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Lawrence Livermore National Laboratory
Andrew G. MacPhee17th Topical Conference on High Temperature Plasma Diagnostics
Albuquerque,NM Wed 14th May 2008
UCRL-PRES-403581
Lawrence Livermore National Laboratory, P. O. Box 808, Livermore, CA 94551
This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344
Diagnostics for Fast Ignition Science
2Lawrence Livermore National Laboratory
Collaborators
F. Beg, T. Bartal, S. Chawla, T. Ma, J. King, J. Pasley, B. Westover, M.S. Wei
R. Stephens, K. Akli
L. D. Van Woerkom, R.R. Freeman, E. Chowdhury, D.W. Schumacher,D. Offermann, T. Link, V. Ovchinnikov
C. Chen, M. Porkolab, MIT, USA
Y.Y. Tsui, University of Alberta, Canada
J. Bonlie, R. Coombs, H. Chen, M. Foord, S. P. Hatchett, D. Hey, A.J. Kemp, M. H. Key, A. B. Langdon, B. F. Lasinski, A. J. Mackinnon, B. Maddox, N. Izumi, H-S. Park, P. K. Patel, T.H.Phillips, D. Price, M. Tabak, R. Town
3Lawrence Livermore National Laboratory
Density plot from 2D indirect drive fast ignition hydro design
~100m
For efficient burn with low driver energy 1.5 <R<2 gcm-2
For high gain with low driver energy 300 < < 500 gcm-3
Ignition 18 kJ in 23 ps , =36 m , 1.1x1020 Wcm-2
Laser intensity must reach several 1020 Wcm-2 in ~20ps
1) How efficiently can we couple 1-3 MeV electrons to the imploded plasma?
2) How much pre-formed plasma can we tolerate?
*M. Tabak, J. Hammer, M.E. Glinsky, et al, Phys. Plasmas 1, 1626 (1994); S. Atzeni, et. al, Phys. Plasmas 14, 052702 (2007)
Fast Ignition*: Initiate burn prior to peak compression with an intense beam of energetic electrons
Integrated experiments on Omega-EP, NIF-ARC and FIREX will use neutron yield and fluorescence from tracers to measure efficiency and transport
Short pulse experiments on Titan allow diagnostics development, pre-pulse evaluation and code benchmarking
4Lawrence Livermore National Laboratory
Scope of talk
On shot laser diagnostics at Titan
Electron energy deposition and transport
Measuring the hot electron spectrum
5Lawrence Livermore National Laboratory
On shot diagnostics are an essential record for modeling experiments
6m lens
150J 0.6ps, 1 from pulse compressor
Initial set-up microscope
Interferometer
2, 1ps, 10mJ probe beam
0 100 200 300 4000
100
200
300
400
500
600
700
y (
m)
x (m)
Full aperture retro-focus system
Pre-pulse monitor
`
`
Equivalent plane monitor
0 20 40 60 800
20
40
60
80
y (
m)
x (m)
6Lawrence Livermore National Laboratory
The pre-pulse monitor is vital for modeling laser target interaction
35 36 37 38 39 40 41 42 43 44 45-0.01
0
0.01
0.02
0.03
0.04
0.05Prepulse monitor:080123s2Ch1.txt
Time (NS)
Sign
al (V
)
80 81 82 83 84 85 86 87 88 89 90-0.01
0
0.01
0.02
0.03
0.04
0.05Prepulse monitor:080225s1Ch1.txt
Time (NS)
Sign
al (V
)
80 81 82 83 84 85 86 87 88 89 90-0.01
0
0.01
0.02
0.03
0.04
0.05Prepulse monitor:080225s2Ch1.txt
Time (NS)
Sign
al (V
)
80 81 82 83 84 85 86 87 88 89 90-0.01
0
0.01
0.02
0.03
0.04
0.05Prepulse monitor:080226s5Ch1.txt
Time (NS)
Sign
al (V
)
SF ~ 5 mJ Spike ~ 2.5 mJ
-3 ns
-0.1 ns
Time (ns)0 5-5
*Ying Tsui, University of Alberta
Min Typical Max
~3ns
superfluorescence
0.3mJ 5mJ 70mJ
~1ps pre-pulse 1mJ 2.5mJ 30mJ (at 1.4ns, <Feb)
Combined energy contrast vs main pulse
105 2x104 1.5x103
7Lawrence Livermore National Laboratory
Electron density from interferograms agree well with 2D hydro using pre-pulse data
0 100 200 300 4000
100
200
300
400
500
600
700
y (m
)
x (m)
150J, 2ps shot on 25m aluminum foil: 70 mJ SF + 30 mJ spike
0 50 100 150 200 250 30010
