutward wheret h eplasmahasalreadybeens h i f t e d outward,and ntheabsenceo ft h ephase v i c ev e r s a ; hencet h eperturbationgrows.I s h i f t ,n1andφl wouldbe9 0 ーoutofp h a s e ,a sshowni nF i g .6・ 14, and d r i f twaveswouldbepurelyo s c i l l a t o r y . Ther o l eo fr e s i s t i v i t ycomesi n becauset h ef i e l dE 1 mustn o tbe s h o r t ‑ c i 1c u i t e dbye l e c t r o nf l o walongB 0 .Electronーion c o l l i s i o n s ,t o g e t h e r r e s tandtrougho ft h ewave,makei t w i t halongdistance 弘之 betweenc p o s s i b l et ohavear e s i s t i v ep o t e n t i a ldropandaf i n i t ev a l u eo fE 1 .The d i s p e r s i o nr e l a t i o nf o rr e s i s t i v ed r i f twaYesi sapproximately I: ; ~ i u u ( w‑w*)= 0 I .6・ 10. A t o r o i d a lhydrogenp l a s m aw i t hc i r c u l a rc r o s ss e c t i o nh a smajorr a d i u s R =5 0c m ,minorr a d i u sa=2c m ,B =IT,KT,=1 0e V ,KT,=Ie V ,andn 0= 1019m• Taking n 0 / n ; ,= α/ 2 and[!;=(KT,+KT;)/MR,e s t i m a t ethe 日rowth r a t e so ft h em = Ir e s i s t i v ed r i f twaveandt h em = Ig r a v i t a u o n a lf l u t emode. (Onec a nc : s u a l l ya p p l yt h es l a b ‑ g e o m e t r yf o r m u l a st oc y l i n d r i c a lgeometryb y r e p l a c i n gk ,b ym f r ,wherem i st h ea z i m u t h a lmoden u m b e r . ) (6司 65] PROBLEM - 9 -ヲ ω z 0 9- σ 三 [ 6 ‑ 6 6 ] [6 ・67] γHIーや liA y i sl a r g ecomparedwithw,E q .[ 6 ‑ 6 4 ]canbesatis自ed onlyi fw ' ー "w * ・ Int h a tc a s e ,wemayr e p l a c ew byw*i nt h ef i r s tt e r m .Solvingf o rw ,we theno b t a i n IfσH |…*+州内)| andS t a b i l i t y Asanexampleofani n s t a b i l i t ydrivenbya n i s o t r o p yoft h ed i s t r i b u t i o n f u n c t i o n ,weg i v eap h y s i c a lp i c t u r e(duet oB .D.F r i e d )oft h eWeibel i n s t a b i l i t y ,i nwhichamagneticp e r t u r b a t i o ni smadet ogrow.Thisw i l la l s o s e r v ea sanexampleofane l e c t r o m a g n e t i ci n s t a b i l i t y .L e tt h ei o n sbef i x e d , i r e c t i o n s . andl e tt h ee l e c t r o n sbeh o t t e ri ntheyd i r e c t i o nthani nt h exorzd i r e c t i o n s( F i g . Therei sthenapreponderanceoff a s te l e c t r o n si nthe 土y d 6 ‑ 1 5 ) ,butequalnumbersf l o wupanddown,s ot h a tt h e r ei snon e tc u r r e n t . , zcosk x spontaneously a r i s e s from n o i s e . The Suppose a f i e l d B =B Lorentzf o r c e‑evラ B thenbendst h ee l e c t r o nt r a j e c t o r i e sa sshownby i t ht h er e s u l tt h a t downward‑moving e l e c t r o n s t h e dashed cur、 es, w [ 6 ‑ 6 4 ] and ’ R7k Equilibγium THE WEIBEL INSTABILITY* 6.9 where I~~ 223 a r er e a l ,andw i scomplexwhent h ed i s c r i m i n a n to ft h eq u a d r a t i ci s e a c t i v ei n s t a b i l i t y .Int h el a t t e r ,t h ecoe伍 cients n e g a t i v e ;t h i si st y p i c a lo far a r e complex, s ow i sa l w a y s complex; t h i si st y p i c a lo f ad i s s i p a t i v e i n s t a b i l i t y . B 『+ I ¥ ¥ I v角 •h This shows t h a t Im(w) i s always p o s i t i v e and i sp r o p o r t i o n a lt ot h e resistivityη. D r i f twavesa r e ,t h e r e f o r e ,u n s t a b l eandw i l le v e n t u a l l yoccur i nanyplasmawithad e n s i t yg r a d i e n t .F o r t u n a t e l y ,t h egrowthr a t ei s r a t h e rs m a l l , and t h e r e are ways t os t o pi ta l t o g e t h e r by makingBo nonuniform. o rt h ef l u t ei n s t a b i l i t yandE q .[6崎64] f o rt h e Notet h a tE q .[6・52] f d r i f ti n s t a b i l i t yhaved i f f e r e n ts t r u c t u r e s .Int h eformer,t h ecoe伍 cients ~ x B z FIGURE6 ‑ 1 5 *As a l u t et oag o o df r i e n d ,E r i c hW e i b e l( 1 9 2 5 ‑ 1 9 8 3 ) . 一一-・‘ー 『宇田Fー 226 f 1( v x ) Chai争ter f 2 ( v ) 227 、(z K i n e t i cT h e o r y S四四 v x v x FIGURE7‑1 Exampleso fn o n ‑ M a x w e l l i a nd i s t r i b u t i o nf u n c t i o n s . Vy Thei n t e g r a lo ft h i si sw r i t t e ni ns e v e r a le q u i v a l e n tw a y s : 3V tt vv rr ∞∞∞∞ JU J ) ) ’ (( f JffJ U 一一一一 ) flif ’’r ( J t v r ョ d, z u ∞∞ U χ d, F115 ’ ι ∞∞ U llL . d 「 ∞∞ 一一 --よ ) pi t η r ( -- ι “ Yx T h r e e ‑ d i m e n s i o n a lv e l o c i t ys p a c e . FIGURE7‑2 , [n -] Notet h a tdvi sn o tav e c t o r ;i ts t a n d sf o rat h r e e ‑ d i m e n s i o n a lvolume elementi nv e l o c i t ys p a c e .I ffi snormalizeds ot h a t に/(r, v,t) の= 1 Byusingt h ed e f i n i t ei n t e g r a l に回p (-x2)ゐ= .J手 ( 7 ‑ 2 ] f i ti sap r o b a b i l i t y ,whichwedenoteby Thus f ( r , v , t )= η (r, t ) / ( r ,v ,t ) onee a s i l yv e r i f i e st h a tt h ei n t e g r a lo ffmoverdvxdv,dv,i su n i t y . Therea r es e v e r a laveragev e l o c i t i e so faMaxwelliand i s t r i b u t i o n t h a ta r ecommonlyu s e d .InS e c t i o n1 . 3 ,wesawt h a tt h erooトmean-square v e l o c i t yi sgiγen by ( 7 ‑ 3 ] Notet h a tfi ss t i l laf u n c t i o no fsevenv a r i a b l e s ,s i n c et h eshapeo ft h e d i s t r i b u t i o n ,a sw e l la st h ed e n s i t y ,c昌n changew i t hspaceandt i m e .From E q .(7・2], i ti sc l e a rthat[hast h edimensions( m / s e c )3 ;andc o n s e q u e n t l y , fromE q .(7・3], fh a st h edimensionss e c 3 ‑ m‑6. Ap a r t i c u l a r l yimportantd i s t r i b u t i o nf u n c t i o ni st h eM a x w e l l i a n : ん= (m/27TKT)山 exp (-v2/v~ ) ( ; ; 2 ' ) 1 1 2= (3KT/m)112 =(v;+v;+v;1)112 and = v , h (2KT/m)112 ( 7 ‑ 7 ] Theaveragemagnitudeo ft h ev e l o c i t yI vI ,ors i m p l yi i ,i sfounda sf o l l o w s : ( 7 ‑ 4 ] 古=に泊v) d3v ( 7 ‑ 5 ] Since ん is i s o t r o p i c ,t h ei n t e g r a li smoste a s i l ydonei ns p h e r i c a lc o o r d i n ュ a t e si nv space( F i g .7‑2). S i n c et h evolumeelemento feachs p h e r i c a l where v ( 7 ‑ 6 ] 一ι ( 7 ‑ 8 ] 司喝匝.,・ー 228 s h e l li s4 7 T v 2d v ,wehave Seveη v= (m/27rKT)日|市xp (‑v2/v~h)]47Tv2 dv g ( v )=41Tn(m/21TKT )" [ 7 ‑ 9 ] J : J =(1TV~S31241Tv;\, [ 7 ‑ 1 0 ] J[] Thed e f i n i t ei n t e g r a lhasav a l u e~' foundbyi n t e g r a t i o nbyp a r t s .Thus 五= 2 7 T-•12v,h =2(2KT/7rm)112 [7・ 11] Thev e l o c i t ycomponenti nas i n g l ediγection, s a yv . ,h a sadi汀erent a v e r a g e . o rani s o t r o p i cdistribu山n; but doesn o t : Ofcourse,元 vanishes f G . J l v , I =JI 叫ん(v)d九 I m ¥1 2I X [7・ 12] "'ー f-v~\ 「"' f-v~\ L , ,dv,exp \古j J ̲ " 'dv, 州市 I2vx 叫 l二円 dvx Jo ( 7 ‑ 1 3 ] 、 u th ノ FromE q .[ 7 ‑ 6 ] ,eacho ft h ef i r s ttwoi n t e g r a l sh a st h ev a l u e1 T112v,h ・ The l a s ti n t e g r a li ss i m p l eandh a st h ev a l u ev~,. Thuswehave 1 2 l v x l = (7TV~h)-312間 ~h = 1T ー 112v,h =(2KT/1Tm)1 ( 7 ‑ 1 4 ] Therandomf l u xc r o s s i n ganimaginaryp l a n efromones i d et ot h eo t h e r i sg i v e nby I 'random =おlvxl = ~n (3KT/m)112 I v i= 2(2KT/7rm)112 / v . I= (2KT/ πm)112 v .= 0 <) <) [ 7 ‑ 1 8 ] (7・ 15] HerewehaveusedE q .[ 7 ‑ 1 1 ]andt h ef a c tt h a tonlyh a l ft h ep a r t i c l e s c r o s st h eplanei ne i t h e rd i r e c t i o n .Tosummarize:ForaM a x w e l l i a n , Vrms = < ) F i g u r e7 ‑ 3showst h ed i f f e r e n c ebetweeng ( v }andaone』dimensional Maxwelliand i s t r i b u t i o n f ( v x ) .Althoughf(vx)i smaximumf o rV x= 0 ,g(v) i sz e r of o rv=0 .Thisi sj u s taconsequenceo ft h ev a n i s h i n go ft h e .Sometimesg(v)i sc a r e l e s s l y キvolumei nphases p a c e( F i g .7 ‑ 2 )f o rv=0 denotedbyf ( v ) ,a sd i s t i n c tfromf ( v ) ;butg ( v }i sadi 圧e1 e n tf u n c t i o no f v }i so fi t sargument.FromE q .[ 7 ‑ 1 8 ] ,i ti sc l e a rt h a t i t sargumentthanf( g ( v )h a sdimensionss e c / m 4 . I ti si m p o s s i b l et odrawap i c t u r eo ff ( r ,v )a tag i , キ e nt i m eIu n l e s s we reduce t h e numbero fd i m e n s i o n s .I n aone‑dimensional s y s t e m , f ( x ,v x )canbed e p i c t e da sas u r f a c e( F i g .7 ‑ 4 ) .I n t e r s e c t i o n so ft h a ts u r f a c e r et h ev e l o c i t yd i s t r i b u t i o n sf ( v , ) .I n t e r s e c t i o n s w i t hp l a n e sx=constanta w i t hp l a n e sv ,=c o n s t a n tg i v ed e n s i t yp r o f i l e sf o rp a r t i c l e sw i t hag i v e n Vx ・ If a l lt h ec u r v e sf ( v , }happent ohavet h esamesh昌 pe, acurvethrough t h epeakswouldr e p r e s e n tt h ed e n s i t yp r o f i l e .Thedashedc u r v e si nFig目 7 ‑ 4a r ei n t e r s e c t i o n sw i t hp l a n e sf=constant;t h e s ea r el e v e lcur、es, o r .A projectionofthesecurvesontothex ‑ v ,planew i l l c u r v e so fc o n s t a n tf g i v eat o p o g r a p h i c a lmapof よ Such mapsa r ev e r yu s e f u lf o rg e t t i n ga p r e l i m i n a r yi d e ao fhowt h eplasmab e h a v e s ;anexamplew i l lbeg i v e n i nt h en e x ts e c t i o n . Anothert y p eo fcontourmapcanbemadef o rfi fwec o n s i d e rf ( v } a tag i v e np o i n ti ns p a c e .Fori n s t a n c e ,i ft h emotioni stwod i m e n s i o n a l , t h ec o n t o u r so ff(ぬ, v,) w i l l be c i r c l e si ff i si s o t r o p i ci nv . ,v , . An CO I[exp(一戸)J/ dy A ~- exp (‑v"/v;h) ' ‑ t / 9 ,.。0 =同子j 229 K i n e t i cT h e o r y ForaM a x w e l l i a n ,wes e efromEq 目[ 7-9] t h a t Cha戸ter g( v ) f ( v x ) ( 7 ‑ 7 ] (7・ 11] ( 7 ‑ 1 4 ] [ 7 ‑ 1 6 ] Forani s o t r o p i cd i s t r i b u t i o nl i k eaM a x w e l l i a n ,wecand e f i n eanother f u n c t i o ng ( v }whichi saf u n c t i o no ft h es c a l a rmagnitudeo fvsucht h a t 。 rg(りの=にf付 [ 7 ‑ 1 7 ] 、i x 。 ‑ 3 One‑andthree・dimensional M a x w e l l i a nv e l o c i t yd i s t r i b u t i o n s . FIGURE7 --ー』 v 軍事一 230 Chapleγ f v y S e v e n 2 3 1 Kiηetic Theoり’ vx v x C o n t o u r so fc o n s t a n tff o rat w o ‑ d i m e n s i o n a l ,a n i s o t r o p i c FIGURE7 . 5 d i s t r i b u t i o n . FIGURE7 . 4 As p a t i a l l yv a r y i n go n e ‑ d i m e n s i o n a ld i s t r i b u t i o nf ( x ,v . ) . v y ~nisotropic d附ibu山n wouldhaveellipti叫 contours ( F i g .7 ‑ 5 ) .A d r i f t ュ mgMaxwellianwouldhavec i r c u l a rcontoursd i s p l a c e dfromt h eo r i 1 2 : i n . andabeamo fparticles 同veling i nt h e d i r e c t i o nwouldshowup a s e p a r a t es p i k e( F i g .7 ‑ 6 ) . x DRIFTINGMAXWELLIAN s ; Al o s sconed i s t r i b u t i o no fam i r r o r ‑ c o n f i n e dplasmacanber e p r e s e n ュ t e dbyc o n t o u r soffi nv.L. v us p a c e .Figure7 ‑7showshowt h e s ewould l o o k . / 7 . 2 EQUATIONSOFKINETICTHEORY vx Thefundamentale q u a t i o nw h i c h / ( r ,v ,t )h a stos a t i s f yi st h eBoltzmann e q u a t i o n : *+v·V/+~·~=(わc [7・ 19] HereFist h ef o r c ea c t i n gont h ep a r t i c l e s ,and( a / f a t ) ,i st h etimer a t e o fchangeoffduet oc o l l i s i o n s .ThesymbolV s t a n d s ,a su s u a l ,f o rt h e g r a d i e n ti n( x ,y ,z )s p a c e .Thesymbola/avorV"s t a n d sf o rt h eg r a d i e n t C o n t o u r so fc o n s t a n tff o rad r i f t i n gM a x w e l l i a nd i s t r i b u t i o nanda “ beam” i ntwod i m e n s i o n s . ~ FIGURE7 ‑ 6 232 C h a p t e r S e v e n vx / 233 K i n e t i cT h e o r y 同 図 Vl /~ x A group o fp o i n t si np h a s e FIGURE7 ‑ 8 s p a c e ,r e p r e s e n t i n gt h ep o s i ‑ t i o nandv e l o c i t yc o o r d i n a t e s o fagroupo fp a r t i c l e s ,r e t a i n s t h esamep h a s e ‑ s p a c ed e n s i t y a si tmovesw i t ht i m e . FIGURE7‑7 C o n t o u r so fc o n s t a n tff o ral o s s ‑ c o n ed i s t r i b u t i o n .Hereu11andUム stand f o rt h ecomponentso fva l o n gandp e r p e n d i c u l a rt ot h em a g n e t i cf i e l d , r e s p e c t i v e l y . i n¥ ' e l o c i t ys p a c e : δA a ̲a ̲a ーー=孟一一+アー一+量一- a v av, 。v, av, [ 7 ‑ 2 0 ] The meaning o ft h e Boltzmann e q u a t i o n becomes c l e a ri f one rememberst h a tfi saf u n c t i o no fsevenindependentv a r i a b l e s .Thet o t a l d e r i v a t i v eoffw i t ht i m ei s ,t h e r e f o r e g_ =~+ !l 生 + !l 企 + !l 生 + !l~ + !L 生~+ !L 生 d t a t a xd t a yd t a zd t a v ,d t a v ,d t 'avζ dt [ 7 ‑ 2 1 ] Here,a f / o ti st h ee x p l i c i tdependenceont i m e .Then e x tt h r e etermsa r e j u s tvキV f .Witht h ehelpo fNewton ’ s t h i r dl a w , dv d t m‑=l' Boltzmannequation[7 ・ 19] s i m p l ys a y st h a td f / d ti szerou n l e s st h e r ea r e c o l l i s i o n s .Thatt h i sshouldbet r u ecanbeseenfromt h eone‑dimensional exampleshowni nF i g .7 ‑ 8 xd v ,a tA a l l Thegroupo fp a r t i c l e si nani n f i n i t e s i m a lelementd h 礼ve v e l o c i t yv , andp o s i t i o nx .Thed e n s i t yo fp a r t i c l e si nt h i sphase ( x ,v ,) .Ast i m ep a s s e s ,t h e s ep a r t i c l e sw i l lmovet oadi 汀erent s p a c ei sj u s tf xa sar e s u l to ft h e i rv e l o c i t yv ,andw i l lchanget h e i r¥ キ e l o c i t ya sar e s u l t o ft h ef o r c e sa c t i n gonthem.S i n c et h ef o r c e sdependonxandv ,o n l y , i l lbea c c e l e r a t e dt h esameamount.A f t e ratime a l lt h ep a r t i c l e sa tA w , Ia l lt h ep a r t i c l e sw i l la r r i v ea tB i nphases p a c e .S i n c ea l lt h ep a r t i c l e s movedt o g e t h e r ,t h ed e n s i t ya tB w i l lbet h esamea sa tA.I ft h e r ea r e 仁ollisions, howe 、 er, t h ep a r t i c l e scanbes c a t t e r e d ;andfcanbechanged a f /a t) c ‑ byt h eterm( I nas u f f i c i e n t l yh o tp l a s m a ,c o l l i s i o n scanben e g l e c t e d .I f ,f u r t h e r ュ more,t h ef o r c eFise n t i r e l ye l e c t r o m a g n e t i c ,E q .[ 7 ‑ 1 9 ]t a k e st h es p e c i a l form [ 7 ‑ 2 2 ] t h el a s tt h r e etermsa r erecognizeda s( F/m )・ (of/ov). Asd i s c u s s e dp r e ュ v i o u s l yi nS e c t i o n3 . 3 ,t h et o t a ld e r i v a t i v ed f / d tcanbei n t e r p r e t e da st h e r a t eo fchangea sseeni naframemovingw i t ht h ep a r t i c l e s .Thedi 圧erence i st h a tnowwemustc o n s i d e rt h ep a r t i c l e st obemovingi ns i x ‑ d i m e n s i o n a l ( r ,v )s p a c e ;d f / d ti st h ec o n v e c t i v ed e r i v a t i v ei n phase space ・ The 。f q a f -+v·V/+ー(E+vXB )・一= O a t m a v [ 7 ‑ 2 3 ] Thisi sc a l l e dt h eV l a s o vequatioη. Becauseo fi t scomparatives i m p l i c i t y , t h i si st h eequationmostcommonlys t u d i e di nk i n e t i ct h e o r y . When 『咽’- 234 C h a p t e r S e v e n v x t h e r ea r ec o l l i s i o n sw i t hn e u t r a latoms,thec o l l i s i o ntermi nEq.( 7‑ 1 9 ] canbeapproximatedby (ご)=仁f [ 7 ‑ 2 4 ] wheref ni st h ed i s t r i b u t i o nf u n c t i o no ft h en e u t r a la t o m s ,andri sa c o n s t a n tc o l l i s i o nt i m e .Thisi sc a l l e daK rookc o l l i s i o nteγ-m. I ti st h ek i n e t i c g e n e r a l i z a t i o no ft h ec o l l i s i o ntermi nE q .( 5 ‑ 5 ] .Whent h e r ea r eCoulomb c o l l l i s i o n s ,E q .( 7 ‑ 1 9 ]canbeapproximatedby d f a 1 d t av 2avav 235 K i n e t i cT h e o r y a 2 -'-=一一・(/(6.v))一一一:(/( 6.v 6 . v ) ) 。 x Appearanceo ft h egrapho fF i g .7 ‑ 9whenaplasmawavee x i s t si nt h e FIGURE7 ‑ 1 0 e l e c t r o nbeam.Thee n t i r ep a t t e r nmovest ot h er i g h tw i t ht h ep h a s e v e l o c i t yo ft h ew a v e .I ft h eo b s e r v e rg o e st ot h eframeo ft h ew a v e ,t h e p a t t e r nwoulds t a n ds t i l l ,ande l e c t r o n swouldh es e e nt ot r a c et h ec u r v e w i t ht h ev e l o c i t yv0‑ vφ目 [7羽l Thisi sc a l l e dt h eF o k k e r ‑ P l a n c ke q u a t i o n ;i tt a k e si n t oaccountb i n a r y Coulombc o l l i s i o n so n l y .Here,6 . vi st h echangeo fv e l o c i t yi nac o l l i s i o n , and Eq 目( 7-25] i s a shorthand way o fw r i t i n ga r a t h e r complicated e x p r e s s i o n . Thef a c tt h a td f / d ti sc o n s t a n ti nt h eabsenceo fc o l l i s i o n smeans t h a tp a r t i c l e sf o l l o wt h econtourso fc o n s t a n tfa st h e ymovearoundi n phases p a c e .Asanexampleo fhowt h e s econtourscanbeu s e d ,c o n s i d e r t h ebeam‑plasmai n s t a b i l i t yo fS e c t i o n6 . 6 .Int h eunperturbedp l a s m a , h econtouro fconstant/i sas t r a i g h t t h ee l e c t r o n sa l lhavev e l o c i t yv0,andt ‑ 9 ) .Thefunctionf ( x ,v , )i saw a l lr i s i n gouto ft h eplaneo f l i n e( F i g .7 t h epapera tv ,= V o .Thee l e c t r o n smovealongt h et r a j e c t o r yshown. Whenawaved e v e l o p s ,t h ee l e c t r i cf i e l dE1 c a u s e se l e c t r o n st osu狂er changes i n Vx a st h e ystream a l o n g . The t r a j e c t o r y then d e v e l o p sa s i n u s o i d a lr i p p l e( F i g . 7・ 10). Thisr i p p l et r a v e l sa tt h ephasev e l o c i t y , -e 中 1 FREEELECTRON -一一一昔』 x Thep o t e n t i a lo faplasmaw a v e ,a ss e e nbyane l e c t r o n .Thep a t t e r nmoves FIGURE7 ‑ 1 1 w i t ht h ev e l o c i t yv.,・ An e l e c t r o nw i t hs m a l lv e l o c i t yr e l a t i v et ot h ewavewould het r a p p e di nap o t e n t i a lt r o u g handh ec a r r i e da l o n gw i t ht h ew a v e . . v x nott h ep a r t i c l e¥ ' e l o c i t y .P a r t i c l e ss t a yont h ecurvea st h e ymover e l a t i v e t ot h ewave.I fE1becomesv e r yl a r g ea st h ewaveg r o w s ,andi ft h e r e a r eafewc o l l i s i o n s ,somee l e c t r o n sw i l lbetrappedi nt h ee l e c t r o s t a t i c p o t e n t i a lo ft h ewave.I nc o o r d i n a t es p a c e ,t h ewavep o t e n t i a lappears ‑ 1 1 .Inphases p a c e ,f ( x ,v , )w i l lhavepeakswherevert h e r ei s a si nF i g .7 ‑ 1 2 ) .S i n c et h econtoursoffa r ea l s oe l e c t r o n ap o t e n t i a ltrough( F i g .7 t r a j e c t o r i e s ,ones e e st h a tsomee l e c t r o n smovei nc l o s e do r b i t si nphase s p a c e ;t h e s ea r ej u s tt h etrappede l e c t r o n s . E l e c t r o n trapping i s an o n l i n e a r phenomenon which cannotbe t r e a t e dbys t r a i g h t f o r w a r ds o l u t i o no ft h eVlasove q u a t i o n . However, e l e c t r o nt r a j e c t o r i e scanbef o l l o w e donacomputer,andt h er e s u l t sa r e v 0 。 x FIGURE7 ‑ 9 R e p r e s e n t a t i o ni no n e ‑ d i m e n s i o n a lphases p a c eo fabeamo fe l e c t r o n sa l l w i t ht h esamev e l o c i t yv0・ The d i s t r i b u t i o nfunctionf(x,九) i si n f i n i t ea l o n g t h el i n eandz e r oe l s e w h e r e .Thel i n ei sa l s ot h et r a j e c t o r yo fi n d i v i d u a l e l e c t r o n s ,whichmovei nt h ed i r e c t i o no ft h ea r r o w . -・・・・ー一一一 『噌闘- 236 v S i n c evi sanindependentv a r i a b l eandt h e r e f o r ei snota征ected byt h e operatorV,t h esecondtermg i v e s Chapleγ u n 一一一 -v) v n 一一 ,a v v PIB -- J ftd v V , 一一 V Jω fj v nee .ι , E2 ., a x v S四四 237 K i n e t i cTheoη [ 7 ‑ 2 8 ] た'-------~ノ~ー------···<;,;,玄\「-------~ 勿~協,._A.物ゐ~あ~偽~あ~ノ x 修後物後~~後〆後物グマ後係修~可え ー/ー~----ー\」-----~ー------ー\」J「一一------- ~ FIGURE7 ‑ 1 2 E l e c t r o nt r a j e c t o r i e s ,o rc o n t o u r so fc o n s t a n t / ,a ss e e ni nt h ewavef r a m e ,i n whicht h ep a t t e r ni ss t a t i o n a r y .T h i st y p eo fd i a g r a m ,a p p r o p r i a t ef o rf i n i t e d i s t r i b u t i o n sf ( v ) ,i se a s i e rt ou n d e r s t a n dt h a nt h eS・function d i s t r i b u t i o no f F i g .7 ‑ 1 0 . ω〈凶ZOZ一 UE 一ト02 一 o f t e npresentedi nt h eformo fap l o tl i k eF i g .7 ‑ 1 2 .Anexampleo fa numericalr e s u l ti sshowni nF i g .7・ 13. Thisi sf o ratwo‑streami n s t a b i l i t y x= 0whichs e p a r a t e s i nwhichi n i t i a l l yt h econtoursoffhaveagapnearv e l e c t r o n smovingi no p p o s i t ed i r e c t i o n s .Thedevelopmento ft h i su n i n ュ h a b i t e dgapwithtimei sshownbyt h eshadedr e g i o n si nF i g .7 ‑ 1 3 .This ( v )i nawaywhich f i g u r eshowst h a tt h ei n s t a b i l i t yp r o g r e s s i v e l yd i s t o r t sf wouldbehardt od e s c r i b ea n a l y t i c a l l y . 参疹矛考参~参湯メ I》ィめて物》イ 卿刈後~~ヘ{ 7 . 3 DERIVATIONOFTHEFLUIDEQUATIONS Thef l u i d equationswe have been usinga r e simply moments o ft h e Boltzmanne q u a t i o n .Thel o w e s tmomenti sobtainedbyi n t e g r a t i n gE q . (7司 19] w i t hFs p e c i a l i z e dt ot h eLorentzf o r c e : f f v·Vfdv づ f *dv+ B)か= f (お dv ( E+vx Thef i r s ttermg i v e s 一一 d, 加一ω .. ’ ’zE ’ JJ 一一 一h ω a” v a v ma E2 判。ーR -o l ., -t d. -- x -一一一一一ーー- [7・26] [ 7 ‑ 2 7 ] 一一一一ー一一一ー一一ー一ー一 一ー一一日ーーーー・・・ーーーーーー- . . P h a s e ‑ s p a c ec o n t o u r sf o re l e c t r o n si nat w o ‑ s t r e a mi n s t a b i l i t y .Theshaded FIGURE 7 ‑ 1 3 r e g i o n ,i n i t i a l l yr e p r e s e n t i n glowv e l o c i t i e si nt h eJ a bf r a m e ,i sd e v o i do f e l e c t r o n s .Ast h ei n s t a b i l i t yd e v e l o p sp a s tt h el i n e a rs t a g e ,t h e s eemptyr e g i o n s i np h a s es p a c et w i s ti n t os h a p e sr e s e m b l i n g“ water bags. ”[ From H.L .B e r k , C .E .N i e l s o n ,andK .V .R o b e r t s ,P h y s .F l u i d s1 3 ,986( 1 9 7 0 ) . ] ‑ キ 、 一一一一一一一 238 C h a p t e r Seveη wheret h eaveragev e l o c i t yu i st h ef l u i dv e l o c i t ybyd e f i n i t i o n .TheE termv a n i s h e sf o rt h ef o l l o w i n gr e a s o n : I E·~dv= If· (仰v f = fEキdS=O Thef i r s ttwoi n t e g r a l sont h er i g h t ‑ h a n ds i d ev a n i s hf o rt h esamer e a s o n s a sb e f o r e ,anda v / a vi sj u s tt h ei d e n t i t yt e n s o r. IEγE t h e r e f o r ehave r J Thep e r f e c td i v e r g e n c ei si n t e g r a t e dtog i v et h ev a l u eo ffEont h es u r f a c e a n i s h e si ff • O f a s t e rthanv‑2a su • oo, a si sn e c e s s a r y a tv=OJ.Thisv f o ranyd i s t r i b u t i o nw i t hf i n i t ee n e r g y .ThevxB termcanbew r i t t e n a sf o l l o w s : F i n a l l y ,t oe v a l u a t et h esecondi n t e g r a li nE q .( 7 ‑ 3 2 ] ,wef i r s tmakeu s e o ft h ef a c tt h a tvi sanindependentv a r i a b l en o tr e l a t e dt oV andw r i t e Jv ( vキ V)fdv=JVキ( f v v )dv=V キ Jf v vdv v .Jfvvdv=v .nvv S i n c eui sa l r e a d yan 一一 ハり u n v 仰でω m r r 2V 目 ( nu脅) The quantity 畑nww [ 7 ‑ 3 9 ] i sp r e c i s e l ywhat [ 7 ‑ 4 0 ] Theremainingtermi nE q .( 7 ‑ 3 9 ]canbew r i t t e n V キ( n u u )=uVキ(nu)+n(u V)u [ 7 ‑ 3 2 ] [ 7 ‑ 4 1 ] C o l l e c t i n gourr e s u l t sfromE q .(7句 33], ( 7 ‑ 3 5 ] ,( 7 ‑ 4 0 ] ,and( 7 ‑ 4 1 ] ,wecan w r i t eE q .( 7 ‑ 3 2 ]a s Theright嶋hand s i d ei st h echangeo fmomentumduet oc o l l i s i o n sand w i l lg i v et h etermP ; ;i nE q .( 5 ‑ 5 8 ] .Thef i r s ttermi nE q .( 7 ‑ 3 2 ]g i v e s Jv*dv =サ j vfdv 言明~(nu) =V キ(nuu)+V キ(η苛苛)+ P=mn育育 ー「\ Ja t m wehave Theaverage 骨 is o b v i o u s l yzero 目 i smeantbyt h es t r e s st e n s o rP : I v ' ! l . .dv+m r v ( v V)fdv+qr v(E+vxB).互の= r mv (引の J J av J ¥ a t } ' 'Jr 呂verage, V· (η否干) [ 7 ‑ 3 1 ] Then e x tmomento ft h eBoltzmanne q u a t i o ni so b t a i n e dbym u l t i p l y i n g E q .( 7 ‑ 1 9 ]bymvandi n t e g r a t i n goverd v .Wehave 「 [7・37] Nowwemays e p a r a t evi n t ot h ea v e r a g e(日 uid) v e l o c i t yuandat h e r m a l v e l o c i t yw: [ 7 ‑ 3 8 ] v=u+w c o n t i n u i t y : ) [7品] S i n c et h eaverageo faq u a n t i t yi sl / nt i m e si t sweightedi n t e g r a lo v e r v ,wehave Thef i r s ti n t e g r a lcana g a i nbeconvertedt oas u r f a c ei n t e g r a l . Fora M a x w e l l i a n ,ff a l l sf a s t e rthananypowero fva su • oo, andt h ei n t e g r a l t h e r e f o r ev a n i s h e s .Thesecondi n t e g r a lv a n i s h e sb e c a u s evラBisperpenュ d i c u l a rt oa / a v .F i n a l l y ,t h ef o u r t htermi nE q .( 7 ‑ 2 6 ]v a n i s h e sb e c a u s e c o l l i s i o n scannotchanget h et o t a lnumbero fp a r t i c l e s( r e c o m b i n a t i o ni s n o tc o n s i d e r e dh e r e ) .Equations(7-27 ]ー( 7-30] theny i e l dt h eequatioη of ( J dV (7・35] j 似 B) ·~dv= J ~· 山 B)dv- J f~ X 似 B) dv=0 げ + r q v(E+vxB )キ~ dv=‑q ( E+vxB)fdv= ‑qn( E+uxB ) [ 7 ‑ 2 9 ] m~ (nu)+mu V ・ (nu)+ 刑n (uキ¥l)u+V 。t P‑qη (E +uxB)=P , , [ 7 ‑ 3 3 ] [ 7 ‑ 4 2 ] Thet h i r di n t e g r a li nE q .( 7 ‑ 3 2 ]canbew r i t t e n Combiningt h ef i r s ttwotermsw i t ht h eh e l po fE q . (7 ・31], wef i n a l l y l u i dequatioη of m o t i o n : o b t a i nt h ef j 加 vXB) ·~dv= J fキ(fv(E+vXB)]dv mn [子(u· V)u]=州+ uxB)‑VキP+P,1 ‑ I ·肝 X 1vf B )dv‑ f(E+vxB )キ f vdv J ロ [ 7 ‑ 4 3 ] Thise q u a t i o nd e s c r i b e st h ef l o wo fmomentum.Tot r e a tt h ef l o w o fe n e r g y ,wemayt a k et h en e x tmomento fBoltzmanne q u a t i o nby 一一-・・』』ー一一一一一 239 K i n e t i cT h e o r ) " 240 Chαpte r 5ι・。t m S u b s t i t u t i n gf o r[ 1anddividi時 equatioη ’ in whicht h ec o e f f i c i e n to fthermalc o n d u c t i v i t yK woulda r i s e fs t a t e i nt h esamemannera sd i dt h es t r e s st e n s o rP .Theeq田tion o Pc cP'i sas i m p l eformo ft h eh e a tf l o wequationf o rK = 0 . 2 4 1 by i k E 0 E . ,weh ave K i n e t i cT h e o r y l 一三二 f ff 並生王山 kmε。 J [ 7 ‑ 5 0 ] JJw ‑kvx a c t o r e douti fwer e p l a c ef ubyanormalizedf u n c t i o n Af a c t o rn0canbef f o : 7 . 4 PLASMA OSCILLATIONSAND LANDAUDAMPING ;if'Xl 1=一今旦 Asanelementaryi l l u s t r a t i o no ft h euseo ft h eVlasove q u a t i o n ,wes h a l l d e r i v et h ed i s p e r s i o nr e l a t i o nf o re l e c t r o nplasmao s c i l l a t i o n s ,whichwe t r e a t e dfromt h ef l u i dp o i n to fviewi nS e c t i o n4 . 3 .Thisd e r i v a t i o nw i l l r e q u i r eaknowledgeo fcontouri n t e g r a t i o n .Thosen o tf a m i l i a rw i t ht h i s mays k i pt oS e c t i o n7 . 5 .A s i m p l e rbutlongerd e r i v a t i o nn o tusingt h e t h e o r yo fcomplexv a r i a b l e sappearsi nS e c t i o n7 . 6 . I nz e r o t ho r d e r ,weassumeauniformplasmaw i t had i s t r i b u t i o n f o ( v ) ,andwel e tBo=Eo= 0 .Inf i r s to r d e r ,wedenotet h ep e r t u r b a t i o n i n f ( r ,v ,t )byf 1 ( r ,v ,t ) : f ( r ,v , t )=ん( v) +f1(r,v ,I ) 「∞「"' afo(v.,v , .v,)/aiら d v ,I dv,I l l Loo / m ( v x )=(m/2TrKT)112exp(ーηバ/ 2KT) I ~ r "'仏(vx)/av =ー| 一一一一-~ dvx k"LooVx ー (w/k) [ 7 ‑ 4 4 ] 。fo dVx ! 1=主主並立主 m w ‑kvx d, U ThenE q .( 7 ‑ 4 5 ]becomes m [ 7 ‑ 5 2 ] [ 7 ‑ 5 3 ] [7司 54] Here,fo i sunderstoodt obeaone‑dimensionald i s t r i b u t i o nf u n c t i o n , t h ei n t e g r a t i o n soverv ,andv ,havingbeenmade.Equation[7 ” 54] h o l d s f o ranye q u i l i b r i u md i s t r i b u t i o nf0(v);i np a r t i c u l a r ,i ff ui sM a x w e l l i a n , E q .[ 7 ‑ 5 2 ]i st obeusedf o ri t . Thei n t e g r a li nE q .[7尚54] i sn o ts t r a i g h t f o r w a r dt oe v a l u a t ebecause /k .Onemightt h i n kt h a tt h es i n g u l a r i t ywould o ft h es i n g u l a r i t ya tv=w beo fnoc o n c e r n ,becausei np r a c t i c ew i sa l m o s tneverr e a l ;wavesa r e u s u a l l ys l i g h t l ydampedbyc o l l i s i o n sora r ea m p l i f i e dbysomei n s t a b i l i t y sar e a lq u a n t i t y ,t h edenominatori n mechanism.S i n c et h ev e l o c i t yvi E q .( 7 ‑ 5 4 ]neverv a n i s h e s .Landauwast h ef i r s tt ot r e a tt h i sequation p r o p e r l y .Hefoundt h a teventhought h es i n g u l a r i t yl i e so f ft h epatho f i n t e g r a t i o n ,i t s presencei n t r o d u c e s animportantm o d i f i c a t i o nt ot h e plasmawaved i s p e r s i o nrelation‑anE圧ect n o tp r e d i c t e dbyt h ef l u i d t h e o r y . Considerani n i t i a lv a l u eproblemi nwhicht h eplasmai sg i v e na s i n u s o i d a lp e r t u r b a t i o n ,andt h e r e f o r eki sr e a l .I ft h ep e r t u r b a t i o ngrows [7・ 46] ‑iwf1+ikvJ1= ‑ Ex ア ド μ 一ωi wt) 一九パ MV u Asb e f o r e ,weassumet h ei o n sa r emassiveandf i x e dandt h a tt h ewaves a r eplanewavesi nt h exd i r e c t i o n f ,c ce<(kx -- -引 U [ 7 ‑ 4 5 ] A山 M一ぺ ∞叫 一一 a v [ 7 ‑ 5 1 ] S i n c ewea r ed e a l i n gw i t haone‑dimensionalproblemwemaydropt h e s u b s c r i p tx ,b eingc a r e f u ln o tt oconfusev ( w h i c hi sr e a l l yv x )w i t ht h e t o t a lv e l o c i t yvusede a r l i e r : dF f o ヱ= O dvx Thed i s p e r s i o nr e l a t i o ni s ,t h e r e f o r e , mill ー+ v"Vfi 一一 E1 a t m ‑Rvx Ifん is aM axwellianorsomeotherf a c t o r a b l ed i s t r i b u t i o n ,t h ei n t e g r a t i o n s overv , and v , can b ec a r r i e d out e a s i l y . What remains i st h eo n e ュ 0 ( v x l キF ori n s t a n c e ,aone‑dimensional: ¥ ! a x w e l ュ dimensionald i s t r i b u t i o nf l i a nd i s t r i b u t i o ni s S i n c evi snowanindependentv a r i a b l eandi sn o tt obel i n e a r i z e d ,t h e f i r s t ‑ o r d e rV l a s o ve q u a t i o nf o re l e c t r o n si s 。f1 ', W J.ー∞止 00 [7・47] [ 7 ‑ 4 8 ] Poisson ’s e q u a t i o ng i v e s I J EuV·E1=ik仏= ‑en1= ‑e J 川ロ 一一ー一一一ー・』百九一、-一一 一γ 『r- 242 l m ( v ) ord e c a y s ,w w i l lbecomplex.Thei n t e g r a li nE q .( 7 ‑ 5 4 ]mustbet r e a t e d a sacontouri n t e g r a li nt h ecomplexvp l a n e .P o s s i b l ec o n t o u r sa r eshown i nF i g .7・ 14 f o r( a )anu n s t a b l ewave,w i t hIm(w)>0 ,and( b )adamped wave,withIm(w )く 0. Normally,onewoulde v a l u a t et h el i n ei n t e g r a l x i sbyt h er e s i d u etheorem: alongt h er e a lva Cha戸ter S e v e n IGdv+ I 山c, Gdv= 2 T r i R ( w / k ) 243 K i n e t i cTheoγy R e ( v ) w/k (7・ 55] Jc2 whereG i st h ei n t e g r a n d ,C1i st h epathalongt h er e a la x i s ,C2i st h e st h er e s i d u ea tw / k .Thisworksi ft h e s e m i c i r c l ea ti n f i n i t y ,andR(w/k)i i n t e g r a loverC2v a n i s h e s .U n f o r t u n a t e l y ,t h i sdoesn o thappenf o ra 乱1axwellian d i s t r i b u t i o n ,whichc o n t a i n st h ef a c t o r I n t e g r a t i o nc o n t o u ri nt h . ecomplexvp l a n ef o rt h ec a s eo fs m a l l FIGURE7 ‑ 1 5 lm(w). exp(-v2/v~ ) Thisf a c t o rbecomesl a r g ef o ru →土 ico, andt h ec o n t r i b u t i o nfromC2 cannotben e g l e c t e d .Landaushowedt h a twhent h eproblemi sproperly t r e a t e da sani n i t i a lv a l u eproblemt h ec o r r e c tcontourt ou s ei st h ecurve C1passingbelowt h esingularity 目 This i n t e g r a lmusti ng e n e r a lbee v a l u ュ r i e dandContehaveprovidedt a b l e sf o rt h ec a s e a t e dn~merically, andF whenf ai saM a x w e l l i a n . Althoughane x a c ta n a l y s i so ft h i sproblemi sc o m p l i c a t e d ,wecan o b t a i nanapproximated i s p e r s i o nr e l a t i o nf o rt h ec a s eo fl a r g ephase v e l o c i t yandweakdamping.Int h i sc a s e ,t h ep o l ea tw /kl i e sneart h e x i s( F i g .7 ‑ 1 5 ) .Thecontour p r e s c r i b e d by Landau i s then a r e a lv a l m ( v ) l m ( v ) えい) vφ v 。 N o r m a l i z e dM a x w e l l i a nd i s t r i b u t i o nf o rt h ec a s eUφ x i sw i t has m a l ls e m i c i r c l earoundt h ep o l e . s t r a i g h tl i n ealongt h eRe (ν ) a I ngoingaroundt h ep o l e ,oneo b t a i n s2 7 r it i m e sh a l ft h er e s i d u et h e r e . ThenE q .( 7 ‑ 5 4 ]becomes ; rr ' "一一一一一- a / a / a v . aん I dv +Z7r一一| 1=ラず IPI "L L o ov R e ( v ) LU { ) ( a ) FIGURE7・ 14 I n t e g r a t i o nc o n t o u r sf o rt h e Landau problem f o r( a ) Im( w )>O and (b)Im(w )く 0. 》 v,h. ー (w/k) l I av ' v = w / k j r 1 . s B 1 whereP s t a n d sf o rt h eCauchyp r i n c i p a lv a l u e .Toe v a l u a t et h i s ,we x i sbuts t o pj u s tbeforeencounteringt h e i n t e g r a t ealongt h er e a lv a p o l e .I ft h ephasev e l o c i t yuφ = w/ki ss u f f i c i e n t l yl a r g e ,a sweassume, t h e r ew i l l notbe muchc o n t r i b u t i o n from t h en e g l e c t e dp a r to ft h e c o n t o u r ,s i n c ebothf aandaん/av a r ev e r ys m a l lt h e r e( F i g .7 ‑ 1 6 ) .The i n t e g r a li nE q .( 7 ‑ 5 6 ]canbee v a l u a t e dbyi n t e g r a t i o nbyp a r t s : 日土=[土]二- L:~会=日告(7-57] FIGURE7 ‑ 1 6 『「 244 S i n c et h i si sj u s tanaverageo f( v‑ vφ )-2 o vert h ed i s t r i b u t i o n ,t h er e a l p a r to ft h ed i s p e r s i o nr e l a t i o ncanbew r i t t e n Treatingt h eimaginaryterma ss m a l l ,wecanb r i n gi tt ot h er i g h t ‑ h a n d s i d eandt a k et h esquarer o o tbyTaylors e r i e se x p a n s i o n .Wetheno b t a i n 2 2円 I 3v2 4v3 = v;2(1+十マ+万+ )¥ [7・ 59] Wenowlet ん be Maxwellianande v a l u a t e; ‑ 2 .Rememberingthatvhere i sana b b r e v i a t i o nf o rv . ,wecanw r i t e ω 2 w 、 α2ηZ w ;3KT, 2 = ω け寸一一- k 廿 w~ 2wの [ 7 ‑ 6 3 ] I ft h eti町 ermal c o r r e c t ni ss m a l l ,wemayr e p l a c ew2byw~ i nthe 町ond t e r m .Wethenhave 2 3K7二 2 2 = ω = ωρ +一一- k' whichi st h esamea sE q .[ 4 ‑ 3 0 ] ,obtainedfromthe 臼 uid equationswith 3 . Wenowr e t u r nt ot h eimaginarytermi nE q .[ 7 ‑ 5 6 ] .I ne v a l u a t i n g t h i ss m a l lt e r m ,i tw i l lbes u f f i c i e n t l ya c c u r a t et on e g l e c tt h ethermal c o r r e c t i o nt ot h er e a lp a r to fw andl e tw2= w!.FromE q s .[ 7 ‑ 5 7 ]and [ 7 ‑ 6 0 ] ,wes e et h a tt h ep r i n c i p a lv a l u eo ft h ei n t e g r a li nE q .[ 7 ‑ 5 6 ]i s 2, 2 a p p r o x i m a t e l yk/ w. Equation[7 ” 56] nowbecomes 2 w :afoI t7T-n 一一| k ζ av Iv 「φ [ 7 ‑ 6 5 ] ω 2hv 一一 φ U 、、‘,』,,, U 、 11 』tJ Ri- oh ιo Ar H い一利U ’ 9hのurrz ralL ・- T ω 一’ R yaA ω faE1、、 ‘ , 9 -v':;;:wp (託)叫三訪問p (子) [ 7 ‑ 6 9 ] [7・70] S i n c eIm(w)i sn e g a t i v e ,t h e r ei sac o l l i s i o n l e s sdampingo fplasmaw a Y e s ; a m p i n g .Asi se v i d e n tfromE q .