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ICFT/P2006-054
PERSISTENT SURVEILLANCE FORPIPELINE PROTECTION AND THREAT INTERDICTION
9th International Fast Ignition WorkshopCambridge, MA
3 November 2006
Designing and Fabricating a Proton Beam Source Suitable for Fast
Ignition Targets
Richard B. Stephens General Atomics
ICFT/P2006-054
P.PatelM. Roth et al
ICFT/P2006-054
Contributors from a large collaboration
M Mauldin, E Giraldez,C Shearer
M Foord, A J MacKinnon, P Patel, R A Snavely, S C Wilks,
K Akli, F Beg, S Chen, H-K Chung, D J Clark, K Fournier, R R Freeman, J S Green, C D Gregory, P-M Gu, G Gregori, H Habara, S P Hatchett, D Hey, K Highbarger, J M Hill, J A King, R Kodama, J A Koch, K L Lancaster, C D Murphy,, H Nakamura, M Nakatsutsumi, P A Norreys, N Patel, J Pasley , H-S Park, C Stoeckl, M Storm, M Tabak, M Tampo, W Theobold, K Tanaka, R Town, M S Wei, L van Woerkom, R Weber, T Yabuuchi, B Zhang
•This work is from a US Fusion Energy Program Concept Exploration collaboration between LLNL, General Atomics, UC Davis, Ohio State and UCSD
•International collaborations at RAL have enabled the experiments
•Synergy with an LLNL ‘Short Pulse’ S&T Initiative has helped the work
ICFT/P2006-054
Proton ignition concept has evolved
• Initial concept avoided complexity– External focusing surface– Simple proton transport
• Velocity spread cause problems– Energy must be delivered in short time
• Simple solutions …– Reduce energy spread (M. Hegelich, LANL)
Reduce separation
• Introduce new problems Protection from the imploding shell
25
10
20
30
40
50
60
70
00 5 10 15 20
Tp (MeV)
Eig (
kJ)
d = 4 mm
d = 2 mm
d = 1 mm
Roth et al., Phys. Rev. Lett. 86, 436 (2001)
Atzeni et al., Nucl Fusion 42, L1 (2002)
ICFT/P2006-054
Use a reentrant cone for protection
Laser
Protects proton source from coronal plasma
Limits accelerating surface
Causes focusing edge effects
Scatters proton beam
ICFT/P2006-054
Tested concept by making prototype
• Cone dimensions same as for electrons– 30° full cone opening
• Focusing surface same as for hemi tests(existing focal length data)
– rc= 170 m
– dfocus ~290 m
Limits accelerating area (125 m dia)
• Target Cu foil - 32 m thick (29 mg/cm2)– Stops < 4 MeV protons
ICFT/P2006-054
Proton source area depends on energy
• Accelerating electrons cool off as they travel to the edge
Hybrid PIC LSP simulation
M. Foord - LLNL
100 fs, 50 m FWHM Gaussian beam 45 J beam
Patel et al., Phys. Rev. Lett. 91, 125004 (2003)
200 m dia includes most useful protons (flat foil data)
Our source will have limited energy output
ICFT/P2006-054
Low energy protons are most important to ignition
t [ps]
Temporal et al., Phys of Plasma 9 3098 (2002)
45 65 85 105 125
100
200
300
10
20
30
40
Pro
ton
En
ergy
[M
eV]
Pow
er [
TW
]
Fusion Emission
Proton Deposition
Useful for
ignition
Protons must deliver energy in short time for ignition
limits useful proton energy range
Sim parameters: Proton spectrum: Tp = 3 MeV, dn/desqrt()e-
/Tp
Total proton energy = 26 kJ Proton beam radius = 10 m
Source distance = 4 mmTarget density = 400 g/cc
ICFT/P2006-054
Protons are not easily scattered
• Scattering angle E-
2
3 Mev Protons ~ 5° 15 Mev Protons ~ 1°
• Broadens spot 5-10 m
15°
5 m Au
1-5°
200 m
The cone tip can be far from the compressed core
End wall scattering is insignificant
ICFT/P2006-054
Prototype proton focusing cone was constructed
Construction is feasible
ICFT/P2006-054
Kimager
600 650 700 750 800 850 900 950 1000
-1000
-500
0
500
( . .)Intensity a u
160 m
0
500
1000
1500
2000
2500
7.8 8 8.2 8.4 8.6 8.8 9 9.2
Energy (KeV)
back surface
front surface
K
Kβ
HOPG
Initial tests show moderate proton focusing and heating
ICFT/P2006-054
Proton heating is reasonable for conditions
• Ratio of HOPG intensities gives slope temp 1-4 MeV for protons
• K spots have 106 counts - to be compared to equivalent shots using full hemi
• Focal spot is rather large - 160 m– Could be consequence of side walls
changing the proton focus.
ICFT/P2006-054
Measure focus changes by radiographing grids
• Send proton beam through grid and detect with RCF stack
• Magnification determines focus position, fuzziness of grid shows focus size, number of grids show source area
• These experiments are in preparation
Put grids in flat washers for simpler construction
ICFT/P2006-054
ICFT/P2006-054
Hi-Z mix?
more compact?
improve eff’y?
Conversion to protons, focusing/ heating?
Blob R ~ 0.44 g cm-2
<> ~ 120 g cm-3
<T> ~ 0.4 keVTotal Energy in blob ~ 0.6 kJ
Backlit radiograph (8 keV) at imploded max R
457
µm
40 µm
CD2vacuum
PW laser55* beams,pulse-shape“26”
Omega EP hydro simulations (S. Hatchett)
• What is signature of heating, increased emission? Ka fluorescence? X-ray scattering? neutron production? Abs spectroscopy?
Will use data to design integrated experiments for Omega EP
ICFT/P2006-054
• The proton focal spot radius reduces as laser focal spot increases
50 um spot
z=50 m 55 m 60 m
10 um spotz=50 m (long axis) 55 m 60 m
• Trade-off between fully illuminating surface, and building edge effect
Laser spot size influences proton focus
ICFT/P2006-054
Tight laser spot gives ‘aberrated’ proton focus
X-
20m heated spot
PW laser
Laser
Proton heating
Cu K image
Gekko PW data
320 m Al shell
Protons
X-ray phc image Cu Kimage
X-ray phc image
Cu Kimage
RAL PW
data