LA-UR-
04-7M
Approved for public release;
distribution is unlimited.
Title:
Gas-filled hohlraum experiments at the National Ignition
Facility
_-
2
Author(s) : J . C Fernandez
.
, C. Gautier, S . Robe rt Goldman ,G . G rimm ,
B . M . Hegelich , J . Kline, D. Montgomery, N . Lanier, H .
Rose , D. Schmidt, D. Swift and J . Workman - LANL
Sharon Alvarez , Dan Bower , D. Braun , K. Campbell , E.
DeWald , S. Glenzer ,J . Holder , Jim Kamperschroer , Joe
Kimbrough , Bob Kirkwood , O. Landen , Tom McCarv i lle , B .
MacGowan , A. MacKinnon , C. Niemann , J . Schei n, M .
Subm itted to:
46th Annual Meeting of the Divis ion of Plasma Physics
November 15-19 , 200 4
Savannah , GA
o Los Alamos
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Form 836 (8/00)
Gas-filled hohlrau m
experiments at th e
National Igniti o n Facility
Presented by : Juan C . Fernandez
Los Alamos National Laboratory
Collaborators :
C . Gautier , S . Robert Goldman ,
Grimm , B . M . Hegelich , J . Kline ,
Montgomery , N . Lanier , H . Rose ,
Schmidt , D . Swift and J . Workman
Los Alamos National Laboratory
Sharon Alvarez, Dan Bower, D . Braun, K . Campbell, E . DeWald, S . Glenzer, J .
Holder, Jim Kamperschroer, Joe Kimbrough, Bob Kirkwood, O . Landen, Tom
McCarville, B . MacGowan, A . MacKinnon, C . Niemann, J . Schein, M . Schneider,
Phil Watts, B . Young
Lawrence Livermore National Laboratory
APS DPP Conferen c e , Savannah , GA , Nov . 15 , 2004
phw"' i ~ ~ ~' ard physics division
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Outline :
Motivation : purpose of hohlraum developmen t
Experimental conditions : laser pulse, target geometry & gas-fill specie s
LPI Expectations based on Nova backscattering result s
Wall motion predictions and measurement s
LPI diagnostics
LPI and radiation temperature result s
Plasma conditions and predicted LPI gain s
Summary
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Initial LANL gas - filled hohlraum campaigns on NIF ~
support the national ignition program .
1
• Experiments support two campaigns that rely on long-pulse drive :
- Beryllium Ablator Micro-Structure (BAMS) characterizatio n
- Laser-plasma instabilities (LPI) characterization & mitigatio n
BAMS hohlraum design requirements :
- Shaped , long-pulse x-ray drive -* high Raleigh-Taylor growth
- Low , constant early drive ( " foot ") to control melt of driven sample
- High laser coupling efficiency -> high peak driv e
- High spatial uniformity of the driv e
S
LPI hohlraum design requirements for ignition-relevant experiments :
- Relevant dimensionless plasma parameters , especially at peakdrive (kkp '- 0 . 2 - 0 . 5 for SRS & SBS , n e/nc 0 .05 - 0 . 1, ioni c
composition , T / Te - 0 . 3 - 0 . 5 , etc .
- Long scale lengths , quasi-homogeneou s
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These shots used a high-contrast shaped laser pulse ~
M
suitable for future ablator -characterization experiments .
•
•
Four overlapped beams (Quad) were used .
Foot power is 0 .06TW, peak power is 7 TW, contrast ratio is 117 .
Kudos to NIF fps for repeatedly matching the request so well .
N040914-002-999 : 3 . 52 kJ lA L Pulse i n One Beamlin e
2000
1800
1600
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The NIF shots had a C0 2 gas fill (high SBS and low SRS
predicted ), or C3-18 (high SRS and low SBS predicted) .
•
, •
~
C02 : Pressures were 1 .02 & 1 .03 Atm, ---> neln, = 6 .2%, kk p = 0 .48 for
plasma waves (SRS, assuming peak Te = 2 .75 keV) .
C3H8 :Pressures were 1 .04 & 1 .07 Atm, -* ne/n~ = 7 .4 & 7 .7%, kkp =
0 .44 & 0 .42 for plasma waves (SRS, peak Te = 2 .75 keV) .
