Review of Fast Ignition
HEDLP Workshop
Washington
Michael H. Key
Lawrence Livermore National Laboratory
August 25 to 27, 2008
Work performed under the auspices of the U.S. Department of Energy by
the University of California, Lawrence Livermore National Laboratory under
Contract No. W-7405-ENG-48.
UCRL-PRES-
Acknowledgements
K. Akli2, F. Beg5, R. Betti6, D. S. Clark1, S. N. Chen5, R.R. Freeman2,3
S Hansen1,S.P. Hatchett1, D. Hey2, J.A. King2, A. J. Kemp1, B.F. Lasinski1
B.Langdon1,T. Ma5, A.J. MacKinnon1, D. Meyerhofer10, P.K. Patel1, J. Pasley5
R.B. Stephens4, C. Stoeckl6, M. Foord1, M. Tabak1, W. Theobald6, M. Storm6
R.P.J. Town1, S.C. Wilks1, L. VanWoerkom3, M.S. Wei5, R. Weber3, B. Zhang2
1Lawrence
2Department
Livermore National Laboratory, Livermore, CA 94550, USA
of Applied Sciences, University of California Davis, CA 95616, USA
3Ohio
State University, Columbus Ohio, 43210 USA
4General
5
Atomics, San Diego, CA, 92186, USA
University of California, San Diego, San Diego, CA, 92186, USA
6Laboratory
of Laser Energetics, University of Rochester, NY, USA
Special thanks for advice and information :
Mike Dunne, Wolfgang Theobald, Javier Honrubia, Hiroshi Azechi,
Riccardo Betti
Outline
•Concept of FI
•Ignition requirements and gain
•Cone coupled electron FI
•Channel electron FI
•Proton and mid Z ion ignition
•Major integrated experiments
•Summary
Fast Ignition is ICF with separate compression and ignition drivers
Hole boring
for laser to
penetrate
close Light
to
pressure
densebores
fuel hole in
coronal
plasma
Laser
Hole boring
Ignition
10010
kJ,kJ,
2010psps
• Laser hole boring and
heating by laser generated
electrons was the first FI
concept
• 1MeV electron range
matched to ignition hot
spot
1 MeV electrons
heat DT fuel to
10 keV 300 g/cc
Pre-compressed
fuel 300 gcm-3
• Absorption of intense laser
light produces forward
directed electrons
• e-beam temperature =
ponderomotive potential
Fast ignition
M Tabak, S Wilks et al. Phys. Plasmas1,1626, (1994)
Several modeling studies have confirmed that FI offers
high gain at low driver energy
2D simulations of
ignition and burn
by 15kJ, 2MeV,
20µm, 15ps e-beam
Gain
e.g. R. Betti, A.A. Solodov, J.A. Delettrez, C. Zhou, Phys. Plasmas 13, 100703 (2006)
Maximum FI gain
at 300g/cc
200
150
200kJ PW
100kJ PW
100
50
0
0.5
1
1.5
2
Driver Energy (MJ)
>100x gain with 500kJ driver is attractive for IFE
2.5
The cone coupled FI concept provides a clear path for the laser
with the electron source close to the ignition spot
<rR>DT=2.2 g cm-2
Laser
Au cone
100mm
S Hatchett et al. - 30th Anom. Abs. Conf. Maryland, May 2000
Radiation - hydro simulations are well developed for ICF
and allow hydro--design optimization for FI
The first cone coupled fast ignition experiment at the Gekko
laser in Japan gave very encouraging results
Gekko “Cone” implosion
Implosion
beams
• 1000x increased DD neutrons
R Kodama et.al. Nature 412(2001)798
and 418(2002)933.
30%
coupling
0.5 PW
laser
15%
coupling
• 0.5PW ignitor beam gave ≈ 20% energy coupling to imploded CD
SP Laser
50 mm
Outstanding question for FI is
What coupling is the efficiency
at ignition scale ?
