Thomson-Scattering Study of the Coronal Plasma Conditions ...
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D. H. Froula et al.University of RochesterLaboratory for Laser Energetics
41st Annual Anomalous Absorption Conference
San Diego, CA19–24 June 2011
Thomson-Scattering Study of the Coronal Plasma Conditions in Direct-Drive Implosions
263.0
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262.50.0 0.4
Shot 59726 Shot 59727
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Wav
elen
gth
(n
m)
Time (ns)
The electron and ion temperatures measured with Thomson scattering show agreement with nonlocal simulations
E19915
• A robust direct-drive-ignition design will require accurate modeling of the underdense plasma to allow laser–plasma instabilities (LPI) mitigation
• Thomson scattering is used to validate our nonlocal hydrodynamic model in the coronal plasma – simulations agree well with electron and ion-temperature measurements made 400 nm from the initial target surface – simulations over-estimate the fluid velocity by 20%
• Future experiments will explore regimes closer to the critical surface
These are the first measurements of direct drive coronal conditions.
Summary
Collaborators
D. H. Edgell, W. Seka, I. V. Igumenshchev, P. B. Radha, and V. N. Gonchorov
University of RochesterLaboratory for Laser Energetics
J. S. Ross
Lawrence Livermore National Laboratory
Two primary laser–plasma instabilities are a concern for direct drive and require an understanding of the underdense hydrodynamics
E19921
A robust direct-drive-ignition design will require accurate modeling of the underdense plasma to allow LPI mitigation.
1.0
10.0
0.10.5 1.0 1.5 2.0 2.50.0
Ho
t el
ectr
on
en
ergy
(%
)
〈I〉Lc
Two-plasmon decay scales withhydrodynamic properties at ncr/4
230 Te
Rbeam/Rtarget
30
0
10
20
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2
0
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Sca
tter
ed e
ner
gy (
%)
vrm
s (%
)
No
min
al
Calculations suggest an optimumspot size where CBET is minimized
*L-I
keVW cm m
T230
2-
e
14 nc
^^ ^
hh h
G TL
ec\CBET
S. X. Hu, “Simulation and Analysis of Long Scale-Length Plasma Experiments at the Omega EP Laser Facility,” this conference.
W. Seka, “Reducing the Cross-Beam Energy Transfer in Direct-Drive Implosions Through Laser-Irradiation Control,” this conference.
*A. Simon et al., Phys. Fluids 26, 3107 (1983).
Thomson-scattering measurements were performed on direct-drive low-adiabat-implosion experiments
E19916
• 20 kJ of 351-nm light (59 beams) is used to drive a standard implosion
• Triple-picket pulse shape is designed for a low adiabat
• A 263-nm probe beam is used for Thomson scattering
• Scattered light is collected from a 60-nm × 75-nm × 75-nm volume 400 nm from the initial target surface
• Ion-acoustic waves propagating along the target radius are probed
ka = 2 k4~ sin(63/2) = 1.0 k4~
4~ probe TIM-6
TIM-6
k4~
63°
ks
ka
vflow
Nonlocal hydrodynamic simulation parameters in the coronal plasma
E19948
The initial Thomson scattering measurements are made 400 nm from the initial target surface.
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t = 1.85 ns t = 1.85 ns
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TS volume
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Ele
ctro
n t
emp
erat
ure
(ke
V)
Radius (mm)
1021
1022
10200.2 0.4 0.6
TS volume
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lect
ron
den
sity
(cm
3 )
Radius (mm)
Thomson scattering from the ion-acoustic waves in CH plasmas provides a measure of Te, Ti, Vf
E19917
263.0
263.5
262.50.0 0.4
Shot 59726
Time for plasma to propagate to scattering volume
(GvH ~ 430 nm/0.57 ns = 7.5 × 107 cm/s)
Direct reflection
Drive laserspulse shape
Ion-acousticfeatures
Plasma fluidvelocity
Shot 59727
0.8 1.2 1.6 2.0 2.4 2.8
Wav
elen
gth
(n
m)
Time (ns)
4
6
8
2
0–8 –6 –4 –2 0–10
Ps
(arb
. un
its)
TeTe
Wavelength shift (Å)
4~ probe beam
The electron temperature is determined from the wavelength separation in the ion-acoustic features
E19918
• The electron temperature is given by the wavelength separation of the ion-acoustic features
• The electron temperature is measured to within 20%
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Ps
(arb
itra
ry u
nit
s)
Wavelength shift (Å)
Te = 1.8 + 0.2 keVTe = 1.8 – 0.2 keVTe = 1.8 keV
–5 –4 –3 –2 –1 0
Wavelength shift (Å)
t = 1.85 nsTeTe
The measured electron and ion temperatures are in good agreement with nonlocal hydrodynamic modeling
E19919
• Late-time temperature discrepancies indicate anomalous absorption
• Simulations over estimate the flow velocity by 20%
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Ele
ctro
n t
emp
erat
ure
(ke
V)
Time (ns)
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1
2
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8
1.0
Te
Ti
1.5 2.0 2.5 3.00.5
Flo
w V
elo
city
(×
107
cm/s
)
Time (ns)
4~ light reflected from the target probes plasma properties at the ncr/4 surface
E19922
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Time (ns)
4~ Thomson scattering, shot 59726
Target
300 nm
200 nm
4~ light is reflected from
the ncr/4 surface
30 nmThomsonscattering
Turning-pointreflection
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elen
gth
(n
m)
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300 m
30 m200 m
-II
exp2
10-0
210.
n
n
n=
^f
hp> H
The wavelength shift and absorption of light propagating through the turning point is modeled
E19920
–2
0
2
0.0
Hydrodynamic simulation (nonlocal model)
Measurement
Calculation
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Wav
elen
gth
(Å
)
Time (ns)
–2
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Wav
elen
gth
(Å
)
Many of the main features are reproduced by the simulations, but late-time discrepancies indicate over-estimated flow
E19920a
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Measured
Calculations
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Time (ns)
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Wav
elen
gth
(Å
)
–1
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Time (ns)
0
1
2
0.0
Scattered light provides information about the hydrodynamic properties at the ncr/4 surface.
The electron and ion temperatures measured with Thomson scattering show agreement with nonlocal simulations
E19915
• A robust direct-drive-ignition design will require accurate modeling of the underdense plasma to allow laser–plasma instabilities (LPI) mitigation
• Thomson scattering is used to validate our nonlocal hydrodynamic model in the coronal plasma – simulations agree well with electron and ion-temperature measurements made 400 nm from the initial target surface – simulations over-estimate the fluid velocity by 20%
• Future experiments will explore regimes closer to the critical surface
These are the first measurements of direct drive coronal conditions.
Summary/Conclusions
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