[ 7 ‑ 7 0 ] ,t h i sdamping t h i si sC且lied Landaud o rkλD = 0(1). i se x t r e m e l ys m a l lf o rs m a l lkλ0, butbecomesimportantf Thise f f e c ti sconnectedw i t hf 1 ,t h ed i s t o r t i o no ft h ed i s t r i b u t i o nf u n c t i o n causedbyt h ewa、·e. THEMEANINGOFLANDAUDAMPING 7 . 5 γ = w' ¥ k " v ; h 1 [ 7 ‑ 6 4 ] m 1=ーτ + ( 一w2 ¥ 刊号)=ー0.2叫(託)叫示I) [ 7 ‑ 6 2 ] o 1 2k"k . . . / 7 Tv ; h ノ αJηz [ 7 ‑ 6 8 ] Im(w )=一一~ーっ土ーァ exp \ τ--;;- J t h e r ebeingo n l yonedegreeo ffreedom.Thed i s p e r s i o nr e l a t i o n[ 7 ‑ 5 8 ] t h e nbecomes κ [ 7 ‑ 6 7 ] キwemayapproximateuφby wp/ki nt h ec o e f f i c i e n t ,buti nt h eexponent st h e n wemustkeept h ethermalc o r r e c t i o ni nE q .[7 ” 64]. Thedampingi g i v e nby [ 7 ‑ 6 1 ] l w! k2I k2 KT,) = τす十吉い+ 3 寸一一l ..‘ EatJ ~ = (1TV;h)-l/2 (才)叫ず) =- ~exp (ず) [ 7 ‑ 6 0 ] か;; = ~KT, aaEEEL I ff oi saone‑dimensionalM a x w e l l i a n ,wehave Theoddtermsv a n i s hupont a k i n gt h ea v e r a g e ,andwehave ロ;7士宮= v;2(1 与) ra - h φ v¥‑ 2 -, 、 f v;2 い一石 J ohAUF ω 一k ( v-vq, )九 ゐMV u h a sbeenassumed,wecanexpand( v‑ vφ )- 2: ω ω > 一一 S i n c eh + T 一2 [ 7 ‑ 5 8 ] fist ‘、 - ωρ 一一一一一一一宮 1‑ k2(V‑ V q , ) A m M Cha1争ter S四e汎 [ 7 ‑ 6 6 ] Thet h e o r e t i c a ld i s c o v e r yo fwavedampingwithoutenergyd i s s i p a t i o n byc o l l i s i o n si s perhapst h emostastoundingr e s u l to fplasmap h y s i c s r e s e a r c h .Thatt h i si sar e a le f f e c th a sbeendemonstratedi nt h el a b o r a ュ t o r y .Althoughas i m p l ep h y s i c a le x p l a n a t i o nf o rt h i sdampingi snow a v a i l a b l e ,i ti satriumpho fa p p l i e dmathematicst h a tt h i sunexpected e f f e c twasf i r s td i s c o v e r e dp u r e l ym a t h e m a t i c a l l yi nt h ec o u r s eo fac a r e f u l a n a l y s i so facontouri n t e g r a l . Landaudampingi sac h a r a c t e r i s t i co f c o l l i s i o n l e s sp l a s m a s ,buti tmaya l s ohavea p p l i c a t i o ni no t h e rf i e l d s .For i n s t a n c e ,i nt h ek i n e t i ct r e a t m e n to fg a l a x yf o r m a t i o n ,s t a r s can be c o n s i d e r e da satomso faplasmai n t e r a c t i n gv i ag r a v i t a t i o n a lr a t h e rt h a n 一一一」←一一 一 245 K i n e t i cT h e o r y マ「 246 Cha1やter S四肌 e l e c t r o m a g n e t i cf o r c e s .I n s t a b i l i t i e so ft h eg a so fs t a r scanc a u s es p i r a l armst oform,butt h i sp r o c e s si sl i m i t e dbyLandaudamping. Tos e ewhati sr e p o n s i b l ef o rLandaudamping,wef i r s tn o t i c et h a t r i s e sfromt h ep o l ea tv = v<b. C o n s e q u e n t l y ,t h ee f f e c ti sc o n ュ Im(w)a n e c t e dw i t ht h o s ep a r t i c l e si nt h ed i s t r i b u t i o nt h a thaveav e l o c i t yn e a r l y e q u a lt ot h ephasev e l o c i t y ‑ t h e“ resonant particles. ” These p a r t i c l e s t r a v e lalongw i t ht h ewaveanddon o ts e ear a p i d l yf l u c t u a t i n ge l e c t r i c a n ,t h e r e f o r e ,exchange 町rgy w i t ht h ewaveeffe出ely. f i e l d :T~ey c Thee a s i e s twayt ounderstandt h i sexchangeo fenergyi st op i c t u r ea s u r f e rt r y i n gt oc a t c hanoceanwave( F i g .7 ‑ 1 7 ) .(Warning:t h i sp i c t u r e i so n l yf o rd i r e c t i n gourt h i n k i n galongt h er i g h tl i n e s ;i tdoesnotc o r r e c t l y ft h esurfboardi snotmoving,i tmerelybobsup e x p l a i nE q .( 7 ‑ 7 0 ] . )I anddowna st h ewavegoesbyanddoesnotg a i nanyenergyonth~ a v e r a g e .S i m i l a r l y ,ab o a tp r o p e l l e dmuchf a s t e rthant h ewavecannot exchangemuchenergyw i t ht h ew a v e . However,i ft h esurfboardh a s almostt h esamev e l o c i t ya st h ew a v e ,i tcanbecaughtandpushedalong byt h ewave;t h i si s ,a f t e ra l l ,t h emainpurposeo ft h ee x e r c i s e .I nt h a t c a s e ,t h esurfboard g a i n se n e r g y , and t h e r e f o r et h e wave mustl o s e energyandi sdamped.Ont h eo t h e rhand,i ft h esurfboardshouldbe movings l i g h t l yf a s t e rthant h ew a v e ,i twouldpushont h ewavea si t movesu p h i l l ;thent h ewavec o u l dg a i ne n e r g y .I nap l a s m a ,t h e r ea r e e l e c t r o n sbothf a s t e rands l o w e rthant h ew a v e .AMaxwelliand i s t r i b u t i o n . however, h a s more s l o we l e c t r o n s than f a s t ones ( F i g .7 ‑ 1 8 ) . Conュ s e q u e n t l y ,t h e r ea r emorep a r t i c l e st a k i n genergyfromt h ewavethan 247 fm( v ) 。 K i n e t i cTheoη1 vφ v D i s t o r t i o no faM a x w e l l i a nd i s t r i b u t i o ni nt h er e g i o n FIGURE7 ‑ 1 8 v= v~ c a u s e db yLandaud a m p i n g . D 。 iuv ’?’ ( vφ v Adouble‑humpedd i s t r i b u t i o nandt h er e g i o nwhere FIGURE7 ‑ 1 9 i n s t a b i l i t i e sw i l ld e v e l o p . v i c ev e r s a ,andt h ewavei sdamped.Asp a r t i c l e sw i t hv= vφare trapped sf l a t t e n e dneart h ephasev e l o c i t y .Thisd i s t o r t i o ni s i nt h ew a v e ,f(v)i f i ( v )whichwec a l c u l a t e d .Ass e e ni nF i g .7 ‑ 1 8 ,t h eperturbedd i s t r i b u t i o n f u n c t i o nc o n t a i n st h esame numbero fp a r t i c l e s buth a sgained t o t a l energy( a tt h eexpenseo ft h ew a v e ) . o n t a i n e dmore Fromt h i sd i s c u s s i o n ,onecans u r m i s et h a ti ffo (ν ) c f a s tp a r t i c l e sthans l o wp a r t i c l e s ,awavecanbee x c i t e d .I n d e e d ,from sp o s i t i v ei fa f 0 / a vi sp o s i t i v ea t E q .( 7 ‑ 6 7 ] ,i ti sapparentt h a tIm(w)i v=vφ・ Such ad i s t r i b u t i o ni sshowni nF i g .7・ 19. Wavesw i t huφin t h e r e g i o no fp o s i t i v es l o p ew i l lbeu n s t a b l e ,g a i n i n gener訂以 the expense ft h et w o ュ o ft h ep a r t i c l e s .Thisi sj u s tt h efinite・temperature analogyo )e l e c t r o ns t r e a m s streami n s t a b i l i t y .Whent h e r ea r etwoc o l d(KT=0 c J PARTICLE GAINSENERGY FIGURE7 ‑ 1 7 Customaryp h y s i c a lp i c t u r eo fLandaud a m p i n g . 一-圃-』 ?ー 248 C h a p t e r S e v e n i nm o t i o n ,f o ( v )c o n s i s t so f two ふ functions. This i sc l e a r l yu n s t a b l e b e c a u s ea f o / a vi si n f i n i t e ;and,i n d e e d ,wefoundt h ei n s t a b i l i t yfrom 日 uid t h e o r y .Whent h es t r e a m shavef i n i t et e m p e r a t u r e ,k i n e t i ct h e o r y t e l l su st h a tt h er e l a t i v ed e n s i t i e sandtemperatureso ft h etwos t r e a m s mustbesucha st ohavear e g i o no fp o s i t i v ea f 0 / a vbetweenthem;more p r e c i s e l y ,t h et o t a ld i s t r i b u t i o nf u n c t i o n must have a minimum f o r i n s t a b i l i t y . Thep h y s i c a lp i c t u r eo fas u r f e rc a t c h i n gwavesi sverya p p e a l i n g , buti ti sn o tp r e c i s eenought og i v eu sar e a lunderstandingo fLandau damping. There a r ea c t u a l l y two k i n d so f Landau damping: l i n e a r Landau damping, and n o n l i n e a r Landau damping. Both k i n d sa r e fap証rticle i scaught independento fd i s s i p a t i v ec o l l i s i o n a lmechanisms.I i nt h ep o t e n t i a lw e l lo fawave,t h ephenomenoni sc a l l e d“ trapping. ” As i nt h ec a s eo ft h es u r f e r ,p a r t i c l e scanindeedg a i no rl o s eenergyi n t r a p p i n g .However,t r a p p i n gdoesn o tl i ew i t h i nt h epurviewo ft h el i n e a r t h e o r y .Thatt h i si st r u ecanbeseenfromt h ee q u a t i o no fmotion m d2x/dt2= qE(x) 。 q̲ a f 1 m u v [ 7 ‑ 7 1 ] Whenawavegrowst oal a r g ea m p l i t u d e ,c o l l i s i o n l e s sdampingw i t h t r a p p i n g does o c c u r . One then f i n d st h a tt h e wave does not decay m o n o t o n i c a l l y ;r a t h e r ,t h eamplitudef l u c t u a t e sduringt h edecaya st h e trappedp a r t i c l e sbouncebackandf o r t hi nt h ep o t e n t i a lw e l l s .Thisi s n o n l i n e a rLandaudamping.S i n c et h er e s u l to fE q .[ 7 ‑ 6 7 ]wasderived fromalineaγtheory, i tmusta r i s efromadi狂erent p h y s i c a le f f e c t .The q u e s t i o ni s :Canuntrappede l e c t r o n smovingc l o s et ot h ephasev e l o c i t y o ft h ewaveexchangeenergyw i t ht h ewave?Beforeg i v i n gt h ea n s w e r , l e tu sexaminet h eenergyo fsuche l e c t r o n s . [ 7 ‑ 7 2 ] Here,E(x)i st obee v a l u a t e di nt h el a b o r a t o r yf r a m e ,whichi se a s y ;but t or n a k eupf o ri t ,t h e r ei st h e( vキV)vt e r m .Then e g l e c to f( v 1キV ) v 1i n l i n e a rt h e o r yamountst ot h esamet h i n ga su s i n gunperturbedo r b i t s . 7 ‑ 4 5 ] , I nk i n e t i ct h e o r y ,t h en o n l i n e a rtermt h a ti sn e g l e c t e di s ,fromE q .( ---av K i n e t i cT h e o r y D i s s e c t i o no fad i s t r i b u t i o n/0(υ ) i n t oal a r g enumbero f FIGURE7-2骨 m o n o e n e r g e t i cbeamsw i t hv e l o c i t yuandd e n s i t yn•. I fonee v a l u a t e sE(x)byi n s e r t i n gt h ee x a c tv a l u eo fx ,t h eequationwould ssomethingl i k es i nk x .Whati sdonei nl i n e a r ben o n l i n e a r ,s i n c eE(x)i h eunperturbedo r b i t ;i . e . ,x= X o+ v o l .ThenE q . t h e o r yi st ou s ef o rxt [ 7 ‑ 7 1 ]i sl i n e a r .Thisa p p r o x i m a t i o n ,however,i snol o n g e rv a l i dwhen tencountersap o t e n t i a lh i l ll a r g eenough ap a r t i c l ei strapped. 市Vhen i t or e f l e c ti t ,i t sv e l o c i t yandp o s i t i o na r e ,o fc o u r s e ,g r e a t l ya f f e c t e dby t h ewaveanda r enotc l o s et ot h e i runperturbedv a l u e s .I nf l u i dt h e o r y , t h ee q u a t i o no fmotioni s 市[~+(v· 吋 = qE(x) 249 も( v) TheK i n e t i cEnergyo faBeamo fE l e c t r o n s 7 . 5 . 1 Wemayd i v i d et h ee l e c t r o nd i s t r i b u t i o nf 0 ( v )i n t oal a r g enumbero f monoenergeticbeams( F i g .7‑20). Consideroneo ft h e s ebeams:I th a s e n s i t ynu・ The v e l o c i t yu mayl i enearv < f ‑ , unperturbedv e l o c i t yu andd s ot h a tt h i sbeammayc o n s i s to fr e s o n a n te l e c t r o n s .Wenowt u r nona )andc o n s i d e rt h ek i n e t i cenergyo ft h ebeama s plasmao s c i l l a t i o nE(x,t i tmovesthrought h ec r e s t sandt r o u g h so ft h ew a v e .Thewavei scaused byas e l f ‑ c o n s i s t e n tmotiono fa l lt h ebeamst o g e t h e r .I fnui ss m a l lenough ( t h enumbero fbeamsl a r g eenough),t h ebeambeingexaminedh a sa n e g l i g i b l ee f f e c tont h ewaveandmaybec o n s i d e r e da smovingi nag i v e n [ 7 ‑ 7 3 ] Whenp a r t i c l e sa r et r a p p e d ,t h e yr e v e r s et h e i rd i r e c t i o no ft r a v e lr e l a t i v e ( v )i sg r e a t l yd i s t u r b e dnear t ot h ew a v e ,s ot h ed i s t r i b u t i o nf u n c t i o nf v=w / k .Thismeanst h a ta [ i / a vi scomparablet oa f 0 / a v ,andt h eterm [ 7 ‑ 7 3 ]i snotn e g l i g i b l e .Hence,t r a p p i n gi snoti nt h el i n e a rt h e o r y . ーム T 250 Cha世Uγ S e v e n f i e l dE ( x ,t ) .L et E =E0sin(kx φ =(E。/ k) 一 wt) =-dゆ/ dx c o s(kx ー wt) 251 K i n e t i cT h e o r y [ 7 ‑ 7 4 ] V中一ー』 [ 7 ‑ 7 5 ] E Thel i n e a r i z e df l u i de q u a t i o nf o rt h ebeami s 隅 l与 + u包) = -eEo 州kx 一 wt) 、 dl [ 7 ‑ 7 6 ] dX ノ Ap o s s i b l es o l u t i o ni s e E 0c o s(kx ー wt) 日--;;:---;;;-ヨ正一 [ 7 ‑ 7 7 ] Thisi st h ev e l o c i t ymodulationcausedbyt h ewavea st h ebeame l e c t r o n s movep a s t .Toc o n s e r v ep a r t i c l ef l u x ,t h e r ei sacorrespondingo s c i l l a t i o n i nd e n s i t y ,g i v e nbyt h el i n e a r i z e dc o n t i n u i t ye q u a t i o n : 。冗 1 i ) n , ー』ーニ + u -一二= i l t i l x a v , ‑n.. 一_: ‑i l x S i n c ev1i sp r o p o r t i o n a lt oc o s(kx ー wt), wecant r yn 1=五 l c o s(kx S u b s t i t u t i o no ft h i si n t oE q .[ 7 ‑ 7 8 ]y i e l d s e E 0 kc o s(kx 一 wt) . 崎市 (w‑ k u ) " u>v中 , v [ 7 ‑ 7 8 ] uくV中 , v ー wt). [ 7 ‑ 7 9 ] 1 n η ,= -n ”ー一一ー一一一一ーー一一一τ- 子、 b 昌〆τ ー巴φ F i g u r e7‑21showswhatE q s .[7・77] and[ 7 ‑ 7 9 ]mean.Thef i r s ttwo c u r v e sshowonewavelengtho fE ando ft h ep o t e n t i a l-eφseen byt h e o rt h ec a s e beame l e c t r o n s .Thet h i r d curvei s ap l o to fE q . [7司77] f w -ku く 0, o ru>vφ. Thisi se a s i l yunderstood:Whent h ee l e c t r o na h a sclimbedt h ep o t e n t i a lh i l l ,i t sv e l o c i t yi ss m a l l ,andv i c ev e r s a .The f o u r t hcurvei sv1f o rt h ec a s eu く Uφ, and i ti ss e e nt h a tt h es i g ni s ,movingt ot h el e f ti nt h eframe r e v e r s e d .Thisi sb e c a u s et h ee l e c t r o nb o ft h ewave,i sd e c e l e r a t e dgoingupt ot h et o po ft h ep o t e n t i a lb a r r i e r ; buts i n c ei ti smovingt h eo p p o s i t eway,i t sv e l o c i t yv 1i nt h ep o s i t i v ex d i r e c t i o ni smaximumt h e r e .Themovingp o t e n t i a lh i l la c c e l e r a t e se l e c ュ t r o nbt ot h er i g h t ,s obyt h et i m ei tr e a c h e st h et o p ,i th a st h emaximum h ed e n s i t yn 1 ,a sg i v e nbyE q . v 1 .Thef i n a lc u r v eonF i g .7‑21showst [ 7 ‑ 7 9 ] .T hisdoesn o tchanges i g nw i t hu‑vφ, because i nt h eframeo f r es l o w e s ta tt h etopo ft h e t h ewave,bothe l e c t r o na ande l e c t r o nba p o t e n t i a lh i l l ,andt h e r e f o r et h ed e n s i t yi sh i g h e s tt h e r e .Thep o i n ti s t h a tt h er e l a t i v ephasebetweenηl andv1changess i g nw i t hu‑vφ・ 。 kx‑wt 官 2π P h a s er e l a t i o n so fvelocity 岨d d e n s i t yf o re l e c t r o n smovingi na n FIGURE7 ‑ 2 1 e l e c t r o s t a t i cw a v e . Wemaynowcomputet h ek i n e t i cenergyWko ft h ebeam: Wk = ~m(nu +n1)(u+V 1 ) 2 = ~m (ηuU2 +nuVI+2un1V1+n1u2+2nuUV1+ πivil [ 7 ‑ 8 0 ) Thel a s tt h r e etermsc o n t a i noddpowerso fo s c i l l a t i n gq u a n t i t i e s ,s ot h e y h a n g ei nM生 due w i l lv a n i s hwhenwea v e r a g eoveraw a v e l e n g t h .Thec t ot h ewavei sfoundbys u b t r a c t i n gt h ef i r s tt e r m ,whichi st h eo r i g i n a l ~圃・.』 ア 252 e n e r g y .Theaverageenergychangei sthen Chapteγ ('1Wk)= ~m (ηuvi S回開 W , k +2u司 1V1) 2 5 3 K i n e t i cTheoη [ 7 ‑ 8 1 ] FromE q .( 7 ‑ 7 7 ] ,wehave 20 E二 一U R 一, 一m 2e一ω 一一 r、、 , n 21 η U u -9 [7・ 82] t h ef a c t o r~ r e p r e s e n t i n g( c o s 2(kx ー wt)). S i m i l a r l y ,fromE q .( 7 ‑ 7 9 ] ,we have wko 2 2 Fマハ h叫 2叫(百 1V1)=nu~二寸 m (w-ku )ー [ 7 ‑ 8 3 ] u ‑ l v 1I u u + l v 1I C o n s e q u e n t l y , 2£~ 「 mL(w‑ku"L The q u a d r a t i c r e l a t i o n b e t w e e n FIGURE7 ‑ 2 3 k i n e t i ce n e r g yandv e l o c i t yc a u s e sa s y m m e t r i cv e l o c i t yp e r t u r b a t i o nt o g i v er i s et o an i n c r e a s e da v e r a g e e n e r g y . 2ku 1 (w‑ku)J ('1W.)= mnu 寸←」アτl !+一一一一 1 4 2 2 nueEo w +ku 4 m (w‑ku)3 [7・ 84] Thisr e s u l tshowst h a t( ' 1Wk)dependsont h eframeo ft h eo b s e r v e r andt h a ti tdoesnotchanges e c u l a r l ywitht i m e .Considert h ep i c t u r eo f af r i c t i o n l e s sb l o c ks l i d i n goveraw a s h b o a r d ‑ l i k es u r f a c e( F i g .7 ‑ 2 2 ) .I n ki sp r o p o r t i o n a lto ー (ku ) ‑ 2 ,a ss e e nby t h eframeo ft h ewashboard,1 1w nE q .(7司84]. I ti si n t u i t i v e l yc l e a rt h a t( 1 )( Af竹) i sn e g a t i v e , t a k i n gw = 0i s i n c et h eb l o c kspendsmoret i m ea tt h epeaksthana tt h ev a l l e y s ,and ( 2 )t h eb l o c kdoes n o tg a i no rl o s eenergyon t h ea v e r a g e , oncet h e o s c i l l a t i o ni ss t a r t e d .Nowi fonegoesi n t oaframei nwhicht h ewashboard av e l o c i t yu n a f f e c t e dbyt h emotion i smovingw i t has t e a d yv e l o c i t yw/k( o ft h eb l o c k ,s i n c ewehaveassumedt h a tnui sn e g l i g i b l ys m a l lcompared w i t ht h ed e n s i t yo ft h ewholep l a s m a ) .i ti ss t i l lt r u et h a tt h eb l o c kdoes notg a i norl o s eenergyont h ea v e r a g e ,oncet h eo s c i l l a t i o ni ss t a r t e d . h ev e l o c i t yw /k ,andhence ButE q .( 7 ‑ 8 4 ]t e l l su st h a t( AWk)dependsont ont h eframeo ft h eo b s e r v e r .I np a r t i c u l a r ,i tshowst h a tabeamh a s 口- 4初ラお\ ~ v r e s e n c eo ft h ewavethani ni t sabsencei fw ‑ ku く O l e s senergyi 日 the p o ru>vφ, and i th a smoreenergyi fw ‑ku>0o ru く Uφ・ The r e a s o n f o rt h i scanbet r a c e dbackt ot h ephaser e l a t i o nbetweenn1andv1 ・ As F i g .7 ‑ 2 3s h o w s ,Wki sap a r a b o l i cf u n c t i o no fv .Asvo s c i l l a t e sbetween u ー Ivi iandu+Ivi i,Wkwillattainanaveragevaluelargerthanthe h a tt h ep a r t i c l espendsane q u a lamount e q u i l i b r i u mvalue れも 0, providedt o ft i m ei neachh a l fo ft h eo s c i l l a t i o n .Thise f f e c ti st h emeaningo ft h e f i r s ttermi nE q .( 7 ‑ 8 1 ] ,whichi sp o s i t i v ed e f i n i t e .Thesecondtermi n t h a te q u a t i o ni sac o r r e c t i o nduet ot h ef a c tt h a tt h ep a r t i c l edoesnot d i s t r i b u t ei t st i m ee q u a l l y .I nF i g .7 ‑ 2 1 ,ones e e st h a tbothe l e c t r o na ande l e c t r o nbspendmoret i m ea tt h et o po ft h ep o t e n t i a lh i l lt h a na t e a c h e st h a tp o i n ta f t e rap e r i o do fd e c e l e r ュ t h eb o t t o m ,bute l e c t r o nar sn e g a t i v et h e r e ,w h i l ee l e c t r o nbr e a c h e st h a tp o i n t a t i o n ,s ot h a tv1 i sp o s i t i v et h e r e . a f t e rap e r i o do fa c c e l e r a t i o n( t ot h er i g h t ) ,s ot h a tv1i ' 1Wk)t ochanges i g na tu= Uφ・ Thise f f e c tc a u s e s( ~ 乞必必0:00必必必必必タ初??タ務労労労労協労わ円円形労労労労労a 一一F TheE f f e c to fI n i t i a lConditions 7 . 5 . 2 む3 k Ther e s u l twehavej u s td e r i v e d ,however,s t i l lh a snothingt odow i t h l i n e a rLandaudamping.Dampingr e q u i r e sacontinuousi n c r e a s eo fWk e c h a n i c a la n a l o g yf o rane l e c t r o nmovingi namovingp o t e n t i a l . FIGURE7 ‑ 2 2 M よ 『”F 254 C h a p t e r S e v e n L iW;) f o r a tt h e expense o f wave e n e r g y , but we have found t h a t( untrappedp a r t i c l e si sc o n s t a n ti nt i m e .I fn e i t h e rt h euntrappedp a r t i c l e s norp a r t i c l et r a p p i n gi sr e s p o n s i b l ef o rl i n e a rLandaudamping,what i s ?Theanswercanbeg l e a n e dfromt h ef o l l o w i n go b s e r v a t i o n :I f(AW;) i sp o s i t i v e ,s a y ,t h e r emusthavebeenat i m ewheni twasi n c r e a s i n g . I n d e e d ,t h e r ea r ep a r t i c l e si nt h eo r i g i n a ld i s t r i b u t i o n which have tt i m ett h e yhavenoty e tgoneah a l f ュ v e l o c i t i e ss oc l o s et oUφthat a wavelengthr e l a t i v et ot h ew a v e .Fort h e s ep a r t i c l e s ,onecannott a k et h e a v e r a g e( C l .W ; ) .Thesep a r t i c l e sc a na b s o r benergyfromt h ewaveand i m eg o e so n ,t h enumber a r ep r o p e r l yc a l l e dthe “ resonant” particles. Ast o fr e s o n a n te l e c t r o n sd e c r e a s e s ,s i n c eani n c r e a s i n gnumberw i l lhave h e i ro r i g i n a lp o s i t i o n s .Thedampingr a t e , s h i f t e dmorethanjλfrom t however,cans t a yc o n s t a n t ,s i n c et h eamplitudei snows m a l l e r ,andi t t a k e sfewere l e c t r o n st omamtainac o n s t a n tdampingr a t e . ft h ei n i t i a lc o n d i t i o n si smoste a s i l ys e e nfromap h a s e ュ Thee狂ect o ‑ 2 4 ) .Here,wehavedrawnt h ep h a s e ‑ s p a c etrajeひ s p a c ediagram( F i g .7 t o r i e so fe l e c t r o n s ,anda l s ot h ee l e c t r o s t a t i cp o t e n t i a l-eφi whicht h e y s e e .Wehaveassumedt h a tt h i se l e c t r o s t a t i cwavee x i s t sa tt=0 ,andt h a t t h ed i s t r i b u t i o nf 0 ( v ) ,shownp l o t t e di nap l a n ep e r p e n d i c u l a rt ot h e vI a tt h a t p a p e r ,i suniformi ns p a c eandm o n o t o n i c a l l ydecreasi時 with I t i m e .Forc l a r i t y ,t h es i z eo ft h ewaveh a sbeeng r e a t l ye x a g g e r a t e d .Of 1 ( v )a tt= 0 . c o u r s e ,t h ee x i s t e n c eo fawavei m p l i e st h ee x i s t e n c eo fanf However,t h edampingc a u s e dbyt h i si sah i g h e r ‑ o r d e re f f e c tn e g l e c t e d i nt h el i n e a rt h e o r y .Nowl e tu sgot ot h ewavef r a m e ,s ot h a tt h ep a t t e r n ‑ 2 4doesnotmove,andc o n s i d e rt h emotiono ft h ee l e c t r o n s . o fF i g .7 t a r to u ta tt h et o po ft h ep o t e n t i a lh i l landmove E l e c t r o n si n i t i a l l ya tA s t ot h er i g h t ,s i n c et h e yhavev>vφ・ Electrons i n i t i a l l ya tB movet ot h e tC andD s t a r ta tt h ep o t e n t i a l l e f t ,s i n c et h e yhaveu く Uφ・ Those a troughandmovet ot h er i g h tandl e f t ,r e s p e c t i v e l y .E l e c t r o n ss t a r t i n g ogoovert h ep o t e n t i a l ont h ec l o s e dc o n t o u r sEhaveinsu伍cient energyt h i l landa r et r a p p e d .I nt h el i m i to fs m a l li n i t i a lwavea m p l i t u d e ,t h e p o p u l a t i o no ft h etrappede l e c t r o n scanbemadea r b i t r a r i l ys m a l l .A f t e r ts h o r tenought h a tnoneo ft h ee l e c t r o n sa tA,B,C o rD sometime, h a sgonemorethanh a l faw a v e l e n g t h ,t h ee l e c t r o n sw i l lhavemovedt o t h ep o s i t i o n smarkedbyopenc i r c l e s .I ti ss e e nt h a tt h ee l e c t r o n sa tA andD havegainede n e r g y ,w h i l et h o s ea tB andC havel o s te n e r g y . Now,i ff 0 ( v )wasi n i t i a l l yuniformi ns p a c e ,t h e r ewereo r i g i n a l l ymore tC ,andmorea tD thana tB.T h e r e f o r e ,t h e r ei s e l e c t r o n sa tA thana an e tg a i no fenergybyt h ee l e c t r o n s ,andhencean e tl o s so fwave e n e r g y .Thisi sl i n e a rLandaudamping,andi ti sc r i t i c a l l ydependenton t h eassumedi n i t i a lc o n d i t i o n s .A f t e ralongt i m e ,t h ee l e c t r o n sa r es o smearedo u ti nphaset h a tt h ei n i t i a ld i s t r i b u t i o ni sf o r g o t t e n ,andt h e r e i snof u r t h e raverageenergyg a i n ,a swefoundi nt h ep r e v i o u ss e c t i o n . h o s ew i t hu く Uφ, I nt h i sp i c t u r e ,botht h ee l e c t r o n sw i t hv>vφand t whenaveragedoveraw a v e l e n g t h ,g a i nenergya tt h eexpenseo ft h e w a v e .Thisapparentc o n t r a d i c t i o nw i t ht h ei d e adevelopedi nt h ep i c t u r e o ft h es u r f e rw i l lber e s o l v e ds h o r t l y . 2 5 5 K i n e t i cT h e o r y v v ゆ >) J Q ' l : x 0 -eφ1 x P h a s e ‑ s p a c et r a j e c t o r i e s( t o p )f o re l e c t r o n smovingi nap o t e n t i a lwave( b o t t o m ) . FIGURE7 ‑ 2 4 Thee n t i r ep a t t e r nmovest ot h er i g h t .Thea r r o w sr e f e rt ot h ed i r e c t i o no f e l e c t r o nm o t i o nr e l a t i v et ot h ewavep a t t e r n .Thee q u i l i b r i u md i s t r i b u t i o n/0(υ ) i sp l o t t e di nap l a n ep e r p e n d i c u l a rt ot h ep a p e r . 256 7.6 A PHYSICALDERIVATIONOFLANDAU DAMPING v1 /a x .Thuswetake ordert omatcht h esamef a c t o ri na Cha戸ler Seveη 257 K i n e t i cTheoη Wea r enowi nap o s i t i o nt od e r i v et h eLandaudampingr a t ew i t h o u t n t e g r a t i o n .Asb e f o r e ,wed i v i d et h eplasmaupi n t o r e c o u r s etocontouri beamso fv e l o c i t yuanddensity and examinet h e i rmotioni nawave eE1k 1 n 1= nu 一孟一戸て五子 ~, E = 」1s i n(kχ ー wt) [ 7 ‑ 8 5 ] FromE q .[ 7 ‑ 7 7 ] ,t ev e l o c i t yo feachbeami s eE1c o s(kx‑wt) v , =一一一一一一一一一一一 .市 w ‑ku [ 7 ‑ 8 6 ] Thiss o l u t i o ns a t i s f i e st h ee q u a t i o no fmotion [ 7 ‑ 7 6 ] , buti tdoesn o t tt=O .I ti sc l e a rt h a tt h i si n i t i a l s a t i s f yt h ei n i t i a lc o n d i t i o nv 1=0a e r yl a r g ei nt h e c o n d i t i o nmustbeimposed; o t h e r w i s e ,v1wouldbev h eplasmawouldbei nas p e c i a l l yprep呪red v i c i n i t yo fu= w/k, andt s t a t ei n i t i a l l y .Wecanf i xupE q .[ 7 ‑ 8 6 ]t os a t i s f yt h ei n i t i a lc o n d i t i o nby u n c t i o no fkx‑k u t .Thec omposites o l u t i o nwould addingan 昌rbitrary f h eoperatoront h el e f t ‑ h a n ds i d eo fE q . s t i l ls a t i s f yE q .(7・ 76] becauset [7・76], whena p p l i e dt of(kx‑k u t ) ,g i v e sz e r o .O b v i o u s l y ,t og e tv 1= O a tt= 0 ,t h ef u n c t i o nf(k涜- kut) mustbet a k e nt obe ‑cos( k x‑k u t ) . Thusweh a v e ,i n s t e a do fEq冒[ 7-86], ‑eE1c o s( k x wt)‑ c o s( k x‑k u t ) V 1=一一一一 ' m w ‑Rn [7・ 87] N e x t ,wemusts o l v et h ee q u a t i o no fc o n t i n u i t y[7・ 78] f o rn1 ,a g a i ns u b j e c t tt=0 .S i n c ewea r enowmuchc l e v e r e r t ot h ei n i t i a lc o n d i t i o nn 1=0a t h a nb e f o r e ,wemayt r yas o l u t i o no ft h eform n1 =冗 1[cos (kx ー wt) ‑c o s( k x‑k u t ) ] [ 7 ‑ 8 8 ] 克1 sm(kx ー wt)= -n , 一一- 'm 2 (w‑ku)" [7・ 90] Thisc l e a r l yv a n i s h e sa tt= 0 ,andonecane a s i l yv e r i f yt h a ti ts a t i s f i e s E q .( 7 ‑ 7 8 ] . Thesee x p r e s s i o n sf o rv1andη1 a l l o wu snowt oc a l c u l a t et h ework donebyt h ewaveoneachbeam.Thef o r c ea c t i n gonau n i tvolumeo f eachbeami s Fu= ‑eE1 s i n(kx 一 wt)(n,, +n1) [ 7 ‑ 9 1 ] andt h e r e f o r ei t senergychangesa tt h er a t e di-γ 一一= F , , ( u+v 1 )= d t eE1s i n( k x wt )(九日+ nuV1 +n1u+ η1V1) ①②③③ [ 7 ‑ 9 2 ] now t a k et h es p a t i a l average o v e ra wavelength 目 The f i r s t term , , ui sc o n s t a n t .The f o u r t htermcan be n e g l e c t e d v a n i s h e s because n becausei ti ssecondo r d e r ,buti nanyc a s ei tcanbeshownt ohavez e r o a v e r a g e .Theterms ( and ( can bee v a l u a t e du s i n gE q s .[ 7 ‑ 8 7 ]and [ 7 ‑ 9 0 ]andt h ei d e n t i t i e s 1へfe k x‑wt)c o s( k x‑k u t ) )= - ~sin ( w t‑k u t ) ( s i n( [ 7 ‑ 9 3 ] ( s i n( k x wt)s i n( k x‑k u t ) )= ~cos ( w t‑k u t ) Ther e s u l ti se a s i l yseent obe ( o / i ) , ,= ~n,, 戸ιず日 I n s e r t i n gt h i si n t oE q .[ 7 ‑ 7 8 ]andusingE q .(7 ・87] f o rv 1 ,wef i n d eE1ks i n( k x‑wt)‑ s i n(kx‑kut) ×[ cos (kx 一 wt) ‑c o s( k x‑ kut ) ー (w ‑k u ) ts i n( k x‑k u t ) ] [7・ 89] A p p a r e n t l y ,wewerenotc l e v e renough,s i n c et h es i n( k x wt) f a c t o r u t ) ,w hichcame doesn o tc a n c e l .Tog e tatermo ft h eforms i n(kx‑k ,wecanaddatermo ft h eformAts i n( k x‑k u t ) fromt h eaddedtermi nv1 t on 1 .Thistermo b v i o u s l yv a n i s h e sa tt= 0 ,andi tw i l lg i Y et h es i n( k x‑ k u t )t ermwhent h eoperatoront h el e f t ‑ h a n ds i d eo fE q .(7 司 78] o p e r a t e s ont h etf a c t o r .Whent h eo p e r a t o ro p e r a t e sont h es i n(kx‑kut)f a c t o r , i ty i e l d sz e r o .Thec o e f f i c i e n tA mustbep r o p o r t i o n a lt o(w ku)‑1 i n +ku i nw -kut ) 一 (w ‑k u ) tc o s(wt‑kut)l I (w-ku )ー」 [7・ 94] Notet h a tt h eo n l ytermst h a ts u r v i v et h ea v e r a g i n gp r o c e s scomefrom t h ei n i t i a lc o n d i t i o n s . Thet o t a lworkdoneont h ep a r t i c l e si sfoundbysummingovera l l t h ebeams: ~(おι = f や(れぬ= η。 jぞ(説 du 258 C h a p t e r S e v e n I n s e r t i n gE q .(7・94] andusingt h ed e f i n i t i o no fω炉 we thenf i n df o rt h e r a t eo fchangeo fk i n e t i cenergy Comparingt h i sw i t hE q .[ 7 ‑ 1 0 1 ] ,wef i n d r 1e2E~ ε叩 (事)= 一- εoEi w;I I ~ 州wt ‑kut)du d tI 2 L Jfo(u ) ー一一一一ー- w‑ku ( ~Wk )=了一一」」了=ニデ=( WE) 生 ‑k u i tc o s( w t‑k u t )kndnl (w-ku γ.. ~~つ u 一向 tL ai 「"' w-Ru dん sin (w-k吋, 」∞ l 一一… L " ' du w ‑ku ‑J (WE )= εo(E2)/2 = εoEi/4 [ 7 ‑ 9 9 ] Thei n t e g r a t e dp a r tv a n i s h e sf o rw e l l ‑ b e h a v e df u n c t i o n sf 0 ( u ) ,andwe have Thesecondp a r ti st h ek i n e t i cenergyo fo s c i l l a t i o no ft h ep a r t i c l e s .I f wea g a i nd i v i d et h eplasmaupi n t obeams,E q .[ 7 ‑ 8 4 ]g i v e st h eenergy perbeam: u 一k ー,ilJ 一ω 対一一 ι 一u reE』 E EEL 21 E一, I 一ω pu- 一d吐 一一 九一四川 司i 品 A m -u dWw w 2 「"' • f s i n(w‑k u ) ! l 寸ケ= Ww 了的| fb(u>I 一一一つ一一 I du αE [ 7 ‑ 1 0 0 ] lP2 i ( ' ' f0(u ) 「 2ku 1 (~Wk )=÷一一一| 一一一一一τ11 +一一一一| 4 m L"'(,曲 - ku γL 曲 - kuJ \ W -flu 」 r1・ 107] 昆J τr t 帝国 L 曲 - llu J r1・ 108] Thus dWw T " 27TW 合/ω\ー ω ト,/ω\ d t =V V . , W p kk J O ¥ " k J= V V w 1 T W J ; ' i f O ¥ " k } [ 7 ‑ 1 0 1 ] [ 7 ‑ 1 0 9 ] S i n c eIm( w )i st h egrowthr a t eo fE1,andWwi sp r o p o r t i o n a lt oEi,we musthave dWw/dt= 2[Im(w))Ww [ 7 ‑ 1 0 2 ] u [7・ 110] Hence UsingE q .( 7 ‑ 7 9 ]f o rπ1, wehave 1=~こす J」=三二[∞主包4 Eom τ (w -ku ) 品 εom L " '(w‑ku)' L よ"' δ! {ペ k hm キ r s i n(w 二ku)tl u‑ ‑ ;J=一 I . I Thesecondtermi nt h eb r a c k e t scanben e g l e c t e di nt h el i m i tw/k > v,h, whichwes h a l lt a k ei nordert ocomparew i t hourp r e v i o u sr e s u l t s .The d i s p e r s i o nr e l a t i o ni sfoundbyPoisson ’s e q u a t i o n : c o s(kx 一副t) = ‑eL:n1 R whereuh a sbeens e te q u a lt ow/k( ac o n s t a n t ) ,s i n c eo n l yv e l o c i t i e sv e r y c l o s et ot h i sw i l lc o n t r i b u t et ot h ei n t e g r a l .Inf a c t ,f o rs u f f i c i e n t l yl a r g e , tt h es q u a r eb r a c k e tcanbeapproximatedbyad e l t af u n c t i o n : I nd e r i v i n gt h i sr e s u l t ,wed i dn o tu s et h ec o r r e c ti n i t i a lc o n d i t i o n s ,which a r eimportantf o rt h er e s o n a n tp a r t i c l e s ;however,t h el a t t e rc o n t r i b u t e v e r yl i t t l et ot h et o t a lenergyo ft h ew a v e .Summingovert h ebeams,we have kεoE1 [ 7 ‑ 1 0 6 ] dW 2 ff ' s i n(w‑ k u ) t l " ' 寸~=- Www パ l uf,山)一一一ァー| Thisi st obes e te q u a ltot h er a t eo fl o s so fwaveenergyd e n s i t yWw. Thewaveenergyc o n s i s t so ftwopart~. .Thef i r s tp a r ti st h eenergyd e n s i t y o ft h ee l e c t r o s t a t i cf i e l d : + a, I n t e g r a t i o nbyp a r t sg i v e s [7・ 98] J d w ‑Im ん A df s i n( w t‑k u t ) l . I ん(u)du ÷l u auL J̲"' rlL f " '; " ‑ [ 7 ‑ 1 0 5 ] Ther a t eo fchangeo ft h i si sg i v e nbyt h en e g a t i v eo fE q .[ 7 ‑ 9 8 ] : JJ 山 W 1 = ~EoE1wp I duL w ‑ku l w ‑ku [ 7 ‑ 1 0 4 ] 生 Ww = εoEi/2 川 7 L"' e Thus [ 7 ‑ 9 6 ] =:εぷw; r "'ん(u)duf~但ゴ~+ u!{̲̲rsin(wt‑kut)n ~ ηz …一日 r J + fo(u ) ~in (wt‑kut ) ー (w 259 K i n e t i cT h e o r y Im(w )=ら勾!~r竺 主民 [ 7 ‑ 1 0 3 ] ¥kl i nagreementw i t ht h ep r e v i o u sr e s u l t ,E q .( 7 ‑ 6 7 ] ,f o rw= Wp・ 一一-・』ーー [7・ 111] 260 261 九( v) Cha世ter K i n e t i cTheoη s i n( ωー ku)t (w‑ku) Seveη ーV w‑ku FIGURE7 ‑ 2 5 Af u n c t i o n which d e s c r i b e st h er e l a t i v ec o n t r i b u t i o no fv a r i o u s v e l o c i t yg r o u p st oLandaud a m p i n g . TheResonantP a r t i c l e s Wea r enowi nap o s i t i o nt os e ep r e c i s e l ywhicha r et h er e s o n a n tp a r t i c l e s ‑ 2 5g i v e sap l o to f t h a tc o n t r i b u t et ol i n e a rLandaudamping.F i g u r e7 nt h ei n t e g r a n do fE q .[ 7 ‑ 1 0 7 ] .Wes e et h a t t h ef a c t o rmultiplyingf~ (u) i t h el a r g e s t con 汀ibut Iv 一 Uφ11 く 7T/k = λ/ 2; i . e . ,t h o s ep a r t i c l e si nt h ei n i t i a ld i s t r i b u t i o nt h a t havenoty e tt r a v e l e dah a l f ‑ w a v e l e n g t hr e l a t i v et ot h ew a v e .Thewidth o ft h ec e n t r a lpeaknarrowsw i t ht i m e ,a se x p e c t e d .Thes u b s i d i a r ypeaks i nt h e“ diffraction pattern ” of F i g .7 ‑ 2 5comefromp a r t i c l e st h a thave t r a v e l e di n t oneighboringh a l f ‑ w a v e l e n g t h so ft h ewavep o t e n t i a l .These p a r t i c l e sr a p i d l ybecomespreadouti np h a s e ,s ot h a tt h e yc o n t r i b u t e l i t t l eont h ea v e r a g e ;t h ei n i t i a ld i s t r i b u t i o ni sf o r g o t t e n .Notet h a tt h e widtho ft h ec e n t r a lpeaki sindependento ft h ei n i t i a lamplitudeo ft h e wave; h e n c e ,t h e resonant p a r t i c l e s may i n c l u d e both trapped and untrappedp a r t i c l e s .Thisphenomenoni su n r e l a t e dt op a r t i c l et r a p p i n g . 。 v AM a x w e l l i a nd i s t r i b u t i o ns e e nfromamovingf r a m ea p p e a r st o FIGURE7 ‑ 2 6 h a v ear e g i o no fu n s t a b l es l o p e . oddf u n c t i o no fw ‑ k u ;andonewouldi n f e rfromt h i st h a tp a r t i c l e s t r a v e l i n gf a s t e rthant h ewaveg i v eenergyt oi t ,w h i l et h o s et r a v e l i n g s l o w e rthant h ewavet a k eenergyfromi t .Thetwod e s c r i p t i o n sd i f f e r byani n t e g r a t i o nbyp a r t s .Bothd e s c r i p t i o n sa r ec o r r e c t ;whichonei s t ob echosendependsonwhetheronew i s h e st ohave ん(u) o rf~ (u) i n t h ei n t e g r a n d . f A secondparadoxc o n c e r n st h eq u e s t i o no fG a l i l e a ni n v a r i a n c e .I wet a k et h eviewt h a tdampingr e q u i r e st h e r ebefewerp a r t i c l e st r a ¥ ' e l i n g f a s t e rthant h ewavethans l o w e r ,t h e r ei snoproblema slonga sonei s i nt h eframei nwhicht h eplasmai sa tr e s t .However,i foneg o e si n t o anotherframemovingw i t hav e l o c i t yV ( F i g .7 ‑ 2 6 ) ,t h e r ewouldappear t obemorep a r t i c l e sf a s t e rthant h ewavethans l o w e r ,andonewould e x p e c tt h ewavet ogrowi n s t e a do fd e c a y .Thisparadoxi sremovedby 7 ‑ 1 0 0 ] ,whichwen e g l e c t e d .Asshown r e i n s e r t i n gt h esecondtermi nE q .[ 5 . 1 ,t h i stermcanmake( D .W,)n e g a t i v e .I n d e e d ,i nt h eframe i nS e c t i o n7. shown i nF i g .7 ‑ 2 6 ,t h esecondtermi nE q .