Calculated view s
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NIF target
viewer
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MST
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SBS backscattering from Nova quasi -homogeneous plasmas
is very non linear & highly dependent on acoustic damping .*
SBS and SRS are anti-correlated as damping of acoustic waves is varied .
LA RGE G A S-F I LLED HOHLR A U M S, f/4, RP P
30
■
% .
A
• C 5H12 ♦ C5D12 ■ CF4
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• 80% CF4 + 20% CSH12
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* Fernandez etal., PRL 77 (1996) 2702 ; Phys. Plasmas 4 (1997) 1849 ; Phys. Plasmas 7 (2000) 3743 .
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Gated images of X-ray self-emission are qualitatively
consistent with calculated hohlraum Au-wall motion .
Simulatio n
C31-18 gas fil l
> 10 keV x-rays @
peak pulse
No self-focusing
Au-g~
Interface
', .-----shot-roe 409Z*- Safi----- .
C3 Ha gas fil l
> 10 keV x- rays @
aser
lase r
0
Simulation
with self focusing
C31-18 gas fil l
> 10 keV x-rays @
peak puls e
Nk
------- ~trot~4~2~~r ------ ♦
----------- Goz ga s 4m --------> 10 keV x -rays @
peak puls e
,~
laser
LASNEX
simulatio n
5e20 electron
density @
peak pulse
1e2 1
1 .5e21
Edge of detector stri p
s
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Jcfport c :\My DocumentslPresentationslConferenceslaps0411
, .
The NIF optical diagnostics are used to measure the
back-scattered light from SRS and SBS .
•
The FABS diagnosti c
measures direct backscattered light into beam s
- Spectrally resolve d
- Time resolved
1
Viewing camera s
& calibration laser (NBI )
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Camera FOV
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,
The Near Back-scatterin g
Imaging (NBI) diagnosti c
measures back-scattered
light out to - f / 2 . 5
-Filtered to separate
SBS & SRS
- Time integrated : assume
same history as in FAB S
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2x2 mz scatter
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Jcfpo rt c:\My Documents l Presentatio n s l Conferences laps0411
SBS reflectivity was very high and very reproducible on ~ •
`
all shots , regardless of the gas -fill species .
Example : Shot N040924-002-99, with a C3H8 gas fil l
- Expected SBS reflectivity - 1 %
•
Reflectivity : 8% in FABS + 17% in NBI + 7% inter-beam = 32% .
NBI FAB S
fabs_g31 b_SbS-040924-002-999 .tif
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Jcfpo rt c :\My Documentsl Presentations l Conferences l aps041 1
SRS reflectivity was very low and very reproducible on
all shots , regardless of the gas -fill species .
, ~
`
•
Example : Shot N040924-002-99, with a C3H8 gas fill
- Expected SRS reflectivity - 25 %
•
Reflectivity : -0 .3% in FABS + 0 .5% in NBI + 0 .2% inter-beam = 1 % .
NBI
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The laser-power reflectivity is very high , seriously
degrading the peak radiation temperature .
Example : Shot N040924-002-99 ,
with a C3H8 gas fil l
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troMe pegin s
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Another simulation with 33% lower
laser energy reproduces the peak
radiation temperature observed .
T~M
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Jcfport c :1 My Documents l P resentationsl Conferencesl aps041 1
Hohlraum plasma conditions at 6 ns yield high SBS
linear convective gain .
Electron density (1020 cm-3 )
8
4
2
20 GF=1 .8X108
15 in gas fil l
c
0
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LEH j gas es-- ; --* Au
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wavelength (nm )
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Summary :
► ~
• We have fielded on N I F a gas-filled hohlraum designed for future
ignition experiments .
•
Wall-motion measurements are consistent with LASNEX simulations .
• LPI back-scattering results have confounded expectations :
- Stimulated Brillouin (SBS) dominates Raman (SRS) for any gas-fil l
species .
- Measured SBS time-averaged reflectivity values are high, pea k
values are even higher .
- SRS and SBS peak while laser-pulse is rising .
• Plasma conditions at the onset of high back-scattering yield high SB S
convective linear gain .
- Wavelengths of the back-scattered light is predicted by linea r
theory .
Phv1Ci --
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