17
1018
1019
1020
1021
1022
1023
Aluminum: 100mjSuperFl+0mjPrePulse(green), 70mjSF+30mjPP(red); Probe080130s05(+)
Z (um)
XN
E (
cm-3
)
Ne (c
m-3)
(+) ne interferogram data(-------) ne simulation: 100 mJ SF only(-------) ne simulation: 70 mJ SF + 30 mJ spike
Density plateau due to spike
1017
1018
1019
1020
1021
1022
0 50 100 150 200 250Z(um)
Castor2 simulation with U of A EOS for Al:Interferogram:
Together, interferometry and pre-pulse measurements let us benchmark hydro codes
*Ying Tsui, U of A, ** Sebastian Le Pape LLNL
8Lawrence Livermore National Laboratory
There is good agreement between equivalent plane images for system shots and the low power alignment pulse
0 20 40 60 800
20
40
60
80
y (
m)
x (m)0 20 40 60 80
0
20
40
60
80
y (
m)
x (m)
System shot #02042408Low power (OPCPA) alignment pulse
20 40 60 80 1000.0
0.2
0.4
0.6
0.8
1.0
x(m)
20
40
60
80
100
In
ten
sit
y
y(
m)
Binned lineouts through both spots:
Full shot
1E17 1E18 1E19 1E20 1E210.0
0.2
0.4
0.6
0.8
1.0
Inte
gra
ted
po
wer
fra
ctio
n
Intensity (Wcm-2)
Fraction of power above given intensity:
50% >4x1019
20% >1020
Low power (scaled)
Full shotLow power (scaled)
9Lawrence Livermore National Laboratory
These experiments rely on k- fluorescence for measuring coupling efficiency and Bremsstrahlung spectra for measuring Thot
Thin front Al layer: No laser excitation of Cu k-
Titan Laser 150J, 0.6ps, ~1020Wcm-2
Thick rear Al layer: Electrons make only one pass through Cu tracer
Cu fluor layer:k- fluorescence measures hot electron yield
e-
e-
e- Bremsstrahlung + k-
10Lawrence Livermore National Laboratory
Multiple diagnostics on Titan are used to characterize energy deposition, conversion efficiency and the hot electron spectrum
K- crystal imager axis
Hot e- spatial distribution
XUV multilayer imager axis
Temperature map
Specular reflection Single hit CCD Calibrates…
Sig
nal (
Ph/
J/S
r/eV
)
Energy (keV)
…absolute K- yield from HOPG crystal spectrometer
0.1 1 100.01
0.1
1
dN
/dE
(E
lect
ron
s/M
eV
)
Electron energy (MeV)
Thot diagnostic
Long pulse beam introduces controlled pre-pulse
Main pulse ~140J 600fs~1020Wcm-2
11Lawrence Livermore National Laboratory
The reflection of laser light from oblique targets is important for coupling in cones*
K- image
Ray-trace
Laser bounce
*Tony Link, OSU, HELDA 2008
Grazing angle
Reflectivity (%)
Power on target (TW)
62 1.8 193
15 54 20
15 52 55
15 39 190 Cu foil target
Spectralon™ plate
Laser incident at angle to target surface
Image recorded on 16bit CCD
Laser light reflected from cone wall can provide usefulenergy at the tip
Reflection at 75º to normal ~20x reflection at 28º
S and P have similar reflectivity at 75º
f/3 incident beam scatters ~diffusely into a f/2 cone of rays
12Lawrence Livermore National Laboratory
XUV images measure the black body temperature at the rear surface of the target*
T e fro
m 2
56eV
cha
nnel
Te from 68eV channel
• Ultra intense laser-target interactions create MeV electrons
• Planckian emission from rear surface peaks in the XUV
• Temperature corresponds to Lasnex 2d rad. hydro run with matching integrated XUV signal within mirror bandwidth
• Used to constrain hybrid PIC codes
Filter
Laser: 1m, 150J0.6ps, ~1020Wcm-2
Back illuminatedCCD
Spherical XUV multilayer mirror
Plane XUVmirror
25m CD target image at 256eV Tight focus peak intensity 1020Wcm-2
*Tammy Ma, These proceedings (B15)
13Lawrence Livermore National Laboratory
A spherically bent crystal imager is used to measure the k- source size
• Crystal imager for Cu K- radiation: 5eV bandwidth, 10x magnification, 20m resolution => hot electron source size