[ 7 ‑ 1 0 0 ]i sn o tn e g l i g i b l e , (ム肌) i snegat閃, and t h ewaveappearst ohaven e g a t i v eenergy( t h a t i s ,t h e r ei smoreenergyi nt h eq u i e s c e n t ,d r i f t i n gMaxwelliand i s t r i b u t i o n thani nt h ep r e s e n c eo fano s c i l l a t i o n ) .Thewave “ grows ,” but adding energyt oan e g a t i v eenergywavemakesi t samplituded e c r e a s e . 7. 6 . 2 TwoParadoxesResolved F i g u r e7 ‑ 2 5showst h a tt h ei n t e g r a n di nE q .[ 7 ‑ 1 0 7 ]i sanevenf u n c t i o n u ,s ot h a tp a r t i c l e sgoingbothf a s t e rthant h ewaveands l o w e r o fw ‑ k thant h ewaveaddt oLandaudamping.Thisi st h ep h y s i c a lp i c t u r ewe ‑ 2 4 .Ont h eo t h e rhand,t h es l o p eo ft h ec u r v eo fF i g . foundi nF i g .7 7・25, w hichr e p r e s e n t st h ef a c t o ri r .t h ei n t e g r a n do fE q .[ 7 ‑ 1 0 6 ] ,i san . 7 BGKAND VANKAMPENMODES 7 Wehaveseent h a tLandaudampingi sd i r e c t l yconnectedt ot h er e q u i r e ュ mentt h a t/ 0 ( v )bei n i t i a l l yuniformi ns p a c e .Ont h eo t h e rhand,onecan 哩F 262 Chα世ter 263 K i n e t i cTheoη トコ仏トコ O 区出ト凶一O 己ZU比広ω←z S e v e n g e n e r a t eundampede l e c t r o nwavesi ff ( v ,t= 0 )i smadet obec o n s t a n t alongt h ep a r t i c l et r a j e c t o r i e si n i t i a l l y .I ti se a s yt os e efromF i g .7 ‑ 2 4 t h a tt h ep a r t i c l e sw i l ln e i t h e rg a i nnorl o s ee n e r g y ,ont h ea v e r a g e ,i f t h eplasmai si n i t i a l l yprepareds ot h a tt h ed e n s i t yi sc o n s t a n talongeach .B .B e r n s t e i n . t r a j e c t o r y .Suchawavei sc a l l e daBGKmode,s i n c ei twasI J.M.G町民 and M.D .K r u s k a lwhof i r s tshowedt h a tundampedwave~ o fa r b i t r a r yw,k ,a m p l i t u d e ,andwaveformwerep o s s i b l e .Thec r u c i a l parametert oa d j u s ti nt a i l o r i n gf ( v ,t= 0 )t oformaBGKmodei st h e fwe t a k et h e r e l a t i v enumbero ftrapped and untrapped p a r t i c l e s .I s m a l l ‑ a m p l i t u d el i m i to faBGKmode,weo b t a i nwhati sc a l l e daVan Kampenmode.I nt h i sl i m i t ,o n l yt h ep a r t i c l e sw i t hv= vφare t r a p p e d . ( v ,t= O ) Wecanchanget h enumbero ftrappedp a r t i c l e sbyaddingt of atermp r o p o r t i o n a lt oo(v‑ vφ ). Examinationo fF i g .7 ‑ 2 4w i l lshowt h a t a u s edamping‑atal a t e r addingp a r t i c l e salongt h el i n ev=九 will notc t i m e ,t h e r ea r ej u s ta smanyp a r t i c l e sg a i n i n genergya sl o s i n ge n e r g y . I nf a c t ,bychoosingd i s t r i b u t i o n sw i t ha ‑ f u n c t i o n sa totherv a l u e so fU和 onecang e n e r a t eundampedVanKampenmodeso fa r b i t r a r yh・ Such smgularm i t i a lc o n d i t i o n sa r e ,however,notp h y s i c a l .Tog e tasmoothly ( v ,t= 0 ) , one must sum over Van Kampen modes w i t ha varymgf sundamped, t h et o t a lp e r ュ d i s t r i b u t i o no fuφ5・ Although eachmodei t u r b a t i o nw i l lshowLandaudampingbecauset h ev a r i o u smodesg e tout o fphasew i t honea n o t h e r . 10 20 30 40 PROBESEPARATION I n t e r f e r o m e t e rt r a c eshowingt h ep e r t u r b e dd e n s i t yp a t t e r ni nadamped FIGURE7 ‑ 2 7 p l a s m aw a v e .[FromJ .H.MalmbergandC .B .W h a r t o n ,P h y s .R e v .L e t t .1 7 ,1 7 5 ( 1 9 6 6 ) . ] e l e c t r o n si naMaxwelliand i s t r i b u t i o n .C o n s e q u e n t l y ,t h el o g a r i t h mo f k )s houldbep r o p o r t i o n a lt o(vφ/v 出)2. F i g u r e7 ‑ 2 8showst h e Im( k ) / R e( agreement o b t a i n e d between t h e measurements and t h et h e o r e t i c a l c ur、 e As i m i l a rexperimentbyD e r f l e randSimonenwasdonei np l a n e geometry,s ot h a tt h er e s u l t sf o rRe(ω ) ιan becomparedw i t hE q .[ 7 ‑ 6 4 ] . F i g u r e7 ‑ 2 9showst h e i rmeasurementso fRe( k )andIm( k )a td i f f e r e n t f r e q u e n c i e s .Thedashedc u r v er e p r e s e n t sE q .(7・ 64] andi st h esamea s t h eonedrawni nF i g .4 ‑ 5 .Thee x p e r i m e n t a lp o i n t sd e v i a t efromt h e dashedcurvebecauseo ft h eh i g h e r ‑ o r d e rtermsi nt h eexpansiono fE q . [7 ・ 59]. Thet h e o r e t i c a lc u r v ec a l c u l a t e dfromE q .( 7 ‑ 5 4 ] ,however,f i t s t h ed a t aw e l l . 7 . 8 EXPERIMENTALVERIFICATION AlthoughLandau ’s d e r i v a t i o no fc o l l i s i o n l e s sdampingwass h o r tand n e a t , It was not c l e a rt h a ti t concerned a p h y s i c a l l yo b s e r v a b l e phenomenonu n t i l] .M.Dawsongavet h el o n g e r ,i n t u i t i v ed e r i v a t i o n whichwasparaphrasedi nS e c t i o n7 . 6 .Event h e n ,t h e r eweredoubts t h a tt h eproperc o n d i t i o n sc o u l dbee s t a b l i s h e di nt h el a b o r a t o r y .These d o u b t s were removed i n 1965 by an experiment by Malmbergand Wharton.Theyusedprobest oe x c i t eandd e t e c tplasmawavesalonga c o l l i s i o n l e s splasmacolumn.Thephaseandamplitudeo ft h ewavesa s af u n c t i o no fd i s t a n c ewereo b t a i n e dbyi n t e r f e r o m e t r y .A t r a c i n go ft h e s p a t i a lv a r i a t i o no ft h edampedwavei sshowni nF i g .7 ‑ 2 7 .S i n c ei nt h e experimentw wasr e a lb u tkwascomplex,t h er e s u l tweo b t a i n e di nE q . [7・70] c annot be compared w i t ht h ed a t a .I n s t e a d ,ac a l c u l a t i o no f Im( k ) / R e( k )f o rr e a lw h a st obemade.Thisr a t i oa l s oc o n t a i n st h e sp r o p o r t i o n a lt ot h enumbero fr e s o n a n t f a c t o rexp(‑v!/v;¥,),whichi P l a s m aw a v e sa r eg e n e r a t e di nap l a s m aw i t hn=1 0 1 7m‑3andKT,=1 0e V . I fk=1 0 4m ‑ 1 .c a l c u l a t et h ea p p r o x i m a t eLandaudampingr a t eJ l m(ω/叫) J. 7・ 1. 7・2. Ane l e c t r o np l a s m awavew i t hI ‑ c mw a v e l e n g t hi se x c i t e di na1 0 ‑ e Vp l a s m a w i t hn=1 0 1 5m‑3Thee x c i t a t i o ni st h e nr e m o v e d ,andt h ewaveLandaudamps a w a y .Howl o n gd o e si tt a k ef o rt h ea m p l i t u d et of a l lb yaf a c t o ro fe? .. ・圃 圃園 PROBLEおfS 喜各〉 264 . 1 0 Cha:争t肝 S制肌 200 265 K i n e t i cT h e o r y 。 。 . 0 5 haEA 〈 -- N 工 11Aιo pDnO Tl vv - 6GU .。 vhvh . 0 1 T 芸 4C > u z 100 w a w 。∞ 包 10 15 20 Bc;~o .~グ • : I ' ノ// /'/ 手’ /・勺/ 0 LL 5 900 10 d S P " コ .005 0 。 ∞/o / - wi Jh ・n lm(k) R e ( k ). 0 2 。 Q . C D . . ̲ •. . . . ‑ キ / / ~·~ 25 ノ (vゅ/Vth) 2 ノ / .‑ キ / ( 3KT/m)l!L FIGURE 7 ‑ 2 8 V e r i f i c a t i o no fLandaudampingi nt h eMalmberg‑Wharton l o cc i t . ) experiment( / / / / 子3. Ani n f i n i t e ,uniform plasmawith 日出 ions h a sane l e c t r o nd目tribu tunc~ion composedo f{ ! )aM axwelliand i s t r i b u t i o nof “ plasma ” electrons w i t h / / ノ tr e s ti nt h el a b o r a t o r y ,and( 2 )aM a x w e l l i a n d e n s i t ynp andtemperatureTp a d i s t r i b . u t i o nof “ beam ” electrons w i t hd e n s i t yn ,andtemperature 九 centered a t v= Vx. < F i g .P 7 ‑ 3 ) .I fn ,i si n f i n i t e s i m a l l ys m a l l ,plasmao s c i l l a t i o n st r a v e l i n gi n i r e c t i o na r eLandau‑damped.I fn ,i sl a r g e ,t h e r ew i l lbeat w o ‑ s t r e a m t h exd ,a twhichi n s t a b i l i t ys e t si ncanbefoundbys e t t i n gt h e i n s t a b i l i t y .Thec r i t i c a ln s l o p eo ft h et o t a ld i s t r i b u t i o nf u n c t i o ne q u a lt oz e r o .Tokeept h ea l g e b r as i m p l e , sf o l l o w s . wecan 白 nd anapproximateanswera ノ 0 / 0 0 . 8 1 . 6 2 . 4 k (mmキ1) Experimentalmeasuremento ft h ed i s p e r s i o nr e l a t i o nf o rplasma FIGURE7 ‑ 2 9 wavesi nplaneg e o m e t r y .[FromH.D e r f l e randT .Sim0nen,J .Appl. P h y s .3 8 ,5018( 1 9 6 7 ) . ] ( a )W r i t e~xpressions for んや) andf , ( v ) ,u s i n gt h ea b b r e v i a t i o n sv=v . ,a 2= 2KT./m,b 2= 2KT,/m. { b ) Assumet h a tt h ephasev e l o c i t yUφwill bet h ev a l u eo fva twhichf 6 ( v )h a s t h el a r g e s tp o s i t i v es l o p e .Finduφand f~ (vφ ). ( d ) ForV > b, showt h a tt h ec r i t i c a lbeamd e n s i t yi sg i v e napproximatelyby , " "T .V 1, a ユ= (2e)'12 二三- exp ( c ) Findf~ (vφ ) andsetf~ (vφ )+ f;(vφ ) = 0 . πp 一一一ーーーー・・・.馳』ι " " ( ‑ V 2 / a ' ) 266 267 7 ‑ 6 .C o n s i d e rt h eo n e ‑ d i m e n s i o n a ld i s t r i b u t i o nf u n c t i o n Chα争ter Seven f ( v )= A ゆ仏八 f ( v )= 0 ( b )Uset h eV l a s o vandP o i s s o ne q u a t i o n st od e r i v eani n t e g r a le x p r e s s i o nf o r e l e c t r o s t a t i ce l e c t r o nplasmaw a v e s . vx ( c )E v a l u a t et h ei n t e g r a lando b t a i nad i s p e r s i o nr e l a t i o nw ( k ) ,k eepingt e r m s tot h i r do r d e ri nt h es m a l lq u a n t i t ykvm/w. Unperturbedd i s t r i b u t i o n functions ん( vx) andf , ( v x )f o rt h e plasmaandbeame l e c t r o n s ,r e s p e c t i v e l y ,i nabeam‑plasma m t e r a c t i o n . ー M一 ? ‑ 4 .Tomodelawarmp l a s m a ,assumet h a tt h ei o nande l e c t r o nd i s t r i b u t i o n f u n c t i o n sa r eg i v e nby IONLANDAU DAMPING 7.9 均一T O U υ AFμ fawavehasa E l e c t r o n sarenottheonlyp o s s i b l eresonantp a r t i c l e s .I slowenoughphase, キ e l o c i t yt omatchthethermalv e l o c i t yofi o n s ,ion Landaudampingcano c c u r .Theiona c o u s t i cwave,f o ri n s t a n c e ,i sg r e a t l y 4 ‑ 4 1 ]t h a tthedispersion a f f e c t e dbyLandaudamping.R e c a l lfromE q .( r e l a t i o nf o rionwavesi s I = =( K T ,i f K T ; ) v , f ; o ( v )=生寸土寸 符· v キ+a' ( a )D e r i v et h ee x a c td i s p e r s i o nr e l a t i o ni nt h eV l a s o vf o r m a l i s massumingan e l e c t r o s t a t i cp e r t u r b a t i o n . ( b )O b t a i nanapproximatee x p r e s s i o nf o rt h ed i s p e r s i o nr e l a t i o ni fw :5n. Underwhatc o n d i t i o n sa r et h ewavesw e a k l ydamped?E x p l a i np h y s i c a l l ywh~ w=nρfor v e r yl a r g ek . ん, ( v) = g o ( v )+h o ( v ) ‑-1- - ト、\~ ) O U J u 1b < ( U =n Jη O ’n( ) U 』2e -a e an 『 lb - uη ηn , 町一作+ n 一一一一 。 E un o p l P ( a )D e r i v et h ed i s p e r s i o nr e l a t i o nf o rh i g h ‑ f r e q u e n c ye l e c t r o s t a t i cp e r t u r b a t i o n s . h a tas o l u t i o ne x i s t si nwhichIm( w )>O ( i . e . , ( b )I nt h el i m i tw/k < a, showt growingo s c i l l a t i o n s ) . [ 7 ‑ 1 1 2 ] If ~; I 0 1 where -2 --+ i12 I fT ,. , ;T ; ,thephasevelocityl i e si ntheregionwhere/ 0 1(v)hasanegative s l o p e ,a sshown i nF i g .7 ‑ 3 0 ( A ) . Consequently, ion waves are h e a v i l y f T , > Ti Landau‑damped i f T, 三 T,・ Ion waves areobservableonlyi [ F i g .7 ‑ 3 0 ( B ) ] ,s ot h a tthe phase 、elocity l i e sf a ri n thet a i loftheion 河locity d i s t r i b u t i o n .A c l e v e rwayt ointroduceLandaudampingi na 7 ‑ 5 .C o n s i d e ran unmagnetized plasmaw i t ha 自xed, n e u t r a l i z i n gi o nb a c k ュ ground.Theo n e ‑ d i m e n s i o n a le i e c t r o nv e l o c i t yd i s t r i b u t i o ni sg i , キ e nby ( ) lvl く Vm lvl 三 Vm ( a )C a l c u l a t et h ev旦lue o ft h ec o n s t a n tA i nt e r m so ft h eplasmad e n s i t yn 0 . v FIGURE P7・3 K i n e t i cTheoη 、4 0 ( A ) Te"'Ti j 一一 ‘ v r / > V 0 ( 8 ) Te>>T i , ,t h ephase FIGURE7 ‑ 3 0 E x p l a n a t i o no fLandaudampingofi o na c o u s t i cw a v e s .ForT,= T h e r ea r ev e r yfew v e l o c i t yl i e sw e l lw i t h i nt h ei o nd i s t r i b u t i o n ;f o rT , > T,, t i o n sa tt h ephasev e l o c i t y .Additiono fal i g h ti o ns p e c i e s (dashedc u r v e ) mcreasesLandaudamping. 268 Chaeヤteγ S四四 c o n t r o l l e dmannerwasemployedbyA l e x e f f ,J o n e s ,andMontgomery. A weaklydampedi o nwavewasc r e a t e di nah e a v y ‑ i o nplasma( s u c ha s m a l lamounto fal i g h tatom( h e l i u m )wast h e n xenon)w i t hT , > T;. A s added.S i n c et h eheliumhadaboutt h esametemperaturea st h exenon buthadmuchs m a l l e rm a s s ,i t sd i s t r i b u t i o nf u n c t i o nwasmuchb r o a d e r . i g .7 ‑ 3 0 ( B ) .Ther e s o n a n theliumio巾 a sshownbyt h edashedcu附 in F thencausedt h ewavet odamp. This i sa contouri n t e g r a l ,a se x p l a i n e di nS e c t i o n7 . 4 , and a n a l y t i c ( ( )i s c o n t i n u a t i o nt ot h elowerh a l fp l a n emustbeusedi fIm((}く 0. Z rku s u a l l yh a san acomplexf u n c t i o no facomplexargument( s i n c ew o imaginary p a r t ) . Inc a s e swhereZ(() cannotbeapproximated byan a s y m p t o t i cf o r m u l a ,onecanu s et h et a b l e so fF r i e dand Conteo ra standardcomputers u b r o u t i n e . ntermso fZ((),wet a k et h ed e r i v a t i v ew i t hr e s p e c t Toe x p r e s sn1;i t o ( : 7 . 9 . 1 ThePlasmaDispersionFunction バ)=よ「 2 Loo( s‑() 7r"" Toi n t r o d u c esomeo ft h estandardterminologyo fk i n e t i ct h e o r y ,we nowc a l c u l a t et h ei o n Landau dampingo fi o na c o u s t i cwaves i nt h e absenceo fmagneticf i e l d s .I o n sande l e c t r o n sf o l l o wt h eV l a s o ve q u a t i o n ( 7 ‑ 2 3 ]andhavep e r t u r b a t i o n so ft h eformo fE q .( 7 ‑ 4 6 ]i n d i c a t i n gp l a n e wavespropagatingi nt h exd i r e c t i o n .Thes o l u t i o nf o r/ 1i sg i v e nbyE q . ( 7 ‑ 4 8 ]w i t ha p p r o p r i a t em o d i f i c a t i o n s : / i ;=一並互並立竺 ’ m; w ‑kv; I n t e g r a t i o nbyp a r t sy i e l d s , Z ’(() m ,; ̲ " 'w ‑ lw1 キ J ' ̲ ̲ ̲ O i t,hリ 7r s‑( iq;E:ηOi n1;=ァーすi Z ’((;) [ 7 ‑ 1 1 9 ] εoV キ E= ikεoE =Iq内1 [ 7 ‑ 1 2 0 ] ( 7 ‑ 1 1 4 ] Combining t h el a s t two e q u a t i o n s ,s e p a r a t i n gout t h ee l e c t r o n term e x p l i c i t l y ,andd e f i n i n g r " '(d/ds)(e‑'2) iIi 一亡でT Tη吉| J_"' , 1 < 一一一一---;--- ds s‑~j 2 =与 z’((,)+ I半 z’(る) U 出' [ 7 ‑ 1 1 6 ] k i= 2w;/v~, = λ ♂ [ 7 ‑ 1 2 3 ] k 2 / k i= ~z’(ι) [ 7 ‑ 1 2 4 ] wetheno b t a i n Wenowd e f i n et h epl.αsma d i s p e r s i o nf u n c t i o nZ ( ( ) : バ)=ゴ7言 t:S ゐ [ 7 ‑ 1 2 2 ] j '九hj E l e c t r o nplasmawavescanbeo b t a i n e dbys e t t i n gf l p ;= 0( i n f i n i t e l y m a s s i v ei o n s ) .D e f i n i n g [ 7 ‑ 1 1 7 ] Im(O>O r、 2 k 2 where ( ;=w/kv 向 [ 7 ‑ 1 2 1 ] weo b t a i nt h ed i s p e r s i o nr e l a t i o n r i t e n 1 ;a s Introducingt h edummyi n t e g r a t i o nv a r i a b l e s=む/ v,h;. wecanw κ'fftjl/lhj 官 一一一一- ds Poisson ’s e q u a t i o ni s [ 7 ‑ 1 1 5 ] U耐 ’…, 7 ̲i q ; E n 0 ; 1 τLoo f l p ;=(η o;ZJe2 /εoM;)112 ̲ v 守Iv市2 ‑ d / d s ) ( e' 2 ), I r " '( +「7言| Rm;v<hi L e tt h ee q u i l i b r i u mdistributions ん; beone‑dimensionalM a x w e l l i a n s : 山0 一「7す 6 l s‑(J "' Thef i r s ttermv a n i s h e s ,a si tmustf o ranyw e l l ‑ b e h a v e dd i s t r i b u t i o n r i t t e n f u n c t i o n .Equation(7旬 116] cannowbew ;s t a n df o rE , ,v町; and t h ej t hs p e c i e sh a schargeq ; ,mass whereE andv m ; ,andp a r t i c l ev e l o c i t yv;・ The d e n s i t yp e r t u r b a t i o no ft h ej t hs p e c i e s i sg i v e nby J‑oo I r ‑ e ‑ ' 2 1 " ' =「721 一一一| [ 7 ‑ 1 1 3 ] r " '1;(v;)dv; 一一一一| ‑ iq; ("'ーーヂ iJfoJa打 川=| / dv; 269 K i n e t i cT h e o r y [ 7 ‑ 1 1 8 ] whichi st h esamea sE q .(7・54] when/ 0 ,i sM a x w e l l i a n . 一ーム 一一一一一一→ 寸話量董琶& 270 C h a p t e r S e v e n 7.9.2 IonWavesandTheirDamping キ , To o b t a i ni o nw a v e s , go back t oE q .[ 7 ‑ 1 2 2 ] and u s et h ef a c tt h a t smuchs m a l l e rthar 由,; he悶よ~is s m a l l ,an t h e i rphasev e l o c i t yw/ki . wecanexpandZ ( ( , )i napowers e r i e s : Z (ι) =i "; ; .e‑ < ;‑2ι(1-k; +・・・) I Z’(乙) = -2i 、l7T(,e [7・125] 31¥ It t i¥ 2t iJ B [7・126] sassumedl a r g e ,t fi sl a r g e ;andwecanapproximatedbyB / 2 S i n c eBi i nt h esecondt e r m .Thus 。一 [ 7 ‑ 1 3 0 ] 2 w2 2KT,/3 白 ZT,\ 2 ‑ γ l 一+一一一) = ZKT,+3KT, ¥ 2 2 T ; / M [ 7 ‑ 1 3 1 ] T h i si st h ei o nwa 、e d i s p e r s i o nr e l a t i o n[ 4‑41]w i t hγi =3 ,g e n e r a l i z e d . t oa r b i t r a r yZ Wenows u b s t i t u t eE q s .[ 7 ‑ 1 2 9 ]and[ 7 ‑ 1 3 0 ]i n t oE q .[ 7 ‑ 1 2 8 ]r e t a i n i n g t h eLandaut e r m : λ~$ =必日立と=.'..~ 2kT, 2 T ; 1, t h ed i s p e r s i o nr e l a t i o nbecomes I ‑olI 3 ¥ , ‑ , . nι r包 22 J , yι /> a u + B 一す 2 一8 一o 一一 、、BEE + 3 一 JC ,, ・ eaE ・ E B‘、、 l l [ 7 ‑ 1 2 8 ] 2 -'~ ‑ ~1 、/ 7f [,e '• = ‑ +ー·I t i¥ BJ Z’(え;)= W + Ol Thetermk2λ1 r e p r e s e n t st h ed e v i a t i o nfromq u a s i n e u t r a l i t y . Wenows p e c i a l i z et ot h ec a s eo fas i n g l ei o ns p e c i e s .Sinceηo, =Z,ηo •. t h ec o e f f i c i e n ti nE q .[ 7 ‑ 1 2 7 ]i s < 一一 [ 7 ‑ 1 2 7 ] Jνth] Fork2A1 03一9 “ vd 丸d 去( I +お=~ n λb L プ土 Z’(乙)= I+eA;',=l " : i , ; n o ,eιε oM 2 ーす l I +ーーす I=- 23 n [7・ 129] 7 ‑ 1 2 8 ]becomes a p p r o x i m a t i o n .Equation( E l e c t r o nLandaudampingcanu s u a l l yben e g l e c t e di ni o nwavesb e c a u s e t h es l o p eo ff.(v) i ss m a l lneari t sp e a k .ReplacingZ’(ふ) by‑2i nE q . ( 7 ‑ 1 2 2 ]g i v e st h ei o nwaved i s p e r s i o nr e l a t i o n 。 h n~, t2 ‑2 ' '+(, +2(;q4 十・・ I ft h edampingi ss m a l l ,wecann e g l e c tt h eLandautermi nt h ef i r s t Theimaginarytermcomesfromt h er e s i d u ea tap o l el y i n gneart h e x i s( o fE q .[7句56]) andr e p r e s e n t se l e c t r o nLandaudamping.For r e a lsa (, < 1, t h ed e r i v a t i v eo fE q .[7句 125] g i v e s Z ' ( ( , ) = ‑ 2 i . . / ; ( , e ''-2 +・・・= ‑2 Too b t a i nana n a l y t i cr e s u l t ,wec o n s i d e rt h elimit (,> 1, correspond‑ i n gt ol a r g etemperaturer a t i oB" " Z T , / T ; .Thea s y m p t o t i ce x p r e s s i o n f o rZ ’((,) is ) t 7= (午) 112(!+i,;;B t ,e‑q S o l v i n gt h i se q u a t i o ni san o n t r i v i a lproblem 目 Suppose wet a k er e a l kandcomplexw t os t u d ydampingi nt i m e .Thent h er e a landimaginary d j u s t e ds ot h a tIm(Z ’) =0andRe(Z ’) = 2TJZ乙. p a r t so fw mustbea Therea r ei ng e n e r a lmanyp o s s i b l er o o t sw t h a ts a t i s f yt h i s ,a l lo fthem e a s tdamped,dominantr o o ti st h eonehaving havingImw く 0. Thel p a c ei su s u a l l yt r e a t e dbytaki時 w r e a l t h es m a l l e s tII即"'· Dampi時 in s andkcomplex.Againweg e tas e r i e so fr o o t skw i t hImk>0 ,represent ” i n gs p a t i a ldamping.However,t h edominantr o o tdoesn o tcorrespond t ot h esamev a l u eo f( ;a si nt h ecomplexw c a s e .I tt u r n soutt h a tt h e s p a t i a lproblemh a st obet r e a t e dw i t hs p e c i a la t t e n t i o nt ot h ee x c i t a t i o n mechanisma tt h eboundariesandw i t hmorec a r e f u lt r e a t m e n to ft h e e l e c t r o ntermZ’(乙). Expandingt h esquarer o o t ,wehave !3+8¥1121 ,=(T) 1 (1-2i 仏 V ¥ [ 7 ‑ 1 3 2 ] Theapproximatedampingr a t ei sfoundbyu s i n gE q .[ 7 ‑ 1 3 0 ]i nt h e imaginaryt e n n : Imt; lmw Ret, Rew 一一一一=一一一= (τT\ 1/2 ¥ 8 / II。{+θげ " (‑) 8 ( 3+B)' e ‑ ' whereB=ZT,/T,andRewi sg i v e nbyE q .[ 7 ‑ 1 3 1 ] . ・・圃.固・・ [ 7 ‑ 1 3 3 ] 271 K i n e t i cT h e o r y 272 Thisasy~ptotic e~preぉion, a c c u r a t ef o rl a r g e( } ,showsanexponenュ t i a ldecreasein 中mping withi n c r e a s i n g0 .When( Jf a l l sbelowI O ,E q . [7ぺ 33] becomesmaccurate,andthedampingmustbecomputedfrom ~q. [7‑128], which employs the Z‑function. For the experimentally mterestingregion1.く O く l 0 ,t h ef o l l o w i n gsimpleformulai sana n a l y t i c f i tt ot h ee x a c ts o l u t i o n : C h a p t e r S e v e n ‑Imw/Rew= l.I0714exp(‑(J2) [ 7 ‑ 1 3 4 1 Theseapproximationsarecomparedwiththee x a c tr e s u l ti nF i g .7 ‑ 3 1 . ION LANDAU DAMPING , , Whathappenswhenc o l l i s i o n sa r eaddedt oionLandaudamping? S u r p r i s i n g l yl i t t l e .I o n ‑ e l e c t r o nc o l l i s i o n sareweakbecausethei o nand e l e c t r o nf l u i d s movealmosti nu n i s o n ,c r e a t i n gl i t t l ef r i c t i o nbetween them.Ion‑ionc o l l i s i o n s( i o nv i s c o s i t y )candampi o na c o u s t i cwaves,but we know t h a tsound waves m a i rcan propagate w e l li ns p i t eo ft h e dominanceofc o l l i s i o n s .A c t u a l l y ,c o l l i s i o n ss p o i lthep a r t i c l eresonances e s s t h a tcauseLandaudamping,andonef i n d st h a tthet o t a ldampingi sl thant h eLandaudampingu n l e s sthec o l l i s i o nr a t ei sextremelyl a r g e . I nsummary,i o nLandaudampingi salmostalwaysthedominantp r o c e s s w i t hi o nwaves,andt h i sv a r i e se x p o n e n t i a l l ywithther a t i oZT,/T;・ A 7 ‑ 7 .I o na c o u s t i cwaveso f1 ‑ c mw a v e l e n g t ha r ee x c i t e di nas i n g l ei o n i z e dxenon (A=1 3 1 )plasmaw i t hT ,=1eVandT ,=0 . 1eV 目 If t h ee x c i t e ri st u r n e do旺, howl o n gd o e si tt a k ef o rt h ew a v e st oLandaudampto 1 / eo ft h e i ri n i t i a l 3 m p l i t u d e ? oc 10‑1 7 ‑ 8 .I o nw a v e swithλ = 5cma r ee x c i t e di nas i n g l yi o n i z e da r g o nplasmaw i t h n ,= 1 0 1 6m 3 ,T,=2eV,T,=0 . 2e V ;andt h eLandaudampingr a t ei sm e a s u r e d . Ahydrogeni m p u r i t yo fd e n s i t ynH=an,i st h e ni n t r o d u c e d .C a l c u l a t et h ev a l u e ofαthat w i l ld o u b l et h edampingr a t e . 。 ‑lmw Rew 7 ‑ 9 .I nl a s e rf u s i o ne x p e r i m e n t soneo f t e ne n c o u n t e r sah o te l e c t r o nd i s t r i b u t i o n w i t hd e n s i t yn ,andt e m p e r a t u r eT,i na d d i t i o nt ot h eu s u a lp o p u l a t i o nw i t hn , . T,・ The h o te l e c t r o n sc a nchanget h edampingo fi o nwavesandhencea百ect s u c hp r o c e s s e sa ss t i m u l a t e dB r i l l o u i ns c a t t e r i n g .AssumeZ= 1i o n sw i t hn ,and ,= T,fT,”仇= T,/T,”日= n,/n,, 1 一日= n,/n,, ε = m/Mand T , ,andd e f i n ee k~, = n , e 2/εoKT,. 1 0 ‑ 2 A EXACT SOLUTION B ASYMPTOTIC EXPRESSION ( a )W r i t et h ei o nwaved i s p e r s i o nr e l a t i o nf o rt h i sthree‑componentp l a s m a , expandingt h ee l e c t r o nZ ‑ f u n c t i o n s C EMPIRICAL FORMULA ( b )Showt h a te l e c t r o nLandaudampingi sn o ta p p r e c i a b l yi n c r e a s e dby叫 T , > if T,. ( c )Showt h a ti o nLandaudampingi sd e c r e a s e db yn , ,andt h a tt h ee f f e c tc a n b ee x p r e s s e da sani n c r e a s ei nt h ee f f e c t i v et e m p e r a t u r er a t i oTJT,. 1 0 ‑ 3 . 0 1 273 K i n e t i cTheoη 0 . 1 10 0 ‑ 1 = T/ZT0 FIGURE7 ‑ 3 1 IonLandaudampingo fa c o u s t i cw a v e s .( A )i st h ee x a c ts o l u t i o no fE q .[7・ 128]; ( B )i st h ea s y m p t o t i cf o r m u l a ,E q .[7・ 133];阻d ( C )i st h ee m p i r i c a lf i t ,E q . [ 7 ‑ 1 3 4 ] ,goodf o rl く O く 10. 7 ‑ 1 0 .Thed i s p e r s i o nr e l a t i o nf o re l e c t r o np l a s m aw a v e sp r o p a g a t i n ga l o n gB , , Z c a nb eo b t a i n e dfromt h ed i e l e c t r i ct e n s o rE (AppendixB )andPoisson ’s e q u a t i o n , v"(ε ・ E) =0 ,whereE=‑ V < / J .Wet h e nh a v e ,f o rauniformp l a s m a , -~トお= εuk;φ =。 PROBLEMS 守F 274 C h a p t e r S e v e n 。r €,, = 0 .F o rac o l dp l a s m a ,P r o b l e m4 ‑ 4andE q .[ B ‑ 1 8 ]g i v e €,, = 1 w : 崎市 o r ‑ ; : ; ; ; 275 x= r Ls i nw , tfromE q.[ 2 ‑ 7 ] : x+w~x w ー=叫 K i n e t i cT h e o r y i ( k r 1 y i nw ォw < ) q = ‑E,e [ 7 ‑ 1 3 8 ] ηz F o rah o tp l a s m a ,E q .( 7 ‑ 1 2 4 ]g i v e s Theg e n e r a t i n gf u n c t i o nf o rt h eB e s s e lf u n c t i o n s] n ( z )i s 2 ,、 ε = I ーとと Z’{三斗 " 0 。。 k2 v~" ゐ \ kv,,.J 一 υ L : t "]π (z) e ''ト l/<)/2 = Bye x p a n d i n gt h eZ ‑ f u n c t i o ni nt h ep r o p e rl i m i t s ,showt h a tt h i se q u a t i o ny i e l d s t h eBohmG r o s swavef r e q u e n c y( E q .[ 4 ‑ 3 0 ] )andt h eLandaudampingr a t e( E q . [ 7 ‑ 7 0 ] ) . [ 7 ‑ 1 3 9 ] n~ ー∞ L e t t i n gz=k r Landt=exp( i w , I ) ,weo b t a i n 。。 e'h1.•inw" = L :]n(kγLl e ' " w c < [ 7 ‑ 1 4 0 ] ‑00 7.10 KINETIC EFFECTS INA MAGNETIC FIELD ,, αo : i '+w;x= . J . . . . E ,Lfn(kγLl e‑ i ( w ‑ n w , ) < Whene i t h e rt h edemagneticf i d dBoo rt h eo s c i l l a t i n gmagneticf i e l d nt h eVlasove q u a t i o n[ 7 ‑ 2 3 ]f o rac o l l i s i o n l e s s B1i sf i n i t e ,t h evラBtermi plasmamustbei n c l u d e d .Thel i n e a r i z e de q u a t i o n[ 7 ‑ 4 5 ]i sthenr e p l a c e d by a 1 1 q m q m a f 1 ム+ v·V/1 +ー( v X B0)・」ー=一一( E1 十 v a t a v f。 xB1 )・ 2 a v [7・ 135] Resonantp a r t i c l e smovingalongBos t i l lc a u s eLandaudampingi fw/k= twonewk i n e t i ce f f e c t snowappearwhicha r econnectedw i t h t h ev e l o c i t ycomponentVム perpendicular t oB 0 .Oneo ft h e s ei sc y c l o t r o n damping,whichw i l l! : l ed i s c u s s e dl a t e r ;t h eo t h e ri st h eg e n e r a t i o no f c y c l o t r o nh a r m o n i c s ,l e a d i n gt ot h ep o s s i b i l i t yo ft h eo s c i l l a t i o n scomュ monlyc a l l e dB e r n s t e i nw a v e s . Harmonics o ft h ec y c l o t r o n frequency a r e generated when t h e r b i t sa r ed i s t o r t e dbyt h ewavef i e l d sE 1and particles ’ circular Larmoro f f e c t sa r en e g l e c t e di nordinaryf l u i dt h e o r ybutcan B 1 .Thesefinite -γL e beta!ぽer n t oaccountt oorderk2 r 7 .byincludi時 the viscosityτr. A k i n e t i c t r e a t m e n tcanbea c c u r a t eevenf o rk2γr = 0(1).Tounderstandhow harmonicsa r i s e ,c o n s i d e rt h emotiono fap a r t i c l ei nane l e c t r i cf i e l d : i(kx-w <) E= E,e x [7・ 1361 v 山 but < Thee q u a t i o no fmotion( c f .E q .[ 2 ‑ 1 0 ] )i s 1 x+w,x= ‑E, r. i(kx‑w<) [ 7 ‑ 1 3 7 ] 作1 I fk r Li sn o ts m a l l ,t h eexponentv a r i e sfromones i d eo ft h eo r b i tt ot h e o t h e r . Wecanapproximatek x bys u b s t i t u t i n gt h eundisturbed o r b i t [ 7 ‑ 1 4 1 ] ‑oo ηl Thef o l l o w i n gs o l u t i o ncanbev e r i f i e dbyd i r e c ts u b s t i t u t i o n : x= q ‑ Zミ ln ( k r L )e i ( w ‑ n w , ) < m ~x / 9 ::る w~ 一 (w 9 nw,) ζ [ 7 ‑ 1 4 2 ] Thisshowst h a tt h emotionh a sfrequencycomponentsd i f f e r i n gfrom t h edrivi 時 frequencv bym u l t i p l e so fw" andt h a tt h eampliwdeso f t h e s ecomponentsa r ep r o p o r t i o n a lt ofn(krL)/[w :一(ω ー ηwe)"]. When h eamplitudebecomesl a r g e .Thishappens t h edenominator 、 anishes, t whenw ‑nw,=土 w,. o rw = (n 土 l)w ,, η = 0 ,土 l ,土 2, . . .,t h a ti s ,when t h ef i e l dE ( x ,t )r e s o n a t e sw i t hanyharmonico fw , .I nt h ef l u i dl i m i t krL • 0, ] n( k r L )canbeapproximatedby(kγd2)"/n ! ,whicha pproaches 0f o ra l lne x c e p tn= 0 .Forn= 0 ,t h ecoe 伍cient i nE q .[ 7 ‑ 1 4 2 ]becomes (ω ?ー ω ヨ) 1 ,whichi st h ef l u i dr e s u l t( c f .E q .[ 4 ‑ 5 7 ] )c o n t a i n i n go n l yt h e fundamentalc y c l o t r o nf r e q u e n c y . TheHotPlasmaD i e l e c t r i cTensor 7 . 1 0 . 1 A f t e rF o u r i e ra n a l y s i so ff 1 ( r ,v ,I )i ns p a c eandt i m e ,E q .[ 7 ‑ 1 3 5 ]canbe s o l v e df o raMaxwelliand i s t r i b u t i o nf 0 ( v ) ,andt h er e s u l t i n ge x p r e s s i o n s f 1 ( k ,v ,w)canbeusedt oc a l c u l a t et h ed e n s i t yandc u r r e n to feachspecies 目 Ther e s u l ti su s u a l l ye x p r e s s e di nt h eformo fane q u i v a l e n td i e l e c t r i c tensorε, such t h a tt h edisplacementv e c t o rD = ε ・ E canbeusedi nt h e M a x w e l l ' se q u a t i o n sV キD = 0andV xB= オ0Dt oc a l c u l a t ed i s p e r s i o n r e l a t i o n sf o rv a r i o u swaves( s e eAppendixB ) .Thea l g e b r ai shorrendous o rn o n r e l a ュ andt h e r e f o r eo m i t t e d .Wequoteo n l yar e s t r i c t e dr e s u l t、alid f t i v i s t i cplasmasw i t hi s o t r o p i cpress凶re(Tム= T u )andnoz e r o ‑ o r d e rd r i f t s 276 C h a p t e r S e v e n V o j ;t h e s er e s t r i c t i o n sa r ee a s i l yremoved,butt h eg e n e r a lformulas 丘町 t o oc l u t t e r e df o rourp u r p o s e s .Wef u r t h e rassumek=丸呈+ k , z .withz bei 時 the directionofB0;nogene叫ty i sl o s tby 犯t山g k~ e q u a . l~o z e r o , s i n c et h e plasmai si s o t r o p i ci nt h e plane perpendicular t o Bo目 The elementso fε R = ε/εo a r ethen 2 E x x= b Cノ x ノq B/ク B z x 277 K i n e t i cT h e o r y J芯JグZ ‑ L 竺 ~Co ‑I n21,,(b)Z(ム co 1+ s u.I u ャ l +~;; T ベ山仲 2b2[1n(b ) →; (b )附礼) 九=一句x=i~ 土宗ぺ。 2η [ )一 ι; (b ( a ) [ 7 ‑ 1 4 3 ] ε" = ε之3 ( 2 b ) " ' I ~土芸(~) 112e b(o E , ,= ‑ E , ,= ‑i 1;,(b )附n) 2 h・"' whereZ(()i st h eplasmad i s p e r s i o nf u n c t i o no fE q .( 7 ‑ 1 1 8 ) ,J , , ( b )i st h e nthorderB e s s e lf u n c t i o no fimaginaryargument,andt h eothersymbols a r edefinedby 2, ω 抑 = no,L.,e / ε oms C市=(ω +加1")/k,vths Cos=w/k山hs ω口= IZ,cBo/前J PROBLEM . 1 0 . 2 CyclotronDamping 7 -ro ヨヮ 2 7 ‑ 1 1 .I nt h el i m i to fz e r ot e m p e r a t u r e ,showt h a tt h ee l e m e n t sofεin E q .[ 7 ‑ 1 4 3 ] r e d u c et ot h ec o l d ‑ p l a s m ad i e l e c t r i ct e n s o rg i v e ni nAppendixB . [ l , , ( b )‑ ε"= 1 ーエヲ e b C o L: ム (b )ムZ’(ム) u’ ( b ) Themechanismo fc y c l o t r o nd a m p i n g . FIGURE7 ‑ 3 2 [ 7 ‑ 1 4 4 ] v~hs = 2KT,/m, b ,= ~k~rL, = k;KT,/m,~,/;, ,w i t ht h eunderstandingt h a twρ, b, ( o ,and Thef i r s tsumi sovers p e c i e ss ム all dependons ,andt h a tthe 土問nds f o rthe 叩1 o ft h ec h a r g e .The second sum i s over t h e harmonic number n . The primes i n d i c a t e d i f f e r e n t i a t i o nw i t hr e s p e c tt ot h eargument. Asf o r e s e e n ,t h e r eappearB e s s e lf u n c t i o n so ft h ef i n i t e ‑ r Lparameter b .[Thechangefrom ム (b) t oI n( b )o c c u r si nt h ei n t e g r a t i o noverv e l o c i t i e s .l o n t a i nZ’(ム), whichgive~ Theelementso fei n v o l v i n gmotionalong」c r i s et oLandaudampingwhenn=0andw/k,=v出・ The n" "0terms nowmakep o s s i b l eanotherc o l l i s o n l e s sdampingmechanism,c y c l o t r o n damping,whicho c c u r swhen(ω 士 ηWc)/k, = V t h キ When a p a r t i c l e moving along Bo i n a wave w i t hf i n i t ek ,h a st h e , v ,equalto 土ηw, r i g h tv e l o c i t y ,i ts e e saD o p p l e r ‑ s h i f t e dfrequencyw ‑k andi st h e r e f o r es u b j e c tt ocontinuousa c c e l e r a t i o nbyt h eelectric 白eld Eム of t h ewave.Thosep a r t i c l e sw i t ht h e“ right ” phase r e l a t i v et oEム will g a i ne n e r g y ;t h o s ew i t ht h e“ wrong” phase w i l ll o s ee n e r g y .S i n c et h e energychange i st h ef o r c et i m e st h ed i s t a n c e ,t h ef a s t e ra c c e l e r a t e d p a r t i c l e sg a i nmoreenergyperu n i tt i m ethanwhatt h es l o w e rd e c e l e r a t e d p a r t i c l e sl o s e .Therei s ,t h e r e f o r e ,an e tg a i no fenergybyt h ep a r t i c l e s , on t h ea v e r a g e ,a tt h eexpenseo ft h ewavee n e r g y ; and t h ewavei s h e damped.Thismechanismdiぽers fromLandaudampingbecauset energygainedi si nt h ed i r e c t i o nperpendiculart oB 0 ,andhenceperpenュ d i c u l a rt ot h ev e l o c i t ycomponentt h a tb r i n g st h ep a r t i c l ei n t or e s o n a n c e . Theresonancei snote a s i l ydestroyedbyphenomenasucha st r a p p i n g . Furthermore,t h emeree x i s t e n c eo fresonantp a r t i c l e ss u f f i c e st oc a u s e b(v,), as in Landau damping; one does n o t need a n e g a t i v es l o p eJ damping. Toc l a r i f yt h ep h y s i c a lmechanismo fc y c l o t r o ndamping,c o n s i d e r awavew i t hk=丸圭 + k , ま with k ,p o s i t i v e .Thewavee l e c t r i cf i e l dEょ can be decomposed i n t ol e f t ‑ and r i g h t ‑ h a n dc i r c u l a r l yp o l a r i z e d comュ p o n e n t s ,a sshowni nF i g .7 ‑ 3 2 .Fort h el e f t ‑ h a n dcomponent,t h ev e c t o r Eム at p o s i t i o n sA,B ,andC alongt h eza x i sappearsa sshowni nF i g . 278 C h a p t e r S e v e n , ' Theexpre鈴ion i nthe 押iare b r a c k e t scanbe 討I叩Iified i na . , f e . ; valg~braic s t e p st o2k~ [C-n +C~Z((,.)] byu s i n gt h ed;fi~i山ns b=k2;v ゐ / 2w~ and ( , ,= ( w+n w c ) / k eachs p e c i e s ,wecanw r i t eE q .[ 7 ‑ 1 4 7 ]a s ∞ 一一 日リ ( )] ハu ハυ r h Z ’’’d ’bv + ’by n ( ’nu) [ y’ヨ rt ∞寸ム一一 一 e ’hM ” b S す十] + 2D + ’hn 2z LK 2x ( 7 ‑ 1 4 8 ] ThetermC ‑ n / C oi s1 n w , / w .S i n c el n ( b )=Ln(b),t h eterml , . ( b ) n w , / w sumst oz e r owhenng o e sfrom 一co t oa : : > ;h e n c e ,Cn ! C ocanber e p l a c e d by 1 . Defini時 k2 =k ;+k~. weo b t a i nt h ege悶ral d叩ers f o rB e r n s t e i nwa、’es : ) 一一 rL 引 rム d ∞ hυ ’ + d l rt ∞工一 すfHS 2D 一す-ム + K7R 7 ‑ 3 2 a .S i n c et h ewavepropagatesi nt h e+ま direction, as t a t i o n a r ye l e c t r o n ,B ,andA i ns u c c e s s i o nandt h e r e f o r e wouldsamplet h ev e c t o r sa tC woulds e eal e f t ‑ r o t a t i n gE ‑ f i e l d .I twouldn o tbea c c e l e r a t e db e c a u s ei t s Larmorg y r a t i o ni si nt h er i g h t ‑ h a n d( c l o c k w i s e )d i r e c t i o n .However,i f d i r e c t i o n ,i twould t h ee l e c t r o nweremovingf a s t e rthant h ewavei nt h ez ,andCi nt h a torderandhencewouldber e s o n a n t l y s e et h ev e c t o r sa tA,B , v ,=一w" The a c c e l e r a t e di fi t sv e l o c i t ys a t i s f i e dt h ec o n d i t i o n w ‑k r i g h t ‑ h a n dcomponento fEwouldappeara sshowni nF i g .7 ‑ 3 2 b .Now ane l e c t r o nwoulds e eac l o c k w i s er o t a t i n gE ‑ f i e l di fi tmovedmores l o w l y t h a nt h ew a v e ,s ot h a tt h ev e c t o r sa tC ,B , and A weresampled i n s u c c e s s i o n .Thise l e c t r o nwouldbea c c e l e r a t e di fi tmett h ec o n d i t i o n w ‑k , v ,=+w"A p l a n eo re l l i p t i c a l l yp o l a r i z e dwavewould,t h e r e f o r e , b ec y c l o t r o ndampedb ye l e c t r o n smovingi ne i t h e rd i r e c t i o ni nt h ewave f r a m e . ) [ 7 ‑ 1 4 9 ] (A) E l e c t r o nBeγ州仰 Wαves・ Let u sf i r s tc o n s i d e rhigh-fre~uency waves e r n s t e i nWaves 7 . 