The energy required in the ignition hot spot and the optimum
electron energy are well established
S. Atzeni, Phys. Plas. 8, 3316 (1999)
M Tabak et al Fus. Sci. Tech. (2006)
Optimal ignition criteria:
T = 12keV, rR = 0.6 g/cm2
Eign
Fast Ignition region
r
E
2r
DT
z
t
1.85


r
 140 
kJ
3 
100 g /cm 
For r = 300 g/cm3 assembly
we need to deliver to the fuel:
E = 18kJ in <2MeV> electrons
P = 0.9 PW
=> t = 20ps
I = 6.8x1019 W/cm2 => r = 20mm
• Coupling efficiency depends on:
– laser conversion to electrons
– energy spectrum of electrons
– collimation of electron transport
– cone tip to dense plasma separation
Maximizing coupling efficiency at full scale is the
overall design challenge in FI
Hybrid PIC coupled to hydro-modeling predicts the electron
transport and electron coupling efficiency to the ignition spot
300kJ drive 1D fuel
With B field 43 kJ
No B field 115 kJ
A A Solodov et al. ( preprint of publication )
The focusing effect of azimuthal B from dB/dt= curl(E)
increases transport efficiency by factor >2.5x
Increased source divergence and distance to fuel increase the
ignition energy - reduction by B field collimation is robust
Coupling of electron
source to ignition hot
spot can be > 50%
efficient for typical
beam divergence and
transport distance
J Honrubia and J Meyer ter Vehn EPS Plasma Conf 2008
Cold target experiments at <1PW show typically 40o cone
angle of electron transport
600
500
Spot diameter, µm
180 mm
RAL
100J,0.8 ps
40ocone
400
LULI
20J,0.5 ps
300
200
2500
RAL data
5000
7500 10000 12500
0905xray03
Cone angle 40o
Min radius 37 mm
100
0
0
100
200
300
400
thickness, µm
AlAlthickness
micron
R Stephens et al. Phys Rev E,69, 066414, ( 2004)
500
Al
20 mm
Cu
20mm
New warm plasma experiments are planned using long pulse beams
to prepare plasma ( A Mackinnon talk to follow )
Recent 2D PIC modeling predicts a cooler two temperature
electron source and 30 to 35% conversion to electrons
Chrisman ,
Sentoku
and Kemp
PoP, 2008
Cool component is from light pressure steepened interface
and hot component from critical density shelf
A Kemp et al. PRL 2008
H Sakagami et al. FIW 2008
Possibility of optimizing Thot and absorption efficiency
using low density foam layer to tailor the density profile
Coupling efficiency and effective Thot inferred from Ohmic
potential limited transport in cone- wire targets at Vulcan PW
256 XUV
1mm 10 mm
500 µm
•Sensitivity to pre-pulse and cone wall thickness
measured at Titan
M Key et al Proc IFSA 2005 and J King et al PoP ( submitted)
Electron source studies with the Titan laser also point to
eletron temperature < ponderomotive potential
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
•Hybrid PIC modeling of K data gives conversion efficiency
•Thot analysis using focal spot power fraction v intensity
• Bremsstrahlung data consistent with CSK PIC modeling
More in talk by R Stephens to follow
Point designs require simultaneous optimizing of many aspects of
the hot electron generation, electron transport and hydrodynamics
Near 1-D isochoric implosions to
minimize low density high
temperature hotspot at center
Minimize high-Z cone
material in fuel
Cone tip
survival
clear path
for laser
Compressed fuel
Minimize transport
distance from cone to fuel
Cone
The cone tip hydro problem is very challenging at full scale because at fixed
separation of tip and ignition spot the pressure is much higher relative to
smaller scale e.g. Gekko experiment
1D target designs for direct-drive FI use massive wetted
foam shells insensitive to fluid instability
25 kJ Omega Scale
40 mm
90 mm
298 mm
rR3g/cm2
rR1.9g/cm2
rR0.7g/cm2
<r>300-500g/cm3
R. Betti and C. Zhou, Phys. Plasmas 12, 110702 (2005)
CH implosions with low adiabat were tested on OMEGA
EL20kJ
P25-34atm 1.3 V2•107cm/s
D-3He fusion proton energy loss measured the high rR
D2
or
D3He
a.u.