• Line shift due to ionization of low Z Cu tracer limits crystal imager effectiveness for hot plasmas*
• For higher opacity integrated experiments a 16keV imager (Zr K-) is being developed that if successful will be less sensitive to line shift
Spherically bent quartz (211) 30m Cu foil, 500m x 500m ~5.1018 Wcm-2
500 m Cu foiltargetLaser
2d: 3.082Å, B @ n=2, 8.04keV=1.31°
J.A. Koch et al., Rev. Sci. Instrum. 74, 2130 (2003), *K.U. Akli, Phys. Plasmas 14, 023102 (2007),
Image plate or CCD
~60m FWHM
14Lawrence Livermore National Laboratory
10 20 30 40 50 600.0
0.2
0.4
0.6
0.8
1.0Zr K-
Tx
Energy (keV)
Mo filter Tx
Pd filter Tx
Ag K-
~12 m Agtarget
Laser
20m Pd
30m Mo
Image plate
6x6 Ta pinhole array
30m , 500m thk
PdFilter
MoFilter
• Contrast K / Brem: ~1.4• Signal to background: ~6:1• Absolute calibration is in progress0 100 200 300
0.0
0.1
0.2
0.3
0.4
0.5
0.6
Sig
nal
(p
sl)
x (m)
Pinhole limited width <30m
A pinhole camera with Ross pair filtering is insensitive to k- line shift in hot plasmas
15Lawrence Livermore National Laboratory
K- imaging and Lasnex modeling show pre-pulse in cones is a significant issue
15mJ2ns nc
300m1e18
5e21
60m
Density on axis
Lasnex hydro of pre-pulse plasma:
See also Sophie Baton, LULI, submitted to POP
~80% K-yield within 200m of tip
750 m
nc @ 60m
~80% deposited within 200m`
Cu K- image
Titan: 15mJ pre-pulse
4.5J300ps
1e22
1e15
2e19
300m
nc
80m
nc at 80m, ne ~1019 at 300mTitan: ~1J pre-pulse
nc @ 80m
<20% deposited within 200m`
<20% K- yield within 200m of tip
Anticipated NIF-ARC scale pre-pulse
Cu K- image
16Lawrence Livermore National Laboratory
A HOPG crystal spectrometer measures the absolute K- yield produced by hot electrons in the buried tracer layer
crystal
Image Plate
Direct Block
TCC
9758 eV
HOPG spectrometer
*K. Akli, GA, These proceedings
k- signal from HOPG normalized against single hit CCD averaged over several shots
Cu k- 8keV
Cu k- 8.9keV
17Lawrence Livermore National Laboratory
Single hit CCD provides absolute calibration for HOPG
~20% error in ccd efficiency CCD
~10% error in single event determination
Filter Tx × solid angle × CCD × Laser energy
k- event countsk yield =
Single events recorded at CCD plane
Histogram of single events
= X-ray spectrum
Zoom
Cu k-
k-
18Lawrence Livermore National Laboratory
An absolutely calibrated Bremsstrahlung spectrometer is used to measure the hot electron spectrum*
Dosimeters(Image Plates or TLD’s)
CollimatorElectron
Spectrometer
Pb + plastic housing
• Sensitive from 10-400keV X-rays• Vacuum electron spectrometer
removes charges particles from line of sight.
• Sensitive from 0.1-4 MeV electrons**
*R. Nolte et al, Rad. Prot. Dosim., (1999); C. Chen, These proceedings (B3)**H. Chen These proceedings (D37)
19Lawrence Livermore National Laboratory
Spectrometer Response matrix
(modeled: ITS)
Target Response matrix(modeled: ITS)
he- …
Al Ti Fe Cu
IP 1 IP 4
… Pb
… IP 13…
Recordedsignal
Deconvolvedelectron spectrum
inside target
The hot electron spectrum is deconvolved from the bremsstrahlung spectrum using the Monte Carlo code ITS*
30° full angle
8m diam.
source
Vary I, T minimize SD vs dosimeters TEeIEf /
*C. Chen, These proceedings (B3)
20Lawrence Livermore National Laboratory
A 1-T Boltzmann distribution provides a good fit to the measured data*
*C. Chen, These proceedings (B3)
100
1000
10000
100000
1 3 5 7 9 11 13
One temperature fit: (1.3±0.15) MeV
using ITS Monte Carlo model
8% conversion (~10J) to 1-3MeV electrons from ITS using Brem.