1 0 . 3 B E l e c t r o s t a t i c waves propagating a tr i g h ta n g l e st o Bo a t harmonics o ft h ec y c l o t r o nfrequencya r ec a l l e dB e r n s t e i nw a v e s .Thed i s p e r s i o n r e l a t i o ncanb efoundbyusingt h ed i e l e c t r i ce l e m e n t sg i v e ni nE q .( 7 ‑ 1 4 3 ] q u a t i o nVキeキE=0 .I fweassumee l e c t r o s t a t i cp e r t u r b a ュ i nPoisson ’s e o n s i d e r w呂ves o ft h e form φ1= t i o n s such t h a tE 1= -Vφ1, and c φl e xpi ( kキr‑w t ) ,Poisson ’ s equationcanbew r i t t e n k :ε口+ 2kムε,, +k ;ε"= 0 ? : . ( 7 ‑ 1 4 5 1 ‑ z Notet h a twehavechosenac o o r d i n a t esystemt h a th a skl y i n gi nt h ex p l a n e ,s ot h a tk ,=0 .Wen e x ts u b s t i t u t ef o r<xx. ε,,, andE日 from E q . ntermso fZ ( ( n )w i t ht h ei d e n t i t y ( 7 ‑ 1 4 3 ]ande x p r e s sZ ’((n) i Z’(ム) i nwhicht h ei o n sdon o tmove.Thesewavesa r en o ts e n s i t i v et os m a l l 白viations fromperpendicularpropagation,andwemay 詑t k ,=0 ,. s o t h a tCn • co. Therei s ,t h e r e f o r e ,noc y c l o t r o ndamping;t h egapsi nt h e spectrumt h a twes h a l lf i n da r en o tcausedbysuchdamping.Forl a r g e wemaγre凶ce Z (ふ) by 一 1/(,., accordingt oE q ._(7 ” 129]. Tト E n=0 fE q .( 7 ‑ 1 4 9 ] thenc a n c e l so u t ,andwecan termi nt h ese仁ond sumo d i v i d et h esumi n t otwosums,a sf o l l o w s : = ‑2(1+CZ(OJ k : ̲+~k~e-b[I I,亀 (b )(!一ふ/C,, [ 7 ‑ 1 5 0 ] o r ∞「"' W I “ k~ +工 k~e-b n~I l,.(b)l2 一戸五:- ~J=U ( 7 ‑ 1 4 6 ] ( 7 ‑ 1 5 1 ] Theb r a c k e tc o l l a p s e st oas i n g l etermuponcombiningo v e racommon denominator: i r e c t l yfromt h ei n t e g r a le x p r e s s i o n sf o rZ(()andZ’(よ), PROBLEM 7‑12.ProveEq.(7‑146]d ~ 2 2 =ヱ与 e → I 1,.(b ) 」竺竺プ ’ - I Equation(7・ 145] 'kょ becom自 [ 7 ‑ 1 5 2 ] “~ 一四ー『ーーー一一一一一一一 一ー一ー--ーーーーー一一ー~ーー 一一 ~ 一ω (7・ 147] F一 h仰 」 司ヤーτ , nkム(! +ふZ) ‑2 k ; ( , . ( l+( n Z )I =0 ヤム電 xI k2 ニ z-21::.i Lx b \bJ ワニ’0 00 '"、"" 2 n~ d i s p e r s i o nr e l a t i o n 的寸一叫 'W w Usingt h ed e f i n i t i o n so fknandb ,oneo b t a i n st h ewell‑knownk ,=0 民吋い I ~e-b(o I ム(b) 「_ 2 η~1 (7・ 153] 279 K i n e t i cT h e o r y 280 S e v e n 281 K i n e t i cT h e o r y 6 Chai骨teγ 山= 1込 2 5 一叩 51 a ( w ,b ) 4 。 αp We 3 ‑2 2 αJ h w!wC 2 3 FIGURE7 ‑ 3 3 Thef u n c t i o na(w,b)f o re l e c t r o nB e r n s t e i nw a v e s .[FromI .B .B e r n s t e i n , P h y s .R e v .1 0 9 ,1 0( 1 9 5 8 ) . ) Wenows p e c i a l i z et ot h ec a s eo fe l e c t r o no s c i l l a t i o n s .Droppingt h e sumovers p e c i e s ,weo b t a i nfromE q .( 7 ‑ 1 5 2 ] k~ 凸 2 手 e-01n(b) τす= ~w , F<o ムーす一一一言 η n~I α> 2 , = a(w,b) )f o ronev a l u eo fb i sshowni nF i g .7 ‑ 3 3 .Thep o s s i b l e Thef u n c t i o na(w,b r efoundbydrawi時 a h o r i z o n t a l l i n e a t a ( w , b )= k~/k~ >0 . v a l u e so fwa I ti sthenc l e a rt h a tp o s s i b l ev a l u e so fw l i ej u s taboveeachc y c l o t r o n harmonic,andt h a tt h e r ei saforbiddengapj u s tbeloweachharmonic. Too b t a i nt h ef l u i dl i m i t ,wer e p l a c eI n( b )byi t ss m a l l ‑ bv a l u e( b / 2 ) "/η ! i nE q .(7・ 153]. Onlyt h eπ = 1termremainsi nt h el i m i tb • 0, andwe o b t a i n αJ c 0 ~ \ αJ c I 9 αJ p =一言一一一言 ω 3 4 5 kム「L [ 7 ‑ 1 5 4 ] -nαJ c 1 = ~~f1~ - 1r 2 [ 7 ‑ 1 5 5 ] 一 w, o rw2= w!+w;= w~ , whichi st h eupperh y b r i do s c i l l a t i o n .Ask ょ→ 0, t h i sfrequencymustbeoneo ft h er o o t s .I fwhf a l l sbetweentwohigh harmonicso fω。 the shapeo ft h ew ‑kc u r v e schangesnearw = wht o a l l o wt h i stoo c c u r .Thew‑kc u r v e sa r ecomputedbym u l t i p l y i n gE q . (7・ 154] by2w;;w; t oo b t a i nkiγ~ = 4w 弘 (w, b ) .Theresulti時 curves f o rw/w,v s .kムrL a r eshowni nF i g .7” 34 f o rv a r i o u sv a l u e so fw;;w;. ‑ 3 4 E l e c t r o nB e r n s t e i nwaved i s p e r s i o nr e l a t i o n .[ A d a p t e df r o m FIGURE7 r a w f o r d ,f .A戸pl. P h y s .3 6 ,2930( 1 9 6 5 ) . ) F .W.C Notet h a tf o reachsuchv a l u e ,t h ec u r v e schangei nc h a r a c t e rabovet h e correspondingh y b r i df r e q u e n c yf o rt h a tc a s e .Att h eextremel e f to ft h e diagram,wheret h ephasev e l o c i t yapproachest h espeedo fl i g h twaves i nt h ep l a s m a ,t h e s ec u r v e smustbemodifiedbyi n c l u d i n ge l e c t r o m a g ュ n e t i cc o r r e c t i o n s . E l e c t r o nB e r n s t e i nmodeshavebeend e t e c t e di nt h el a b o r a t o r y ,b u t i n e x p l i c a b l yl a r g espontaneouso s c i l l a t i o n sa thighharmonicso fw ,have a l s obeens e e ni ng a sd i s c h a r g e s .Thes t o r yi st o olongt ot e l lh e r e . ( B )I o nB e r n s t e i nW a v e s .I nt h ec a s eo fwavesa ti o nc y c l o t r o nh a r m o n i c s , o nB e r n s t e i nw a v e s ,f o rwhichk ,= 0 , oneh a st od i s t i n g u i s hbetweenpuγe i e u t r a l i z e di o nB e r n s t e i nw a v e s ,f o rwhichk ,h a sas m a l lbutf i n i t e andn v a l u e .Thed i f f e r e n c e ,a swehaveseene a r l i e rf o rlowerh y b r i do s c i l l a ュ ,a l l o w se l e c t r o n st of l o walongBot oc a n c e lcharge t i o n s ,i st h a tf i n i t ek Cha骨ter S e v e n s e p a r a t i o n s . Though t h ek ,= 0c a s eh a sa l r e a d ybeen t r e a t e di nE q . [7・ 153], t h ed i s t i n c t i o nbetweent h etwoc a s e sw i l lbec l e a r e ri fwego backas t e pt oE q s .[ 7 ‑ 1 4 8 ]and[ 7 ‑ 1 4 9 ] .S e p a r a t i n goutt h eπ = 0term andu s i n gE q .( 7 ‑ 1 4 6 ] ,wehave 軍孝i弘 282 283 \ K i n e t i cT h e o r y 」ーー一一 k~ +ピ + ~k~e-610 (的)[一~Z'((o) ーーーーー ーーーーーーーー一ーーーーーー- •650 600 ,‘手•o [7・ 156] 円 u ~2 AU寸 2 .. nU r (Nヱギ)』 Thed i v i d i n gl i n ebetweenpureandn e u t r a l i z e di o nB e r n s t e i nwavesl i e s !(o , > l f o rt h ee l e c t r o n s ,wecanu s eE q . i nt h ee l e c t r o nη = O 町m I ' ( ( 0 , )= 1 / ( 6 , .S i n c ew/k, 》 U山tl [ 7 ‑ 1 2 9 ]t ow r i t eZ cannotf l o wr a p i d l yenoughalongBot oc a n c e lc h a r g e .I f( 0 ,< 1, wec an u s eE q .[7 ・ 126] t ow r i t eZ ’((o,) =‑ 2 .I nt h i sC証se wehavew /k之《 v,1 andt h ee l e c t r o n shavetimet of o l l o wt h eBoltzmannr e l a t i o n[ 3 ‑73] Takingf i r s tt h e( o ,> l c a s e ,wenotet h a t(0;> l i sn e c e s s a r i l yt r u e nE q .[ 7 ‑ 1 5 6 ]becomes a l s o ,s ot h a ttheη = 0termi 325 司、 -k;j~ + ~e 6l0(b)/ ̲ J LαJαJ Herewehavet a k e nb, • O ando m i t t e dt h es u b s c r i p tfromb ;・ Theη "" 0 t e r m si nE q .[ 7 ‑ 1 5 6 ]a r et r e a t e da sb e f o r e ,s ot h a tt h ee l e c t r o np a r ti s g i v e nbyE q .[ 7 ‑ 1 5 5 ] ,andt h ei o np a r tbyt h ei o ntermi nE q .( 7 ‑ 1 5 3 ] . Thepurei o nB e r n s t e i nwaved i s p e r s i o nr e l a t i o nthenbecomes 2 r ~2 2 1 w H k ,, ト寸一弓 e w L b 2「 0 Wp lo(b)j+k11I 一一「ーす一寸 - e J L w 一 w, u ,b 日U ’ 司haaE eaEJ i ナη 、ノ一一 J 一 c Oi 寸 tuQ ’ 一 ー 一,r, ’ ナω i ラ ∞ γ白戸 ; [ 7 ‑ 1 5 7 ] S i n c e(0 , > l i m p l i e ss m a l lk ; ,thefirsttermi su s u a l l y町gligible・ To examinet h ef l u i dl i m i t ,wecans e tt h esecondb r a c k e tt oz e r o ,s e p a r a t e e r m ,anduset h es m a l l ‑ bexpansiono fI n ( b ) ,o b t a i n i n g outt h eπ = 1t 1̲ w ; fl;子 η2n;(b/2)"-1 一万一一ーす一一言一一文言 - ω ー w, w ‑H, L 9 " "" n--;;2η !( w 4 ー η·n;) n =U [ 7 ‑ 1 5 8 ] Thesumv a n i s h e sf o rb= 0 ,andt h eremainingtermsa r ee q u a lt ot h e fAppendixB .Thec o n d i t i o nS=0y i e l d st h eupperand q u a n t i t yS o l o w e rh y r b i df r e q u e n c i e s( s e et h ee q u a t i o nf o l l o w i n gE q .[ 4 ‑ 7 0 ] ) .Thus, f o rkム→ 0, t h elow‑frequencyr o o tapproachesw1・ For f i n i t eb ,oneo f t h etermsi nt h esumcanb a l a n c et h ee l e c t r o ntermi fw =nil"s ot h e r e a r er o o t sneart h ei o nc y c l o t r o nh a r m o n i c s .Thed i s p e r s i o nc u r v e sw / f l , 2 k(mm‑1) 4 6 ‑ 3 5 Purei o nB e r n s t e i nw a v e s :a g r e e m e n tb e t w e e nt h e o r yande x p e r i ュ FIGURE7 .P .) . ! .S c h m i t t ,P h y s .R e v . menti naQ‑machinep l a s m a .[ F r o mJ L e t t .3 1 ,9 8 2( 1 9 7 3 ) . ] f l p2 ‑b 『”。 l 。 v s .kJ.rLi resemblet h ee l e c t r o nc u r v e si nF i g .7 ‑ 3 4 .Thel o w e s ttwor o o t s f o rt h ei o nc a s ea r eshown i nF i g .7 ‑ 3 5 ,t o g e t h e rw i t he x p e r i m e n t a l measurementsv e r i f y i n gt h ed i s p e r s i o nr e l a t i o n . Thelowerbrancheso ft h eB e r n s t e i nwaved i s p e r s i o nr e l a t i o ne x h i b i t t h ebackward‑wavephenomenon,i nwhicht h ew ‑kcurveh a san e g a t i v e s l o p e ,i n d i c a t i n gt h a tt h e group v e l o c i t y1 so p p o s i t ei nd i r e c t i o nt o t h ephasev e l o c i t y .Thatbackwardwavesa c t u a l l ye x i s ti nt h el a b o r a t o r y s .kmeasurementso ft h et y p eshown h a sbeenv e r i f i e dnoto n l ybyw v i nF i g .7 ‑ 3 5 , buta l s obywavei n t e r f e r o m e t e rt r a c e swhichshowt h e motion o f phase f r o n t si nt h e backward d i r e c t i o n from r e c e i v e rt o transロ11tter. F i n a l l y ,wec o n s i d e rn e u t r a l i z e dB e r n s t e i nwa、 es, f o rwhich( 0 ,i s s m a l landZ ’ ((0,) = 2 .Thee l e c t r o nη = 0termi nE q .(7・ 156] becomes s i m p l yk~,. Assumingt h a t(0; > l s t i l lh o l d s ,t h ea n a l y s i sl e a d i n gt oE q . LM ・市川 Lt 加山 eγ 2rLS t ot h el o w e rh y b r i dresonancew = w 1 .I ndeed,a sk ょrLi → O t h eenvelope 、 3 αJ De 2 2 。 3 4 kムru FIGURE7 ‑ 3 6 N e u t r a l i z e di o nB e r n s t e i nmodes:a g r e e m e n tb e t w e e nt h e o r y ande x p e r i m e n ti naHemicrowaved i s c h a r g e .[ F r o mE .A u l t andH.I k e z i ,P h y s .F l u i d s1 3 ,2 8 7 4( 1 9 7 0 ) . ] (7 ” 157] i sunchanged,andE q .[ 7 J l 5 6 ]becomes 。r k~ n : :" " 1 I o ( b )I k ; 1 1+元一一昔 e L R . zαJ 」 「 2 n : 2 一一手 ι (b) l +k~I ト「,".'..L... +. . . . : . j ;‑P . Y I= o ~L w ζ 一 W~ fl~ b‑ , . ' ; : I一一一寸一一 (w ηfl ,)之- ] j ~ < [ 7 ‑ 1 5 9 ] fork ; 《 k~ , anapproximater e l a t i o nf o rn e u t r a l i z e di o nB e r n s t e i nwaves canbew r i t t e n 「 2 n 2 2 ‑ ~ミ ln(b) 1 1+k2A1j ト寸三ムマ+→ - e-b I-一一一一 I= L w 一 W, f l ,b n'‑;:I (w/ ηn, -1 )ーJ o r1品OJ :、~ote t h a te l e c t r o ntemperaturei snowc o n t a i n e dmλ0, whereaspure fk2λ1 i s i o nB e r n s t e i nw a v e s ,E q .[ 7 ‑ 1 5 7 ] ,a r eindependento fKT,.I s m a l l ,t h eb r a c k e ti nE q .( 7 ‑ 1 6 0 ]mustbel a r g e ;andt h i scanhappeno n l y h en e u t r a l i z e dmodesa r en o ts e n s i t i v e neararesonancew = nn,・ Thus t t h ed i s p e r s i o nc u r v e sapproachest h ee l e c t r o s t a t i ci o nc y c l o t r o nwave r e l a t i o n( 4 ‑ 6 7 ] ,whichi st h ef l u i dl i m i tf o rn e u t r a l i z e dw a v e s . N e u t r a l i z e dB e r n s t e i nmodesa r enota sw e l ldocumentedi ne x p e r i ュ menta spureB e r n s t e i nmodes,butweshowi nF i g .7 ‑ 3 6onec a s ei n whicht h eformerhavebeens e e n . of 285 K i n e t i cT h e o r y !~ C h a p t e rE i g h t NONLINEAR E F F E C T S INTRODUCTION 8 . 1 Upt ot h i sp o i n t ,wehavel i m i t e doura t t e n t i o na l m o s te x c l u s i v e l yt o l i n e a rphenomena;t h a ti s ,t ophenomenad e s c r i b a b l ebye q u a t i o n si n whicht h edependentv a r i a b l eo c c u r st onoh i g h e rthant h ef i r s tpower. Thee n t i r et r e a t m e n to fwavesi nChapter4 ,f o ri n s t a n c e ,dependedon t h ep r o c e s so fl i n e a r i z a t i o n ,i nwhichh i g h e r ‑ o r d e rtermswereregarded a ss m a l landweren e g l e c t e d .Thisprocedureenabledu st oc o n s i d e ro n l y one F o u r i e rcomponenta ta t i m e ,w i t ht h es e c u r ef e e l i n gt h a tany n o n s i n u s o i d a lwavecanbehandleds i m p l ybyaddingupt h ea p p r o p r i a t e d i s t r i b u t i o no fF o u r i e rcomponents.Thisworksa slonga st h ewave amplitudei ss m a l lenought h a tt h el i n e a re q u a t i o n sa r ev a l i d . U n f o r t u n a t e l y ,i nmanye x p e r i m e n t swavesa r enolongerd e s c r i b a b l e byt h el i n e a rt h e o r ybyt h et i m et h e ya r eo b s e r v e d .C o n s i d e r ,f o ri n s t a n c e , t h ec a s eo fd r i f tw a v e s .Becauset h e ya r eu n s t a b l e ,d r i f twaveswould, a c c o r d i n gt ol i n e a rt h e o r y ,i n c r e a s et h e i ramplitudee x p o n e n t i a l l y .This p e r i o do fgrowthi sn o tn o r m a l l yobserved‑sinceoneu s u a l l ydoesnot knowwhent os t a r tlooking‑buti n s t e a doneo b s e r v e st h ewaveso n l y a f t e rt h e yhavegrownt oal a r g e ,s t e a d ya m p l i t u d e .Thef a c tt h a tt h e wavesa r enol o n g e rgrowingmeanst h a tt h el i n e a rt h e o r yi snol o n g e r .v a l i d ,andsomen o n l i n e a re f f e c ti sl i m i t i n gt h ea m p l i t u d e .T h e o r e t i c a l u r p r i s i n g l y e x p l a n a t i o no ft h i selementaryo b s e r v a t i o nh a sprovedtobeas di伍cult p roblem,s i n c et h eo b s e r v e damplitudea ts a t u r a t i o ni sr a t h e r s m a l l . 287 n州、 e 引 v 。 v v , ゆ b Ad o u b l e ‑ h u m p e d ,u n s t a b l ee l e c t r o nd i s t r i b u t i o n . FIGURE8 ‑ 1 t h eprimarywavet oformo t h e rwavesa tt h eb e a tf r e q u e n c i e s .Theb e a t wavesm t u r ncangrows ol a r g et h a tt h e ycani n t e r a c tandformmany moreb e a tf r e q u e n c i e s ,u n t i lt h espectrumbecomesc o n t i n u o u s .I ti s i n t e r e s t i n gt od i s c u s st h ed i r e c t i o no fenergyf l o wi nat u r b u l e n ts p e c t r u m . I nf l u i dd y n a m i c s ,long咽wavelength modesdecayi n t os h o r t ‑ w a v e l e n g t h modes,b e c a u s et h el a r g ee d d i e sc o n t a i nmoreenergyandcandecay o n l ybys p l i t t i n gi n t os m a l le d d i e s ,whicha r eeachl e s se n e r g e t i c .The s m a l l e s te d d i e sthenc o n v e r tt h e i rk i n e t i cmotioni n t oh e a tbyv i s c o u s damping.I nap l a s m a ,u s u a l l yt h eo p p o s i t eo c c u r s .S h o r t ‑ w a v e l e n g t h modes tend t oc o a l e s c ei n t ol o n g ‑ w a v e l e n g t h modes, whicha r el e s s e n e r g e t i c .Thisi sb e c a u s et h ee l e c t r i cf i e l denergyE 2 / 8 T Ti so forder fφ2 / 8 7 r ,s ot h a ti feφis f i x e d( u s u a l l ybyKT,),t h es m a l l ‑ k ,long-λmodes havel e s se n e r g y .Asac o n s e q u e n c e ,energyw i l lbet r a n s f e r r e dt os m a l l k byi n s t a b i l i t i e sa tl a r g ek ,andsomemechanism mustbefoundt o d i s s i p a t et h ee n e r g y .Nosuchprobleme x i s t sa tl a r g ek ,whereLandau dampingcano c c u r .FormotionsalongB0,n o n l i n e a r“ modulational ” i n s t a b i l i t i e sc o u l dc a u s et h eenergya ts m a l lkt obecoupledt oi o n sand t oh e a tthem.Formotionsp e r p e n d i c u l a rt oB0,t h el a r g e s te d d i e sw i l l havew a v e l e n g t h so ft h eordero ft h eplasmar a d i u sandc o u l dc a u s e plasmal o s st ot h ew a l l sbyc o n v e c t i o n . Althoughproblemss t i l lremaint obes o l v e di nt h el i n e a rt h e o r yo f wavesandi n s t a b i l i t i e s ,t h emainstreamo fplasmar e s e a r c hh a sturned t ot h emuchl e s sw e l lunderstooda r e ao fn o n l i n e a rphenomena.The examplesi nt h ef o l l o w i n gs e c t i o n sw i l lg i v eani d e ao fsomeo ft h ee f f e c t s t h a thavebeens t u d i e di nt h e o r yandi ne x p e r i m e n t . 9U カ も(v) 叩 A wavecanundergoanumbero fchangeswheni t samplitudeg e t s l a r g e .I tcanchangei t sshape‑say, fromas i n ewave t oal o p s i d e d, t r i a n g u l a rwaveform.Thisi st h esamea ss a y i n gt h a tF o u r i e rcomponents a to t h e rf r e q u e n c i e s( o rwavenumbers)a r eg e n e r a t e d .U l t i m a t e l y ,t h e wavecan “ break ,'’ like oceanwavesonab e a c h ,c o n v e r t i n gt h ewave energy i n t othermalenergyo ft h ep a r t i c l e s .A l a r g ewavecan t r a p p a r t i c l e si ni t sp o t e n t i a lt r o u g h s ,t h u schangingt h ep r o p e r t i e so ft h e mediumi nwhichi tp r o p a g a t e s .Wehavea l r e a d yencounteredt h i sE圧ect i nd i s c u s s i n gn o n l i n e a rLandaudamping. I faplasmai ss os t r o n g l y e x c i t e dt h a tac o n t i n u o u sspectrumo ff r e q u e n c i e si sp r e s e n t ,i ti si na s t a t eo ft u r b u l e n c e .T hiss t a t emustbed e s c r i b e ds t a t i s t i c a l l y ,a si nt h ec a s e o fo r d i n a r yf l u i dhydrodynamics.Animportantconsequenceo fplasma t u r b u l e n c ei sanomalousr e s i s t i v i t y ,i nwhiche l e c t r o n sa r esloweddown byc o l l i s i o n sw i t hrandome l e c t r i cf i e l df l u c t u a t i o n s ,r a t h e rthanw i t h i o n s .Thise f f e c ti susedf o rohmich e a t i n go faplasma( S e c t i o n5 . 6 . 3 )t o temperaturess ohight h a to r d i n a r yr e s i s t i v i t yi si n s u f f i c i e n t . Nonlinearphenomenacanbegroupedi n t ot h r e ebroadc a t e g o r i e s : 1 .B a s i c a l l yn o n l i n e a r i z a b l eproble前s. D i f f u s i o ni naf u l l yi o n i z e dg a s , f o ri n s t a n c e ,i si n t r i n s i c a l l yan o n l i n e a rproblem( S e c t i o n5 . 8 )because t h ed i f f u s i o ncoe伍cient v a r i e sw i t hd e n s i t y .I nS e c t i o n6 . 1 ,wehaves e e n t h a tproblemso fhydromagnetice q u i l i b r i u ma r en o n l i n e a r .InS e c t i o n 8 . 2 ,wes h a l lg i v eaf u r t h e rexample‑theimportants u b j e c to fplasma s h e a t h s . 2 . Waveψarticle i n t e r a c t i o n s .P a r t i c l et r a p p i n g( S e c t i o n 7. 5 )i san exampleo ft h i sandcanl e a dt on o n l i n e a rdamping.A c l a s s i cexample i st h eq u a s i l i n e a re f f e c t ,i nwhicht h ee q u i l i b r i u mo ft h eplasmai schanged byt h ew a v e s .Considert h ec a s eo faplasmaw i t hane l e c t r o nbeam( F i g . 8 ‑ 1 ) .S i n c et h ed i s t r i b u t i o nf u n c t i o nh a sar e g i o nwheredfo/dvi sp o s i t i v e , t h esystemh a si n v e r s eLandaudamping,andplasmao s c i l l a t i o n sw i t hUφ i nt h ep o s i t i v e ‑ s l o p er e g i o na r eu n s t a b l e( E q . [7・67]). The r e s o n a n t e l e c t r o n sa r et h ef i r s tt obea f f e c t e dbyw a v e ‑ p a r t i c l ei n t e r a c t i o n s ,and t h e i rd i s t r i b u t i o nf u n c t i o nw i l lbechangedbyt h ewavee l e c t r i cf i e l d .The wavesa r es t a b i l i z e dwhenf . ( v )i sf l a t t e n e dbyt h ew a v e s ,a sshownbyt h e dashedl i n ei nF i g .8 ‑ 1 ,s ot h a tt h enewe q u i l i b r i u md i s t r i b u t i o nnol o n g e r h a sap o s i t i v es l o p e .Thisi sat y p i c a lq u a s i l i n e a re f f e c t .Anotherexample o fw a v e ‑ p a r t i c l ei n t e r a c t i o n s ,t h a to fplasmawavee c h o e s ,w i l lbeg i v e n i nS e c t i o n8 . 6 . 3 . Wave-山ave i n t e r a c t i o n s .Wavesc ani n t e r a c tw i t heacho t h e reven i nt h ef l u i dd e s c r i p t i o n ,i nwhichi n d i v i d u a lp a r t i c l ee f f e c t sa r en e g l e c t e d . As i n g l ewavecandecaybyf i r s tg e n e r a t i n gharmonicso fi t sfundamental f r e q u e n c y .Theseharmonicsc a nt h e ni n t e r a c tw i t heacho t h e randw i t h 2 ・ m亦 C h a p t e r E i g h t N 288 290 C h a p t e r E i g h t 8 . 2 SHEATHS 291 。 Nonli:町田 Ina l lp r a c t i c a l plasma d e v i c e s ,t h e plasma i scontained in 旦 vacuum chambero ff i n i t es i z e . Whathappenst ot h e plasmaa tt h ew a l l ? For s i m p l i c i t y ,l e tu sc o n f i n eoura t t e n t i o nt oaonedimensionalmodelw i t h ‑ 2 ) .Supposetherei snoa p p r e c i a b l ee l e c t r i cf i e l d nomagneticf i e l d( F i g .8 i n s i d et h eplasma;wecanthenl e tt h epotentialφbe z e r ot h e r e .When i o n s and e l e c t r o n sh i tt h ew a l l ,t h e y recombine and a r el o s t .S i n c e e l e c t r o n shavemuchhigherthermalv e l o c i t i e sthani o n s ,t h e ya r el o s t f a s t e randl e a v et h eplasmawithan e tp o s i t i v ec h a r g e .Theplasmamust then have a p o t e n t i a lp o s i t i v ew i t hr e s p e c tt ot h ew a l l ;i . e . ,t h ew a l l potentialφ山 is n e g a t i v e .Thisp o t e n t i a lcannotbed i s t r i b u t e dovert h e e n t i r eplasma,sin 仁e Debyes h i e l d i n g( S e c t i o n1 . 4 )w i l lcon 自 ne t h epoten t i a lv a r i a t i o nt oal a y e ro ft h eordero fs e v e r a lDebyel e n g t h si nt h i c k n e s s . Thisl a y e r ,whichmuste x i s tonall 仁old w a l l sw i t hwhicht h eplasmai s i nc o n t a c t ,i sc a l l e das h e a t h .Thef u n c t i o no fas h e a t hi st oformap o t e n t i a l b a r r i e rs ot h a tt h emoremobiles p e c i e s ,u s u a l l ye l e c t r o n s ,i sc o n f i n e d e l e c t r o s t a t i c a l l y .Theh e i g h to ft h eb a r r i e ra d j u s t si t s e l fs ot h a tt h ef l u x o fe l e c t r o n st h a thaveenoughenergyt ogoovert h eb a r r i e rt ot h ew a l l i sj u s te q u a lt ot h ef l u xo fi o n srea仁hing t h ew a l l //I ゆ 於く φ= 0 4ー①⑦ー+ 。一て二コ φw x ‑ d x 。 8 . 2 . 1 TheNecessityforSheaths 。 d FIGURE8 ‑ 2 Theplasmap o t e n t i a lφforms s h e a t h sn e a rt h ew a l l ss ot h a t e l e c t r o n sa r er e f l e c t e d .TheCoulombb a r r i e reφ山 adjusts i t s e l fs o t h a te q u a lnumberso fi o n sande l e c t r o n sr e a c ht h ew a l l sp e r s e c o n d . ー一一一週・』 u o WALL φ l a n a rs h e a t h . Cold i o n sa r e FIGURE8 ‑ 3 The p o t e n t i a l φin ap assumedt oe n t e rt h es h e a t hw i t hauniformv e l o c i t yUo・ ThePlanarSheathEquation 8 . 2 . 2 I nS e c t i o nl . 4 ,wel i n e a r i z e d Poisson ’ s equation t od e r i v et h e Debye l e n g t h .Toexaminet h ee x a c tbehaviorofφ (x) i nt h es h e a t h ,wemust t r e a tt h enonlinear problem;wes h a l lf i n dt h a tt h e r ei s nota l w a y sa s o l u t i o n .Figure8 ‑ 3showst h es i t u a t i o nnearoneo ft h ew a l l s .Att h e p l a n ex= 0 ,i o n sa r eimaginedt oe n t e rt h esheathregionfromt h emain plasmaw i t had r i f tv e l o c i t yu0・ This d r i f ti sneededt oaccountf o rt h e l o s so fi o n st ot h ew a l lfromt h e1 egioni nwhicht h e ywerec r e a t e dby ;= 0 ,s ot h a ta l li o n shavet h e i o n i z a t i o n .Fors i m p l i c i t y ,weassume T v e l o c i t yu 0a tx= 0 .Wec o n s i d e rt h es t e a d ys t a t eproblemi nac o l l i s i o n l e s s odecreasemonotonically s h e a t hr e g i o n .Thepotentialφis assumedt w i t hx .Actually, φcould haves p a t i a lo s c i l l a t i o n s ,andthent h e r ewould betrappedp a r t i c l e si nt h es t e a d ys t a t e .Thisdoesnothappeni np r a c t i c e becaused i s s i p a t i v ep r o c e s s e stendt od e s t r o yanysuchh i g h l yorganized s t a t e . I fu( x )i st h ei o nv e l o c i t y ,c o n s e 1v a t i o no fenergyr e q u i r e s iη川 2 = ~mu6 eφ (x) !l~ ~子f u= ( 2 [ 8 ‑ 1 ] [ 8 キ 2 ] E f f e c t s 292 Cha争ler E i g h t Thei o nequationo fc o n t i n u i t ytheng i v e st h ei o nd e n s i t yn ,i ntermso f t h ed e n s i t yn0i nt h emainp l a s r o a : n , [ 8 ‑ 3 ] I 2eφ \ I/ 2 η ;(x) = ηol l τ寸ヲ l ¥ [ 8 ‑ 5 ] [ 8 ‑ 6 ] Thes t r u c t u r eo ft h i sequationcanbes e e nmorec l e a r l yi fwes i m p l i f y i tw i t ht h ef o l l o w i n gchangesi nn o t a t i o n : x ( ηoe2 ¥1;2υ (= 一= xi ームー) λn ¥coKT) Uo JU = 一一一一寸吉 . . . (K1,/川 j [8・ 7] ThenEq.[ 8 ‑ 6 ]becomes x "= (I 十手)- 1/2 g寸 [ 8 ‑ 8 ] wheret h eprimedenotesd/dfThisi st h en o n l i n e a requationo faplane s h e a t h ,andi thasana c c e p t a b l es o l u t i o no n l yi fJ t ti sl a r g eenough.The t tw i l lbecomeapparenti nt h ef o l l o w i n gs e c t i o n reasonf o rt h esymbolJ onshockw a v e s . J t t 2>I \ . ; U ' or ¥ 11>0 J u0>(KT,川1)1/2 [8 ・ 11] Thisi n e q u a l i t yi sknowna stheBohms h e a t h criterioη. I ts a y st h a ti o n s mustentert h esheathr e g i o nw i t hav e l o c i t yg r e a t e rthant h ea c o u s t i c v e l o c i t yv, ・ To g i v et h ei o n st h i sd i r e c t e dv e l o c i t yu0, t h e r emustbea t(= 0i s f i n i t ee l e c t r i cf i e l di nt h ep l a s m a .Ourassumptiont h a tx’= 0a t h e r e f o r eonlyanapproximateo n e ,madep o s s i b l ebyt h ef a c tt h a tt h e s c a l eo ft h esheathr e g i o ni su s u a l l ymuchs m a l l e rthant h es c a l eo ft h e mainplasmaregioni nwhicht h ei o n sa r ea c c e l e r a t e d .Thev a l u eo fu0 i ssomewhata r b i t r a r y ,dependingonwherev t ̲ echooset oputt h ebounュ h eplasmaandt h es h e a t h .Ofc o u r s e ,t h ei o nf l u x daryx= 0betweent nou0i sf i x e dbyt h eio日 production r a t e ,s oi fu0i sv a r i e d ,t h ev a l u eo f noa tx= 0w i l lvaryi n v e r s e l yw i t hu0 ・ If t h ei o n shave 白 nite temperature, i l lbesomewhatl o w e r . t h ec r i t i c a ld r i f tv e l o c i t yu0w Thep h y s i c a lreasonf o rt h eBohmc r i t e r i o ni se a s i l yseenfroma p l o to ft h ei o nande l e c t r o nd e n s i t i e sv s .x ( F i g .8 ‑ 4 ) .Thee l e c t r o nd e n s i t y 叫 falls e x p o n e n t i a l l yw i t hx .accordingtotheBoltzmannrelation.The n ; 2 [u。>( Iく T/M)1/2] ' : Equation[ 8 ‑ 8 ]canbei n t e g r a t e doncebym u l t i p l y i n gboths i d e sbyx n i l [u。<( IくT/M)1/2] Qnn [ 8 ‑ 9 ] where(1 i sadummyv a r i a b l e .S i n c ex=0a t(=0 ,t h ei n t e g r a t i o n s e a s i l yy i e l d か~かが[(I +茅(2 ] 1+e x ー l E f f e c t s 9 !J+I x 十三/+・・ー I> 0 J 2 8 . 2 . 3 TheBohmSheathC r i t e r i o n r川 293 Nonlinea:γ l IX2 一つ+一. I I of -y "(一一一言+ 仁losely: εo~ = e (…=)=十 eφ X J t t 2 2.M. γ Poisson ’s e ' q u a t i o ni sthen KT., L [ 8 ‑ 4 ] η,(x) = n0e xp(eφ/ K 工) ーム- f J t t J 1+一 i¥1110/ I ns t e a d ys t a l e ,t h ee l e c t r o n sw i l lf o l l o wt h eBoltzmannrelation x= h eright‑handtermsi nTaylors e r i e s : f o rx < I, wecanexpandt 一一ー』 TO WALL [ 8 ‑ 1 0 ] I fE=0i nt h eplasma,wemusts e tx : 1=0a t(=0 .A secondi n t e g r a t i o n t of i n dxwouldhavet obedonen u m e r i c a l l y ;butwhatevert h eanswer i s ,t h eright‑hands i d eo fE q .( 8 ‑ 1O ]mustbep o s i t i v ef o ra l lX キI np a r t i c u l a r , 。 x =ー巴ゆ/ Iく Te V a r i a t i o no fi o nande l e c t r o nd e n s i t y( l o g a r i t h m i cs c a l e )w i t hn o r ‑ FIGURE8 ‑ 4 m a l i z e dp o t e n t i a lxi nas h e a t h .Thei o nd e n s i t yi sdrawnf o rtwo e s st h a nt h ec r i t i c a lv e l o c i t y . c a s e s :u 0g r e a t e rt h a nandu0l . d 1! . d 1 =スです吉 (2x ·ι [ 8 ‑ 1 2 ] Multiplyingbyx 'andintegratingfrom{ ; 1=乙 to { ; 1={;,wehave ~(x ’2 ‑x : 2 )= ‑ . / 2 . d 1 ( x 1 1 2‑x : 1 2 ) rs・ 13] t h ep l a c ewherewes t a r t e dn e g l e c t i n gn , .Wecanr e d e f i n e ot h a tx ,= 0a t{ ;=乙. Wes h a l la l s on e g l e c tx : .s i n c et h e t h ez e r oo fx s s l o p eo ft h ep o t e n t i a lcurvecanbeexpectedt obemuchs t e e p e ri nt h e 叫= 0r egionthani nt h efinite一n, r e g i o n .ThenE q .[ 8 ‑ 1 3 ]becomes . 2 . 5 E l e c t r o s t a t i cProbes 8 where 乙 is x ' 2= 2 3 1 2 . d 1 x 1 1 2 x ’= 2 3 ; 1 . ; U1 1 2 x1 1 1 rs・ 14] or dx/x111= 2 3 ; 1 . d 1 1 1 2d { ; I n t e g r a t i n gfrom {;=乙 to {;=乙+ d/λD ={ ; w a l l ,Wehave h~4 = 2 3 / 4 . ; U1 / 2d/λD J7 HA q一9 or [ 8 ‑ 1 5 ] [8・ 16] Thesheathc r i t e r i o n ,E q .[ 8 ‑ 1 1 ] ,canbeusedt oe s t i m a t et h ef l u xo fi o n s t oan e g a t i v e l yb i a s e dprobei nap l a s m a .I ft h eprobehasas u r f a c earea A, and i ft h ei o n se n t e r i n gt h es h e a t h have a d r i f tv e l o c i t y u0 三 (KT,川1) 1 1 2 ,thent h ei o nc u r r e n tc o l l e c t e di s I=n,eA(K7二川I)1;2 Thee l e c t r o ncurrentcanben e g l e c t e di ft h eprobei ss u f f i c i e n t l yn e g a t i v e e l a t i v et ot h eplasmat or e p e la l lbutt h et a i lo ft h e ( s e v e r a lt i m e sKT,)r Maxwelliane l e c t r o nd i s t r i b u t i o n .Thed e n s i t yn ,i st h eplasmad e n s i t ya t t h eedgeo fthes h e a t h .Letu sd e f i n et h esheathedget obet h ep l a c e se x a c t l y(KTJM)112.Toac仁elerate i o n st ot h i sv e l o c i t yr e q u i r e s whereu0i apresheathp o t e n t i a lJφ |三;KT,/e, sot!凶 the s h e a t hedgeh a sap o t e n t i a l [ 8 ‑ 1 7 ] φ, backt ot h ev a r i a b l e su 0andφ , and notingt h a tt h ei o nc u r r e n t i n t ot h ew a l li sJ= eη 0u0, wethenf i n d Ch 司 nging J= '±.1~今 1も~ 9¥M! d [ 8 ‑ 1 9 ] [ 8 ‑ 1 8 ] = ~KT,/e [ 8 ‑ 2 0 ] r e l a t i v et ot h ebodyo ft h ep l a s m a .I ft h ee l e c t r o n sa r eMaxwellian,t h i s , : determinesn η, =nae 'φ,/ kT, = η 0e 112=061η0 [8・ 21] Qd 2x¥ 1 1 2 ¥ ft t 配町 I x ’'={ I +一言) ハU S i n c en,(x)f a l l se x p o n e n t i a l l yw i t hx .t h ee l e c t r o nd e n s i t ycanben e g l e c t e d e x tt ot h ew a l l( o ranyn e g a t i v ee l e c t r o d e ) . i nt h eregiono fl a r g exn Poisson ’s equationi sthenapproximately nJ 8.2.4 TheChild‑LangmuirLaw Thisi sj u s tt h ewell‑knownChild‑Langmuirlawo fs p a c e ‑ c h a r g e ‑ l i m i t e d currenti naplaned i o d e . Thep o t e n t i a lv a r i a t i o ni naplasmaw a l lsystemcanbed i v i d e di n t o t h r e ep a r t s .Nearestt h ew且 II i sane l e c t r o n ‑ f r e er e g i o nwhoset h i c k n e s s di sgivenbyEq.[ 8 ‑ 1 8 ] . Here] i sdeterminedbyt h ei o nproduction r a t e ,andφw i sdeterminedbyt h ee q u a l i t yo fe l e c t r o nandi o nf l u x e s . ,i sa p p r e c i a b l e ;a sshowni nS e c t i o n1 . 4 , Nextcomesaregioni nwhichn t h i sregionhast h es c a l eo ft h eDebyel e n g t h .F i n a l l y ,t h e r ei saregion w i t hmuchl a r g e rs c a l el e n g t h ,the “ presheath ,'’ in whicht h ei o n sa r e 0byap o t e n t i a ldrop! φJ ?.~KT,/e. a c c e l e r a t e dt ot h erequiredv e l o c i t yu Dependingontheexperiment,t h es c a l eo ft h epresheathmaybes e tby t h eplasmar a d i u s ,t h ec o l l i s i o nmeanf r e ep a t h ,ort h ei o n i z a t i o nmechanュ i s m .Thep o t e n t i a ld i s t r i b u t i o n ,of 仁ourse, v a r i e s smoothly;t h ed i v i s i o n i n t ot h r e er e g i o n si smadeo n l yf o rconvenien 仁E andi smadep o s s i b l eby t h ed i s p a r i t yi ns c a l el e n g t h s .Int h ee a r l ydayso fg a sd i s c h a r g e s ,s h e a t h s couldbeobserveda sdarkl a y e r swherenoe l e c t r o n swerepresentt o e x c i t eatomst oe m i s s i o n .S u b s e q u e n t l y ,t h ep o t e n t i a lv a r i a t i o nhasbeen measuredbythee l e c t r o s t a t i cd e f l e c t i o no fat h i ne l e c t r o nbeams h o t p a r a l l e lt oaw a l l . N E i g h t i o nd e n s i t ya l s of a l l s ,s i n c et h ei o n sa r ea c c e l e r a t e dbyt h esheathp o t e n t i a l . I ft h ei o n ss t a r tw i t hal a r g eenergy ,問 (x) f a l l ss l o w l y ,s i n c et h esheath f i e l dc a u s e sa1e l a t i v e l yminorchangei nt h eions ’ velocity. I ft h ei o n s ; ( x )f a l l sf a s t ,andcangobelowthen,c u r v e . s t a r tw i t has m a l le n e r g y ,n , ηz i sp o s i t i v enearx= O ;andE q .[ 8 ‑ 6 ]t e l l susthatφ (x) Inthat 仁社se, n mustcurveupward,i nc o n t r a d i c t i o nt ot h erequirementt h a tt h esheath mustr e p e le l e c t r o n s .Inorderf o rt h i snott ohappen,t h es l o p eo fn ; ( x ) a tx= 0 must bes m a l l e r( i na b s o l u t ev a l u e ) than t h a to fn , ( x ) ;t h i s c o n d i t i o ni si d e n t i c a lw i t ht h ec o n d i t i o n. d 1 2> I 2m f lvp 294 C h a p t e r } Ts 296 C h a p t e r E i g h t Forourpurposesi ti sa c c u r a t eenough t or e p l a c e0.61 witharound / 2 ;thus,the “ saturation ioncurrent” to anegativeprobe numberl i k e1 i sapproximately ls=~n0eA(KT,/M)112 [ 8 ‑ 2 2 ] I s ,sometimesc a l l e dthe “ Bohm current ,'’ gives t h eplasmad e n s i t ye a s i l y , oncet h etemperaturei sknown. I ft h eDebyelengthλ0, andhencet h esheatht h i c k n e s s ,i sv e r ys m a l l compared t ot h e probe dimensions, t h ea r e ao ft h e sheath edge i s E仔ectively t h esamea st h eareaA oft h eprobes u r f a c e ,r e g a r d l e s so fi t s s h a p e .Atlowd e n s i t i e s ,however , λ0 canbecomel a r g e ,s ot h a tsomei o n s enteringt h esheathcano r b i tt h eprobeandm i s si t .C昌lculations o fo r b i t s .LangmuirandL .Tonksュ f o rv a r i o u sprobeshapesweref i r s tmadebyI ot h i smethodofmeasureュ hencet h ename “ Langmuir probe ” ascribed t ment.Thought e d i o u s ,t h e s ec a l c u l a t i o n scang i v ea c c u r a t edeterminaュ t i o n sofplasmad e n s i t ybecauseana r b i t r a r yd e f i n i t i o nofsheathedge doesnothavet obemade.Byvaryingt h eprobev o l t a g e ,t h eMaxwellian e l e c t r o nd i s t r i b u t i o ni s sampled, and t h e current v o l t a g e curve o fa Langmuirprobecana l s oy i e l dt h ee l e c t r o ntemperature.Thee l e c t r o ュ s t a t i cprobewast h ef i r s tplasmad i a g n o s t i candi ss t i l lt h es i m p l e s tand t h e mostlo日lized measurementd e v i c e . Unfortunately, m a t e r i a le l e c ュ t r o d e scanbei n s e r t e donlyi nlowdensity ,仁ool p l a s m a s . PROBLEMS 8 ‑ 1 . Ap r o b ewhosecolle仁u ngs u r f a c ei sas q u a r et a n t a l u mf o i l2ラ2mmi na r e a f100オ.Ai nas i n g l yi o n i z e da r g o n i sfoundt og i v eas a t u r a t i o nion 仁urrent o fK1二= 2e V ,whati st h ea p p r o x i m a t ep l a s m a p l a s m a( a t o m i cw e i g h t= 40). I o n s ! ) d e n s i t y ?