Atomic collisions in fusion
plasma physics
An introduction to the course Atomic Physics
in Fusion, ED2235
Henric Bergsåker 26 Oct 2011
Atomic collisions in fusion
• Atomic collisions and plasma performance
Plasma resistivity and ohmic heating
Radiative cooling
Transport
Collisions in edge plasma physics
Ion implantation and backscattering at surfaces
Sputtering at surfaces
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Diagnostics involving atomic collisions
Types of collisions
Classical mechanics vs Quantum mechanics
Key quantities
Course outline and schedule
Plasma resistivity
The plasma resistivity is due to elastic collisions
me1/ 2 e2 ln 
s  0.51 2
3/ 2
3 0 (2 Te )
E J
  s
2
n
Z
 j j
j
n Z
j
j
j
 s Z eff
P   j
2
Radiation losses
Ploss   LZ ne nz
Z
In a low density plasma the charge
state distribution and radiating power
density depends on electron impact
ionisation and excitation.
Plots: Y. Ding, Master thesis KTH 2008
Transport and collisions
Classical diffusion
Neoclassical diffusion
D
D
2
c
q2  2
 3/ 2  c
Parallel transport on open field lines
is important for impurity control with
a divertor. Impurities created in the
divertor are confined there by the
collisional friction drag by the majority
ion flow towards the divertor plates.
Backscattering at surfaces
Upper: H -> C
W.Eckstein et al.
Lower: C -> C
H. Bergsåker et al.
Ion implantation
W. Eckstein et al. 2005
Physical sputtering
Upper: few collisions view, J. Bohdansky.
Lower: Monte-Carlo (TRIM), W Eckstein et al.
Modelling of deposition in
castellation gaps.
Experiments in TEXTOR
A. Litnovsky et al. , PSI San Diego
X-ray tomography
m/n=1 mode behaviour during
sawtooth activity in the HT-7
tokamak.
T.P. Ma et al. Phys. Lett.
A361(2007)136.
Neutral particle analysis
The central ion temperature
can be measured by neutral particle
analysis.
M. Bagatin et al. Fus. Eng. Design
25(1995)425.
Charge exchange spectroscopy
Studies of fully stripped O
following
H0+O8+ -> H++(O7+)*
R.C. Isler et al.
Nucl Inst. Meth. B9(1985)673.
Charge exchange spectroscopy
Fast CXRS in JT-60U.
Measurements of Ti and grad Ti
using a line in the C5+ spectrum
After H0+C6+ -> H++(C5+)*
M. Yoshida et al. Fus. Eng. Des.
2009 in press.
Impurity and H flux from emission
spectroscopy
The images show hydrocarbon
emission from the divertor region
of DIII-D.
In principle the flux density of
neutrals entering the plasma can
be measured spatially resolved in
this way.
M. Groth et al. J.Nucl.Mater
363-365(2007)157.
Atomic beam edge diagnostics
Observation of three lines in neutral He.
The intensity ratios give both Te and ne
B. Schweer et al. J.Nucl.Mater. 266269(1999)673.
Important types of collisions
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•
•
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e H e H
H  AH  A
Elastic collision
e  H  e  H  h
Bremsstrahlung
HA H A
 h
Electron impact ionisation e  H (1s)  e  e  H
e  H (i )  e  H ( f )
Electron impact excitation
Radiative recombination
e  H  H  h
A
 h
Dielectronic recombination e  A  A
Charge transfer
H H H H
HA H A
 h



q

( q 1) 

q


( q 1) **
( q 1) *
q

( q 1) 
Classical vs Quantum mechanics
Intended learning outcomes
Having completed the course you should be able to:
• Recall definitions of basic concepts in atomic physics and the size of
key atomic quantities
• Apply methods of wave mechanics and classical
mechanics&electrodynamics to problems in atomic physics
• Explain the significance of different approximations when estimating
atomic quantities
• Predict the general behaviour of fusion relevant atomic physics
quantities based on dominating physical mechanisms
• Construct simple numerical or analytic models of fusion plasma
phenomena with input from atomic physics databases
• Present and discuss fusion related atomic physics material, both in
writing and orally
Schedule
Tentative schedule
sem = seminar room 1419, Teknikringen 31
kosm= kosmos, top floor
Henric Bergsåker, henricb@kth.se, 08-7906094, 073 9850300
Examination
• Five assignments, solving problems and
discussing fusion plasma physics issues
involving atomic physics (50%)
• Presentations (10%)
• Final written examination: basic facts,
solving problems, discuss the physics
(40%)