15% conversion to 1-3MeV electrons from ITS using absolute K- yield
Estimate based on K- yield is more sensitive to lower energy electrons
121J, 1020Wcm-2
Non-refluxing Cu foil target
Next step: 2 Temperature fit, hybrid PIC simulations to include
ohmic potentials, return currents, resistivity
conversion efficiency may drop
MeV
/mm
2
Dosimeter layer
21Lawrence Livermore National Laboratory
This 1 temperature analysis using ITS shows that Thot scales with intensity at a lower rate than suggested by pondermotive scaling
0
0.5
1
1.5
2
0 50 100 150I (10^18) W/ cm^2
Th
ot
(MeV
)
Ponderomotive scaling
Beg scaling
Bremsstrahlung data
Beg scaling:
Thot(MeV)= 0.1(I 2/(1017W/cm2m2))1/3
Pondermotive scaling:
Thot(MeV)= (I2/(1019W/cm2m2))1/2
22Lawrence Livermore National Laboratory
Summary
On shot laser diagnostics are crucial for benchmarking simulations:
• Interferometry agrees with 2D hydro for foil targets using the measured pre-pulse
• Equivalent Plane imaging demonstrates consistent intensity distribution between the Titan alignment beam and full system shots
The 1-T hot electron spectrum analysis shows less than pondermotive scaling
We need to include hybrid PIC simulations and a 2-T model to better understand both conversion efficiency and the electron energy spectrum
23Lawrence Livermore National Laboratory
Backup slides
24Lawrence Livermore National Laboratory
XUV spectroscopy measurements give a lower bound on black body imaging results*
45°
*Tammy Ma, These proceedings (B15)
Inte
nsi
ty r
atio
Front (plume)
Rear (surface)
Gold coated cylindrical mirror
Harada grating
CD Target
Measured line ratios agree with synthetic spectra at given T,
25Lawrence Livermore National Laboratory
. . .
92-1
00 M
eV
1-1.
1 ke
V
1389
-100
MeV
0-5
keV
92-100 MeV
1-1.1 keVC1,1C1,2
C1,3 ... C1,150
C2,1
C3,1
C13,1 C13,150 ... ... ...
...
...
...
C2,2
...
... ...
123
Energy per photon deposited in each IP
T1,1T1,2
T1,3 ... T1,80
T2,1
T3,1
T150,1 T150,80 ... ... ...
... ...
...
T2,2
...
... .... . .
Number of photons generated per e-
=××
Target response matrix: ITS150 photon energy bins × 80 electron energy bins
. . .. . .
Cannon response matrix: ITS13 Image Plate Layers
× 150 photon energy bins
Image plate signal:13 dosimeter readings
Electron spectrum:
80 electron energy bins
N1
N2
N3
N80
...
D1
D2
D3
D13
...
Vary I, T minimize SD vs dosimeters TEeIEf /
Bremsstrahlung analysis
26Lawrence Livermore National Laboratory
20 um Cu
25 um Cu
August conesApril cones
Low mass @ 28 deg
Low mass @ 75 deg
10 Al/30 Cu August
Al/Cu/Al August
1.00E+09
1.00E+10
1.00E+11
1.00E+12
1.00E+17 1.00E+18 1.00E+19 1.00E+20 1.00E+21
20 um Cu 25 um Cu August cones April cones
Low mass @ 28 deg Low mass @ 75 deg 10 Al/30 Cu August Al/Cu/Al August
multiple pass-refluxing
Cones have the highest yield
Single pass
Oblique incidence
*K. Akli, GA, These proceedings
Absolute yield depends on target and laser configuration
27Lawrence Livermore National Laboratory
Tight focus at tip
FocusDown-stream 800m
FocusDown-stream 400m
FocusUp-stream 400m
68eV XUV channel ~8keV Cu K- channel Ray-trace aberrated Titan beam
0 200 400 600 8000.000
0.002
0.004
0.006
0.008
Sig
na
l (P
SL
/J)
Distance Along Cone Axis (m)
~100m tight and 400m defocus k- peak
Best focus ~1.1MeV
800m defocus~0.25MeV
400m defocus~0.4MeV
nc at ~40m (from hydro)
~155m 800m defocus k- peak
XUV poster GP8.00065: Tammy Ma
Foil Cone:Thot: ~1MeV 1.1MeV
k- yield: 7x109 Ph/J/Sr 2.5x1010 Ph/J/Sr
Efficiency ~50%
~140m to tip
~200m to tip
~180m to tip
~180m to tip
XUV and K- imaging are used to measure coupling and transport in cones S Baton LULI, LVW OSU POP