( H i n t :Boths i d e so ft h eprobe 仁olle仁I i 8 ‑ 2 .A s o l a rs a t e l l i t ec o n s i s t i n go f1 0km2o fp h o t o v o l t a i cp a n e l si sp l a c e di n s y n c h r o n o u so r b i taroundt h ee a r t h .I ti simmersedi naIeVa t o m i chydrogen p l a s m aa td e n s i t y 106m ‑ ' . Durings o l a rs t o r m st h es a t e l l i t ei sbombardedb y e n e r g e t i cele仁llons, w h i c hc h a r g ei tt oap o t e n t i a lo f 2k V .Calεulate the 日 ux o fe n e r g e t i ci o n sbombardinge a c hm2o ft h ep a n e l s . Thes h e a t hc r i t e r i o no fE q .[ 8 ‑ 1 1 ]w a sd e r i v e df o rac o l d ‑ i o np l a s m a .Suppose t h eio 日 distribution hadat h e r m a ls p r e a di nv e l o c i t yaroundana v e r a g ed r i f t s p e e du 0 .W ithoutm a t h e m a t i c s ,i n d i c a t ew h e t h e ry o uwoulde x p e c tt h ev a l u eo f u 0t ob ea b o v eo rb e l o wt h eBohmv a l u e ,ande x p l a i nw h y . 8・3. Ani o nv e l o c i t ya n a l y z e rc o n s i s t so fas t a i n l e s ss t e e lc y l i n d e r5m mi nd i a m e t e r w i t h oneend c o v e r e dw i t ha 品 ne tungstenη】es hg r i d( g r i d I )ー Behind t h i s , 8・4. i n s i d et h ec y l i n d e r ,a r eas e r i e so fi n s u l a t e d ,parallεl g r i d s .G r i dIi sat “日 oating” p o t e n t i a l ‑ i t>s n o te l e c t r i c a l l yc o n n e c t e d .G r i d2i sb i a s e dn e g a t i v et or e p e la l l e l e c t r o n scomingt h r o u g hg r i d1 ,b u ti tt r a n s m i t si o n s .G r i d3i st h ea n a l y z e r g r i d ,b i a s e ds oa st ode日 lerate i o n s紅白lerated b yg r i d2 .Thosei o n sa b l et o p a s st h r o u g hg r i d3a r ea l lc o l l e c t e db yac o l l e c t o rp l a t e .G r i d4i sas u p p r e s s o r g r i dt h a tt u r n sb a c ks e c o n d a r ye l e c t r o n se m i t t e dbyt h ec o l l e c t o r .I ft h ep l a s m a d e n s i t yi st o oh i g h ,as p a c ec h a r g eproblemo c c u r sn e a rg r i d3b e c a u s et h ei o n d e n s i t yi ss ol a r g et h a tap o t e n t i a lh i l lf o r m si nf r o n to fg r i d3andr e p e l si o n s w h i c hwouldo t h e r w i s er e a c hg r i d3 .Usingt h eC h i l d Langmuirl a w ,e s t i m a t e t h emaximumm e a n i n g f u lHe+c u r r e n tt h a tc a nb emeasuredona4mm‑diam c o l l e c t o ri fg r i d s2and3a r es e p a r a t e db yImmand100V . ION ACOUSTIC SHOCK WAVES 8 . 3 Whenaj e tt r a v e l sf a s t e rth 昌 n sound,i tcr回tes ashockwave.Thisi sa b a s i c a l l ynonlinearphenomenon,s i n c et h e r ei snoperiodwhent h ewave i ss m a l landgrowing.Thej e ti sf a s t e rthant h espeedofwavesi na i r ,s o t h eundisturbedmediumcannotbe “ warned ” by precursors i g n a l sbefore t h el a r g eshockwaveh i t si t .Inhydrodynamicshockw司 ves, collisions 昌 re dominant. Shockwaves 司 lso e x i s ti np l a s m a s ,evenwhen t h e r ea r eno c o l l i s i o n s .A magnetics h o c k ,the “ bow shock ,” is generatedbyt h ee a r t h a si tplowsthrought h ei n t e r p l a n e t a r yplasmawhiledraggingalonga d i p o l emagneticf i e l d .Wes h a l ld i s c u s sasimplerexample:a 仁ollisionless, one‑dimensionalshockwavewhichdevelopsfromalarge‑amplitudei o n wave. TheSagdeevP o t e n t i a l 8 . 3 . 1 Figure85showst h ei d e a l i z e dp o t e n t i a lp r o f i l eofani o na c o u s t i cshock w a v e .Thereason f o rt h i sshapew i l lbegiven p r e s e n t l y . Thewavei s ot h eframemovingwith t r a v e l i n gt ot h el e f tw i t hav e l o c i t yu0 目 If wegot i l lbec o n s t a n ti nt i m e ,andwew i l ls e ea t h ewave,t h efunctionφ (x) w streamofplasmaimpingingont h ewavefromt h el e f twithav e l o c i t y Uo ・ For s i m p l i c i t y ,l e tT ;bez e r o ,s ot h a ta l lt h ei o n sarei n c i d e n twith t h esamev e l o c i t yu 0 ,andl e tt h ee l e c t r o n sbeMaxwellian.Sincet h eshock movesmuchmores l o w l ythant h ee l e c t r o nthermalspeed,t h es h i f ti n t h ec e n t e rv e l o c i t yo ft h eMaxwelliancanben e g l e c t e d .Thev e l o c i t yo f t h ei o n si nt h eshockwavei s ,fromenergyc o n s e r v a t i o n , u=(u~ - ¥j-(2 [ 8 ‑ 2 3 ] 297 Nonlinear E f f e c t s 298 『唖ー- Ch αpt e r UPSTREAM Thebehavioroft h es o l u t i o no fEq.[ 8 ‑ 2 7 ]wasmade仁lear byR .Z . Sagdeev, who used an analogy t o an o s c i l l a t o ri nap o t e n t i a lw e l l . s c i l l a t o rs u b j e c t e dt oaforce‑mdV(x)/dx Thedisplacementx ofano DOWNSTREAM -一曽』 E i g h t i sgivenby ーー一遍・- uo d 2 x /d t2 = 。 x FIGURE8 ‑ 5 T y p i c a lp o t e n t i a ld i s t r i b u t i o ni nani o na c o u s t i cshockw a v e .The wavemovest ot h el e f t ,s ot h a ti nt h ewaveframei o n ss t r e a mi n t o t h ewavefromt h el e f tw i t hv e l o c i t yu0 内)= I ハイ I -(I 茅)] I fn0 i st h ed e n s i t yoft h eundisturbed p l a s m a ,t h ei o nd e n s i t yi nt h e shocki s 同=~= n0(1 一議) 1/2 [8・ 24] The e l e c t r o nd e n s i t yi s given by t h e Boltzmann r e l a t i o n . Poisson ’s equationtheng i v e s εo~ヲ= e(n, ーザ [ 8 ‑ 2 5 ] Thisi s ,o fc o u r s e ,t h esameequation( E q .[ 8 ‑ 6 ] )a swehadf o ras h e a t h . A shockwavei snomorethanasheathmovingthroughaplasma.We nowintroducet h edimensionlessv a r i a b l e s e<D x 三+一一- KT, ~=_!__ λ口 .;({= コ」缶百 ( KT,/M)1 2 [ 8 ‑ 2 6 ] Notet h a twehavechangedt h es i g ni nt h ed e f i n i t i o nofxs oa st okeep xpositiveinthisproblemaswellasinthesheathproblem.Thequanuty Cら キ i ns i g no fX x n whichdi 仔ers fromt h esheathequation[ 8 ‑ 8 ]onlybecauseoft h echange ) d [8・ 27] ( ne dx , e 、 J ρaa E『 -- EJ .;({ ソ 一一 X ¥ 一向 l . ; ( {i sc a l l e dt h eMachnumbeγof t h es h o c k .Equation[8-25 ]仁an nowbe 〆 ,y I 2x¥̲ , 1 2 dV(x) ~= ex-( I‑ -τi =一一一一 [ 8 ‑ 2 9 ] For. M ,l y i n gi nac e r t a i nr a n g e ,t h i sfunctionhast h eshapeshowni nF i g . 8 ‑ 6 .I ft h i swerear e a lw e l l ,ap a r t i c l eenteringfromt h el e f tw i l lgot o x>0 ) ,r e f l e c t , and return t ox = 0 , t h e right‑hand s i d eo ft h ew e l l( makinga s i n g l et r a n s i t .S i m i l a r l y , aq u a s i p a r t i c l ei n our analogyw i l l oX = 0 ,a sshowni n makeas i n g l eexcursiont op o s i t i v exandreturnt o l i t o n ;i ti sa p o t e n t i a land d e n s i t y F i g .8 ‑ 7 . Such ap u l s ei sc a l l e d as d i s t u r b a n c epropagatingt ot h el e f ti nF i g .8 ‑7withv e l o c i t yuo ・ Now,i fap a r t i c l es u f f e r sal o s sofenergywhilei nt h ew e l l ,i tw i l l neverreturnt ox = 0butw i l lo s c i l l a t e( i nt i m e )aboutsomep o s i t i v evalue o fx .S i m i l a r l y ,al i t t l ed i s s i p a t i o nw i l lmaket h ep o t e n t i a lofashockwave se x a c t l yt h e o s c i l l a t e( i ns p a c e )aboutsomep o s i t i v ev a l u eofφThis i behaviordepictedi nF i g .8 ‑ 5 .A c t u a l l y ,d i s s i p a t i o ni snotneededf o rt h i s ; r e f l e c t i o no fi o n sfromt h eshockf r o n thast h esameE征ect. Tounderstand t h i s ,imaginet h a tt h ei o n shaveas m a l lthermalspreadi nenergyand h ewavef r o n ti sj u s tl a r g eenought or e f l e c tsome t h a tt h eheighteφof t o ft h ei o n sbackto t h el e f t ,whilet h er e s tgoovert h ep o t e n t i a lh i l lt o t h er i g h t . The r e f l e c t e di o n s cause an i n c r e a s ei ni o nd e n s i t yi nt h e upstreamregiont ot h el e f toft h eshockf r o n t( F i g .8 ‑ 5 ) .Thismeans t h a tt h eq u a n t i t y もγritten d t " [8 ・ 28] I ft h eright‑hands i d eo fE q .[8 ” 27] i sdefineda s‑dV/dx.theequation l a y i n gt h er o l e i st h esamea st h a tofano s c i l l a t o r ,witht h ep o t e n t i a lX p o fx ,andd /d i ;r e p l a c i n gd / d t .Theq u a s ip o t e n t i a lV(x)i ssometimesc a l l e d 8 ‑ 2 7 ] t h eSagdeevp o t e n t i a l .Thefun仁tion V(x)canbefoundfromEq.[ byi n t e g r a t i o nwitht h eboundaryc o n d i t i o n V(x ) 二 O a tX = 0 : 。 。 dV/d x [ 8 ‑ 3 0 1 i sd e c r e a s e d .S i n c e ’ is t h eanalogo fd x / d ti nt h eo s c i l l a t o rproblem, ourv i r t u a lo s c i l l a t o rh a sl o s tv e l o c i t yandi strappedi nt h ep o t e n t i a lw e l l o fF i g .8 . 6 . 299 NonlineαT E f f e c t s p a r t i c l ew i l lnotber e f l e c t e d ,andt h ep o t e n t i a lw i l lr i s ei n d e f i n i t e l y .From E q .( 8 ‑ 2 9 ) ,wer e q u i r e 300 Chapleγ E i g h t 。 f ー I くが[ 1-(1 -茅) χ [8 ・ 32] f o rsomex>0 .I ft h elowerc r i t i c a lMachnumberi ssurpassed(必> 1 ) , t h el e f thands i d e ,representingt h ei n t e g r a loft h ee l e c t r o nd e n s i t yfrom zerot ox .i si n i t i a l l yl a r g e rthant h er i g h thands i d e ,representingt h e i n t e g r a loft h ei o nd e n s i t y .Asxi n c r e a s e s ,t h er i g h thands i d ecanc a t c h upwithwitht h el e f t ‑ h a n ds i d ei f. ; ( { 2i snott o ol a r g e .However,because o fthesquarer o o t ,t h el a r g e s tv a l u excanhavei s. ; { { . 2/ 2 .Thisi sbecause eφcannot exceed~Mu~ ; otherw日, ions wouldbeexcluded from t h e plasmai nt h edownstreamr e g i o n .I n s e r t i n gt h el a r g e s tv a l u eofxi n t o 8 ‑ 3 2 ) ,wehave E q .( v FIGURE8‑6 TheSagdeevp o t e n t i a l V(x). Theupperarrow i st h et r a j e c t o r yo faq u a s i p a r t i c l ed e s c r i b i n ga s o l i t o n :i ti sr e f l e c t e da tt h er i g h tandr e t u r n s . Thelowerarrowsshowt h emotiono faq u a s ip a r ュ t i d et h a th a sl o s tenergyandi st r a p p e di nt h e p o t e n t i a lw e l l . The bouncingback and f o r t h d e s c r i b e st h eo s c i l l a t i o n sbehindashockf r o n t . . ; { { , 2/2 )ー l く必2 exp( or d く 1.6 [8羽] Thisi st h eupperc r i t i c a lMachnumber.Shockwavesi nac o l d ‑ i o nplasma thereforee x i s tonlyf o r1<必く 1.6. Asi nt h ec a s eofs h e a t h s ,t h ep h y s i c a ls i t u a t i o ni sb e s texplainedby adiagramofn ,andn ,v s .x( F i g .8 ‑ 8 ) .Thisdiagramd i f f e r sfromF i g . 8 ‑ 4becauseofthechangeofsignofφ. Sincetheionsarenowdecelerated i l lapproachi n f i n i t ya tx=必 2/2. Thelower r a t h e rthana c c e l e r a t e d ,n;w c r i t i c a lMachnumberensurest h a tt h en ;curvel i e sbelowt h en ,cmv e φ ( o rx l ] ①-ー u。 x( o r ~) FIGURE8‑7 Thep o t e n t i a li nas o l i t o nmovingt ot h el e f t . n e 8.3.2 TheC r i t i c a lMachNumbers Qnn S o l u t i o n sofe i t h e rt h es o l i t o ntypeort h ew a v e ‑ t r a i ntypee x i s tonlyf o r arangeo f . ; { { , ̲A lowerl i m i tf o r . ; { { ,i sg i v e nbyt h econditiont h a t V(x) beap o t e n t i a lw e l l ,r a t h e rthanah i l l . ExpandingE q .( 8 ‑ 2 9 )f o rx < I y i e l d s h "ー (x2 / 2 J U 2 )>0 . ; { { . 2> I [ 8 ‑ 3 1 ] Thisi se x < c r i t e r i o nf o rthee x i s t e n c eofasheatl>( Eq. ( 8 ‑ 1 1) ) . Anupperl i m i tt o . ; { { ,i simposedbyt h ec o n d i t i o nt h a tt h ef u n c t i o n V(x)ofF i g .8‑6mustc r o s st h exa x i sf o rx>O ;o t h e r w i s e ,t h ev i r t u a l 。 x =吋/ KTe mり2 V a r i a t i o no fi o nande l e c t r o nd e n s i t y( l o g a r i t h m i c FIGURE 8・8 s c a l e )w i t hn o r m a l i z e dp o t e n t i a lxi nas o l i t o n .The i o nd e n s i t yi sdrawnf o rtwoc a s e s :Machnumber g r e a t e rt h a nandl e s st h a n1 . 6 . 301 Nonlinear E f f e c t s a ts m a l lx .sothatthepotentialφ (x) startsoffwiththerightsignfori t s 302 C h a p t e r E i g h t curvature ・ When t h ecurven ,1c r o s s e sthen,c u r v e ,t h esolitonφ (x) ( F i g . sl a r g eenought h a tt h e 8 ‑ 7 )hasani n f l e c t i o np o i n t .F i n a l l y ,whenxi u r v e sa r ee q u a l ,t h es o l i t o nr e a c h e sap e a k , a r e a sundert h en; andηe c ,c u r v e sa r er e t r a c e da sxgoesbackt oz e r o .Thee ' q u a l i t y andtheη; 1andn o ft h ea r e a sensurest h a tt h en e tchargei nt h es o l i t o ni sz e r o ;t h e r e f o r e , t h e r ei snoe l e c t r i cf i e l do u t s i d e .I f, , ォ ,i sl a r g e rthan 1 . 6 ,wehavet h e curven ; 2 ,i nwhicht h eareaundert h ecurvei st o os m a l levenwhenx hasreachedi t smaximumv a l u eo f. d { , 2/ 2 . 8 . 3 . 3 WaveSteepening I fonepropagatesani o nwavei nac o l di o nplasma,i tw i l lhavet h ephase v e l o c i t yg i v e nbyE q .[ 4 ‑ 4 2 ] ,correspondingt o, , ォ ,= 1 . How,t h e n ,can onec r e a t eshocksw i t h, , ォ ,>I ?Onemustremembert h a tE q .[ 4 ‑ 4 2 ]was al i n e a rr e s u l tv a l i d only a ts m a l la m p l i t u d e s . As t h e amplitude i s i n c r e a s e d ,ani o nwavespeedsupanda l s ochangesfromas i n ewaveto asawtoothshapewithas t e e pl e a d i n gedge( F i g .8 ‑ 9 ) .Thereasoni st h a t t h ewavee l e c t r i cf i e l dhasa c c e l e r a t e dt h ei o n s .InF i g .8 ‑ 9 ,i o n sa tt h e peako ft h ep o t e n t i a ld i s t r i b u t i o nhaveal a r g e rv e l o c i t yi nt h ed i r e c t i o n h o s ea tt h et r o u g h ,s i n c et h e yhavej u s texperiencedap e r i o d o fuφthan t o fa c c e l e r a t i o na st h ewavepassedb y .Inl i n e a rt h e o r y ,t h i sdi 百erence i nv e l o c i t yi stakeni n t oa c c o u n t ,butnott h edisplacementr e s u l t i n gfrom i t .I n nonlineart h e o r y ,i ti se a s yt os e et h a tt h ei o n sa tt h epeaka r e s h i f t e dt ot h er i g h t ,w h i l et h o s ea tt h etrougha r es h i f t e dt ot h el e f t ,t h u s steepeningt h ewaves h a p e .S i n c et h ed e n s i t yp e r t u r b a t i o ni si nphase w i t ht h ep o t e n t i a l ,morei o n sa r ea c c e l e r a t e dt ot h er i g h tthant ot h el e f t , andt h ewavec a u s e san e tmassf l o wi nt h ed i r e c t i o no fpropagation. This c a u s e st h e wave v e l o c i t yt o exceed t h ea c o u s t i c speed i nt h e undisturbedplasma,s ot h a t , , ォ ,i sl a r g e rthanu n i t y . 303 N o n l i n e a r E f f e c t s ExperimentalObservations 8 . 3 . 4 Ion a c o u s t i c shockwaves o ft h e form shown i nF i g .8 ‑ 5 have been generatedbyR .J .Taylor,D.R.Baker,andH.Ikezi.Todothis,anew h eDP( o rdouble‑plasma)d e v i c e ,wasi n v e n t e d .Figure plasmasour仁e, t 8 ‑ 1 0showss c h e m a t i c a l l yhowi tw o r k s .I d e n t i c a lplasmasa r ec r e a t e di n twoe l e c t r i c a l l yi s o l a t e dchambersbyd i s c h a r g e sbetweenf i l a m e n t sFand t h ew a l l sW.Theplasmasa r es e p a r a t e dbyt h en e g a t i v e l yb i a s e dg r i dG, whichr e p e l se l e c t r o n sandformsani o ns h e a t honboths i d e s .A v o l t a g e p u l s e ,u s u a l l yi nt h eformo faramp,i sa p p l i e dbetweent h etwochambers. Thisc a u s e st h ei o n si nonechambert ostreami n t ot h eo t h e r ,e x c i t i n g w w 一 一一一 P n LINEAR o r φ V中一一- ・--ー勘 V NONLINEAR FIGURE8 ‑ 9 Al a r g e ‑ a m p l i t u d ei o nwaves t e e p e n ss ot h a tt h el e a d i n gedgeh a sal a r g e rs l o p e t h a nt h et r a i l i n ge d g e . S c h e m a t i co faDPmachinei nwhichi o na c o u s t i cs h o c kwaveswereproduced FIGURE8 ‑ 1 0 andd e t e c t e d .[ C f .R .J .Taylor,D.R.Baker,andH.I k e z i ,P h y s .R e v .L e t t .2 4 ,2 0 6 ( 1 9 7 0 ) . ] 304 DoubleLayers 8 . 3 . 5 Chapleγ E i g h t TIME ( オ s ) talli --〉ト一 ωZ出。 60 48 36 24 1 2 18 1 6 305 Nonlineaγ 1 4 1 2 二 10 8 6 DISTANCE 4 2 。 A phenomenonr e l a t e dt os h e a t h sandi o na c o u s t i cshocksi st h a to ft h e double l a y e r . This i sal o c a l i z e dp o t e n t i a l jump, b e l i e v e dt o occur n a t u r a l l yi nt h ei o n o s p h e r e ,whichn e i t h e rpropagatesnori sa t t a c h e dt o aboundary.Thenamecomesfromt h es u c c e s s i v el a y e r sofn e tp o s i t i v e andn e tn e g a t i v echarget h a ta r en e c e s s a r yt oc r e a t eas t e pi nφ (x). Such as t e pcanremains t a t i o n a r yi nspa仁E o n l yi ft h e r ei saplasmaf l o wt h a t Dopplers h i f t sashockf r o n tdownt oz e r ov e l o c i t yi nthel a bframe,or i ft h ed i s t r i b u t i o nf u n c t i o n so ft h et r a n s m i t t e dandr e f l e c t e de l e c t r o n s andi o n soneachs i d eo ft h ed i s c o n t i n u i t ya r es p e c i a l l yt a i l o r e ds oa st o maket h i sp o s s i b l e .Doublel a y e r shavebeenc r e a t e di nt h el a b o r a t o r yi n “ triple-plasma” devices, whicha r es i m i l a rt ot h eDPmachineshowni n F i g .8 ‑ 1 0 ,butw i t h at h i r dexperimentalchamber( w i t h o u tf i l a m e n t s ) i n s e r t e d between t h etwosourcechambers. Bya d j u s t i n gt h er e l a t i v e p o t e n t i a l so ft h et h r e echambers,whicha r ei s o l a t e dbyg r i d s ,streamso f i o n sore l e c t r o n scanbes p i l l e di n t ot h ec e n t e rchambert oformadouble l a y e rt h e r e .Inn a t u r a ls i t u a t i o n sdoublel a y e r sa r el i k e l yt oa r i s ewhere t h e r ea r eg r a d i e n t si nt h emagneticf i e l dB , notwhere B i sz e r oor uniform,a si nl a b o r a t o r ys i m u l a t i o n s .Int h a tc a s e ,theオ.VBf o r c e( E q . [ 2 ‑ 3 8 ] )canplayalarger o l ei nl o c a l i z i n gadoublel a y e rawayfroma l l boundaries.Indeed,t h ethermalb a r r i e ri ntandemmirrorr e a c t o r si s anexampleo fadoublel a y e rw i t hstrongmagnetict r a p p i n g . (cm) ft h ed e n s i t yd i s t r i b u t i o ni nashockwavea tv a r i o u s FIGURE8 ‑ 1 1 Measurementso t i m e s ,showinghowt h ec h a r a c t e r i s t i cs h a p eo fF i g .8 ‑ 5d e v e l o p s .[From ta l . ,l o cc i t . ] T a y l o re al a r g e ‑ a m p l i t u d eplanewave.Thewavei sd e t e c t e dbyamovableprobe orp a r t i c l ev e l o c i t ya n a l y z e rP .Figure8 ‑ 1 1showsmeasurementso ft h e saf u n c t i o no ftimeandprobe d e n s i t yf l u c t u a t i o ni nt h eshodζwave a p o s i t i o n .I ti sseent h a tt h ewavefronts t e e p e n sandthent u r n si n t oa shockwaveo ft h ec l a s s i cs h a p e .Thedampingo ft h eo s c i l l a t i o n si sdue t oc o l l i s i o n s . n ‑ 5 .C a l c u l a t et h emaximump o s s i b l ev e l o c i t yo fani o na c o u s t i cshodに wave i PROBLEM 8 ,= 1 . 5e V ,T ,= 0 . 2e V , a ne x p e r i m e n ts u c ha st h a tshowni nF i g .8 ‑ 1 0 ,whereT andt h eg a si sa r g o n .Whati st h emaximump o s s i b l es h o c kwavea m p l i t u d ei nv o l t s ? . 4 THEPONDEROMOTIVE FORCE 8 Lightwavese x e r tar a d i a t i o np r e s s u r ewhichi su s u a l l yveryweakand hardt od e t e c t .Event h ee s o t e r i cexampleo fcomett a i l s ,formedbyt h e p r e s s u r eo fs u n l i g h t ,i st a i n t e dbyt h eaddede f f e c to fp a r t i c l e sstreaming fromt h es u n .Whenhigh‑poweredmicrowavesorl a s e rbeamsa r eused t oh e a torc o n f i n ep l a s m a s ,however,t h er a d i a t i o npressurecanreach s e v e r a lhundredthousandatmospheres!Whenappliedt oaplasma,t h i s f o r c ei scoupledt ot h ep a r t i c l e si nasomewhats u b t l ewayandi sc a l l e d t h eponderomotivef o r c e .Manyn onlinearphenomenahaveasimplee x p l a ュ n a t i o ni ntermso ft h epondermotivef o r c e . Thee a s i e s twayt od e r i v et h i snonlinearf o r c ei st oconsidert h e motionofane l e c t r o ni nt h eo s c i l l a t i n gE andB f i e l d so fawave.We n e g l e c tdcE0andBof i e l d s .Thee l e c t r o nequationo fmotioni s 間空= ‑e[E(r)+vxB(r)] d t [ 8 ‑ 3 4 ] E f f e c t s 306 C h a p t e r E i g h t Thisequatio 日 i se x a c ti fE andB a r ee v a l u a t e da tt h ei n s t a n t a n e o u s p o s i t i o no ft h ee l e c t r o n .Then o n l i n e a r i t ycomesp a r t l yfromt h evxB t e r m ,whichi ssecondorderbecausebothvandB v a n i s hi nt h ee q u i l i ュ brium,s ot h a tt h etermi snol a r g e rthanv 1xB 1 ,wherev 1andB1a r e t h el i n e a r ‑ t h e o r yv a l u e s .Theotherp a r to ft h en o n l i n e a r i t y ,a swes h a l l s e e ,comesfrome v a l u a t i n gEatt h ea c t u a lp o s i t i o no ft h ep a r t i c l er a t h e r thani t si n i t i a lp o s i t i o n .Assumeawavee l e c t r i cf i e l do ft h eform , ( r )c o swt E= E [ 8 ‑ 3 5 ] where E,(r)仁ontains t h es p a t i a l dependence. I nf i r s to r d e r , we may n e g l e c tthevxB termi nE q .[ 83 4 ]ande v a l u a t eEatt h ei n i t i a lp o s i t i o n ro. 九/\/ e h ave mdv1/dt= e E ( r 0 ) v 1= (e/mw)E,sinwt=dr1/dt o r 1= (e/mw2)E,c o swt [ 8 ‑ 3 6 ] [ 8 ‑ 3 7 ] [ 8 ‑ 3 8 ] I ti simportantt onotet h a ti nanonlinearc a l c u l a t i o n ,wecannotw r i t e e;w, andt a k ei t sr e a lp a r tl a t e r .I n s t e a d ,wew r i t ei t sr e a lp a r te x p l i c i t l y a sc o sw t .Thisi sbecauseproductso fo s c i l l a t i n gf a c t o r sappeari nnonュ l i n e a rt h e o r y ,andt h eo p e r a t i o n so fm u l t i p l y i n gandt a k i n gt h er e a lp a r t donotcommute. Goingt osecondo r d e r ,weexpandE ( r )aboutr 0 : ( r 0 )+(δr, ·VJEIγ = γ。+・・・ E ( r )= E [8・ 39] Wemust nowadd t h e termv 1X B 1 ,whereB1 i sg i v e nby Maxwell’S e q u a t i o n : vxE= ‑ a s / a t B ,=一 (l/w)VxE,l ,~,0sinwl [8・40] Thesecond‑orderp a r to fE q .[ 8 ‑ 3 4 ]i sthen m dv2/dt= -e[(or , ・ V)E+v1 × Bi] 、 ai I mα) 307 Non/ineaγ : E f f e c t s f,n コ ~L,VE': 4mw' " [ 8 ‑ 4 3 ] "'~ Thisi st h ee f f e c t i v enonlinearf o r c eonas i n g l ee l e c t r o n .Thef o r c eper m3i sfNLt i m e st h ee l e c t r o ndensityη0, whichcanbew r i t t e ni ntermso f SinceE~ = 2 (£な we f i n a l l yhavef o rt h eponderomotivefor仁E t h e formula w ; . w ! (ε0§_2) F NL =一 2 V ‑ ‑ ‑ ; : ; ‑ ‑ α) [ 8 ‑ 4 4 ] ; : : I ft h ewave i se l e c t r o m a g n e t i c ,t h esecond term i nE q .[ 8 ‑ 4 2 ]i s dominant,andt h ep h y s i c a lmechanismf o rF N l .i sa sf o l l o w s .E l e c t r o n s o s c i l l a t ei nt h ed i r e c t i o no fE ,butt h ewavemagneticf i e l dd i s t o r t st h e i r o r b i t s .Thati s ,t h eLorentzf o r c e‑evxB pushest h ee l e c t r o n si nt h e d i r e c t i o nofk( s i n c ev i si nt h ed i r e c t i o no fE ,andExBi si nt h ed i r e c t i o n o fk ) .Thephaseso fvandB a r esucht h a tt h emotiondoesnotaverage .I ft h e t ozerooverano s c i l l a t i o n ,butt h e r ei sas e c u l a rd r i f talongk wavehasuniformamplitude,nof o r c ei sneededt omaintaint h i sd r i f t ; buti fthewaveamplitudev a r i e s ,thee l e c t r o n sw i l lp i l eupi nr e g i o n so f s m a l lamplitude,andaf o r c ei sneededt oovercomet h espacec h a r g e . Thisi swhyt h ee仔ective f o r c eFNLi sp r o p o r t i o n a lt ot h eg r a d i e n to f( 」 2 ) . S i n c et h ed r i f tf o reache l e c t r o ni st h esame,FNLi sp r o p o r t i o n a lt ot h e d e n s i t y hencet h ef a c t o rw;/w2i nE ' q .[ 84 4 ] . I ft h ewavei sele仁trostatic, t h ef i r s ttermi nE q .[ 8 ‑ 4 2 ]i sdominant. Thenthep h y s i c a lmechanismi ssimplyt h a tane l e c t r o no s c i l l a t i n galong kI IEmovesf a r t h e ri nt h ehalf-cycle 、vi r e g i o nt oaw e a k ‑ f i e l dregionthanvi仁e v e r s a ,s ot h e r ei san e td r i f t . AlthoughFNLa c t smainlyont h ee l e c t r o n s ,t h ef o r c ei su l t i m a t e l y t r a n s m i t t e dt ot h ei o n s ,s i n c ei ti salow‑frequencyordce f f e c t .When e l e c t r o n sa r ebunchedbyF N L ,ac h a r g e ‑ s e p a r a t i o nf i e l dE白 is c r e a t e d . Thet o t a lf o r c ef e l tbyt h ee l e c t r o n si s [ 8 ‑ 4 1 ] I n s e r t i n gE q s .[ 8 ‑ 3 7 ] ,[ 8 ‑ 3 8 ] ,and[ 8 ‑ 4 0 ]i n t o[ 8 ‑ 4 1 ]andaveragingover time wehave m (色) = ‑~ ~ [(E,キV)E,+E,x(VxE,)]= fNL Whatremainsi s [ 8 ‑ 4 2 ] 'こ Hereweused( s i n 2wt)=( c o s 2wt )=~- Thedoublec r o s sproductcanbe w r i t t e na st h esumo ftwot e r m s ,oneo fwhichc a n c e l st h e( E ,キ V)E,t e r r n . F ,= eE臼+ FNL [ 8 ‑ 4 5 ] w ; m/M, S i n c et h eponderomotivef o r c eont h ei o n si ss m a l l e rbyn ; ; t h efor仁E ont h ei o nf l u i di sapproximately F ;= eE日 = [ 8 ‑ 4 6 ] Summingt h el a s ttwoe q u a t i o n s ,wef i n dt h a tt h ef o r c eont h eplasma i sFNL・ 308 Ad i r e c te f f e c tofFNLi sthes e l f ‑ f o c u s i n go fl a s e rl i g h ti naplasma. InF i g .8 ‑ 1 2weseethatal a s e rbeamo ff i n i t ediametercausesar a d i a l l y directedponderomotivef o r c ei naplasma.Thisf o r c emovesplasmaout slowerandthed i e l e c t r i cconstantεis higher o fthebeam,s ot h a tw p i c t sa saconvexl e n s , i n s i d ethebeamthano u t s i d e .The plasm昌 then a focusingthebeamtoasmallerdiameter. Chapter E i g h t PROBLEMS 309 ( b )Whati st h et o t a lf o r c e ,i nt o n n e s ,e x e r t e db yt h ebeamont h eplasma コ ( c )I fT, 8・7. ニ T, = Nonlinear E f f e c t s 1k eV,howl a r g ead e n s i t yjump 仁an t h el i g h tp r e s s u r es u p p o r t ' S e l f ‑ f o c u s i n go c c u r swhenac y l i n d r i c a l l ysymmetricl a s e rbeamo ff r e q u e n c y wi spropagatedthroughanunderdensep l a s m a ;t h a ti s ,onewhichh a s η く n ,""' εo前w2/e2 I ns t e a d ys t a t e ,t h ebeam’ s i n t e n s i t yp r o f i l eandt h ed e n s i t yd e p r e s s i o nc a u s e d ‑ 1 2 )a r er e l a t e db yf o r c eb a l a n c e .N e g l e c t i n gplasmah e a t i n g b yt h ebeam( F i g .8 (KT""'KT,+KT,= c o n s t a n t ) .p r o v et h er e l a t i o n 8 ‑ 6 . Ao n e ‑ t e r a w a t tl a s e rbeami sf o c u s e dt oas p o t50オmind i a m e t e ronas o l i d t a r g e t .A plasmai sc r e a t e dandh e a t e db yt h ebeam,andi tu i e st oe x p a n d .The ponderomotivef o r c eo ft h ebeam,whicha c t sm a i n l yont h er e g i o no fc r i t i c a l d e n s i t y (π = " "o r w = wρ ), p u s h e st h e plasma b a c k and causes “ profile modi自cation ,” which i sana b r u p tchangei nd e n s i t ya tt h ec r i t i c a ll a y e r . ( a ) Howmuchp r e s s u r e( i nN/m2andi n! b f / i n . 2 )i se x e r t e dbyt h eponderomoュ t i v ef o r c e ?( H i n t :Notet h a tFNLi si nu n i t so fN/m'andt h a tt h eg r a d i e n tl e n g t h c a n c e l so u t .Toc a l c u l a t e( 」 2 ) ,assumec o n s e r v a t i v e l yt h a ti th a st h esamev a l u e a si nvacuum,ands e tt h eIT WP o y n t i n gf l u xe q u a lt ot h ebeam ’s energyd e n s i t y t i m e si t sgroupvelo口 ty i nvacuum ) ¥ 7<E2> η = n0e •o(E')/2n,KT ""' ηo e o (吋 Thequantity 日( 0) i sameasureo ft h er e l a t i v eimportanceo fponderomotive p r e s s u r et oplasmap r e s s u r e PARAMETRIC INSTABILITIES 8 . 5 Themostthoroughlyi n v e s t i g a t e doft h enonlinearwave‑wavei n t e r a c ュ t i o n sarethe “ parametric instabilities ,” so c a l l e dbecauseo fananalogy withparametrica m p l i f i e r s ,well‑knownd e v i c e si ne l e c t r i c a lengineering. A reasonforther e l a t i v e l yadvanceds t a t eofunderstandingoft h i ssul>ject i st h a tthet h e o 1yi sb a s i c a l l yal i n e a rone,butl i n e a raboutano s c i l l a t i n g e q u i l i b r i u m . CoupledO s c i l l a t o r s a s e rbeami scausedbyt h eponderomotivef o r c e . FIGURE 8 ‑ 1 2 Self‑focusingofal M, p M2 Considerthemechanicalmodelo fF i g .8 ‑ 1 3 ,i nwhichtwoo s c i l l a t o r sM1 andM2arecoupledt oabarr e s t i n gonap i v o t .Thep i v o tP i smadet o a t u r a lfrequenciesof s l i d ebackandf o r t ha tafrequencyw0,whilethen sc l e a rt h a t ,i ntheabsenceo ff r i c t i o n , theo s c i l l a t o r sarew1andw2 ・ It i thep i v o tencountersnor e s i s t a n c ea slonga sM,andM2arenotmoving. snotmovingandM2i sputi n t omotion,M, w i l l Furthermore,i fP i 1,theamplitude move;buta slonga sw2i snotthen a t u r a lfrequencyofM e ti n t omotion.The w i l lbes m a l l .Supposenowt h a tbothP andM2ares displacementofM1i sproportionalt otheproducto fthedisplacement fthel e v e rarmand,hence,w i l lvaryi ntimea s o fM2andthelengtho c o sW2Ic o sWal = ~cos [ ( w 2+W o ) I )+ ~cos [(w2 一 Wo)tJ FIGURE 8 ‑ 1 3 Amechanicalanalogofaparametrici n s t a b i l i t y . [ 8 ‑ 4 7 ] I fw1i sequalt oe i t h e rw2+w0orw2 w0,M1w i l lberesonantlye x c i t e d andw i l lgrowt ol a r g eamplitude.OnceM,s t a r t so s c i l l a t i n g ,M2w i l la l s o u s t gainenergy,becauseoneo fthebeatfrequenciesofw1withω 。 is j 8 . 5 . 1 310 C h a p t e r E i g h t i t h e ro s c i l l a t o ri ss t a r t e d ,eachw i l lbee x c i t e d byt h e w 2 . Thus, oncee o u r s e ,comesfrom o t h e r ,andt h esystemi su n s t a b l e .Theenergy ,。f c e s i s t a n c eoncet h er o di ss l a n t e d .I ft h e t h e“pump” P, whichen仁ounters r pumpi sstrongenough,i t so s c i l l a t i o namplitudei suna 汀ected byM1and M2;t h ei n s t a b i l i t ycanthenbet r e a t e dbyal i n e a rtheory 目 In aplasma, y p e so fw a v e s . t h eo s c i l l a t o r sP,凡11, andM2maybedi 仔erent t 8 . 5 . 2 FrequencyMatching Theequationofmotionf o rasimpleharmonico s c i l l a t o rx 1i s ィi2x i o ~ di2 十 wlxi ニ U [8 ・ 48] wherew1i si t sresonantfrequen仁y. I fi ti sdrivenbyatime‑dependent ft h e f o r c ewhichi sproportionalt ot h eproducto ft h eamplitude」0o 2o fasecondo s c i l l a t o r ,t h eequation d r i v e r ,orpump,andt h eamplitudex ofmotionbecomes d 2 x , " ‑‑,,+w]x1=c1x2Eo 且E d2x2 . d t 2 = ~ C 2 X 1 . / : ' , o ‑ W2 一 w , 2 ) x 2c o sw ’t ‑ [ 8 ‑ 5 1 ] Thed r i v i n gtermsont h er i g h t日n e x c i t eo s c i l l a t o r sx 2w i t hf r e q u e n c i e s ω ’= ω 。士 ω =c 1Eoi2~(cos {[w。+(ω。土 w)]t) +cos{[w。 =c 1Eoi2~{cos [(2w 。 ±w)t]+coswt) [ 8 ‑ 5 2 ] Int h eabsenceo fnonlineari n t e r a c t i o n s ,x 2cano n l yhavet h efrequency w 2 ,s owemusthaveω ’= W2 ・ However, t h ed r i v i n gtermscancausea ow2 ・ Furthermore, frequencys h i f ts ot h a tw ’ is onlyapproximatelyequalt ω ’ can b ecomplex,s i n c et h e r ei sdamping(whichh a sbeenn e g l e c t e ds o f a rf o rs i m p l i c i t y ) ,ort h e r ecanbegrowth( i ft h e r ei sani n s t a b i l i t y ) .In 2i sano s c i l l a t o rwith 白 nite Q andcanrespondt oarange e i t h e rc a s e ,x (wo 士 w)]t)) [ 8 ‑ 5 3 ] Thed r i v i n gtermscane x c i t enoto n l yt h eo r i g i n a lo s c i l l a t i o nx 1 ( w ) ,but h a l lconsidert h ec a s eI w 。|〉〉 a l s onewf r e q u e n c i e sw '’= 2wo 士 w. Wes I wi i, s ot h a t2w 。士 w l i e so u t s i d et h erangeoff r e q u e n c i e st owhichx 1 canrespond,andx1(2w 。土 w) canben e g l e c t e d .Wethereforehavet h r e e 1 ( w ) ,x2(w 。 w), andxAw 。+ w ) ,whicharecoupledbyE q s . o s c i l l a t o r s ,x [8 ” 49) and[ 8 ‑ 5 0 ] : (w~ w2)x1(w)‑c1Eo(w 。)[xAw。一 w) +x2(w。+ w)] = 0 [w~ 一 (wo 一 w)2]x2(w。一 w)-c2Eo(w。)x1(w) = 0 [ 8 ‑ 5 4 ] [w~ 一(ω。+ w)2]x2(w 。+ w)‑c2Eo(wo)x1(w)= 0 The d i s p e r s i o nr e l a t i o ni sg i v e n by s e t t i n gt h e determinant of t h e c o e f f i c i e n t sequalt oz e r o : ω =c 2 E o x 1c o sw0tc o swt ニ c2Eoi1~{cos [(w。+ w ) t ]+cos[(w。ー w ) t ] } , , 2 [ 8 ‑ 5 0 ] Let x 1=iic o sw t ,x 2=正2 仁osw ’t, and E。= E0c o sw 0 t . Equation [ 8 ‑ 5 0 ] becomes ( 2 2 ( w 1 w ) i 1cosw ”t [ 8 ‑ 4 9 ] whereci i sac o n s t a n ti n d i c a t i n gt h es t r e n g t ho ft h ec o u p l i n g .A s i m i l a r equationholdsf o rx 2 : ~一十 W2X2 f r e q u e n c i e saboutw 2 .I fw i ss m a l l ,onecans e efromE q .[8 』 52] t h a t i ew i t h i nt h ebandwidthofx 2 ,andonemust bothc h o i c e sf o rω ’ may l a l l o wf o rt h ee x i s t e n c eo ftwoo s c i l l a t o r s ,x2(w 。+ w)andx2(w 。一 ω ) Now l e tx 1= i 1c o sw ”t and x 2=王2 c o s[(w 。土 w ) t ] and i n s e r ti n t o E q .[8・49]: 。f 2 2 一 W1 c2E0 c2Eo . . . . C11',o (wo‑w)2 w~ 。 r‑o Clι 。 0 l=O (wo +w)2 w~ [ 8 ‑ 5 5 ] As o l u t i o nwithIm(w)>0wouldi n d i c a t eani n s t a b i l i t y . Fors m a l lfrequencys h i f t sands m a l ldampingorgrowthr a t e s ,we q u a lt ot h eundisturbedfrequen 仁ies w1 cans e tw andω ’ approximately e andw 2 .Equation[ 85 2 ]theng i v e safrequencymatchingc o n d i t i o n : Wo= W2ア W 1 [ 8 ‑ 5 6 ] When t h eo s c i l l a t o r sa r e waves i n a plasma,wt must be repl 以:ed by w t kキr .Therei sthena l s oawavelengthmatching 仁ondition k o= k2 土 k1 [ 8 ‑ 5 7 ] d e s c r i b i n gsp司 tial b e a t s ;t h a ti s ,t h ep e r i o d i c i t yofp o i n t sofc o n s t r u c t i v e n sp辻仁E The two c o n d i t i o n s[ 8 ‑ 5 6 ] and d e s t r u c t i v e interferen 仁E i and[ 85 7 )a r ee a s i l yunderstoodbyanλlogy w i t hquantummechanics. 311 N o n l i n e a r E f f e c t s I n s t a b i l i t yThreshold 8 . 5 . 3 k k ( C ) (D) a r a l l e l o g r a mc o n s t r u c t i o n sshowingt h eωー and k ‑m atchingc o n d i t i o n sf o r FIGURE8 ‑ 1 4 P t h r e ep a r a m e t r i ci n s t a b i l i t i e s :( A )e l e c t r o nd e c a yi n s t a b i l i t y ,( B )p a r a m e t r i c d e c a yi n s t a b i l i t y ,(C)s t i m u l a t e dB r i l l o u i nb a c k s c a t t e r i n gi n s t a b i l i t y ,and( D ) h ei n c i d e n tw a v e ,andW1 two‑plasmondecayi n s t a b i l i t y .I ne a c hc a s e ,w 。 