Secondary proton
spectrum
measured
predicted
0
5
10
15
Energy (MeV)
• Peak rR is 0.26g/cm,2 the highest rR to date on OMEGA
• Empty shells would achieve rR0.7g/cm2
C. Zhou, W. Theobald, R. Betti, P.B. Radha, V. Smalyuk, C.K.Li et al, PRL2008
NIF can drive full scale FI targets using 650kJ indirect drive
and ID designs for CD and DT are being developed
Be
DT
Be
Trad (eV)
1235 µm
1139 µm
1087 µm
1070 µm
870 µm
density (g/cm3)
Be (0.9%) Cu
10-6g/cm3
DT
time (ns)
radius
Small hotspot rr ~ 2 g/cm2
•Peak power: 70TW
Hydro tests with Be/CD
targets on NIF
will begin in 2010
•Pulse length: 32 ns
•Max blue energy: 650kJ
•Contrast ratio: 35:1
More in talk by D Clark to follow
•Peak Trad = 210eV
Destruction of cone tip by hydro jet and entrainment of ablated high z
cone in to fuel are important design issues
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Stoeckl C. et al., Phys. Plasmas 14 112702 (2007)
CH tamped cone
Nagatomo et al PoP 2007
Direct ignition by the main PW pulse ( super-penetration ) is
an option being considered thro’ modeling and experiment
•
1D hydro- modeling has
established the density profile
Nc/4
•
PIC modeling has shown the main
pulse penetrating beyond critical
density with relativistic self
focusing Y Sentoku et al . Fus
Sci Tech,49,278,(2006)
•
Excessive Thot is a problem which
could be mitigated with a shorter
wavelength
Nc 1gcm-3
1mm
•Nc to >1 gcm-3 requires >200mm penetration -not modeled
•Shorter wavelength would allow penetration closer to the ignition region
There is however no self consistent point design for ignition
The original channeling and hole boring scheme using a prepulse is being studied in the Omega EP project
• 2D PIC modeling has shown channel production up to critical
density in a plasma of full FI scale.
1019 Wcm-2 hole
boring in 1 mm scale
sub criticaL density
plasma
C Ren FIW (2006)
• Lacks modeling to show channel extension by hole boring to bring
the laser close enough to the ignition region (requires ~200 mm hole
boring to few gcm-3)
• The propagation of the main pulse in the channel has not been
modeled
• Shorter wavelength makes channel to higher density
There is so far no point design for high gain
Ion fast ignition by protons or carbon ions offers alternatives
with some attractive features
•Light pressure and
BOA for C ions NEW
J Fernandez et al.
Proc IFSA 2007 and
talk to follow
•TNSA for protons
M Key et al Fus Sci Tech 2006
J Honrubia EPS Plasma Conf 2008
A conceptual design for proton fast ignition illustrates the issues
•Cone maintains vacuum region for proton
plasma jet formation and protects surface of
proton source foil
Laser
•Scattering limits thickness of cone tip
and separation from fuel
Laser 100kJ,3 ps
1020 Wcm-2
Proton
heating
50kJ electrons
200mm
kT=3 MeV
•DT fuel at 500g/cc
•60 mm ignition spot
(same as electron
ignition)
Cu K image
20 kJ protons
kT= 3 MeV
XUV
•Radially uniform proton plasma jet
required for smallest focal spot
PW laser
•Proton source foil protects
rear surface from pre-pulse
-thickness limits conv. efficiency
Requirements based on Ignition
with protons :
Atzeni et al .Nucl Fus 42,(2002)
Modeling of focusing suggests that FI requirements can be met
with open geometry ( cone enclosed study ongoing )
10 mm Au,1mm H , Thot 3 MeV , 47% conversion to protons >3MeV
80% of energy at >3MeV can be delivered to 60 mm focal
spot from an f/1 segment of a 300 mm radius spherical shell
Hybrid PIC modeling by M Foord LLNL using LSP code
Good electron to proton conversion efficiency with no depletion
are predicted for thin Au targets with a hydride layer
Proton conversion efficiency (%)
Hydrides
Thot=880keV
5 mm Au + 1000Ѓ ZH
B
H
Z
C
40
Electron to Proton eff.