is t andw2t h edecayw a v e s .Thes t r a i g h tl i n e sa r et h ed i s p e r s i o nr e l a t i o nf o ri o n w a v e s ;t h enarrowp a r a b o l a s ,t h a tf o rl i g h tw a v e s ;andt h ewidep a r a b o l a s ,t h a t f o re l e c t r o nw a v e s . Parametrici n s t a b i l i t i e sw i l loccura tanyamplitudei ft h e r ei snodamping, but i np r a c t i c eeven a s m a l l amounto fe i t h e rc o l l i s i o n a l or Landau dampingw i l l preventt h ei n s t a b i l i t yu n l e s st h e pumpwavei sr a t h e r s t r o n g . Toc a l c u l a t et h et h r e s h o l d , onemustintroducet h edamping ,andf2oftheoscillatorsx1andx2 ・ Equation (8‑48]thenbecomes r a t e sr d 2 x , 一寸ム+ dt ー " d x , w}x,+2r ,ー」= dt O [ 8 ‑ 5 9 ] γs wp ー w 4 k ( B ) - k eη ( A ) , むコ La 」0andx 2may,f o ri n s t a n c e ,bee l e c t r o m a g n e t i cw a v e s ,s othat 古iw 品w2 a r et h e photon e n e r g i e s . The os仁i!lator x1 m司y t>E a Langmuir 8 ‑ 5 4 ]simplys t a t e st h e wave,orplasmon,w i t henergy nw 卜 Equation [ c o n s e r v a t i o no fenergy.S i m i l a r l y ,E q .[ 8 ‑ 5 3 ]s t a t e st h ec o n s e r v a t i o no f momentumn k . Forplasmaw a v e s ,t h esimultaneouss a t i s f a c t i o no fE q s .[ 8 ‑ 5 2 ]and [ 8 ‑ 5 3 ]i none‑dimensionalproblemsi sp o s s i b l eonlyf o rc e r t a i ncombinaュ t i o n so fw a v e s . The r e q u i r e dr e l a t i o n s h i p sa r eb e s t seen on an w k diagram( F i g .8 ‑ 1 4 ) .Figure8 ‑ 1 4 ( A )showst h ed i s p e r s i o nc u r v e so fan e l e c t r o nplasmawave(Bohm‑Grosswave)andani o na c o u s t i cwave( c f . F i g .4 ‑ 1 3 ) .A large‑amplitudee l e c t r o nwave(w0, k 0 )candecayi n t oa 2 )andani o nwave(w1,k 1 ) .The backwardmovinge l e c t r o nwave(w2,k parallelogramc o n s t r u c t i o nensurest h a tw0=w1+w2andk 0= k 1+k2 ・ Thep o s i t i o n so f (w0,k 0 )and (w2, k 2 )on t h ee l e c t r o ncurve mustbe adjusteds ot h a tt h ed i f f e r e n c ev e c t o rl i e sont h ei o nc u r v e .Notet h a tan e l e c t r o nwavecannotdecay! n t otwoothere l e c t r o nw a v e s ,becauset h e r e e c t o rl i eont h ee l e c t r o nc u r v e . i snowayt omaket h edi 征erence v Figure8 ‑ 1 4 ( B )showst h eparallelogramc o n s t r u c t i o nf o rt h e“ param e t r i cdecay” instability. Here,(w0, k。) i sani n c i d e n te l e c t r o m a g n e t i c waveo fl a r g ephasevelo仁ity (w 。/ k 0= c) .I te x c i t e sane l e c t r o nwaveand ani o nwavemovingi noppos山 directions. S i n c e[ k 0 [i ss m a l l ,wehave [kif= [ k 2 Jandω 。= w1+w2f o rt h i si n s t a b i l i t y . o rt h e“ parametric b a c k s c a t ュ Figure8 ‑ 1 4 ( C )showst h ew‑kdiagramf tering” instability, i nwhichal i g h twavee x c i t e sani o nwaveandanother l i g h twavemovingi nt h eo p p o s i t ed i r e c t i o n .Thiscana l s ohappenwhen t h ei o n wavei sr e p l a c e d bya plasmawave. Byanalogywiths i m i l a r phenomenai ns o l i ds t a t ep h y s i c s ,t h e s ep r o c e s s e sa r ec a l l e d ,r e s p e c t i v e l y , “ stimulated Brillouinscattering” and “ stimulated Ramanscattering. ” Figure8‑14(D)r e p r e s e n t st h etwo‑plasmondecayi n s t a b i l i t yo fan e l e c t r o m a g n e t i cwave.Noiet h a tt h etwodecaywavesarebothe l e c t r o n plasmaw a v e s ,s ot h a tfrequencymatchingcanoccuronlyi fw0= 2wρ- Expressedi ntermso fd e n s i t y ,t h i sc o n d i t i o ni se q u i v a l e n ttoη = ηj4, when n ,i st h ec r i t i c a ld e n s i t y( E q .( 4 ‑ 8 8 ] )a s s o c i a t e dw i t h w0・ This i n s t a b i l i t ycant h e r e f o r ebeexpectedt ooccuro n l yneart h e“ quartercritical ” layer o faninhomogeneousp l a s m a . ζ [ 8 ‑ 5 8 ] れω。=れW2 土白w, 叩 have - constant 九 we 3mvψ M u l t i p l y i n gt h eformerbyPlanck ’ s V 312 C h a p t e r E i g h t Fori n s t a n c e ,i fx 1i sthedisplacementofaspringdampedbyf r i c t i o n , thel a s ttermrepresentsaf o r c eproportionalt ot h evelocity 目 If x 1i sthe e l e c t r o nd e n s i t yi naplasmawavedampedbyelectron‑neutralc o l l i s i o n s , rIi sv c / 2( c f .Problem4 ‑ 5 ) .Examinationo fE q s .[ 8 ‑ 4 9 ] ,[ 8 ‑ 5 0 ] ,and[ 8 ‑ 5 4 ] iw w i l lshowt h a ti ti sa l lr i g h tt ouseexponentialn o t a t i o nandl e td/dt • f o rx 1 andh ,ぉ long a swe keep」0r e a landa l l o wi 1 andi 2t obe complex.Equations[ 8 ‑ 4 9 ]and[ 8 ‑ 5 0 ]be仁ome 314 Chaple γ E i g h t - 2i(w。ー w)f2] = ~c1c2E~ [8・ 601 [ 8 ‑ 6 1 ] Atthreshold,wemays e tIm(w)= 0 .Thel o w e s tthresholdw i l loccura t 8 ‑ 6 1 ] e x a c t frequency matching; i . e . ,w = w1, wo ー w =w2. Then Eq, ( 《| ( a ) Showt h a t ,f o rT , < T, andv ; 三 KT,/m, t h eSBSt h r e s h o l di sg i v e nb y v ,. 4f1v αJ lα> 2 wherew,=k , v ,andr ,i st h ei o nlandaudampingr a t eg i v e nb yE q .[ 7 ‑ 1 3 3 ] . ( b )C a l c u l a t et h et h r e s h o l dl a s e ri n t e n s i t yI0i nW /口n2 f o rSBSo fC02( I0 . 6オm) ,= IOOeV, T ,= IOeV,andn0= l i g h ti nauniformhydrogen p l a s m aw i t hT !Onm‑' ( H i n t .Uset h eS p i t z e rr e s i s t i v i t yt oe v a l u a t ev , , . ) 8 ‑ 1 1 .Thegrowth r a t eo fs t i m u l a t e dB r i l l o u i ns c a t t e r i n gi n ahomogeneous q .[ 86 1 ]b ynegle仁ting t h e plasmaf a rabovet h r e s h o l dc a nbe 印 mputed fromE e tω =叫+ i ya 吋 assume y2 < andn 《叫 Show t h a t d a r npi 時 terms. L w; γ =す(ご)'/2!1ρ whereii0,ζis t h epeako s c i l l a t i n gv e l o c i t yo ft h ee l e c t r o n s . PhysicalMechanism 8.5.4 g i v e s c1C2(E~)出re>h = 16w1w2f1f2 [ 8 ‑ 6 2 ] i t h e rwave. Thethresholdgoest ozerowiththedampingo fe PROBLEMS The <lamping r a t ef 2c a nb efoundfromProblem[ 43 7 b ]f o rν/ω 巴 Wefurtherr e s t r i c tourselvest othesimplec a s eoftwowaves‑thati s , whenw = w1 andω 。一 W = W2butω 。+ w i sf a renoughfromw2t obe nonresonant‑inwhichc a s ethet h i r drowandcolumno fEq.( 8 ‑ 5 5 ]can beignored.I fwenowexpressx 1 ,x 2 ,and」0i ntermso ft h e i rpeakv a l u e s , a si nE q .[ 8 ‑ 5 3 ] ,af a c t o rof1/2appearsonther i g h thands i d e so fEq. [ 8 ‑ 6 0 ] . Discarding the nonresonant terms and eliminatingi 1 and ゐ fromEq.[ 8 ‑ 6 0 ] ,weobtain (w2 ー ω ?十 2iwf1)[(wo 一 w)2 ー w~ v . , "=eE。/ mw 。 (v :れ) (ω ?一 w2 ‑2iwf1)x1(w)= C1x2Eo [ω ;ー(ω ー w0)2 ‑ 2i(w ー wo)f2]x2(w ー Wo) = C2X1Eo andt h r e s h o l dpumpi n t e n s i t yi nahomogeneousplasma 日開 ven b yF q .[ 8 ‑ 6 2 ] . l e c t r o no s c i l l a t i o nv e l o c i t y T h i s1 scommonlye x p r e s s e di nt e r m so f( v~"), therms e 凶used b yt h epumpwave( c f .F q .[ 8 ‑ 3 7 ] ) : J4 . 8 ‑ 8 . Provet h a ts t i m u l a t e dRamans c a t t e r i n gc a n n o to c c u ra tdens山es aboven 8 ‑ 9 .S t i m u l a t e dB r i l l o u i ns c a t t e r i n gi so b s e r v e dwhenaNdg l a s sl a s e r bea~ (λ = 1 . 0 6オm)i r r a d i a t e sas o l i dD2t a r g e t(Z= I ,M =2MH ) .Theb a c k s c a t t e r e d .Fromx‑rayspectra,i ti sdetermined!hat 写Z て l i g h ti sr e d ‑ s h i f t e dby2 1 . 9A Ik e V .Assumingt h a tt h es c a t t e r i n goc仁urs i nt h ereg>on wherew ; < w·, anα u s i n gE q .[ 44 1 )w i t hγ, =3 ,makeane s t i m a t eo ft h ei o nt e m p e r a t u r e . ,i nE q .[ 86 0 )s t a n d 8 ‑ 1 0 . Fors t i m u l a t e dB r i l l o u i ns c a t t e r i n g( S B S ) ,wemayl e tx f o rt h ei o nwaved e n s i t yf l u c t u a t i o nn 1 ,andx 2f o rt h er e f l e c t e dwavee l e c t n c f i e l d」 2 .Thec o u p l i n gcoe 侃口ents a r et h e ng i v e nb y c ,= ε 川ω ;/ω。w2M c 2= w;w2 /η。ωυ n Theparametrice x c i t a t i o no fw且ves canbeunderstood verysimplyi termso ftheponderomotivef o r c e( S e c t i o n8 . 4 ) .Asani l l u s t r a t i o n ,consider t h ec a s eo fanelectromagneticwave( w 0 ,k 0 )drivingane l e c t r o nplasm昌 wave( w 2 ,k 2 )andalow‑frequencyionwave(wi. k1 )[ F i g .8 ‑ l4 ( B ) ] .Since W1i ss m a l l ,w0mustbec l o s et oW p .However,t h ebehaviori sq u i t ed i f f e r e n t o rω 。> w p .Theformerc a s eg i v e sr i s et othe “ oscillating f o rω 。く Wp andf two‑stream"i n s t a b i l i t y(whichw i l lbet r e a t e di nd e t a i l ) ,andthel a t t e rt o t h e“ parametric decay ” instability. Supposet h e r ei sad e n s i t yperturbationi ntheplasmao ftheform n 1c o sk 1 x ;t h i sperturbationcanoccurspontaneouslya sonecomponent o fthethermaln o i s e .Letthepumpwavehaveanelectric 自 eld Eoc o sw0t Int hexd i r e c t i o n ,a sshowni nF i g .8 1 5 .Intheabsenceo fadef i e l dB 0 , t h epumpwavef o l l o w sther e l a t i o nw~ = w!+c2k~ , s ot h a tk0= O f o r ω。= W p .Wemayt hereforeregard」0a ss p a t i a l l yuniform.I fw 。 is l e s s stheresonantfrequencyo fthec o l de l e c t r o nf l u i d ,the thanwρ, which i e l e c t r o n sw i l lmovei nthed i r e c t i o noppositet oE0,whilethei o n sdonot moveonthetimes c a l eo fwo.Thed e n s i t yr i p p l ethencausesacharge s e p a r a t i o n ,a sshowni nF i g .8 ‑ 1 5 .Thee l e c t r o s t a t i cchargesc r e a t eaf i e l d 315 九1onlinenr E f f e c t s E1, whi仁 h o s c i l l a t e sa tt h efrequencyω 。 The pondermotivef o r c edue t ot h et o t a lf i e l di sg i v e nbyE q .[ 844 ]:・ ω :ー ((Eo +E 1 ) 2 ) FNL =一寸 V 一一τ一一一 ε 。 αJo [8・ 63] 瓦 S i n c e」0i suniformandmuchl a r g e rthanE1 ,o n l yt h ec r o s stermi s important: FNL ー -- ~j__ wil a x笠~ 2ε 。 [ 8 ‑ 6 4 ] Thisf o r c edoesn o taveraget oz e r o ,s i n c eE1changess i g nw i t hE o .As TheO s c i l l a t i n gTwo‑StreamI n s t a b i l i t y 8 . 5 . 5 We s h a l l now a c t u a l l yd e r i v et h i ss i m p l e s t example o f a parametric i n s t a b i l i t yw i t ht h eh e l po ft h ep h y s i c a lp i c t u r eg i v e ni nt h el a s ts e c t i o n . Fors i m p l i c i t y ,l e tt h etemperaturesT ,andT,andthe 仁ollision r a t e sv ; E :! t 町 h y s i c a lmechanismo ft h eo s c i l l a t i n gt w o ‑ s t r e a mi n s t a b i l i t y . FIGURE8 ‑ 1 5 P - 1iι Eix 3mv 仰 n Ei‑‑ - ‑ 1 5 ,FNLi sz e r oa tt h epeaksandtroughso fn 1buti sl a r g e seeni nF i g .8 sl a r g e .Thiss p a t i a ld i s t r i b u t i o nc a u s e sFNLt opushe l e c t r o n s whereVηl i fromr e g i o n so flowd e n s i t yt or e g i o n so fhighd e n s i t y .Ther e s u l t i n gdc e l e c t r i cf i e l d drags t h ei o n salonga l s o , and t h ed e n s i t yp e r t u r b a t i o n g r o w s .Thet h r e s h o l dv a l u eo fFNLi st h ev a l u ej u s ts u f f i c i e n tt oovercome t h epressure¥ l n ; 1 ( K T ;+KT,),whichtendst osmootht h ed e n s i t y .The .Thisi sc a l l e dt h e d e n s i t yr i p p l edoesnotp r o p a g a t e ,s ot h a tRe(w1 )= 0 oscillαting t山a-stream i n s t a b i l i t yb ecause t h es l o s h i n g ele仁 trons have a time‑averagedd i s t r i b u t i o nf u n c t i o nwhichi sdoublepeaked,a si nt h e two‑streami n s t a b i l i t y( S e c t i o n6.6 )ー I fw 。 is l a r g e rthan w炉 this p h y s i c a l mechanism does notwork, becausean os仁illator d r i v e nf a s t e rthani t sresonantfrequencymoves o p p o s i t et ot h ed i r e c t i o no ft h ea p p l i e df o r c e( t h i sw i l lbeexplainedmore c l e a r l yi nt h en e x ts e c t i o n ) .Thed i r e c t i o n so fv , ,E 1 ,andFNLa r ethen r e v e r s e donF i g .8 ‑ 1 5 ,andtheponderomotiveforcemovesi o n sfrom denser e g i o n st ol e s sdenser e g i o n s .I ft h ed e n s i t yp e r t u r b a t i o ndidnot move,i twouldd e c a y .However,i fi twereat r a v e l i n gi o na c o u s t i cwave, h echange t h ei n e r t i a ld e l a ybetweent h ea p p l i c a t i o no ft h ef o r c eFNLandt o fi o np o s i t i o n sc a u s e st h ed e n s i t ymaximat omovei n t ot h er e g i o n si n t o whichFNLi spushingt h ei o n s .Thiscanhappen,o fc o u r s e ,onlyi ft h e phasev e l o c i t yo ft h ei o nwaveh a sj u s tt h er i g h tv a l u e .Th 昌t t h i sv a l u e ,canbeseenfromt h ef a c tt h a tt h ephaseo ft h ef o r c eFNLi nF i g . i sv 8 ‑ 1 5( w i t ht h earrowsr e v e r s e dnow)i se x a c t l yt h esamea st h ephaseo f t h ee l e c t r o s t a t i cr e s t o r i n gf o r c ei nani o nwave,wheret h ep o t e n t i a li s maximuma tt h ed e n s i t ymaximumandv i c ev e r s a .Consequently,FNL h ei o nwave.Thee l e c t r o n s , addst ot h er e s t o r i n gfor仁E andaugmentst meanwhile,o s c i l l a t ew i t hl a r g eamplitudei ft h epumpf i e l di sneart h e n a t u r a lfrequencyo ft h ee l e c t r o nf l u i d ;namely,w~ = w ; ペk2v ;" ・ The pumpcannothavee x a c t l yt h efrequencyw2becauset h eb e a tbetween w0 and w2 must be a tt h ei o n wave frequency w1= k v , ,s ot h a tt h e e x p r e s s i o nf o rFNLi nE q .[ 8 ‑ 6 4 ]canhavet h er i g h tfrequen 仁y t oe x c i t e ft h i sfrequencymatchingi ss a t i s f i e d ,v i z . , w 1 = w 。 W2, both i o nw a v e s .I ani o nwaveandane l e c t r o nwavea r ee x c i t e da tt h eexpenseo ft h epump wave.Thisi st h emechanismo ft h eparametricd e c a yi n s t a b i l i t y . nJ O N O E i g h t LK 且 III- Chapt肝 7ys i 316 318 C h a p t e r E i g h t andv ,a l lv a n i s h .Thei o nf l u i dthenobeyst h elow‑frequencye q u a t i o n s Mη。竺竺=仰のE ‑a t ‑ a n ; , a t = FN1 a v ; , a x ー」ニ + no ー」二= O ~ [ 8 ‑ 6 5 ] [ 8 ‑ 6 6 ] S i n c et h ee q u i l i b r i u mi sassumedt obes p a t i a l l yhomogeneous,we may F o u r i e r ‑ a n a l y z ei n space and r e p l a c ea / a x by i k . The l a s t two e q u a t i o n stheng i v e i k a2π ; 1 at ‘ 一一寸ニ+ー- FN1 = M ..む 0 [ 8 ‑ 6 7 ] w i t hF N L g i v e nbyE q .[ 8 ‑ 6 4 ] .Tof i n dE1 ,wemustc o n s i d e rt h emotion o ft h ee l e c t r o n s ,g i v e nby 1a v . a ¥ m(-'::-.-"+v, ア v,I = 、 ai ax e(E。+ £1) [8・ 68] ノ Theright‑hands i d ei sj u s tt h eponderomotivetermusedi nE q .[ 86 5 ] t od r i v et h ei o nw a v e s .I tr e s u l t sfromt h elow‑frequencyb e a tbetween v , 0 and v,h ・ The l e f t ‑ h a n ds i d e can be recognized a sr e l a t e d to t h e e l e c t r o s t a t i cp a r to ft h eponderomotivef o r c ee x p r e s s i o ni nE q .[ 8 ‑ 4 2 ] . Thee l e c t r o nc o n t i n u i t ye q u a t i o ni s 竺己+ ikv"凡 l + ηo伽,J a t ‑ e n , 1 竺竺+ ikηi01 a v . o a t ーニこ= Takingt h etimed e r i v a t i v e ,n e g l e c t i n ga n ,1 /a t ,andusingE q s .[ 8 ‑7 0 ]and [ 8 ‑ 7 2 ] ,weo b t a i n 7 A [ 8 ‑ 7 0 ] L i n e a r i z i n gaboutt h i so s c i l l a t i n ge q u i l i b r i u m ,wehave 生三.!. +ikv,ov,1= 工 £1 =‑! . . . . ( E 1 h+」 1 1 ) a t m m [8・ 71] v , h = a t ‑ e̲ n , h e2 . l ' . J h =一一一一一- m i k t 0 o m ( 8 ‑ 7 2 ] wherewehaveusedE q .[8田69]. Thelow‑frequencyp a r to fE q .[ S ‑ 7 1 ]i s U l . V , o V , h= e E i l ‑ ηz i k e ~ =‑n,11',o ・. [8・ 75] Letn , hvarya sexp( ‑ i w t ) : 。。 (w ; ーザ ) n,h ike = ‑n,1」0 [ 8 ‑ 7 6 ] ηz Equations[ 8 ‑ 6 9 ]and[ 8 ‑ 7 6 ]theng i v et h ehigh‑frequencyf i e l d : E ̲ e 2 ~i1Eo ~ ヱニヱ~ 2 2 I h 一一一一一一一一一一一吉- [8・ 77] εom Wp 一 ωε0m w ρ 一 ω 。 I ns e t t i n gw= w 0wehaveassumedthatthegrowthrateofn , 1i svery s m a l lcomparedw i t ht h efrequencyo fEo ・ The ponderomotivef o r c e f o l l o w sfromE q .[ 8 ‑ 6 4 ] : 2 wheret h es u b s c r i p t shandldenotet h eh i g h ‑andlow‑frequencyp a r t s . , h ,g i v e nby Thef i r s ttermc o n s i s t smostlyo ft h ehigh‑frequencyv e l o c i t yv 。 a t [ 8 ‑ 6 9 ] e e E。=一 - Eocosw 。t m -市 [ 8 ‑ 7 3 ] [ 8 ‑ 7 4 ] a t a キ n , h 2 一一万一+ ωρ叫,h Wemustr e a l i z ea tt h i sp o i n tt h a tt h eq u a n t i t i e sE1 ,v , ,andn e 1eachhave twop a r t s :ahigh‑frequencyp a r t ,i nwhicht h ee l e c t r o n smoveindepenュ d e n t l yo ft h ei o n s ,andalow四frequency p a r t ,i nwhicht h e ymovealong witht h ei o n si naq u a s i n e u t r a lmanner.Tol o w e s to r d e r ,t h emotioni s ahigh‑frequencyonei nresponset ot h es p a t i a l l yuniformf i e l d」 0 : 0 Wea r ei n t e r e s t e di nt h ehigh‑frequencyp a r to ft h i se q u a t i o n .Int h e , icanbeatwithv , ot og i v e middlet e r m ,onlyt h elow‑frequencyd e n s i t yn ahigh‑frequencyterm,i fwer e j e c tphenomenanear2w0andhigher , 1= n ; ibyq u a s i n e u t r a l i t ys owehave harmonics.Butn whereE1i sr e l a t e dt ot h ed e n s i t yn , ibyPoisson ’s e q u a t i o n ik ε 。£1 = = 2 ・, FNL =与 ι 」竺Lす(Eii) w 0m w ,一 ω 。 ( 8 ‑ 7 8 ] Notetl凶 both Elh andFN Lch昌昭e s i g nw凶 w~ ‑ w~. Thisi st h ereason t h eo s c i l l a t i n gtwo‑streami n s t a b i l i t ymechanismdoesnotworkf o rw~ > w ! .Themaximumresponsew i l loccurf o rw i i= w ! ,andwemay町glect t h ef a c t o r( w ! J w i i ) .Equation[8‑67]canthenbewritten 。2n;i e 2 k 2 E ;向 1 7 =2而立τ~ ( 8 ‑ 7 9 ] 319 N o n l i n e a r E f f e c t s 320 C h a p t e r E i g h t S i n c et h elow‑frequencyp e r t u r b a t i o ndoesn o tpropagatei nt h i si n s t a b i l ュ i t y ,wecanl e tn;1= i i i lexpγt, whereyi st h egrowthr a t e .Thus E~ e2k2 2 y 一。 2M間 ω ;一 ω 。 [ 8 ‑ 8 0 ] andγis r e a li fwii く w . ;Theactualvalueofγwill dependonhowsn t h edenominatori nE q .[ 8 ‑7 7 )canbemadewithoutt h eapproximation w2= w~. I f dampi時 is f i n i t e , w!‑w2 w i l l have an imaginary p a r t st h edampingr a t eo ft h ee l e c t r o n p r o p o r t i o n a lt o2f2wρ, where r2i o s c i l l a t i o n s .Thenwehave γcc t。; r~12 RFSIGNALGENERATOR 350MHz HOTF lLAMENTS (CATHODE) METAL し IC RFPOWERAMPLIFIER P < 20W ISOLATIONCAPACITOR CHAMBER (ANODE) [ 8 ‑ 8 1 ] Farabovet h r e s h o l d ,t h eimaginaryp a r to fw w i l lbedominatedbyt h e growthrateγr司 ther thanbyr2 ・ One thenh a s PROBES ぷ2 γ2 cc 三2γcc ( E o l 2 1 3 [ 8 ‑ 8 2 ] γ Thisbehaviorofγwith E。 is t y p i c a lo fa l lparametrici n s t a b i l i t i e s .An e x a c tc a l c u l a t i o nofγand oft h et h r e s h o l dv a l u eo f」0r e q u i r e samore c a r e f u ltreatmento ft h efrequencys h i f tW p wothanwecanp r e s e n there ・ Tos o l v et h eprobleme x a c t l y ,ones o l v e sf o rnil i nE q .[ 8 ‑ 7 6 )and s u b s t i t u t e si n t oE q .[ 8 ‑ 7 9 ) : 。2n,, --云ニ= a t " ‑ i k e .• En M n. . ‑ S c h e m a t i co fane x p e r i m e n ti nwhicht h ep a r a m e t r i cd e c a yi n s t a b i l i t ywas FIGURE8・ 16 v e r i f i e d .[FromA .Y .Wonge ta l . ,PlasmaP h y s i c sandC o n t r o l l e dNuclearF u s i o n ,3 3 5( I n t e r n a t i o n a lA t o m i cEnergyA g e n c y ,V i e n n a ,1971 )ー] R e s e a r c h ,1971,I [ 8 ‑ 8 3 1 Equations[ 8 ‑ 7 5 )and[ 8 ‑ 8 3 )thenc o n s t i t u t eap a i ro fe q u a t i o n so ft h e formo fE q s .[ 8 ‑ 4 9 )and[ 8 ‑ 5 0 ) ,andt h es o l u t i o no fE q .[ 8 ‑ 5 5 )canbe u s e d .Thefrequencyw1 v a n i s h e si nt h a tc a s ebecauset h ei o nwaveh a s w1 = 0i nt h ezero‑temperaturel i m i t . 8 . 5 . 6 TheParametricDecayI n s t a b i l i t y Thed e r i v a t i o nf o rw0>wρfollows t h esamel i n e sa saboveandl e a d sto t h ee x c i t a t i o no faplasmawaveand an i o nwave. Wes h a l lomitt h e a l g e b r a ,whichi ssomewhatl e n g t h i e rthanf o rt h eo s c i l l a t i n gtwo‑stream i n s t a b i l i t y ,buts h a l li n s t e a dd e s c r i b esomeexperimentalo b s e r v a t i o n s . The p a ram e t r i c decay i n s t a b i l i t yi sw e l l documented, having been observedbothi nt h eionosphereandi nt h el a b o r a t o r y .Theo s c i l l a t i n g two‑streami n s t a b i l i t yi snoto f t e ns e e n ,p a r t l ybecauseRe(w)= 0and p a r t l ybecausew0 く wp meanst h a tt h ei n c i d e n twavei se v a n s c e n t .F i g u r e 8・ 16 showst h eapparatuso fS t e n z e landWong,c o n s i s t i n go faplasma s o u r c es i m i l a rt ot h a to fF i g .8 ‑ 1 0 ,ap a i ro fg r i d sbetweenwhicht h e f i e l dEai sgenerated byano s c i l l a t o r ,andaprobeconnected t otwo frequencyspectruma n a l y z e r s .F i g u r e8‑17showss p e c t r ao ft h es i g n a l s d e t e c t e di nt h ep l a s m a .Belowt h r e s h o l d ,t h ehigh‑frequencyspectrum showsonlyt h epumpwavea t400MHz,w h i l et h elow‑frequencys p e c ュ trumshowso n l yas m a l lamounto fn o i s e .Whent h epumpwaveampliト tudei si n c r e a s e ds l i g h t l y ,ani o nwavea t300kHzappearsi nt h el o w ュ frequencyspectrum;anda tt h esamet i m e ,asidebanda t399.7MHz appearsi nt h ehigh‑frequencyspectrum.Thel a t t e ri sane l e c t r o nplasma wavea tt h edi狂erence f r e q u e n c y .Thei o nwavethencanbeobserved t ob e a tw i t ht h epumpwavet og i v eas m a l ls i g n a la tt h esumf r e q u e n c y , 4 0 0 . 3MHz. Thisi n s t a b i l i t yh a sa l s obeenobservedi ni o n o s p h e r i ce x p e r i m e n t s . F i g u r e8‑18showst h egeometryo fani o n o s p h e r i cm o d i f i c a t i o ne x p e r i ュ mentperformedw i t ht h el a r g er a d i ot e l e s c o p ea tP l a t t e v i l l e ,Colorado. 321 Nonlinear E f f e c t s 322 A 2‑MWradiofrequencybeama t7MHzi slaun仁hed fromtheantenna i n t otheionosphere ・ At thel a y e rwherew02:Wp, electronandionwaves are generated, and the ionospheric e l e c t r o n s are heated. In another experimentwiththel a r g edishantennaa tArecibo,PuertoR i c o ,thew andkoftheelectronwavesweremeasuredbyprobingwitha430』 MHz radarbeam andobservingthes c a t t e r i n gfromthegratingformed by theelectrondensityperturbations. Chapter E i g h t 323 Nonlineaγ E f f e c t s EL V A w M11占1 p n r - -- U 「←」 V A 。 N Wl B (U」《υω 江〈 UZ一」)O 凶コト一」止一注《 BELOW THRESHOLD U非日 ’『ー L l h‘ B o u l d e r g安一一一~二 ABOVE THRESHOLD 副~ 、圃’F 。 ‑ 司’ 100 凪Ii 200 J 、 300 400 8 ‑ 1 2 .I nl a s e rf u s i o n ,ap e l l e tc o n t a i n i n gthermonuclearf u e li sh e a t e dbyi n t e n s e h eh e a t i n ge f f i c i e n c y l a s e rbeams.Thep a r a m e t r i cdecayi n s t a b i l i t ycanenhan仁e t byconvertmgl a s e renergyi n t oplasmawavee n e r g y ,whichi st h e nt r a n s f e r r r e d s t oe l e c t r o n sbyLandaudamping.I fani o d i n el a s e rw i t h 1.3・µm wavelengthi u s e d ,a twhatplasmad e n s i t ydoesp a r a m e t r i cdecayt a k ep l a c e ? T l ̲¥ . J . . 500 . 6 ー .4 . 2 400 ‑ 1 8 Geometryofani o n o s p h e r i cm o d i f i c a t i o nexperimenti nwhichradiofrequency FIGURE 8 waveswereabsorbedbyparametricd e c a y .[FromW.F .U t l a u tandR .Cohen, S c i e n c e1 7 4 ,245( 1 9 7 1 ) . ] + . 2 f(kHz) f(MHz) LOWキFREQUENCY SPECTRUM HIGHキFREOUENCY SPECTRUM + . 4 FIGURE 8 ‑ 1 7 Oscillogramsshowingt h efrequencys p e c t r ao fo s c i l l a t i o n sobservedi nt h e d e v i c eo fF i g .8 ‑ 1 6 .Whent h ed r i v i n gpoweri sj u s tbelowt h r e s h o l d ,o n l y n o i s ei sseeni nt h elow‑frequencyspectrumandonlyt h ed r i v e r(pump)s i g n a l i nt h ehigh‑frequencyspectrum.A s l i g h ti n c r e a s ei npowerb r i n g st h esystem above t h r e s h o l d , and t h ef r e q u e n c i e so f a plasma wave and an i o n wave simultaneouslya p p e a r .[ C o u r t e s yo fR .S t e n z e l ,UCLA.] 8 ‑ 1 3 . ( a )D e r i v et h ef o l l o w i n gd i s p e r s i o nr e l a t i o nf o rani o na c o u s t i cwavei n t h ep r e s e n c eo fane x t e r n a l l ya p p l i e dponderomot1vef o r c eFN i : ' v ; ) n 1= ikFNc/M ( w 2+2ifw k where f i st h e damping r a t eo ft h e undriven wave (when FNL= 0 ) .( H i n t : i n t r o d u c ea “ collision frequency ” 11 i nt h eI O ne q u a t i o no fI T I O l I O n ,e v a l u a t efi n v e n t u a l l yr e p l a c e11 byi t sf ‑ e q u i v a l e n t . ) t e r m so f11, ande ( b )E v a l u a t eFN Lf o rt h ec a s eo fs t i m u l a t e dB r i l l o u i ns仁atterin耳 in termso ft h e a m p l i t u d e s」0and」2o ft h epumpandt h eb a c k s c a t t e r e dw a v e ,t e s p e c t i v e l y , t h u sre仁overing t h ec o n s t a n tc ,o fProblem[ 8 ‑ 1 0 ] .( H i n t :c f .E q .[ 8 ‑ 6 4 ] . ) PROBLEMS 324 Ch α争leγ Eight 325 I nF i g .[ 81 7 ]i ti ss e e nt h a tt h euppers i d e b a n da tw 。+ w, i sm i s s i n g . I n d e e d ,i n mostp a r a m e t r i cp r o c e s s e st h euppers i d e b a n di so b s e r v e dt ob e smλlier t h a nt h el o w e rs i d e b a n d .Usings i m p l eenergya r g u m e n t s ,perhapsw i t h aquantumm e c h a n i c a la n a l o g y ,e x p l a i nwhyt h i ss h o u l db es o . 8・ 14. Nonlinear E f f e c t . 1 8.6 PLASMA ECHOES x=0 x =史 X =史’ 凶υZ〈トω一口 SinceLandaudampingdoesnoti n v o l v ec o l l i s i o n sord i s s i p a t i o n ,i ti sa r e v e r s i b l ep r o c e s s .Thatt h i si struei sv i v i d l ydemonstratedbytheremarkュ a b l ephenomenonofplasmaechoes.Figure8‑19showsaschem旦tic o f theexperimer> tal arrangement.A plasmawavewithfrequencyw 1 and wavelengthλ1 i sgenerateda tthef i r s tg r i dandpropagatedt other i g h t . Thewavei sLandau‑dampedt obelowthethresholdofd e t e c t a b i l i t y .A secondwaveofw2andλ2 i sgeneratedbyasecondg r i dadistan 仁E lfrom thef i r s tone.Thesecondwavea l s odampsaway.I fathirdgridconnected t oar e c e i v e rtunedt ow = w2 一 w1 i smovedalongtheplasmacolumn, 1 ) .Whathappensi st h a t i tw i l lf i n danechoa tad i s t a n c el ’= lw2/(w2 w theresonantp a r t i c l e scausingthef i r s twavet odampoutr e t a i n sinformaュ t i o naboutthewavei nt h e i rd i s t r i b u t i o nf u n c t i o n .I fthesecondgridi s madet oreversethechangem theresonantp a r t i c l ed i s t r i b u t i o n ,awave canbemadet oreappear.C l e a r l y ,t h i sprocesscanoccuronlyi navery nearlyc o l l i s i o n l e s splasma.Inf a c t ,theechoamplitudehasbeenuseda s i v e sa p h y s i c a l as e n s i t i v e measureofthec o l l i s i o n rate ・ Figure 8‑20g X=Q x =見’ ・ー .・・ E ・..ー・・・・・~・・.・・岨・・・・・・. F 会ーー・・ ー ・・・・・・・・・・ 一一・一..・ーチ..・・.・.·.···· , ・・ ...・・・・・・・.ー・一.ー .. . .. ‑ . . . . --- ーー ・・;•・.・ ・・』・ーー ・・・・・. 4 ・・ ・.... ... .. ・.・・..ー・. ·I· ・.・.・. ・・・・・・・ J 》.・.・・.・.・·.·.·・...-.・. ....、・・・・・・・・ J .·.•.· J ・.・·.· . ·.・.・ ... .......... ー~.·.· . .キ一 ..~.・: E :・:・:・:・:・:・:・:・:・:・:・:·.ョ..・·.・.·・?・ 5 ・.·.;· -・.・.· . .. キ. ・ . ..,・::・:・::.ー.::・・.ー・.~へー... ·.・.・に …一 -ー・・ー.ー.ー·.・ r.· ·.ー.ー ー・・・…一- . . キ. . . キ . キ . . ·.·・.·.·:・・:..:::::ハ旬::::::;:::::':\''''八勺.,.・:ー:・:・:・:-:·:·>とど:日,.,.,.,. j、~·:-::;:二: J ・.・・:・~-: --...ー ・・・.・・,"'ン二 1 :•;·: ·υ ー-己・ T ・·. ーノートー.:ー::・:・:・;・;-;·:·:·;‘·;・;·ー?ー 《?ー?己<·'.· . ..... ー .~ーー::・:.・〈・.・.. a n キ ; . ‑ : ・:三日?:三日:: :1:::; •:・.:.:・:・:ー:ー:・:・:·:<·: -t:1:1 :·:づ? ~·三日己己.::ーー・::・・:.ー, . …-.... …….. . 一 一一一•.· J ・・...・・・・・・ 1 ・・・・・ ・.-.一一.・ーー ・・・・・・・・ー・.·.~.. ·.’.マ ・ ・,・ ・・ ・.・一.~ 1 ー ....ー・.・・・ーに.ー. ........ー L 一.ー.一一一--- ・.- s ・ヘ.·.~ー~~ーー~~ーマー・・・・・・ .・. …一一 .一.·.·.…., J~~~.MA:i園田町県引桁噌骨折<:罪抑烈糊闇蝿抑閉究開Ht:Y:~:\~: ……. . . . … . .キ. 一 ...・・・…- ー・.. 一一・・・.・.-..- ー :-::.:ー.・.ー.· .-1i:i ’ i ::::::;:;:;:二:;:;:ふ: 2・:ー:・:・:・:・:・.;,:-:ー:・:ロ::::::: F:’ E署>;::二:;: L :二:;:;:ー:ー:・:・:-::-:・::・.~ー 一 -…・山.. 1:0:· 己;:;:::;:;:;:;:ー:ー:・:・・::-:-:.? ・:.: キ . . . . キ . . キ . .キ キ . キ. . .·.'.-'.・!!·>>>と;:;:::;:;:;:;:ー,':·:・:〈・:・:・..・:・::・:.;.;-:-:·:-:: :ー;・ 5 ・・;・;・;・・. ;-.·;;;・・"'::ー・::・・・::・;ー:〈ー;ー;・;・;-:· <t ン;メペーとよペペ:.·.·.・.・~・.ー.-. : ペー. : キ : ‑ :キ :キ : キ : キT ::・::F :・ー・::・ーイ:.:・:: ー :・:.; :···:日手三.?と:??;日:ジー:.::ー:::・:・:・:・.-::: キ ‑ キ キ ‑ ‑キ ‑ キ. . . . . . .キ . キ .. . .キキ :•- ‑ . . ::ー・;・・;・ 4「・;・・;・;・.・;, ..・.・.・・.・.・・..-.:・’; . キ . キ. . , ..・·.·・.・、.・ー.・.·.· . .·;·.·.・・.・...... --一一~.ー .:::::・::: J ・:::•:: .一一 ーー・..-- ·.·.・ E •••• J 一一 、-.-.一一.-.一一一ー ・.. ・ J ~・.,・.· ~:.;・;・・;・ンペロ;·.·;'._ _:ー・.::ー・.·: ・・:.-. :ー :・・・::ー・.・ン; t ;・.・.・・ ·.·.·.・ "r •• ...一・・・ J ,・. J ・ーヘー -.-.一一・ー・·-·-·- むl 凶1 X=O 0 T 2T 3r 4T 5r 6r TlME I EラCITER V GRIDS faplasmaechoe x p e r i m e n t .[FromA .Y .WongandD .R .B a k e r , FIGURE 8 ‑ 1 9 Schematico P h y s .R叩 188, 326( 1 9 6 9 ) . ] ‑ 2 0 Space‑timet r a j e c t o r i e so fg a t e dp a r t i c l e sshowingt h ebunchingt h a tc a u s e s FIGURE 8 e c h o e s .Thed e n s i t ya tv a r i o u sd i s t a n c e si sshowna tt h er i g h t .[FromD .R . h y s .R e v .L e t t .2 0 ,318( 1 9 6 8 ) . ] B a k e r ,N .R .Ahern,andA .Y .Wong,P Z H K 一一 QU Rd 内4 一「 ω 一 2 Z UH K 一一 r : P < 327 Nonlinear E f f e c t s w 咽心J 勺 。 80 - A 斗 も ・--'ニ 95 KHz>←二= 40KHz 2π2π ロ 60 ロ 40 ~ 20 コ ト 。 ロ ロC b ・?・””・. 2 60 pu m D 「 OX 20 日 ロ ロ トヨ 。 ロ 三 40 Rd w 1口口 ロー ̲J 80 < E 二 2.0cm 。 臼 口口 [ 8 ‑ 8 4 ] ♂Cbロ 100 1 P d 内 υ)=州ベW1l 一手) 120 nU E i g h t p i c t u r eo fwhyechoeso c c u r .Thesameb a s i cmechanisml i e sbehind o b s e r v a t i o n sofechoeswithe l e c t r o nplasmawavesorc y c l o t r o nw a v e s . Figure8‑20i sap l o to fd i s t a n c ev s .t i m e ,s ot h a tt h et r a j e c t o r yo fa ,ag r i dp e r i o d i c a l l y p a r t i c l ew i t hagivenv e l o c i t yi sas t r a i g h tl i n e .Atx= 0 a l l o w sbuncheso fp a r t i c l e swithaspreadi nv e l o c i t yt op a s sthrough. Becauseo ft h ev e l o c i t ys p r e a d ,t h ebunchesmixt o g e t h e r ,anda f t e ra d i s t a n c el , the d e n s i t y , shown a tt h er i g h to ft h e diagram, becomes c o n s t a n ti nt i m e .A secondg r i da tx= la l t e r n a t e l yb l o c k sandp a s s e s p a r t i c l e sa tahigherfrequency.Thiss e l e c t i o no fp a r t i c l et r a j e c t o r i e si n space‑timethenc a u s e sabunchingo fp a r t i c l e st oreoccura tx= l ' . Ther e l a t i o nbetweenl 'andlcanbeobtainedfromt h i ss i m p l i f i e d p i c t u r e ,whichn e g l e c t st h ei n f l u e n c eo ft h ewavee l e c t r i cf i e l dont h e p a r t i c l et r a j e c t o r i e s .I ff i ( v )i st h ed i s t r i b u t i o nf u n c t i o na tt h ef i r s tg r i d andi ti smodulatedbyc o sw 1 t ,t h ed i s t r i b u t i o na tx>0w i l lbeg i v e nby ω 一 2 Chα争teγ 口 326 は」 広 Thesecond g r i da tx= lw i l lf u r t h e rmodulatet h i sd i s t r i b u t i o nbya h ed i s t a n c ex l : f a c t o rcontainingw2andt 。 40 」=9.0cm 20 f (山 。 r J -一 X 一 、 Eat ,,aJ ω一 1111J -一刊U )一 ー - X 一 04 ,,L (一 ) ω一 t 94 ω ( ω 匂 尽 r 0 ‘ rEEEEEEL + • 20 I f W2(x‑l)+w1xl =/12(v)2lcosl(w2+w1)t‑ Q= 1 5.0cm 0 0 4 [ 8 ‑ 8 6 ] Theechocomesfromt h esecondt e r m ,whicho s c i l l a t e sa tw =w2 一 W1 andhasanargumentindependento fvi f W2(X‑[ )= W1X 8 12 16 20 24 28 32 36 40 DISTANCEFROMFIRSTGRID(cm} Measurementso fechoa m p l i t u d ep r o f i l e sf o rv a r i o u ss e p a r a ‑ FIGURE8 ‑ 2 1 h ed r i v e rg r i d s .Thes o l i dc i r c l e sc o r r e s p o n d t i o n slbetweent t ot h ec a s ew2 く w" f o rwhichnoechoi se x p e c t e d .[FromB a k e r , o c .c i t . ] A h e r n ,andWong,l or X= W2l/(w2 一 W1 )={ ’ [ 8 ‑ 8 7 ] Thespreadi nv e l o c i t i e s ,t h e r e f o r e ,doesnota f f e c tt h esecondterma t x= l ’, and t hephasemixinghasbeenundone.Wheni n t e g r a t e dover v e l o c i t y ,t h i stermg i v e sad e n s i t yf l u c t u a t i o na tw =w2 一 W1 ・ The f i r s t termi sundetectablebecausephasemixinghassmoothedt h ed e n s i t y 'i sp o s i t i v eo n l yi fW2>w1 ・ The p h y s i c a l p e r t u r b a t i o n s .I ti sc l e a rt h a tl reasoni st h a tt h esecondg r i dhasl e s sd i s t a n c ei nwhicht ounravelt h e p e r t u r b a t i o n simpartedbyt h ef i r s tg r i d ,andhencemustoperatea ta higherf r e q u e n c y . Figure8 ‑ 2 1showst h emeasurementso fBaker,Ahern,andWong i t hli naccordw i t hEq oni o nwavee c h o e s .Thed i s t a n c el ’ varies w [ 8 ‑ 8 7 ] . The s o l i dd o t s , correspondingt ot h ec a s e w2 く w1, show t h e absence o f an e c h o ,a se x p e c t e d . The echo amplitude d e c r e a s e s o l l i s i o n sd e s t r o yt h ecoherenceo ft h ev e l o c i t y w i t hd i s t a n c ebec司use c modulations. 」 329 φ 328 N o n l i n e a r E f f e c t s 。 Ch αpteγ E i g h t 凶 てコ コ- 10 < z x 。 Q ‑ 2 3 At r a p p e dp a r t i c l ebouncingi nt h ep o t e n t i a lw e l lo faw a v e . FIGURE8 (/) ‑20 25 。 Whent h ewavei st h i sl a r g e ,i t sl i n e a rbehaviorcanbeexpectedt obe 」 /kJ ,t h ec o n d i t i o n( 8 ‑ 8 8 ]i se q u i v a l e n tt o g r e a t l ym o d i f i e d .S i n c e| φJ = J 50 DISTANCE x FROMEXCITER(cm) FIGURE8・22 wl町e w =w8, w~ = =JqkE/mJ [ 8 ‑ 8 9 ] Theq u a n t i t yw8is 仁ailed t h ebouncef;γet eηcy becausei ti st h efreqt間1cy o fo s c i l l a t i o no fap a r t i c l etrappeda tt h ebottomo fas i n u s o i d a lp o t e n t i a l w e l l( F i g .8 ‑ 2 7 ) .Thep o t e n t i a li sg i v e nby Measuremento ft h ea m p l i t u d ep r o f i l eo fan o n l i n e a re l e c t r o n waveshowingnonmonotonicd e c a y .[FromR .N .F r a n k l i n , S .M.Hamberger,H .l k e z i ,G .L a m p i s ,andG .J .S m i t h ,P h y s . R e v .L e t t .2 8 ,1 1 1 4( 1 9 7 2 ) . ] φ = φ。(I c o skx)= φ。(~k2x2 +・・・) [ 8 ‑ 9 0 ] Theequationo fmotioni s 8 . 7 NONLINEAR LANDAU DAMPING 2 x Whent h eamplitudeo fane l e c t r o nori o nwavee x c i t e d ,s a y ,byag r i d i sfollowedi ns p a c e ,i ti so f t e nfoundt h a tt h edecayi snote x p o n e n t i a l , a sp r e d i c t e d byl i n e a rt h e o r y ,i ft h eamplitudei sl a r g e .I n s t e a d ,one t y p i c a l l yf i n d st h a tt h eamplituded e c a y s ,growsa g a i n ,andtheno s c i l l a t e s befores e t t l i n gdownt oas t e a d yv a l u e .Suchbehaviorf o rane l e c t r o n wavea t38MHzi sshowni nF i g .8 ‑ 2 2 .Althougho there f f e c t smaya l s o beo p e r a t i v e ,t h e s eo s c i l l a t i o n si namplitude a r ee x a c t l ywhatwouldbe expected from t h e nonlineare f f e c to fp a r t i c l e trappingd i s c u s s e di n . 5 .Trappingofap a r t i c l eo fv e l o c i t yvo c c u r swheni t senergy S e c t i o n7 i nt h ewaveframei ss m a l l e rthant h ewavep o t e n t i a l ;t h a ti s ,when JeφI >~州v-vφ ) 2 Smallwavesw i l lt r a ponlyt h e s ep a r t i c l e smovinga thighspeedsnear 山・ To t r a pal a r g enumbero fp a r t i c l e si nt h emainp a r to ft h ed i s t r i b u t i o n )wouldr e q u i r e ( n e a rv= 0 JqφJ =~mv~ =~m(w/k)2 [ 8 ‑ 8 8 ] ーーす= dt ー o mw 弘= qE= dφ q一一= -qkφ0 dx smkx [8・ 91] Thefrequencyw i snotc o n s t a n tu n l e s sx i ss m a l l ,s i nkx= k x ,andφis approximatelyp a r a b o l i c .Thenw t a k e st h ev a l u ew8definedi nE q .[ 8 ‑ 8 9 ] . When t h eresonantp a r t i c l e sa r er e f l e c t e d byt h ep o t e n t i a l ,t h e yg i v e k i n e t i cenergybackt ot h ewave,andt h eamplitudei n c r e a s e s .Whent h e p a r t i c l e sbouncea g a i nfromt h eothers i d e ,t h eenergygoesbacki n t o t h ep a r t i c l e s ,andt h ewavei sdamped.Thus,onewouldexpecto s c i l l a t i o n s i namplitudea tt h efrequencyw8 i nt h ewaveframe ・ In t h el a b o r a t o r y frame,t h efrequencywouldbeω ’= W B +kvφ ; and t h eamplitudeo s c i l l a ュ [ l+(wn/w )]ー t i o n swouldhavewavenumberk ’= ω ’/ vφ = k Thec o n d i t i o nw82 ' :w t u r n soutt od e f i n et h ebreakdowno fl i n e a r theoryevenwhenotherp r o c e s s e sb e s i d e sp且rticle trappinga r eresponュ s i b l e .Anothert y p eo fn o n l i n e a rLandaudampingi n v o l v e st h eb e a t i n g o f twow a v e s . Suppose t h e r ea r e two high‑hequency e l e c t r o n waves ( w1 ,k1 )and( w 2 ,k 2 ) .Thesewouldb e a tt oformanamplitudeenvelope t r a v e l i n ga tav e l o c i t y(w2 一 w i ) /(k2 一 k1) = dw/dk= Vg.Thisvelocitymay belowenought ol i ew i t h i nt h ei o nd i s t r i b u t i o nf u n c t i o n .Therecanthen beanenergyexchangew i t ht h eresonanti o n s .Thep o t e n t i a lt h ei o n s 330 Chapt肝 E i g h t s e ei st h ee f f e c t i v ep o t e n t i a lduet ot h eponderomotivef o r c e( F i g .8 ‑ 2 4 ) , and Landau damping or growth can o c c u r . Damping provides an E 汀ective W昌y t oh e a ti o n sw i t h high‑frequency waves, which do n o t o r d i n a r i l yi n t e r a c tw i t hi o n s .I ft h ei o nd i s t r i b u t i o ni sdoublehumped, i tcane x c i t et h ee l e c t r o nw a v e s .Suchani n s t a b i l i t yi sc a l l e damodulational instαbility. backgroundplasmat omoveaway,causingal o c a ldepressioni nd e n s i t y c a l l e dac a v i t o n .Plasmaw旦ves trappedi nt h i sc a v i t ythenformani s o l a t e d n v e l o p es o l i t o no re n v e l o p esolitary 山ave. Su仁h s o l u t i o n s s t r u c t u r ec a l l e dane a r edescribedbyt h enonlinearSchrodingere q u a t i o n .Consideringt h e d i f f e r e n c ei nbotht h ep h y s i c a lmodelandt h emathematicalformoft h e governinge q u a t i o n s ,i ti ss u r p r i s i n gt h a ts o l i t o n sandenvelopes o l i t o n s havealmostt h esames h a p e . PROBLEMS Makeagrapht oshowc l e a r l yt h ed e g r e eo fagreementb e t w e e nt h ee c h o d a t ao fF i g .8 ‑ 2 1andE q .[ 8 ‑ 8 7 ] . . 8 . l TheKorteweg‑‑deVriesEquation 8 8・ 15. 一一 一日 4 ハU 1A + 山一ザ 一例。 U 「 U Therea r etwononlinearequationst h a thavebeen t r e a t e de x t e n s i v e l y i n connection w i t h nonlinear plasma w a v e s : The Korteweg‑‑de V r i e s equation and t h e nonlinear Schrらclinger e q u a t i o n . Each concerns a d i f f e r e n tt y p eofn o n l i n e a r i t y .Whenani o na c o u s t i cwaveg a i n sl a r g e amplitude,t h emainnonlineare f f e c ti swaves t e e p e n i n g ,whosep h y s i c a l r i s e sfromt h evキ Vv explanationwasgiveni nS e c t i o n8 . 3 . 3 .Thise 百ect a termi nt h ei o nequationofmotionandi shandled mathematicallyby t h eKorteweg‑deV r i e se q u a t i o n .Thewavet r a i nands o l i t o ns o l u t i o n s o fF i g s .8 ‑ 5and8 ‑ 7a r ea l s op r e d i c t e dbyt h i se q u a t i o n . Whenane l e c t r o nplasmawavegoesn o n l i n e a r ,t h edominantnew e汀ect i st h a tt h eponderomotivef o r c eo ft h eplasmawavesc a u s e st h e + U 一5 8.8 EQUATIONS OF NONLINEAR PLASMA PHYSICS weaklynonlineari o nwave: 町一針 8 ‑ 1 6 .C a l c u l a t et h ebouncefrequen 仁y o fad e e p l yt r a p p e de l e c t r o ni nap l a s m a wavew i t h1 0 ‑ Vrmsa m p l i t u d eandI ‑ c mw a v e l e n g t h . This equation occurs i n many p h y s i c a ls i t u a t i o n s including t h a to fa [ 89 2 ] whereU i samplitude,andrandta r et i m e l i k eands p a c e l i k ev a r i a b l e s , r e s p e c t i v e l y . Although s e v e r a l transformations o fv a r i a b l e sw i l l be n e c e s s a r ybeforet h i sformi so b t a i n e d ,twop h y s i c a lf e a t u r e scanalr回dy be s e e n . The second term i nE q .[ 8 ‑ 9 2 ]i se a s i l y recognized a st h e conve仁tive termv.Vvleadingt owaves t e e p e n i n g .Thet h i r dterma r i s e s h ephasevelo仁ity. fromwaved i s p e r s i o n ;t h a ti s ,t h ekdependenceoft ForT ,= 0 ,i o nwavesobeyt h er e l a t i o n( E q .[ 4 ‑ 4 8 ] ) w2= k 2 c ; ( l+k2λ~f' [ 8 ‑ 9 3 ] Thed i s p e r s i v etermk2λ~ a r i s e sfromt h ed e v i a t i o nfrome x a c tn e u t r < ByTaylor‘- series expansion,onef i n d s [ 8 ‑ 9 4 ] w =kc, ー;k2c,A~ showingt h a tt h edispersi、 f o rt h et h i r dd e r i v a t i v etermi nE q .[ 8 ‑ 9 2 ] .Dispersionmustbek e ̲ r ti n t h etheoryt opreventverys t e e pwavefronts(correspondingt overyl a r g e k )froms p u r i o u s l ydominatingt h enonlinearb e h a v 1 0 r . ' TheKorteweg‑deV r i e sequationadmitso fas o l u t i o ni nt h eform o fas o l i t o n ;t h a ti s ,as i n g l ep u l s ewhichr e t a i n si t sshapea si tpropagates n o tt h ev e l o c i t yo f light !)・ This means t h a tU with smne'velo仁ity c ( dependso n l yont h ev a r i a b l eg‑e rr a t h e rthangorrs e p a r a t e l y .Defining , (= =g e r ,s ot h a tafar= c d / d ( ,anda/ag= d / d [ , ,wecanw r i t eEq.[ 89 2 ] 、、 FIGURE8 ‑ 2 4 Theponderomotivef o r c ec a u s e dbyt h ee n v e l o po famodulatedwavec a nt r a p e l o c i t y . p a r t i c l e sandc a u s ew a v e ‑ p a r t i c l er e s o n a n c e sat」the groupv a s dU " d [ , dU 1d'U d ( , 2d(' A -c 一一 + U 一一+一一~= U [ 8 ‑ 9 5 ] 331 Nonlineαr E f f e c t s 332 333 Thiscanbei n t e g r a t e d : Nonlineaγ Cha争ter E i g h t f ' "dU.. ‑cI E f f e c t s Ir ' "dU2 . I 「 00 d td2T八 Tーで d[ ’十一 l -d[’+ー l h d ? ; ‑ 2J , d?; ’ 0 一一 l ー」二 l ,//’=。 2J { dt\d( ’之 } ~- [8・ 96] v c ’ being adummyv a r i a b l e .I fU(()andi t sd e r i v a t i v e sv a n i s ha tl a r g e ( ?:I • <Xl) theresulti s d i s t a n c e sfromt h es o l i t o nI l 。 I d2U cU--U 乙一一----,,. = 2 2d(L 0 ‑ [ 8 ‑ 9 7 ] M u l t i p l y i n geachtermbydU/d ( ,wecani n t e g r a t eoncemore,o b t a i n i n g i c u 2i u 'H~) =o [ 8 ‑ 9 8 ] or (宮) = ~U2(3c ‑U) [ 8 ‑ 9 9 ] Thisequationi ss a t i s f i e dbyt h es o l i t o ns o l u t i o n U(()= 3 cs e c h 2[ ( c / 2 ) 1 1 2 ( ] [8 ” 1001 a sonecanv e r i f ybyd i r e c ts u b s t i t u t i o n ,makinguseo ft h ei d e n t i t i e s 手(sech ← se山 t川 x ιx r i e sequationd e s c r i b e s Wen e x twisht oshowt h a tt h eKorteweg• de V large‑amplitudei o nw a v e s .Considert h esimplec a s eo fone‑dimensional wavesw i t hc o l di o n s .Thef l u i de q u a t i o n so fmotionandc o n t i n u i t ya r e a v , [8・ 1011 a t a v , eaφ [ 8 ‑ 1 0 3 ] キ a x= 一一て- ma x 一一一 + v, and s e c h 2x+tanh2x= I ‑ 2 5 At r a i no fs o l i t o n s ,g e n e r a t e da tt h el e f t ,a r r a y e da c c o r d i n gt ot h er e l a t i o n FIGURE8 amongs p e e d ,h e i g h t ,andw i d t h . a n ; a(n 山) = 0 一二+ [ 8 ‑ 1 0 4 ] a t a x [8・ 102] Equation(8』 100] d e s c r i b e sas t r u c t u r et h a tl o o k sl i k eF i g .8 ‑7 ,r e a c h ュ t( →土 <Xl. Thes o l i t o nhasspeedc , ingapeaka t(= 0 証nd vanishinga amplitude3 c ,andh a l f ‑ w i d t h( 2 / c ) 1 1 2 .A l la r er e l a t e d ,s ot h a tcs p e c i f i e s t h eenergyo ft h es o l i t o n .Thel a r g e rt h ee n e r g y ,t h el a r g e rt h espeed fs o l i t o n s andamplitude,andt h enarrowert h ew i d t h .Theo仁currence o dependsont h ei n i t i a lc o n d i t i o n s .I ft h ei n i t i a ld i s t u r b a n c ehasenough energyandt h ephasesa r er i g h t ,as o l i t o ncanbegenerated;o t h e r w i s e , al a r g e ‑ a m p l i t u d ewavew i l lappear. I ft h ei n i t i a ld i s t u r b a n c ehast h e energyo fs e v e r a ls o l i t o n s,mdt h ephasesa r er i g h t ,anN ‑ s o l i t o ns o l u t i o n canbeg e n e r a t e d .S i n c et h espeedo ft h es o l i t o n si n c r e a s e sw i t ht h e i r s i z e ,a f t e ratimet h es o l i t o n sw i l ld i s p e r s ethemselvesi n t oanordered a r r a y ,a sshowni nF i g .8 ‑ 2 5 . sthen AssumeBoltzmanne l e c t r o n s( E q .[ 3 ‑ 7 3 ] ) ;Poisson ’s equationi a2φ ψr ‑ a x キ ム eφ/ KT,戸、 e ε 。一τ = et n o キ‑' "1 [ 8 ‑ 1 0 5 ] Thef o l l o w i n gd i m e n s i o n l e s sv a r i a b l e sw i l lmakea l lt h ecoe侃cients u n i t y : x ’= x /λD 2 1/2 = X (η oe ζ / E0KT,) ’ ヲ 1/2 1’= f l p t = t( n 0e 之/ ε oM)' X= eφ/ K 乙 η ’= nJno v '= v / v ,= v(M/KT,) >/ 2 [ 8 ‑ 1 0 6 ] 334 Ours e tofequationsbecomes 335 s ot h a t Chapleγ No ηIiη ea γ E i g h t a v’ , a v’ ax -一一=-- at ’ - ax ’ ax ’ q 向。 [8 ・ 107] a 2 x x dX - Showt h a ts o l i t o ns o l u t i o n sc a ne x i s to n l yf o rl , n [8ー 109] ‑ 2x )>/ 2 く "({ く 1.6 . J i ] andO く Xm拙く 1.3. ‑1 a v 1 a x 1 Oη1 a g a g a g Thusournormalizationi ssucht h a ta l lt h el i n e a rperturbationsa r eequal .Wenextc o l l e c tt h etermsproportionalt o8 2i nE q . andcanbec a l l e dU ( 8 ‑ 1 0 9 ]andt o8512i nE q s .( 8I 0 7 ]and( 8 ‑ 1 0 8 ) .Thisy i e l d st h es e t 。2X1 ーーす= d主一 [ 8 ‑ 1 1 1 ] a v 2 a v 1 a x 2 十 U t 一一一=一一一- a r a g キa t a g 一一一 a n ? a a g a g 。ηl 一二一一二+ー( v2 + η1V1) * I ti sn o tn e c e s s a r yt oe x p l a i nw h y ,t h ee n dw i l lj u s t i f yt h em e a n s [ 8 ‑ 1 1 7 ] [ 8 ‑ 1 1 8 ] [ 8 ‑ 1 1 9 ] a v 1 a x 2 a + +ー(η1V 1 )= 0 a g a g a g [ 8 ‑ 1 2 0 ] F o r t u n a t e l y ,x 2cancelsout,andreplacinga l lf i r s t ‑ o r d e rq u a n t i t i e sbyU r e s u l t si n Wemusta l s otransformt ot h es c a l e dvariables本 = δ3/21 ’ a x 2 Ia x i a v 1 a r a ( ' a g 2a g a r a n 1 a 3 x 1 ←ー+~ー+ー + v1 u ’ = 8v1+82v2 + ・.. T ‘ S o l v i n gf o rn 2i n( 8 ‑ 1 1 7 ]and f o ra v 2 / a gi n( 8 ‑ 1 1 3 ) ,wes u b s t i t u t ei n t o ( 8 ‑ 1 1 9 ] : +S2n2+・.. t ’) 1 X2 n 2+二X1 2 。U I Wethusw r i t e ぜ= 81;2(x ’ [ 8 ‑ 1 1 6 ] ηI = x 1 = V l 三 U [ 8 ‑ 1 1 0 ] x= S x 1+0 2 x 2+・- [ 8 ‑ 1 1 5 ] n t e g r a t i o ng i v e s S i n c ea l lv a n i s ha st • oo, i δT η ’= l + δn1 [ 8 ‑ 1 1 4 ] ηl Doingt h esamei nE q s .( 8 ‑ 1 0 7 ]and( 8 ‑ 1 0 8 ] ,wef i n dt h a tt h el o w e s torder termsa r ep r o p o r t i o n a lt o8 3 1 2 ,andt h e s eg i v e To recover t h e K ‑dV e q u a t i o n , we must expand i nt h e wave amplitudeandkeeponeorderhigherthani nt h el i n e a rt h e o r y .S i n c e f o rs o l i t o n st h e amplitude and speed a r er e l a t e d ,we can choose t h e ,definedt obe expansionparametert obet h eMachnumbere x c e s sS 8 三 JU a~ X1= I +必[(必 2 [ 8 ‑ 1 1 3 ] S u b s t i t u t i n g( 8 ‑ 1 1 1 ]and( 8 ‑ 1 1 3 ]i n t o( 8 ‑ 1 0 9 ] ,wef i n dt h a tt h el o w e s t ュ h e s eg i v e ordertermsa r ep r o p o r t i o n a ltoδ, and t s・ 17. ReduceE q s .[8-107 ]ー[8-109] t oE q .[ 8 ‑ 2 7 ]b ya s s u m i n gt h a tx .n ,’ and u ’ dependo n !yont h ev a r i a b l er 三 X’ .Jit'. I n t e g r a t et w i c ea si nE q s .[ 8 ‑ 9 6 ] ‑ ( 8 ‑ 9 8 ] t oo b t a i n ~( dx/dt;ア = ex ~.r• a x ' ‑ [8・ 108] I fwewere t o transform t oa frame movingwith v e l o c i t yu ’ = JU, we q .( 8 ‑ 2 7 ] . As shown f o l l o w i n gE q .( 8 ‑ 2 7 ] ,t h i ss e to f would re仁over E U . equationsadmitso fs o l i t o ns o l u t i o n sf o rarangeofMachnumbersJ PROBLEM a t : ar 0 ax' ‑ : : ‑ 7 2= e at ’ a̲ 1 ; 2a ‑ 。η ’ a 一一十←τ (η ’u ’) = 0 at ’ Ejfecむ E 向。 一 = a·"" 一 - 8''"---c l [ 8 ‑ 1 1 2 ] 。u au 1a 3 U. . =0 a g 2a g キ ' +U一一一+一一-., a r [ 8 ‑ 1 2 1 ] 336 whichi st h esamea sE q .[ 89 2 ] .Thus,i o nwaveso famplitudeoneorder e s c r i b e dbyt h eKorteweg‑deV r i e se q u a t i o n . higherthanlinear 司 re d Chapleγ E i g h t PROBLEM 3 3 7 N o n l i n e a r E f f e c t s 8 ‑ 1 8 .A s o l i t o nw i t hp四 k a m p l i t u d e1 2Vi se x c i t e di nahydrogenp l a s m aw i t h KT,= 1 0eVandn 0= I0 1 6rn ".Assumingt h a tt h eKortewe 日-de V r i e se q u a t i o n d e s c r i b e st h es o l i t o n ,c a l c u l a t ei t sv e l o c i t y( i nm / s e c )andi t sf u l lw i d t ha th a l f maximum( i nmm).( H i n t :F i r s tshowt h a tt h es o l i t o nv e l o c i t yci se q u a lt ou n i t y i nt h en o r m a l i z e < lu n i t su s e dt od e r i v et h eK ‑ < l Ve q u a t i o n . ) 8 . 8 . 2 TheNonlinearSchrodingerEquation Thisequationh 司S t h estandarddimensionlessform 。 3ψ l 。t a2 ψ2 +戸ーす+ qiψl " L i / I =0 a x [ 8 ‑ 1 2 2 ) whereψis t h ewaveamplitude,i= (一 1)112, and 戸 a ndqa r ec o e f f i c i e n t s whosep h y s i c a l significan 仁E w i l lbeexplaineds h o r t l y . Equation( 8 ‑ 1 2 2 ] di 仔ers fromt h eu s u a lSehrる<linger equation 。ψ112 a2 ψ i n 。t +•- 2ma x ' V(x,t ) ψ =() U山 [ 4 ‑ 3 0 ] 一9h 十言R 九一 HM 2 '3,2 2 = Wp 一一 2 agrowingr i p p l e . Thereasont h es i g no fp qmattersi st h a tpandqf o rplasmawaves i s p e r s i o nd v g /d k turnoutt obep r o p o r t i o n a l ,r e s p e c t i v e l y ,t ot h eEγoup d andt h enor尚iear f r e q u e n c yshiβδw <Xaw/al ψ12. Wes h a l lshowl a t e rt h a t 1A W oe x i s tonlyi nr e g i o n sofs m a l lWpキThet iapping permitswaveso fl a r g ekt u r t h e renhancest h ewavei n t e n s i t yi nt h e o fp a r toft h ekspectrum f r e g i o n swherei twasa l r e a d yh i g h ,thuscausingt h eenvelopt odevelop hy i nt h a tt h ep o t e n t i a l V(x,t )dependsonψitself, makingt h el a s tterm h a t V dependsonlyont h emag凶吋elψ12 nonIi町ar. Note,however,t and notonthe phaseofψ. Thisi st obee x p e c t e d ,a sf司r a se l e c t r o n plasmawavesa r econcerned,becauset h en o n l i n e a r i t ycomesf r o . mt h e h eg r a d i e n to ft h e wave ponderomotive for℃e, which depends on t i n t e n s i t y . Planewaves o l u t i o n so fE q .[ 8 ‑ 1 2 2 ]a r emodulationallyu n s t a b l ei f p q>O ;t h a ti s ,ar i p p l eont h eenvelopeoft h eW孔 ve w i l ltendt ogrow. st h esamea st h a to fF i g .8 ‑ 2 4eventhoughwea r econsider曲 Thepi仁川 re i ingheref l u i d ,ratherthand i s c r e t ep a r t i c l e ,e 任ects. Forplasmaw a v e s , i ti se a s yt os e ehowt h eponderomotiveforce 仁an 仁a use 江 modulational i n s t a b i l i t y . Figme826showsaplasmawavewith 司 rippled e n v e l o p e . The gradient i n wave i n t e n s i t yc a u s e s a ponderomotive f o r c e which movesbothe l e c t r o n sandi o n stowardt h ei n t e n s i t yminima,forminga r i p p l ei nt h eplasmλdensity. Plasmawavesa r etrappedi nr e g i o n so flow d e n s i t ybecauset h e i rd i s p e r s i o nr e l a t i o n ‑ 2 6 The ponderomotive f o r c eo f a plasma wave w i t h nonuniform FIGURE8 i n t e n s i t yc a u s e si o n st of l o wtowardt h ei n t e n s i t yminima.Theresult司 i n gd e n s i t yr i p p l et r a p swavesi ni t st r o u g h s ,t h u senhancingt h e modulationo ft h ee n v e l o p e . 。ω q = 一羽刊 ω [8 ・ 123) Modulationali n s t a b i l i t yoccurswhenp q>0 ;t h a ti s ,whenδwand d v , / d k haveopposites i g n .Figure8 ‑ 2 7i l l u s t r a t e swhyt h i si ss o .InF i g .8‑27A, ar i p p l ei nt h e wave envelope h a s developed a sar e s u l t of random sn e g a t i v e .Thent h ephasev e l o c i t yw/k ,whch f l u c t u a t i o n s .Suppose8wi m a l l e ri nt h eregionofhigh i sproportionalt ow,becomessomewhats i n t e n s i t y .Thisc a u s e st h ewavec r e s t st op i l eupont h el e f tofF i g .8‑27B st h e r e f o r el a r g e andt ospreadoutont h er i g h t .Thel o c a lv a l u eo fki fd v g / d ki sp o s i t i v e ,t h egroupv e l o c i t y ont h el e f tands m a l lont h er i g h t .I w i l lbel a r g e ront h el e f tthant h er i g h t ,s ot h ewaveenergyw i l lp i l eup i n t o as m a l l e rs p a c e . Thus, t h er i p p l ei nt h e envelope w i l l become f8wandd v , /d kwereofthesame narrowerandl a r g e r ,a si nF i g .8‑27C.I s i g n ,t h i smodulationali n s t a b i l i t ywouldnothappen. ‑ ‑ 338 Chα:pteγ E i g h t 339 Nonlinea γ E f f e c t s (A) 一一一一事F ー-ー・ー 一一一---- V中 / // ( B ) Ane n v e l o p es o l i t o n . FIGURE 8 ‑ 2 8 ーーー一ーー-一ーーー vE『 ー--”ー av e l o c i t yV hast h emoreg e n e r a lform( F i g .8‑28) ψ(x, t )= (子) 1 1 2s e c h[(~) 1 1 2( x‑x0 日)] B o ) ] ( C ) xexpi (At+‑ijx fit+ [ 8 ‑ 1 2 5 ) 、、 、、 wherex 0and 0 0arethei n i t i a lp o s i t i o nand p h a s e .I ti sseent h a tt h e magnitude of V a l s oc o n t r o l st h e numberofwavelengths i n s i d et h e envelopea tanygivent i m e . FIGURE 8 ‑ 2 7 M o d u l a t i o n a li n s t a b i l i t yo c c u r s when t h en o n l i n e a r f r e q u e n c ys h i f tandt h egroupv e l o c i t yd i s p e r s i o nh a v e o p p o s i t es i g n s . 8・ 19. Showb yd i r e c ts u b s t i t u t i o nt h a tE q .( 8 ‑ 1 2 4 ]i sas o l u t i o no fE q .( 8 ‑ 1 2 2 ] . r emodulationally Although planewaves o l u t i o n st oE q . [8‑123] a ,t h e r e can bes o l i t a r ys t r u c t u r e sc a l l e de n v e l o p e u n s t a b l ewhenpq>0 s o l i t o n swhicha r estable ・ These a r egeneratedfromt h eb a s i cs o l u t i o n 叫X, t)= (子) 112sech[(~) 112xJ e;A, [8・ 124] whereA i s an a r b i t r a r y constantwhich t i e s together t h e amplitude, w i d t h ,andfrequencyo ft h ep a c k e t .Atanyg i v e nt i m e ,t h edisturbance 8 ‑ 1 0 0 ] )(thought h ehyperbolics e c a n t resemblesasimples o l i t o n( E q .[ )o s c i l l a t e i snotsquaredh e r e ) ,butt h ee x p o n e n t i a lf a c t o rmakesw(x,t betweenp o s i t i v eandn e g a t i v ev a l u e s .Anenvelopes o l i t o nmovingw i t h 8・20. V e r i f yE q .( 8 ‑ 1 2 5 ]b yshowingt h a tif 凶 (x, t )i sas o l u t i o no fE q .( 8 ‑ 1 2 2 ] ,t h e n ψ 二回(x I)叫(ギx ~t + O u ) ] x0‑V t , i sa l s oas o l u t i o n We next wish t o show t h a tt h e nonlinear Schrodinger equation d e s c r i b e slarge‑amplitudee l e c l lonplasmawaves.Theprocedurei st o s o l v es e l f ‑ c o n s i s t e n t l yf o rt h ed e n s i t yc a v i t yt h a tt h ewavesdigbymeans o ft h e i rponderomotivef o r c eandf o rt h ebehavioroft h ewavesi nsuch ac a v i t y . The high‑frequency motion o ft h ee l e c t r o n si s governed by PROBLEMS 340 equations[ 4 ‑ 1 8 ] .[ 4 ‑ 1 9 ] ,and[ 4 ‑ 2 8 ] ,whichwer e w r i t ea s Ch αヤleγ a u e~ 3KT,aη a t m mno a x 一一一一一- E i g h t [ 8 ‑ 1 2 6 ] ハリ 一一 o u 一 x qO 一円U n [ 8 ‑ 1 2 7 ] η ρ ε 一 一 ハリ 司 一ε JF -2 町一間 n 十 k 0 一 m7 n 一2 [ 8 ‑ 1 2 9 ] [8 田 135] ハリ 叫 一一 n 。。 一2 、、、‘,,,, l -、 ESE + A 凶 + [ 8 ‑ 1 3 6 ] Herei ti sunderstoodt h a ta / a ti st h etimed e r i v a t i v eont h eslowtime s c a l e ,althoughu c o n t a i n sbotht h eexp(‑iw0t) f a c t o rand t h es l o w l y varying c o e f f i c i e n tu 1 . We have e s s e n t i a l l y derived t h e nonlinear Schrodingerequation [ 8 ‑ 1 2 2 ] ,buti tremainst oevaluateδηin terms o fI u d2 Thelow‑frequencyequationo fmotionf o rt h ee l e c t r o n si sobtained byn e g l e c t i n gt h ei n e r t i atermi nE q .[ 4 ‑ 2 8 ]andaddingaponderomotive f o r c etermfromE q .[ 8 ‑ 4 4 ] a n w~ a( < o E 2 ) ーす- ' i ! x w~ a x 2 0= ‑enE KT, [ 8 ‑ 1 3 7 ] [8・ 131] 2 、 ei w . , I . . wheret h edots t a n d sf o ratimed e r i v a t i v eont h es l o wt i m es c a l e .We i , ,whichi smuchs m a l l e rthanw i i u 1 : mayt h e r e f o r en e g l e c ti 内2 [ 8 ‑ 1 3 2 ] 一 7一 Here we have setγ,= Is i n c et h e low-frequen 仁y motion should be i s o t h e r m a lr a t h e rthana d i a b a t i c .Wemays e t ー w0Ut) ~=ー (w~Ut 十 2iw0ui) e‑ i w o ' a t " I anda s s u r r ou( x ,t )v i aE q .[ 81 3 1] ,and ( t h e s ebeingunderstood ),仁onvert backt approximatew~ byli nt h ef i r s ttermt oo b t a i n r’ 内・ ・ <'.ZWoUt ム =(wo 一 Wp)/wρ = w~ E ( U t 、 Definingthefrequencys h i f t~ 2 U 一 一X at~ [ 8 ‑ 1 3 4 ] [ , a u : 3 山 l ば- " I‑o →一一寸+ n ' ) u ; ]ei w ; , i キ= 0 a t ' 2ax ・L 2 、。一 nd [ 8 ‑ 1 3 0 ] t w i c ei nt i m e ,weo b t a i n a 2 u ’” E f f e c t s [8 ・ 133] 8η ’= δη/η。 u ’= u(KT,/m) 1 1 2 qJ一oh u ( x ,t )= U 1 ( x ,t )e•wo' で一τ = x ’= x/λD w ’= w/wp 2 一一 ハリ 、、‘E1 ノ + 品一h ω q’hムy ,,SE ,‘、、 一X u 一2 、川 U - qパU 2 叫 7 u 一2 + o n s i s t so fahigh‑frequencyp司 rt o s c i l l a t i n ga tw0( e s s e n ュ Thev e l o c i t yuc t i a l l yt h eplasmafrequency)andalow‑frequencyp a r tu 1describingthe q u a s i n e u t r a lmotiono fe l e c t r o n sf o l l o w i n gt h ei o n sa st h e ymovet oform t h ed e n s i t yc a v i t y .Bothf a s tandslows p a t i a lv a r i a t i o n sa r ei n c l u d e di n111. Let Di 圧erentiating 二 O Wenowtransformt ot h en a t u r a lu n i t s 如一日目 内 Aυ-RAυ 九d 一a t J 3KT,a2u1 I 2 2 2 8 n 一一言+ lw 。一 ω ー ωρ u i Je m a x \ η。 J Nonlineaγ o b t a i n i n g e s c r i b et h ed e n s i t yc a v i t y ;t h i si st h e Wenowr e p l a c en0byn0+8ηto d onlynonlineare f f e c tc o n s i d e r e d .Equation[ 8 ‑ 1 2 9 ]i so fc o u r s ef o l l o w e d byanyo ft h el i n e a rv a r i a b l e s .I tw i l lbeconvenientt ow r i t ei ti nterms fWp;thus o fuandusethede白 nition o - 2iw0向+ [ 8 ‑ 1 2 8 ] ,n ,and u a r e , where n0i st h e uniform unperturbed d e n s i t y ; andE r e s p e c t i v e l y ,t h ep e r t u r b a t i o n si ne l e c t r i cf i e l d ,e l e c t r o nd e n s i t y ,andf l u i d v e l o c i t y .Theseequationsa r el i n e a r i z e d ,s ot h a tn o n l i n e a r i t i e sduet ot h e r enotc o n s i d e r e d .Takingt h etimed e r i v a t i v e uキVuandV キ(πu) termsa o fE q .[ 81 2 7 ]andt h ex d e r i v a t i v eo fE q .[ 8 ‑ 1 2 6 ] ,wecane l i m i n a t eu andE w i t ht h ehelpo f[ 8 ‑ 1 2 8 ]t oo b t a i n 2 [ t ’= ω。t 一ハU 伽一ud庄一以 + 341 S u b s t i t u t i n gi n t oE q .[ 8 ‑ 1 3 0 ]g i v e s [ 8 ‑ 1 3 8 ) by s o l v i n gt h e high-frequen 仁Y e q u a t i o n[ 8 ‑ 1 2 6 ] without t h e thermal c o r r e c t i o n .WithE = -Vφand x= eφ/ KT" E q .[ 8 ‑ 1 3 7 ]becomes i J ニ (x a x 1 m a " ‑l nn ) 一一...:::__ー(u") = 0 2K7二 ax [ 8 ‑ 1 3 9 ) 342 C h a p t e r E i g h t Comparing w i t hE q . [ 8 ‑ 1 2 2 ] , we s e et h a tt h i si st h e nonlinear icanben e g l e c t e dand Schrodingerequationi fL I n t e g r a t i n g ,s e t t i n gn = η 。+ δπ , and usingt h en a t u r a lu n i t s[ 8 ‑ 1 3 4 ] ,we have ~(u2)=tlul2=x ln(l+8n)=x 8n p= 2 q=一言伊て-;;JM) Wemustnowe l i m i n a t exbys o l v i n gt h ec o l d ‑ i o ne q u a t i o n s[ 8 ‑ 1 0 3 ] and[ 8 ‑ 1 0 4 ] .S i n c ewea r enowusingt h ee l e c t r o nv a r i a b l e s[ 8 ‑ 1 3 4 ] ,and s i n c eflp = εωρ, v, = ε (KT,/m)112, whereε = (m/M ) 1 1 2 ,t h edimensionless formo ft h ei o nequationsi s Iau au, a x . a x a x ‘ ε at a a x Ia8η ; -~+ー[( I+ ε at 8 n ; ) u ; ]= 0 ω ’2 =I + δη ’+ 3k ’ 2 [ 8 ‑ 1 4 9 ] wherek ’ = kλ0, andwehavenormalizedw t oWpo. t h ev a l u eo u t s i d et h e d e n s i t yc a v i t y .Thegroupv e l o c i t yi s [ 8 ‑ 1 4 2 ] , dw ’ = (η 。+ δη ;)/ n0 = I+ δη ; and havedropped t h e Herewehaves e tni prime.I ft h es o l i t o ni ss t a t i o n a r yi naframemovingw i t hv e l o c i t yV ,t h e n l y throught h ecombinationg= p e r t u r b a t i o n sdependonx and to v = dk ’ g 3k ’ = [ 8 ‑ 1 5 0 ] ω’ s ot h a t x‑x0 V t .Thus dv~ a一時 V a a a a x a g i山首I F i n a l l y ,i tremainst oshowt h a tpandq a r er e l a t e dt ot h egroup d i s p e r s i o nandnonlinearfrequen 仁Y s h i f ta ss t a t e di nE q .[ 8 ‑ 1 2 3 ] .This i st r u ef o rV2 < m/ M.I nd i m e n s i o n l e s su n i t s ,t h eBohm‑Grossd i s p e r s i o n r e l a t i o n[ 4 ‑ 3 0 ]r e a d s [ 8 ‑ 1 4 1 1 一一一十比一一+一一= O I / m/M \一-- 3 [8・ 140] 3 一一 一ud dk ’ ω’ and 0 8 n ;=コ u, v ForV2 《 ε2, E q .[ 8 ‑ 1 4 6 ]g i v e s on ’= [ 8 ‑ 1 4 4 ] ω ’2=1-tlu'l2+3k ’2 2 u 一8 一 lloε 一一’ 一’一 dq d ’つ 叫 . h a sp r e v i o u s l ys t a t e d e v a W Uponi n s e r t i n gt h i si n t oE q .[ 8 ‑ 1 3 6 ] ,wef i n a l l yhave [ 8 ‑ 1 4 7 ] e イ吐 06 l 口1 Q口 E m p A o r Ea ,, 、、‘‘ ‘ F. ‘- 、 ,, a, z-E - - f一 2E 一dT 一一 U 3A 円。 [ 8 ‑ 1 4 6 ] 一一一向一同《 加 rbir , ω£L ω qムー《, nEq.[ 8 ‑ 1 4 0 ] ,whereδηis r e a l l y8η" we f i n d S u b s t i t u t i n gf o rxi 14 • 22 [ 8 ‑ 1 5 2 ] 円 ll Then [ 8 ‑ 1 4 5 ] iTi + ;会+[Li-H三一 1fl1 什 u = 。 tlu ’12 s ot h a tE q .[8-144 ]仁an bew r i t t e n o b t a i n ε [ 8 ‑ 1 5 1 ] [8 ー 143] Fromt h i sandt h ec o n d i t i o no fq u a s i n e u t r a l i t yf o rt h es l o wmotions,we δn, =on ,= 子X 03一9h a g ag FZ - F 一一 ε 一一__:_:_:_:+一二= ε --9ι au , v ‑ ‑ U でk l va8η i ε U; =-::-ごX 一一 hy va u , ax = 0 一+ ε ag a g ・ “一Ju J andweo b t a i na f t e rl i n e a r i z a t i o n [ 8 ‑ 1 5 3 ] 343 Nonlmeαγ E f f e c t s 344 Ch α pte γ E i f ! , h l I fthe 仁ondition V2 < J i snots a t i s f i e d ,t h ei o ndynamicsmustbe t r e a t e dmorec a r e f u l l y ;onehascouplede l e c t r o nandi o ns o l i t o n swhich e v o l v et o g e t h e ri nt i m e .Thisi st h es i t u a t i o nnormallyencounteredi n experiment 司 nd h a sbeent r e a t e dt h e o r e t i c a l l y . Insummary,aLangmuir‑waves o l i t o ni sd e s c r i b e dbyE q .[ 8 ‑ 1 2 5 ] , w i t hp= r fandq= ! andw i t hψ (x, t )signifyi時 the l owfrequencyp a r t ( x ,t ) ,whereu ,x ,andtarea l li nd i m e n s i o n l e s su n i t s .I n s e r t i n gt h e o fu e t t i n gx0and( ) 0b ez e r o ,we 仁an w r i t eE q .[8 』 125] exp( ‑ i w 0 1 )fa仁 tor andl a sf o l l o w s : 345 Nonlineαγ t0( オ s e c ) u(x t)=4A112s ×叶→[(wo+f A)t 子]) A 己 . 3k ’ V=v~ = τ = 3k ’ 由 Theenvelopeo ft h es o l i t o npropagatesw i t havelo仁ity V ,whichi ss of a r t a仁仁urately i n v o l v e s simultaneously s o l v i n ga u n s p e c i f i e d . To 凸 nd i Korte ;町g←de V r i e sequationd e s c r i b i n gt h emotiono ft h ed e n s i t yc a v i t y , butt h eunderlyingp h y s i c scanbeexplainedmuchmores i m p l y .The ele仁tron p lasmawaveshaveagroupv e l o c i t y ,and V mustbeneart h i s v e l o c i t yi ft h e wave energy i st o move alongw i t ht h ee n v e l o p e .I n dimensionlessu n i t s ,t h i sv e l o c i t yi s ,fromE q .[ 8 ‑ 1 5 0 ] , [ 8 ‑ 1 5 5 ] αJ Thetermi(V/3)xi nt h eexponento fE q .[ 8 ‑ 1 5 4 ]i st h e r e f o r ej u s tt h e i k x factor indicating propagation of the waves i n s i d et h ee n v e l o p e . i( V 2 / 6 ) 1i sj u s t‑ i(~)k 勺’, which canberecognized S i m i l a r l y ,t h ef a c t o r‑ fromE q .[ 8 ‑ 1 4 9 ]a st h eBohm‑Grossfrequencyf o rSη ’= 0 ,t h ef a c t o r ~ comi 時 from expansiono ft h esquarer o o t .Si 町ew 。= wp. t h eterms ω。+ ( V2/6)r e p r e s e n tt h eBohm‑Grossf r e q u e n c y ,andA i st h e r e f o r e t h efrequencys h i f t( i nu n i t so fwρ ) duet ot h ec a v i t yi nδη ’. Thes o l i t o n , amplitudeandwidtha r eg i v e ni nE q .[ 8 ‑ 1 5 4 ]i ntermso ft h es h i f tA 呂 nd t h ehigh‑frequencye l e c t r i cf i e l dcanbefoundfromE q .[ 8 ‑ 1 3 8 ] . C a v i t o n shavebeenobservedi nd e v i c e ss i m i l a rt ot h a to fF i g .8 ‑ 1 6 . F i g u r e s8‑29and8‑30showtwoexperimentsi nwhichs t r u c t u r e sl i k e t h eenvelopes o l i t o n sd i s c u s s e dabovehavebeengeneratedbyi n j e c t i n g high‑powerr fi n t oaq u i e s c e n tp l a s m a .Theseexperimentsi n i t i a t e dt h e i n t e r p r e t a t i o no fl a s e r ‑ f u s i o nd a t ai ntermsof “ profile modification ,”。r t h echangei nd e n s i t yp r o f i l ecausedbyt h eponderomotivef o r c eo fl a s e r 6 3 9 z(cm) . . " ‑ 2 9 A d e n s i t yc a v i t y , or “ ca v iton,” dug by t h e FIGURE8 ponderomotive f o r c eo fa n rf 且eld n e a rt h e c r i t i c a ll a y e r . The h i g h ‑ f r e q u e n c yo s c i l l a t i o n s ( n o tshown)wereprobedw i t hane l e c t r o nbeam. [FromH .C .K i m ,R .L .Stenzel , λnd A .Y .Wong, P h y s .R e v .L e t t .3 3 ,886( 1 9 7 4 ) . ] E f f e c t s M T EJ 凶 346 (/ Cha戸!er E i g h t ρ APPENDICES wo= wpe / 一Z凶トz -Q 」凶一比 N凶、〉トω 。 ( A ) 5 10 15 。 5 RADIALPOSITION(cm) 10 15 ( B ) l e c t r o n and ion wave s o l i t o n s . In ( A )t h elow‑frequencyd e n s i t y FIGURE 8‑30 Coupled e B )t h ehigh・frequency e l e c t r i c c a v i t i e sa r eseent opropagatet ot h el e f t .In( f i e l d ,a smeasuredbywirep r o b e s ,i sfoundt obel a r g ea tt h el o c a ld e n s i t y minima.[FromH.I k e z i ,K.Nishikawa,H.Hojo,andK.M i r n a ,Plαsma P h y s i c sand C o n t r o l l e dNuclearF:山 ion Reseaγch, 1 9 7 4 ,I I ,6 0 9 ,I n t e r n a t i o n a lAtomicEnergy Agency,Vienna,1 9 7 5 . ] radiation near the c r i t i c a ll a y e r , where wp=w0, w0 being the l a s e r frequency. PROBLEMS 8 ‑ 2 1 . Checkt h a tt h er e l a t i o nbetween t h efrequencys h i f tA and t h es o l i t o n amplitude i nE q .[ 8 ‑ 1 5 4 ]i sr e a s o n a b l e by c a l c u l a t i n gt h e average d e n s i t y nw•. (Hinじ d e p r e s s i o ni nt h es o l i t o nandt h ecorrespondingaverage 仁hange i UseE q .[ 81 4 6 ]andassumet h a tt h es目: h2 f a c t o rh a sanaveragev a l u eo f=を overt h es o l i t o nw i d t h . ) A Langmuir‑waves o l i t o nw i t hanenvelopeamplitudeo f3 . 2V p e a k ‑ t o ュ peaki se x c i t e di na2eVplasmaw i t hn0 ニ I 0 1 5m 3 I ft h ee l e c t r o nwavesh a v e kλ 。ニ 0.3 ,五日 d ( a )t h ef u l lwidtha th a l fmaximumo ft h eenvelope( i nmm),( b ) t h enumbero fwavelengthsw i t h i nt h i sw i d t h ,and ( c )t h efrequencys h i f t( i n MHz)awayfromt h el i n e a r ‑ t h e o r yBohm‑Grossfrequen 仁y 8・22. 8 ‑ 2 3 . Ad e n s i t yc a v i t yi nt h eshapeo fasquarew e l li sc r e a t e di naone‑dimensional plasmaw i t hK1;二 3 eV.Thed e n s i t yo u t s i d et h ec a v i t yis '"'二 101,;m へ and t h a t i n s i d ei sn ,= 0 . 4ラ I 0 1 6m ' . I ft h ec a v i t yi slongenought h a tboundaryr e s o n a n c e s canbei g n o r e d ,whati st h ewavelengtho ft h es h o r t e s tele仁tron plasmawavet h a t canbetrappedi nt h ec a v i t y ? 寸 il -- AppendixA 111 U N I T S , CONSTANTS ANDFORMULAS VECTOR RELATIONS UNITS A .I Theformulasi nt h i sbooka r ew r i t t e ni nt h emksu n i t so ft h eI n t e r n a t i o n a l System ( S I ) .I n much o ft h er e s e a r c hl i t e r a t u r e , however, t h ec g s ュ Gaussiansystemi ss t i l lu s e d .Thef o l l o w i n gt a b l ecomparest h evacuum Maxwelle q u a t i o n s ,t h ef l u i de q u a t i o no fm o t i o n ,andt h ei d e a l i z e dOhm ’s lawi nt h etwos y s t e m s : mks・SI V キD = e(n , 一 n,} VラE= ‑B VキB=0 VXH=j+D D = εoE B= オ0H c g s ‑ G a u s s i a n Vキ E= 47Te (ηi ‑n,) cVxE=‑B VキB=O cVxB= 4 7 T j+E € =/ . l=1 mη 空= qn(E+v × B)一円 d t mn~ = qηl E+. !vxB I‑ Vp E+vxB=O E+‑vxB=O c d t ¥ c Theequationo fc o n t i n u i t yi st h esamei nboths y s t e m s . ム J 349 350 A p p e n d i xA I nt h eG a u s s i a ns y s t e m ,a l le l e c t r i c a lq u a n t i t i e sa r ei ne l e c t r o s t a t i c u n i t s( e s u )e x c e p tB ,whichi si ng a u s s( e m u ) ;t h ef a c t o r so fcarew r i t t e n e x p l i c i t l yt o accommodate t h i se x c e p t i o n .I nt h e mks s y s t e m ,B i s measuredi nt e s l a(Wb/m2),e a c ho fwhichi sworth1 0 4g a u s s .E l e c t r i c f i e l d sEa r ei nesu/cmi nc g sandV/minm k s .S i n c eonee s uo fp o t e n t i a l i s300V ,oneesu/cmi st h esamea s3ラ 1 0 4V/m.Ther a t i oo fE t oB i s d i m e n s i o n l e s si nt h eG a u s s i a ns y s t e m ,s ot h a tVE =c E /B .I nt h emks s y s t e m ,E/B h a st h ed i m e n s i o n so fav e l o c i t y ,s ot h a tVE =E/B .T hisf a c t i su s e f u lt okeepi nmindwhenc h e c k i n gt h ed i m e n s i o n so fv a r i o u sterms i nane q u a t i o ni nl o o k i n gf o ra l g e b r a i ce r r o r s . Thec u r r e n td e n s i t yj=nevh a st h esameformi nb o t hs y s t e m s .In cgs , πand v a r e 1・ n cm‑3 and c m / s e c , and e h a st h ev a l u e e= 4 . 8ラ 1 0 ‑ 1 0e s u ;t h e njcomeso u ti ne s u / c m 2 ,whe1e 1e s uo fc u r r e n t r ei nm‑ 3and e q u a l sc ‑ 1emuor1 0 / c= 1 / ( 3x1 0 9 )A.I nmks , ηand va a st h ev a l u ee= 1 . 6x1 0 ‑ 1 9C ;t h e njcomeso u ti nA/m2 m / s e c ,andeh Mostc g sf o r m u l a sc a nbec o n v e r t e dt omksbyr e p l a c i n gB/cbyB and4 1 Tbyε よ 1, wherel/41Tεo=9 × 109. Fori n s t a n c e ,e l e c t r i cf i e l denergy 2 / 8 1 Ti nc g sandε0£2/2 i nmks,andm a g n e t i cf i e l denergy d e n s i t yi sE d e n s i t yi sB2/81Ti nc g sandB2/2 µ,。 in mks.Herewehaveusedt h ef a c t t h a t(εoµ,o) 1 1 2=c=3x 吐 08 m / s e c . su s u a l l yg i v e ni ne l e c t r o nv o l t s .I nc g s ,onemust TheenergyK Ti c o n v e r tT.vtoe r g sbym u l t i p l y i n gby1 . 6ラ 1 0 ‑ 1 2e r g / e V .I nmks,one c o n v e r t s T.v to j o u l e s by m u l t i p l y i n gby 1 . 6x1 0 ‑ 1 9J / e V . This l a s t numberi s ,o fc o u r s e ,j u s tt h ec h a r g eei nmks,s i n c et h a ti showt h e e l e c t r o nv o l ti sd e f i n e d . (M/m)112 K 43 43 . 3 8x1 0 ‑ 1 6erg/。 K 0 ‑ 2 3J/oK 1 1 . 