n
H
35%
ErH3
30%
30
CH
4
20
CH
2
CH
10
0
More in talk by
M Foord to follow
H
LiH
CH
n
MgH CaH CsH ErH
2
ZH
2
3
UH
3
n
Hybrid PIC modeling by M Foord LLNL using LSP code
Definitive integrated Fast Ignition experiments will be
performed with facilities soon to come on line
Omega
EP
PETAL
LIL
FIREX I
NIF ARC
Quad
NIF FI
high gain
HIPER
Schedule
d
Fall 2008
2009-2010
2009-2010
2011
?
?
?
Long
pulse(kJ)
25
60
10
800
800
200
50
Short
pulse(kJ)
2.6 / beam
5.2 max
3.5
10
10
60 1w?
100 2w?
50
Scaled
hydro rR
0.2
?
0.15
2
2 to 3
2 to 3
2 to 3
Density
g/cc
300
?
150
300-500
300-500
300-500
300-500
Hole
boring
Y
?
Y
Cone
guided
Y
Y
Y
Y
5keV
Y
Near
ignition
High gain
Firex II
?
Y
Y
Y
>100
>100
>100
More in talks by W Theobald and A MacKinnon to follow
The high gain and low driver energy and possibility of two
opposed narrow cones of laser beams are attractive for IFE
Pure fusion
and also
fusion fission
hybrids
burning
nuclear
waste,
are possible
I-LIFT (Japan), Hiper (Europe), LIFE (LLNL ) are examples
of study of FI power plant concepts
HED Science and IFE relevance of Fast Ignition ( FI )
•Fast ignition requires extremely high energy density
10keV, 300 to 500 g/cc in (40 mm)3
•FI uses ignition methods (laser generated electron and ion beams)
that can heat any material isochorically (using inertial confinement)
to multi- keV temperature .
•Thermonuclear burn creates still higher energy density
FI cone targets will allow HED science using precise exposure
of matter to extreme energy density and radiation and particle fluxes
•The underlying science of FI is that of more general HED science
•FI is an outstanding example of an application of HED science
•FI has significant advantages for an IFE power plant
( lower driver energy ,higher gain, better laser beam geometry )
•The potential and prospects of FI have led to major investments
worldwide
Scientific challenges and opportunities
•Validated modeling and control of the source characteristics
of laser generated relativistic electrons ( <E>=<2MeV>, >30% conversion )
at FI relevant laser parameters ( >1020 Wcm-2 , ~100kJ, <20 ps )
•Validated modeling and control of transport of electron energy to
ignition spot - (magnetic collimation > 50% electron coupling efficiency )
•Advanced hydrodynamic design meeting multiple constraints for
FI point designs e.g. optimizing implosion around a cone tip
- designing targets for IFE with laser beams restricted to two cones
•Developing >10% efficient ion acceleration concepts to meet FI
requirements ( e.g TNSA , light pressure and BOA concepts )
•Validated modeling and control of the focusing of laser generated
ion beams to meet FI requirements ( 40 micron focal spot )
•Novel HED science using thermonuclear burn
Anticipated technical advances and opportunities
•Better integrated codes ( PIC, hybrid PIC, rad-hydro)benchmarked by experiments - improved target point designs
•Next generation large scale integrated experiments
using point designs ( Omega EP , FirexI , Petal and NIF ARC Quad )
•High gain FI using adapted or new laser facilities
(adapted NIF or LMJ, Firex II , Hiper )
•HED science applications of FI thermonuclear burn
•IFE power plant concepts
( pure fusion and hybrid fission fusion )
•Laser technology for rep rated FI
•Low cost high volume target fabrication and injection
•IFE demo and IFE power production