3 8ラ 1 Boltzmann’s c o n s t a n t eV e l e c t r o nv o l t 0 ‑ 1 9J 1 . 6ラ 1 01 2e r g 1 . 6X 1 1eVo ftemperatureK T 11,600。K 1 1600。K . 8 8x1 0 ‑ 2 0m2 すa5 c r o s ss e c t i o no fH atom 0 3 . 3x1 0 1 9m‑3 d e n s i t yo fn e u t r a latomsa t roomtemperatureand 1mTorrp r e s s u r e mks c g s v e l o c i t yo fl i g h t 3x1 0 8m/sec 3ラ 1 0 1 0cm/sec e e l e c t r o nc h a r g e 1 . 6x1 0 ‑ 1 9c 4 . 8x1 0 ‑ 1 0e s u m e l e c t r o nmass 0 . 9 1x1 0 ‑ 3 0kg 0 . 9 1x1 0 ‑ 2 7g M p r o t o nmass 1 . 6 7x1 0 ‑ 2 7kg 0 ‑ 2 4g 1 . 6 7ラ 1 1837 1837 c M/m 3 . 3X 1 0 1 3cm‑3 Wp plasmaf r e q u e n c y e l e c t r o nc y c l o t r o n f r e q u e n c y c g s ‑ G a u s s i a n (ん= 9000v ' ;sec‑i eB 労1 eB me -t石T戸') 1/2 74帆vi川 ( η川)'へ λD Debyel e n g t h (蛍 neL 丹) TL Larmorr a d i u s m v J . eB VA A l f v e nspeed v , VE a c o u s t i cspeed ( T ,=0 ) E xB d r i f tspeed Handyformula ( ni nc m ‑ 3 ) (手) C o n s t a n t s mks 0 . 8 8x1 0 ‑ 1 6cm2 Formulas αJc A.2 USEFULCONSTANTSANDFORMULAS C o n s t a n t s c g s mks 行iv ょC eB fc =2 . 8GHz/kG 14T ! 1 2 一一ーム mm(H) Bkc B B (µ,op )''宮 (41Tp )''宮 (予) (守) 1 0 6T ! ' 2cm( H ) vs e c E B cE B 108」(V/cm)~ B(G) s e c 2 . 2xI叩 Oげ11 !=叫 CαIπr s e c 3 5 1 U n i t s ,Conslaηts a n dF o r m u l a s , V e c t o rR e l a t i o n s 352 Formulas (AxB )・(C AppeηdixA mks i a m a g n e t i c Vo d d r i f tspeed β m a g n e t i c /plasma p r e s s u r e v , h ee l e c t r o nt h e r m a l speed KT π ’ eB n Handyformula cgs ” Gaussian nKT nKT F万五; E可否τ =(AキC)(BキD )一(A· D)(BキC ) (A × B)×( C × D) = (ABD)C (n ・mcm 3) cKTn ’ eB n × D) ー( ABC)D = (ACD)B ー(BCD)A V· (φA)=A·Vφ + φV·A 10'。" T.\ ー I B Rs e c Vx (φA)=VφXA + φV × A A x(VxB )=V(AキB )ー( A·V)B ー( B キ V)A‑Bx(VラA) (AキV)A=VdA2 )‑A x( VxA) (乎) (乎) 5 . 9x 1 0 7T~し勺一 err一l s e c V キ(AxB )=Bキ( VxA)‑Aキ(VxB ) Vx(AラB)=A(VキB)‑BVキA +( Bキ V)A ー(A·V)B v , . e l e c t r o n ‑ i o n c o l l i s i o nf r e c ; u e n c y ν目 2 10‑6Zπ. lnA ι, = x -τ戸吉7す- sec T.v Wp Z記ー一一ー No e l e c t r o n ‑ e l e c t r o n c o l l i s i o nfrequency =5xl0 ̲6nl nA V x[ ( Aキ V)A]=(Aキ V)(VラA)+(V VxV × で~sec A=V(V·A)ー(V A)(VxA)ー[(Vx A)キV]A V)A ̲1 V × Vφ = O z 4 ( i : j )( ~) o n ‑ i o nc o l l i s i o n V i i i f r e q u e n c y V キ( VxA)=0 1 1 . , ,z ) C y l i n d r i c a lCoordinates( r ,e λ" c o l l i s i o nmean f r e ep a t h V o , c peake l e c t r o n q u i v e rv e l o c i t y 13 ヴ 4 『! v = λ 回目 λ ii =3.4 × 10πlnA cm(H) eE。 eE。 mαJo ηzαJo V~c =7.3/19λ : a I 内向 \72φ =一γIτ0一 γ (予) γ + τ7 一 ae一言+ー azす 2 1a γ0γγδ e (1aA, VxA =一一一一 γδ6 A.3 USEFULVECTORRELATIONS Aキ( BxC )=Bキ( CxA)= C 1a V·A =一一 ( rA γ )+-- A8 c 2 2 V o , c=3 . 7/13λμ“ 一U方e‑ T.v a +‑A, a z .[ar ~)-r +一一- (aAr 芋) 9 +一一 1 a(rA θ )- 1 すlz a z T 内= (VキV)A=[¥72Ar‑?(Ar+2~)]r ・(AxB )呈(ABC) +[内一戸 (Ae -2 す)0 ]+v2A,z A x( BxC )=B(AキC)‑C(AキB) 一一一一一 一 一ー一回M・・』ー T 353 U n i t s ,C o n s t a n t s andFor市u/as, Vecto γ Relations 354 A p p e n d i xA ra s Iasγ aB, I ¥ (AキV)B=去( Ar --:;-:よ + AB - ー + A , 一一一一 A~8) ¥ a r ra B 8 a o AppendixB a z r キ ; Ia s . a s .I ¥ r a o a z r ra B , Ia s , aBλ +まi A , ー」 + A. 一一一 + A. 一一l ' aγV rao ‘ δz J ' +叫んー」 + AB ー」 + A ,~+- A~ ,) THEO悶F OF J WAVESINA COLDUNIFORM PLASMA Aslonga sT,= T ,= 0 ,t h ewavesd e s c r i b e di nChapter4cane a s i l ybe g e n e r a l i z e dt oana r b i t r a r ynumbero fchargedp a r t i c l es p e c i e sandan a r b i t r a r ya n g l eo fp r o p a g a t i o n} (r e l a t i v et ot h emagneticf i e l d .Waves ,sucha si o na c o u s t i cw a v e s ,a r en o ti n c l u d e di n t h a tdependon自nite T t h i st r e a t m e n t . F i r s t ,wed e f i n et h ed i e l e c t r i ct e n s o ro faplasmaa sf o l l o w s .The f o u r t hMaxwelle q u a t i o ni s VxB =µ.。(j + εoE) [ B ‑ 1 ] whereji st h eplasmac u r r e n tduet ot h emotiono ft h ev a r i o u scharged ,w i t hd e n s i t yn , ,chargeq , ,andv e l o c i t yv , : p a r t i c l es p e c i e ss j= L :n,q,v, [ B ‑ 2 ] Consideringt h eplasmat obead i e l e c t r i cw i t hi n t e r n a lc u r r e n t sj ,we mayw r i t eE q .[ B ‑ 1 ]a s VX B=オ , 0 D 一一一 • ---田島』 [ B ‑ 3 ] 3 5 5 …一 356 A 怜endix s ot h a t where B D = E0E+土 j [ B ‑ 4 ] αJ s j=<TキE ヤム Herewehaveassumedanexp(‑iwt)dependencef o ra l lplasmam o t i o n s . L e tt h ec u r r e n tjbep r o p o r t i o n a lto E butnotn e c e s s a r i l yi nt h esame e f i n ea d i r e c t i o n( b e c a u s eo ft h e magneticf i e l dB0z); we maythend h er e l a t i o n c o n d u c t i v i t ytensorσby t Usingt h ei d e n t i t i e s [B・ 5] E q .[B・4] becomes [ B ‑ 1 2 ] [ B ‑ 1 3 ] 土~寸=_!_ I ー丘一一 __!!l_l [ B ‑ 6 ] 1‑(w"Jw)' Thust h ee f f e c t i v ed i e l e c t r i cc o n s t a n to ft h eplasmai st h et e n s o r 定= E o ( I+i σI •ow) a v . 明s ー」= 。t q , ( E+v,× Bo) noq; αJp, 三言ー一一ーー +(三;;;::- ~) i E , ] [ B ‑ 8 ] ヰj, -~~~[(三;;;--:-~-~}Ex [ B ‑ 9 ] εom., v 日 v =一ー一 m,w z q , =ー一一一 戸市, w [Ex 土 i (w口/ w)E,] 。 I 一(ω口/ω )ヱ [E, 平 i (w口/ w)E,] 。 I 一 (w"/w ) 之 i q , ~ v , ,=ーーー-]!,~ = +(~+ヰ;)£,] ’[ B ・ lOa] [B ・ 15] 2 よ j, =-I 勾 E, ε 。(J) [B ・ 16] '(J) [B ・ lOb] Useo fE q .[ B ‑ 1 4 ]i nEq 目[ B-4] g i v e s [ B ‑ l O c ] 土 Dx =Ex ーさ[手 (~+~)Ex けら ω f o rt h es i g no fq,・ The plasmac u r r e n ti s j= Ino,q,v, [B ・ 14] S i m i l a r l y ,theyandzcomponentsa r e wecans e p a r a t eE q .[ B ‑ 8 ]i n t ox ,y ,andzcomponentsands o l v ef o rv , , o b t a i n i n g i q , ω 土 ω口 J ヰム=-~~三[(ゴ;;;::+~)Ex t h ec y c l o t r o nandplasmaf r e q u e n c i e sf o reachs p e c i e sa s 日|守| 2Lw 平 ω口 wecanw r i t eE q .[ B ‑ 1 2 ]a sf o l l o w s : [B・7] whereIi st h eu n i tt e n s o r . Toe v a l u a t eO', weu s et h el i n e a r i z e dAuide q u a t i o no fmotionf o r ,n e g l e c t i n gt h ec o l l i s i o nandp r e s s u r et e r m s : s p e c i e ss where 土 stands uη iform Plasm唱 ←一一一一一一一一言=ー l 一一一ーー+一一一一一 l l ー(ωロ/ wt 2Lw 平 ω白 ω 土 ω白 J D=•o(I +;;シ) キE= εE De品 ning 357 T h e o r yo fWaves iηa C o l d +予(三戸 -~) iE,] [ B ‑ 1 1 ] 一 [ B ‑ 1 7 ] 358 Wed e f i n et h econvenienta b b r e v i a t i o n s The n e x ts t e pi st os e p a r a t eE q .[ B ‑ 2 3 ]i n t o components, usingt h e elementso fεR g i v e ni nE q .[ B ‑ 2 0 ] .Thisprocedurer e a d i l yy i e l d s Append悶 B R =I L 一世(~) sαJ Is‑オ ・ D オ ・i I I I / ,2COS2 8 ‑i ,2 Si l8COS8 ¥ / E x ¥ R.E =I iD S 一 µ, 2 0 1 1E ,I=0 [B・25] ¥オ,2sin8cos8 0 P ー µ, 2s i n 2 ! 、 αJ コ= α'"ノ =I 弓手(五戸) S=~(R +L) 8¥ E J D =~(R ‑L) * [ B ‑ 1 8 ] Fromt h i si ti sc l e a rt h a tt h eE山 E, componentsa r ecoupledt oE,o n l y i foned e v i a t e sfromt h ep r i n c i p a la n g l e s8=0 ,9 0 ー . E q .[ B ‑ 2 5 ]i sas e to ft h r e es i m u l t a n e o u s ,homogeneouse q u a t i o n s ; t h ec o n d i t i o nf o rt h ee x i s t e n c eo fas o l u t i o ni st h a tt h edeterminanto f Rvanish:l l R l l= 0 .Expandingi nminors。f t h esecondcolumn,wethen o b t a i n P =1-I ラ Usingt h e s ei nE q .[ B ‑ 1 7 ] and proceedings i m i l a r l yw i t ht h ey andz components,weo b t a i n (iD)2(P 一 µ, 2s i n 28 ) ÷ (S 一 µ, 2 ) εo1Dx =SEx‑iDE, ε 01D, = iDEx+SE, ×[(S ‑オ ,2c o s 2B)(P 一 µ, 2s i n 2fJ ) 一 µ, 4s i n 2( )c o s 2f J ]=0 [ B ‑ 1 9 ] Byr e p l a c i n gc o s 2J fbyI‑s i n 28 ,wec ans o l v ef o rs i n 2( ) ,o b t a i n i n g ε 01D, =PE, Comparingw i t hE q .[ B ‑ 6 ] ,wes e et h a t IS ‑iD 0 ¥ ε = ε。 l iD S 0J =Eo匂 I0 0 Pl n ‑P(オ,4‑2Sオ,2+RL) s i nI J= 4 2 オ ,( S‑P)+µ, ζ (PS-RL) [ B ‑ 2 0 ] 2n S オ ,•ー (PS+ RL)オ,2+PRL c o sI J= 4 2 オ , (S‑P)+オ , (PS‑RL) VxE=‑:Bands u b s t i t u t i n gVxB =µ, 。ε ・ E, o b t a i n i n g キ E )=一戸 ER. E [ B ‑ 2 8 ] ト Dividingt h el a s ttwoe q u a t i o n s ,weo b t a i n [B・21] t a n( )= Assuminganexp( i kキ r )s p a t i a ldependenceo fEandd e f i n i n gav e c t o r indexo fr e f r a c t i o n オ=̲:̲k [ B ‑ 2 7 ] Wehaveusedt h ei d e n t i t y52‑D2=R L.S i m i l a r l y , もVe n e x td e r i v et h ewaveequationbyt a k i n gt h ec u r lo ft h ee q u a t i o n VxVxE =一μ。εo(正R [B・26] P ( オ ,4‑ 2 5 オ ,2+RL) , , 。 Sµ, 守一 (PS +RL )µ, ζ + PRL [ B ‑ 2 2 ] S i n c e25=R+L ,thenumeratoranddenominatorcanbefactoredt o g i v et h ec o l d ‑ p l a s m ad i s p e r s i o nr e l a t i o n [ B ‑ 2 3 ] P ( オ ,2‑ R ) ( オ ,2‑ L) t a n( )=‑ " " ( S オ , "‑RL)(オ,"‑P) αJ wecanw r i t eE q .[ B ‑ 2 1 ]a s μ ×( µXE )+ εR. E=0 Theuniformplasmai si s o t r o p i ci nt h ex‑yp l a n e ,s owemaychooset h e ya x i ss ot h a tん= 0 ,withoutl o s so fg e n e r a l i t y .I f8i st h ea n g l ebetween kandB 0 ,wethenhave ,s i n8 / 1 ‑ x=オ オ , ,=オ ,c o s8 オ , ,=0 [ B ‑ 2 9 ] Thep r i n c i p a lmodeso fChapter4canber e c o v e r ‑ e dbys e t t i n g ( )=0 ー and90。. When8=0 ー ,t h e r ea r et h r e er o o t s :P =0(Langmuirw a v e ) , オ ,2=R (Rw a v e ) ,andオ ,2=L ( Lw a v e ) .When8= 90。, there a r etwo r o o t s : オ ,2=RL/S( e x t r a o r d i n a r ywave)andオ,2=P ( o r d i n a r yw a v e ) .By i n s e r t i n gt h ed e f i n i t i o n so fE q .[ B ‑ 1 8 ] , onecan v e r i f yt h a tt h e s ea r e [B・24] *N o t et h a tD h e r es t a n d sf o r“ difference ” It 1 sn o tt h ed i s p l a c e m e n tv e c t o rD ーー圃~』ー 359 T h e o r yo fWaves i naC o l d UniformPlasma \ 360 Appeηd叫 B i d e n t i c a lt ot h ed i s p e r s i o nr e l a t i o n sg i v e ni nChapter4 ,w i t ht h ea d d i t i o n o nm o t i o n s . o fc o r r e c t i o n sduetoi Ther e s o n a n c e scanbefoundbyl e t t i n g オgot oc o .Wethenhave t a n 2Ores=‑P/S AppendixC SAMPLE THREE‑HOUR FINALEXAM [B・30] Thisshowst h a tt h eresonancef r e q u e n c i e sdependona n g l e0 .If()= O'。, t h ep o s s i b l es o l u t i o n sa r eP = 0andS = c o .Theformeri st h eplasma resonancew =wp,w h i l et h el a t t e ro c c u r swhene i t h e rR =co( e l e c t r o n o( i o nc y c l o t r o nr e s o n a n c e ) .I f0= 9 0 ー ,t h e c y c l o t r o nr e s o n a n c e )o rL = c p o s s i b l es o l u t i o n sa r eP = c oorS = 0 .Theformercannotoccurf o rf i n i t e ωρand w ,andt h el a t t e ry i e l d st h eupperandl o w e rh y b r i df r e q u e n c i e s , a sw e l la st h et w o ‑ i o nhybridfrequencywhent h e r ei smorethanone 1 0 ns p e c i e s . nE q .[ B ‑ 2 6 ] .Againu s i n g Thec u t o f f scanbefoundbys e t t i n g オ= 0i i n dt h a tt h ec o n d i t i o nf o rcuto狂 is independento f( ) : S2‑D2= RL,wef PRL= 0 [ B ‑ 3 1 ] i e l dt h eW R andw L c u t o f ff r e q u e n c i e s Thec o n d i t i o n sR = 0andL = 0y o fChapter4 ,w i t ht h ea d d i t i o no fi o nc o r r e c t i o n s .Thec o n d i t i o nP = 0 oc u t o f fa sw e l la st or e s o n a n c e .Thisdegeneracy i ss e e ntocorrespondt o rω = ωρ ) i s i sduet oourn e g l e c to fthermalm o t i o n s .A c t u a l l y ,P = 0( ar e s o n a n c ef o 1l o n g i t u d i n a lwavesandac u t o f ff o rt r a n s v e r s ew a v e s . The i n f o r m a t i o n contained i nE q .[ B ‑ 2 9 )i s summarized i nt h e Clemmow‑Mullaly‑Allisdiagram.Onef u r t h e rr e s u l t ,n o ti nt h ediagram, canbeo b t a i n e de a s i l yfromt h i sf o r m u l a t i o n .Themiddlel i n eo fE q . [ B ‑ 2 5 )r e a d s iDEx+(S 一 µ2)E, = 0 [ B ‑ 3 2 ] Thust h ep o l a r i z a t i o ni nt h eplaneperpendiculart oBoi sg i v e nby i E x オ2‑S E, D [ B ‑ 3 3 ] Fromt h i si ti se a s i l yseent h a twavesa r el i n e a r l yp o l a r i z e da tresonance PARTA (ONEHOUR, CLOSED BOOK) I . Thenumbero fe l e c t r o n si naDebyespheref o rη = 1 0 1 7m‑3,KT,= 1 0eVi sapproximately ( A ) 135 ( B ) 0 目 14 ( C )7 . 4ラ 1 0 3 . 7ラ 105 ( D )1 ( E )3 . 5x1010 2 . Thee l e c t r o nplasmafrequencyi naplasmao fd e n s i t yn = 1 0 2 0m‑3 (μ 宮= c o )andc i r c u l a r l yp o l a r i z e da tc u t o f f ( オ2= 0 ,R = 0o rL =O ;t h u s I S S = 土D). ( A ) 90MHz ( B ) 900MHz ( C ) 9GHz ( D ) 90GHz ( E ) Noneo ft h eabovet ow i t h i n10% 3 6 1 362 A怜endix C 3 . A doublychargedheliumn u c l e u so fenergy3 . 5MeVi namagnetic f i e l do f8T h a samaximumLarmorr a d i u so fapproximately 7 . Int h et o r u sshownonp .3 6 2 ,t o r s i o n a lAlfvenwavescanpropagate i nt h ed i r e c t i o n s ( A ) 2mm (A )土f ( B ) 2cm (B )土O ( C ) 20cm (C )土φ (D) 2 m (D) +0o n l y ( E ) 2f t ( E ) ‑0o n l y 4 . A laboratoryplasmawithη = 1 0 1 6m‑3,KT,=2eV,KT;=0 . 1eV, . 3T h a sab e t a( p l a s m apressure/magneticf i e l dp r e s s u r e ) andB = 0 o fapproximately ( A )1 0 ‑ 7 st e nt i m e s denser than plasma B but h a st h esame 8 . PlasmaA i e l a t i v et ot h a t temperatureandc o m p o s i t i o n .Ther e s i s t i v i t yo fA r o fBis ( A ) 100t i m e ss m a l l e r ( B )1 0 ‑ 6 ( B )1 0t i m e ss m a l l e r ( C )1 0 ‑ 4 ( C )a pproximatelyt h esame (D) 1 0 ‑ 2 (D) 1 0t i m e sl a r g e r ( E ) 1 01 ( E )1 00t i m e sl a r g e r 5 . Thegrad‑Bd r i f tv v 8i s l e c t r o nv e l o c i t yl v li na10‑keVMaxwellianplasmai s 9 . Theaver呂ge e ( A )a l w a y si nt h esamed i r e c t i o na sV E 0 2m/sec ( A ) 7ラ 1 ( B )a l w a y so p p o s i t et ov E 0 4m/sec ( B ) 7x1 ( C )s ometimesp a r a l l e lt oB ( C ) 7ラ 1 0 5m/sec (D) a l w a y so p p o s i t et ot h ec u r v a t u r ed r i f tv R ( D ) 7x1 0 6m/sec ( E )s ometimesp a r a l l e lt ot h ediamagneticd r i f tv0 6 .I nt h et o r o i d a lplasmashown,t h ediamagneticc u r r e n tf l o w smainly i nt h ed i r e c t i o n ( E ) 7x 1 0 7m/sec 1 0 . Whicho ft h ef o l l o w i n gw丑ves cannotpropagatewhenBo=O ? (A) +φ ( A )e l e c t r o nplasmawave (B )一φ ( B )t h eo r d i n a r ywave ( C ) +0 1θ ( C )A lfvenwave (D) ‑0 ( D )i o na c o u s t i cwave ( E ) +ま ( E ) Bohm‑Grosswave 363 SampleThree-Houγ F i n a lExam 一一一一一一ー→一一一一 一ーー一一ー『岨・司,ーー ( E ) vφopposite t ov g 12. “ Cutoff” and “ resonance ,” respectively, r e f e rt oc o n d i t i o n swhent h e d i e l e c t r i cc o n s t a n ti s ( A ) 0andco 1 6 .Thew h i s t l e rmodeh a sac i r c u l a rp o l a r i z a t i o nwhichi s ( A )c l o c k w i s el o o k i n gi nt h e+Bod i r e c t i o n ( B )c l o c k w i s el o o k i n gi nt h e‑B0d i r e c t i o n ( C )c o u n t e r c l o c k w i s el o o k i n gi nt h e+kd i r e c t i o n ( D )c o u n t e r c l o c k w i s el o o k i n gi nt h e‑kd i r e c t i o n ( E )b o t h ,s i n c et h ewavei sp l a n ep o l a r i z e d ( B ) coand0 ( C ) 0andl ( D ) land0 ( E )n o tc a l c u l a b l efromt h eplasmaapproximation 1 3 .Thel o w e randupperh y b r i df r e q u e n c i e sa r e ,r e s p e c t i v e l y , ( A ) (!1ρn,/12 and(ω同ん) 1 / 2 ( B ) (。;+ !1~) 112 and( w !+w~ ) 112 ( C )( w , ! 1 , ) 1 1 2and( w !+w~)1'2 1 7 .Thephasev e l o c i t yo fe l e c t r o m a g n e t i cwavesi naplasma ( A )i sa l w a y s>c ( B )i snever>c ( C )i ssometimes>c ( D )i salways ( E )i snever くC くC o tap o s s i b l ewayt oh e a tap l a s m a : 1 8 .Thef o l l o w i n gi sn ( D ) (w!‑w ; ) 1 1 2and(w!+w;)112 ( A )C y c l o t r o nr e s o n a n c eh e a t i n g ( E ) (wRwL)112and(ω凶') ( B )A d i a b a t i ccompression 1 4 .I naf u l l yi o n i z e dp l a s m a ,d i f f u s i o na c r o s sBism a i n l yduet o ( C ) Ohmich e a t i n g ( A )i o n ‑ i o nc o l l i s i o n s ( D )T r a n s i tt i m em a g n e t i cpumping ( B )e l e c t r o n ‑ e l e c t r o nc o l l i s i o n s ( E )N e o c l a s s i c a lt r a n s p o r t ( C )e l e c t r o n ‑ i o nc o l l i s i o n s 1 9 . Thef o l l o w i n gi sn o tap lasmaconfinementd e v i c e : ( D )t h r e e ‑ b o d yc o l l i s i o n s ( A )B a s e b a l lc o i l ( E ) plasmadiamagnetism ( B ) Diamagneticl o o p 1 5 . Ane x p o n e n t i a ld e n s i t ydecayw i t ht i m ei sc h a r a c t e r i s t i co f ( C )F i g u r e ‑ 8s t e l l a r a t o r ( A )f u l l yi o n i z e dp l a s m a sunderc l a s s i c a ld i f f u s i o n ( D )L e v i t a t e do c t o p o l e ( B )f u l l yi o n i z e dp l a s m a sunderr e c o m b i n a t i o n ( E ) Thetap i n c h MD 町 m nb 引 2 ( D ) V; =一九 34h ( C ) dw/dk く O U7 ( E )f u l l yi o n i z e dp l a s m a sw i t hb o t hdi征usion andr e c o m b i n a t i o n gt z ra z ( B ) w/k く O hμ - ( D )weaklyi o n i z e dp l a s m a sunderc l a s s i c a ld i f f u s i o n e ( A )ko p p o s i t et oBo ZF 打 ( C )w eaklyi o n i z e dp l a s m a sunderr e c o m b i n a t i o n m a 1 1 . A “ backward wave ” is onewhichh a s c u 364 AppendixC 司咽司司・・・F’ ’' 366 A 紳endix C 2 0 . Landaudamping r a t eo fd r i f twavesdependsonVn/n,s ot h a tt h ed i f f u s i o nc o e f f i c i e n t D̲ ,c ani t s e l fdependonVn.Takingag e n e r a lformf o rDょ in c y l i n ュ ( A )i scausedby“ resonant” particles d r i c a lg e o m e t r y ,n a m e l y , 4 . Whenanomalousd i f f u s i o ni scausedbyu n s t a b l eo s c i l l a t i o n s ,Fick’s lawo fd i f f u s i o ndoesnotn e c e s s a r i l yh o l d .Fori n s t a n c e ,t h egrowth hv + - よ守 ( b )I fKT,=1 0eV,B =0 . 2T,k ,=1c m ‑ 1 ,andn=1 0 2 1m‑3f i n dt h e r e q u i r e dv a l u eo fk zf o rt h i si n t e r a c t i o ni nahydrogenp l a s m a . Youmayassumenb/η。= 1cm‑1,wherenb= dno/dr・ -a q く U 出・ 、、isf’ n 一7 m/Mi se q u i v a l e n tt oVA q > γ ( a ) Showt h a tt h ec o n d i t i o nβ JI - n 3 . Whenβis l a r g e rthanm /M,therei sap o s s i b i l i t yo fc o u p l i n gbetween ad r i f twaveandanAlfvenwavet oproduceani n s t a b i l i t y .A n e c e s s a r y c o n d i t i o nf o rt h i st ohappeni st h a tt h e r ebesynchronismbetween t h ep a r a l l e lwavev e l o c i t i e so ft h etwowaves( a l o n gB0). η 2 .I n t e l l i g e n tb e i n g sonad i s t a n tp l a n e tt r yt ocommunicatew i t ht h e e a r t hbysendingpowerfulr a d i owavesswepti nfrequencyfrom I O t o50MHze v e r ym i n u t e .Thel i n e a r l yp o l a r i z e de m i s s i o n smustp a s s through a r a d i a t i o nb e l t plasmai n such away t h a tE and k a r e sfoundt h a tdurings o l a rf l a r e s( o nt h e i r p e r p e n d i c u l a rt o B0 ・ It i s u n ) ,f r e q u e n c i e s between 2 4 . 2 5and 28MHzdon o tg e tthrough t h e i rr a d i a t i o nb e l t .Fromt h i sdeducet h eplasmad e n s i t yandmagnetic f i e l dt h e r e .( H i n t :Dunotroundo庄 numbers t o oe a r l y . ) -一 o n s ,~no doubly 1 . Considerac o l dplasmacomposedo fn0hydrogeni i o n i z e dHei o n s ,and2n0e l e c t r o n s .Showt h a tt h e r ea r etwol o w e r ュ h y b r i df r e q u e n c i e sand g i v e an approximatee x p r e s s i o nf o re a c h . [ H i n t : You may u s et h e plasma a p p r o x i m a t i o n ,t h e assumption m/M < 1, andt h eformulasf o rv 1g i v e ni nt h et e x t .(Youneedn o t s o l v et h ee q u a t i o n so fmotiona g a i n ;j u s tu s et h eknowns o l u t i o n . ) ] 8 showt h a tt h et i m eb e h a v i o ro faplasmadecayingunderd i f f u s i o n f o l l o w st h ee q u a t i o n π 一t 列。-Rd PARTB (TWO HOURS, OPENBOOK; DO4 OUTOF5 ) 。 ( E )i st h er e s i d u eo fimaginarys i n g u l a r i t i e sl y i n gonas e m i c i r c l e , JE--、、 ( D )i samathematicalr e s u l twhichdoesn o toccuri nexperiment s r A よ ( C )n evero c c u r si nac o l l i s i o n l e s splasma 一一 D c c u r si nac o l l i s i o n l e s splasma ( B ) alw丑ys o Showa l s ot h a tt h eb e h a v i o ro fweaklyandf u l l yi o n i z e dplasmasi s r e c o v e r e di nt h eproperl i m i t s . 5 .I nsomesemiconductorssucha sg a l l i u ma r s e n i d e ,t h ec u r r e n t ‑ v o l t a g e r e l a t i o nl o o k sl i k et h i s : v Therei sar e g i o no fn e g a t i v er e s i s t a n c eo rm o b i l i t y .Supposeyouhad as u b s t a n c ew i t hn e g a t i v em o b i l i t yf o ra l lv a l u e so fc u r r e n t .Usingt h e e q u a t i o no fmotionf o rweaklyi o n i z e d plasmasw i t h K T =B = 0 , p l u st h eelec~ron c o n t i n u i t ye q u a t i o nandPoisson ’s e q u a t i o n ,perform t h eu s u a ll i n e a r i z e dwavea n a l y s i st oshowt h a tt h e r ei si n s t a b i l i t yf o r µ,, く 0. 367 S a m p l eThree‑How F i n a lEwm ~士士竺ーー← 宇山 台 '.キ. >"コペ~二三予 ··•·•··••·F-.'.)t 日一: . ::三二±て三三τて三c. 戸 γ:ニロJパ乙二. .·」...... <デ一一 三一 • u三L·•·· ジドァ工i INDEX .-\ccesS1bilit 、。 153, 3 9 8 ‘ Acoustic speed.351 A d i a b a t i ccompression ! 2 .49 .-\diabati《川、川 iants, 4 3 A l l v e nvelocit 、 P 1 3 8 ,3 ' > 1 .-\lfvt'n '、山e 1 3 6 energ 、 densit 、 of. I 』9 dampingo f .1 9 i ,4 0 . J s h e a r .HO <orsional, I . J O . ‑ ¥ m b i p o l a rd i f f u s i o n .1 5 9 ,1 7 2 Annihilationo fmagneticf i e l d ,206 Anomalousresisti 、 it 乞, 288 Antimatter 1 2 0 Appleton‑Hartreed i s p e r s i o nr e l a t i o n ,1 5 0 A r e c i b o .322 Aurorab o r e a l i s .I Avogadrosnumber,369 Bananad i f f u s i o n .1 9 4 Bananao r b i t ,1 9 4 6 4 ,2 6 6 ,4 0 7 Beam‑plasmain 日abilitv, 2 B e r n s t e i nw a v e s ,278 e l e c t r o n ,280 i o n ,282 n e u t r a l i z e d .281 B e s s e lf u n c t i o n ,1 6 4 .2 7 5 B e t a ,2 0 3 ,3 5 2 t BGKmode,2 6 1 h e a t h s ,2 9 2 Bohmcriterio1> for s Bohmc u r r e n t .2 9 6 Bohmd i f f u s i o n ,1 9 0 Bohm‑Grossw a v e s .8 8 .2 + 1 Bohmt i m e ,1 9 1 Boltヌ mann c o n s t a n t .4 3 . ?I Boltzmanne q u a t i o n ,230 Boltzmannr e l a t i o n ,7 5 Bouncef r e q u e n c y ,329 Bows h o c k ,e a n h ' s ,297 Bunemani n s t a b t ! i t y ,2 1 4 Caviton 3 3 1 ,3 4 4 Child-Lan耳muir l a w ,2 9 ‑ l 4 6 ,360 Clemmow‑Mullaly‑Allisdi旧日i am.1 CMAdiagram,3 6 0 C02l a s e r ,l l 8 Coldplasmad i s p e r s i o nr e l a t i o n ,359 C o l l e c t i v eb e h a v i o r ,1 1 C o l l t s i o nf r e q u e n c y e l e c t r o n ‑ e l e c t r o n ,352 e l e c t r o n ‑ i o n ,1 7 9 ,352 i o n ‑ i o n ,352 C o l l i s i o n s Coulomb,1 7 9 l i k ep a r t i c l e ,1 7 6 u n l i k e ‑ p a r t i c l e ,1 7 7 417 1 418 Inda Communicationsb l a c k o u t ,1 2 0 s u r f a c e s ,2 0 2 C o n t i n u i t y ,e q u a t i o no f ,5 6 C o n v e c t i v ec e l l s ,1 9 2 C o n v e c t i v ed e r i v a t i ¥ ' e ,5 8 Cosmicr a ya c c e l e r a t i o n ,3 5 Coulombb a r r i e r ,20 Coulombc o l ! i s 1 0 n s ,1 7 9 Coupledo s c i l l a t o r s ,309 Crabn e b u l a ,1 4 ,1 5 2 ,206 C r i t i c a ld e n s i t y ,1 2 0 C r o s s ‑ s e c t i o n d e 」 i m t i o n ,1 5 6 。f H a tom,3 5 1 momemumt r a n s f e r ,1 9 6 C u r v a t u r ed r i f t ,29 C u s p s ,4 5 C u t o f f .1 1 5 ,1 2 6 .3 6 0 ,3 9 9 l e f t ‑ h a n d ,1 2 7 r i g h thand,1 2 7 CutoHf r e q u e n c y ,1 2 7 C y c l o t r o nharmonics,2 7 4 C下clotron h e a t i n g ,1 4 4 C y c l o t r o ndamping,2 7 7 C y c l o t r o nf r e q u e n c y ,2 0 ,356 o fe l e c t r o n s ,8 5 ,3 . 1 1 Cylindrical 仁oordinates, 3 . 1 3 Cons 旧nt-p Dtbyelen耳 th, 1 0 ,3 . ;I Deb下e shieldin 宮, 8 Diamagneticwrrent,7 1 ,20I Diamagneticd r i f t ,69 守 352 D 旧 magnetic l o o p ,208 Diamagnetism,2 1 D i e l e c t r i cc o n s t a n t .8 7 ,1 3 8 l o w ‑ f r e q u e n c y ,5 7 D i e l e c t rl仁 tensor, 3 S S k i n e t i c ,2 7 6 D i f f u s i o n ,1 8 6 a c r o s sB ,1 6 9 am b i p o l a r ,1 8 7 a n o r n a l o u s ,1 7 4 Bohm.1 9 0 o fmagneticf i e l d ,2 0 5 nεoclassical, 1 9 4 D i f f u s i o nc o e f f i c i e n t ,1 5 8 amb i p o l a r ,1 6 0 B o h r n .1 9 0 c l a s s i c a l ,1 8 7 f u l l yio川町d, 1 7 1 parn川 ly i o n i z e d ,1 5 8 D i f f u s i o ne q u a t i o n ,1 8 8 D i f f u s 1 0 nmodes,1 6 2 D i s t r i b u t i o nf u n c t i o n ,2 2 1 Doublel a y e r ,305 DPmachine,3 0 3 Dnfti n s t a b i h t y ,218 D r i f twave,8 1 ,218 D‑Tr e a c t i o n ,1 4 Harmomcs.2 8 8 H a r r i si n s t a b i l i t y ,2 1 0 HCNl a s e r ,1 4 9 He‘ll f l o weqt口Hion, 2 ' 1 0 日明h-fl p l a S 1 n a ,205 Hydromagneticwav白, 136 Earth ’s magneticf i e l d ,46 r i f t ,2 3 ,6 9 ,3 5 1 EラBd E c h o e s ,plasma,3 2 4 E d d i e s ,289 E f f e c t i v em a s s ,1 6 E i n s t e i nr e l a t i o n ,1 . 1 8 E l e c t r o m a g n e t i cwaves,1 1 4 Ele< tron d町、ay i n s t a b i l i t y ,3 1 ' . l Ele仁 tron ・ neutral c o l l i s i o ncross -日ction, 1 9 6 Ele仁 tron t h e r m a l¥ ' e l o c i t y ,352 E l e c t r o n ‑ p l a s m aw a v e s ,8 7 ,2 4 4 k i n e t i cd i s p e r s i o nr e l a t i o n ,2 7 4 n o n l i n e a r ,336 Electron 、 olt, 6 ,3 5 1 E l e c t r o s t a t i ci o nc v c l o t r o nw a v e s .1 1 1 E l e c t r o s t a t i cp r o b e s ,2 9 5 Envelopes o h t o n ,3 3 1 .338 Equilibrium,200 E x t r a o r d i n a r yw a , キ e ,1 2 3 ‑ ! 2 8 .I ろ 3 ICRFh e a t i n g ,1 5 3 Impactp a r a m e t e r ,1 7 9 I n s t a b i l i t i e s c l a s s i f i c a t i o no f ,2 0 8 k i n e t i c ,210 s t r e a n 1 1n g ,209 u m v e r s a l ,210 v e l o c i t yspa 仁ι210 I n s t a b i l i t y beam‑plasma,2 1 キ ! Buneman.2 1 4 d r i f t ,218 e x p l o s i ¥ ' e ,1 9 9 g r a v i t a t i o n a l ,2 1 4 Han 目。 210 l o s sc o n e ,210 RayleighT a y l o r ,2 0 9 t w o ‑ s t r e a m ,2 1 1 l 1 n e r c h a n g ei n s r n b i l i t v ,2 1 5 1 71 2 1 ,1 3 6 I n t e r f e r o m e t e r ,mi仁 rowave, 1 I n v a r i a n c eo fj ,4 5 I n v a r i a n t a d i a b a t i c ,4 9 ] ,' 1 5 オ,3 2 ,4 2 ,4 4 < ! > ,49 l o d inel a s e r .3 2 3 Iona c o u s t i cs h o c k ,297 Iona c o u s t i cv e l o c i t y ,9 6 ,9 8 I o na c o u s t i cw a v e s ,9 5 .2 6 7 ,3 2 3 I o nc y c l o t r o nwaves e l e c t r o m a g n e t i c ,1 5 3 e l e c t r o s t a u c ,1 1 1 ,1 4 9 I o n t z a t i o nfun 仁 tion, : 6 5 I o n o s p h e r e ,1 4 I o n o s p h e r i cm o d i f i c a t i o n ,3 2 1 Ionp r o p u l s i o n ,1 5 Ionw a v e s ,9 5 k i n e t i cd i s p e r s i o nr e l a t i o n ,270 n o n l i n e a r ,3 3 1 Farad山 H》【ation, 1 3 31 3 5 ‑ 1 3 6 F a r ‑ i n f r a r e dl a s e r ,1 4 9 F i < : k ’s l a " "1 . 1 8 F i e l d ‑ e f f e c tt r a n s i s t o r ,1 7 Fmtte‑Larmor‑radiuseffe仁 t , 3 8 F l u i de q u a t i o n s ,6 7 d e r iv at iono l ,236 F l u t ei n s t J b i l i t v ,218 Fokker‑Plancke q u a t i o n ,2 3 4 Fried‑Contef u n c t i o n ,268 Gamma.6 7 Gasc h s c h a r g e s ,1 3 Gau 目 SJ a nu n t t s ,349 G引 ieralized O hm'sla 町, 186 G r a t l ‑ Bd r i f t ,2 7 ,2 8 ,7 3 G r a v i t a t i o n a ld r i f t .2 4 G r a v i t a t i o n a li n s t a b i l i t v ,2 1 4 growthr a t e ,218 Groupd i s p e r s i o n ,337 Groupvelo口 ty, 8 1 ,1 3 5 Guidingc e n t e r ,2 1 Gutdingc e n t e rd r i f t s ,4 3 Kadom 臼ev 】 Nedospasov i n s t a b i l i t y ,1 7 4 1 1 l• Matching, 3 Koneweg‑deVriese q u a t i o n ,3 3 1 Krookc o l l i s i o nt e r m ,2 3 4 H a l lc u r r e n t ,1 8 6 Handyf o r m u l a s ,3 5 1 一一一一一一一ーーーー-圃M・・・...-る .... 一一ー・ー Landaudampmg e l e c t r o n ,2 4 0 ,245 1 0 n ,2 6 7 ,271‑272 nonhnear,2 4 9 ,328 Langmuirふ p,r~bes, 2 95 Langmuir t o n ,346 Langmuirwave,9 4 e n e t g yd e n s i t yo f ,キ 1 4 9 Langmuir'sparadox,6 5 Larmorr a d i u s ,2 0 ,3 5 1 L a s e r C02,1 1 8 f a r ‑ m f r a r e d ,1 6 g a s ,1 6 HCN,1 4 9 L a s e rf u s i o n ,3 2 3 Lehner ト Hoh e x p e r i m e n t ,1 7 4 L i n e a rs o l e n o i d ,1 1 9 L i n e so ff o r c e ,2 7 f r e e z i n go fplasma,1 3 9 I nAf a c t o r ,1 8 1 Longitudinalw a v e s .d e f i n i t i o no f ,1 0 1 Looney‑Brownexpεriment, 89 Loschmidtnumber.7 ,3 ' ¥I ,369 Lossc o n e ,3 4 Lossconed i s t r i b u t i o n ,2 3 2 Lossconei n s t a b i l i t ¥ ' ,210 Lowerh y b r i dfrequenc下・ 113 Lowerhybndh e a t i n g ,l ' i 3 Lw ave,1 2 9 Machnumber,2 9 8 Magnettcf i e l d d t f f u s i o ni n t oplasma,205 e x c l u s i o no f ,2 0 5 spomaneous,1 3 4 ,207 Magneticm i r r o r ,3 0 ,203 Magneticmoment,3 1 ,3 2 ,5 6 如lagnetic p r e s s u r e ,2 0 4 Magnettcpumping,4 4 ,4 8 Magnetosonicvelocit、 .IH Magnetosonicw a v e s ,1 4 2 Magnetosphere,1 4 Malmberg斗,vharton e x p e r i m e n t .262 Maxwelhandistribu 口 on,4,226,229 q u a t i o n s ,5 4 Maxwell ’s e Meanf r e ep a t h ,1 5 7 e l e c t r o n ‑ 1 0 n ,1 9 5 ,352 MHDe n e r g yc o n v e r s 1 0 n ,1 5 MHDe q u a t i o n s ,1 8 4 Microwaves,1 1 7 Mirrorr a t i o ,3 4 419 I n d e x ーーー-,-← 420 I n d e x M o b i l i t y ,1 5 8 t r a n s v e r s e ,1 8 8 Modulationali n s t a b i l i t y ,2 8 9 ,3 3 0 ,3 3 7 ,338 N a v i e r ‑ S t o k e se q u a t i o n ,9 4 N e g a t i v ee n e r g yw a v e s ,2 6 1 N e g a t i v ei o n s ,1 2 1 ,1 5 1 N e o c l a s s i c a ld i f f u s 1 0 n ,1 9 4 Neutrons t a r s ,1 3 Nonlmearfrequencys h i f t ,337 NonlinearSchrodmgere q u a t i o n ,336 Non‑Maxwelliand i s t r i b u t i o n ,226 Ohmich e a t i n g ,1 8 2 .1 9 5 ,1 9 6 Ohm ’ s law,g町肥ralized, 1 8 6 Omega(w )ー matching, 310 Ordinarywave.1 2 2 dampingo f ,1 5 0 O s c i l l a t i n gv e l o c i t y ,352 P a r a l l e l .d e f i n i t i o no f .I O I P a r a m e t r i ch a c k s c a t t e r i n g ,313 P a r a m e t r i cd e c a yi n s t a b i l i t y ,3 1 3 ,3 1 7 ,320 P a r a m e t r i ci n s t a b t l i t i e s ,309 t h r e s h o l d .314 P a r t i a l l yi o n i z e dp l a s m a s ,1 5 5 P a r t i c l et r a j e c t o r i e s ,2 3 5 ,2 3 6 ,237 P e r p e n d i c u l a r ,d e f i n i t i o no f ,I O I Phasev e l o c i 1 y ,80 P h y s i c a lc o n s t a n t s .350 Plasmaapproximation,7 7 ,98 Plasma,d e f i n i t i o no f ,3 Plasmad i s p e r s i o nf u n c t i o n ,268 Plasmae c h o e s ,3 2 4 Plasmaf r e q u e n c y ,8 2 ,8 5 ,3 5 1 ,356 Plasmal e n s .1 1 9 Plasmao s c 1 l l a t i o n s ,240 dampingo f .94 Plasmap a r a m e t e r ,1 1 Plasmapond,1 4 8 Plasmat e m p e r a t u r e ,6 Plasmawav目, summary, 1 4 41 4 5 P o i s s o ne q u a t i o n ,9 P o l " r i z a t i o n ,1 3 0 ,1 3 4 ,360 P o l a r i i a t i o nc u r r e n t ,4 0 P o l a r i z a t i o nd r i f t ,4 0 ,49 Ponderomotivef o r c e ,3 0 5 ,307 P r e s h e a t h ,295 P r e s s u r e ,6 3 P r e s s u r et e n s o r ,6 1,6 4 P r o b e s ,e l e c t r o s t a t i c ,295 P r o f i l em o d i f i c a t i o n ,3 0 8 ,344 P u l s a r ,1 5 ,1 4 8 Pumpwave,310 Q司 machine, 7 0 ,1 0 0 ,1 1 2 ,1 9 0 Q u a r t e r ‑ c r i t i c a ll a y e r ,3 1 3 Q u a s i l i n e a re f f e c t ,2 8 8 Q u a s i n e u t r a h t y ,1 0 Quiverv e l o c i t y ,352 Temp目ature, 4 Thermalv e l o c i t y ,2 2 8 Th町 monuclear f u s i o n ,1 3 Thetap i n c h ,1 9 6 T r a n s v e r s e ,d e f i n i t i o no f ,1 0 1 Trappede l e c t r o n s ,2 3 5 Trapping,288 Trivelpiecト Gould w a v e s ,1 0 6 ‑ 1 0 9 pictwco f .86 Turningp o i n t ,46 Turbulence.2 8 8 ,289 Two,plasmondee町 instability, 3 1 3 Two-strean> instabilitv, 2 1l Radiocommumcauon,1 2 0 Radiot e l e s c o p e ,3 2 1 RandL w a v e s ,p o l a r i z a t i o n ,1 3 5 Randomw a l k ,1 7 2 Rayleigh‑Taylori n s t a b i l i t y ,2 0 9 ,215 Recombmauon r a d i a t i v e ,1 6 7 t h r e e ‑ b o d y ,1 6 7 Recombinationc o e f f i c i e n t ,1 6 7 R白:suve d r i f twave,2 1 8 ,222 R e s i s t i v i t y ,1 7 8 ,1 8 1 p a r a l l e l ,1 8 3 p e r p e n d i c u l a r ,1 8 3 Resonance,1 2 6 Resonancea n g l e ,3 6 0 Resonantp a r t i c l e s ,260 Runawaye l e c t r o n s ,1 8 2 Rwave,1 2 9 l : m v e r s a linstabili 日’, 210 Upperh y b r i df r e q u e n c y ,1 0 4 VanA l l e nb e l t sI ,1 4 ,3 4 ¥ ' a nKampenmode,2 6 1 421 V e c t o rr e l a u o n s ,3 5 2 a n a ly 1 . e r ,296 V e l o c i t ya v e r a g e ,l\lax 、vellian, 228 V e l o c i t y>pac7diagram.2 3 6 ,2 3 7 ,2 5 5 V i s c o s i t y ,6 4 ,6 5 c o l l i s i o n l e s s .6 4 m a g n e t i c ,6 4 ,6 5 V i s c o s i t yt e n s o r ,I i S V l a s o vequanon,233 Velo 口 ty I n d e x 2 8 8 in <eractions, 288 Wav白 in 1 ,c o l dplasma,3 5 5 Waves t e e p e n i n g ,302 Wave‑wavei n t e r a n i o n s .288 Weaklyi o n i z e dg a s e s ,1 5 5 n’ eibel instability.223 W h i s t l e rv . a v e s ,1 3 1 ,1 3 5 1ザavebreaking, Eγave-particle Z ‑ f u n c t i o n ,2 6 8 INDEXTOPROBLDIS Sagdeevp o t e n t i a l ,2 9 7 ,2 9 9 ,300 Sahae q u a t i o n ,I S e l f ‑ f o c u s i n g ,3 0 8 ,3 0 9 ,410 S h e a t h ,1 0 ,290 Sheathc r i t e r i o n ,2 9 2 Shockw a v e s .297 S 1 1 1 g l e ‑ f l u i de q u a t i o n ,1 8 4 Skind e p t h ,1 1 6 S o l a rc o r o n a ,1 4 S o l a rwind,I ,1 4 S o l i t o n ,2 9 9 ,3 0 0 ,3 3 3 .336 c o u p l e d ,3 4 ' 1 Soundw a v e s ,9 4 S p a c e c r a f tr e e n t r y ,1 2 1 Spacep h y s i c s .1 4 S p i t z e rr e s i s t i v l l y ,1 8 1 ,1 8 3 S t a t e ,equationo ( ,6 6 S t e l l a r a t o r ,1 9 2 S t i m u l a t e dB r i l l o u i ns c a t t e r i n g ,3 1 3 ,3 1 4 , 3 1 5 ,3 2 3 ,4 1 1 S t i m u l a t e dRamans c a t t e r i n g ,3 1 3 ,3 1 4 S t i xw a v e s ,1 5 3 S t r e s st e n s o r ,6 1 ,239 S u p e r ‑ A l f v e n i c ,1 5 2 S u p e r s o n i c ,1 5 2 S u s c e p t i b i l i t y e l e c t r i c ,56 m a g n e t i c ,56 、 t o1 ・ 2: 7 t o1 ‑ 7 : 1 3 I8t o1 ‑ 1 1 : 1 7 1・1 1 ・3 2It o27 : 25‑26 2 ‑ 8t o2 ‑ 1 2 : 34‑36 2 ‑ 1 3t o2 ‑ 2 1 : 4 9 ‑ 5 1 3It o32 : 5 8 3 ‑ 3t o3 ‑ 9 74 叩 75 4 ‑ 1 8 1 ト2 t o4-'I ー 唖ー・圃.._ 8 7 4 45t o4 ・6: 9 •l-7 t oキ 1 ‑ 8 : 1 0 7 ‑ 1 0 9 2 0 ‑ 1 2 1 4 ‑ 9t o•l-13: 1 4 ‑ 1 4t o4 ‑ 2 5 : 1 3 5 ‑ 1 3 6 4 ‑ 2 6t o4 ‑ 5 1 : 1 4 8 ‑ 1 . 5 4 5 ‑ 1t o5 ‑ 6 : 1 7 51 7 6 5 ‑ 7 t o 5 ‑ 1 8 : 1%‑197 6 ‑ 1t o6 ‑ 5 : 207‑208 66t o6 ‑ 9 : 214‑215 6 ‑ I O : 2 2 3 7‑ It o7 ‑ 6 : 2 6 3 ‑ 2 6 7 7・ 7 t o7I 0 : 2 7 3 ‑ 2 / . l 8It o8 ‑ 4 : 296‑297 8 ‑ 5 : 3 0 4 8 ‑ 6t o8 ・7 308‑309 8 ‑ 8t o8 ・ 1 I : 314‑315 8・ 12 t o8‑H: 323‑324 8 ‑ 1 5t o S ‑ 1 6 : 3 3 0 8 ‑ 1 7 : 3 3 4 8 ‑ 1 8 : 3 3 6 8 ‑ 1 91 08 ‑ 2 0 3 3 9 4 6 8 ‑ 2 1t o82 3 3