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Channeling in the Corona of Fast Ignition Targets
G. Li, R. Yan, and C. Ren, UR/LLET. Wang, J. Tonge, and W. B. Mori, UCLA
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• Two ways of avoiding loss in corona– Using attached-cone targets– Using a channeling pulse
• Key questions– What are the channeling
speeds?• Density- and intensity-scalings
– Where does the pulse energy go?
• Absorption vs reflection
channeling/hole-boring pulse
ignition pulse
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Channeling in 1000-m plasmas is simulated for different laser intensities
• Previous PIC simulations on channeling used 100-m plasmas
• We are doing PIC simulations with 1000-m plasmas =1 m, I= 1018-20 W/cm2, W0=14 - 40 m, t~10 ps– Plasma density rises from 0 to 1 nc in ~ 1000 m
exponentially • ~exp( x/430 m)• Mi/me=4590 (DT), Ti=Te= 1 keV
• Two types of simulations in 2D– Two separate density region (0.1 - 0.3 nc & 0.3 -1 nc, 10
particles/cell)– Single region (0.1 - 1 nc, 1 particle/cell)
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• Previously I=1019 W/cm2 runs illustrated basic channeling process– Channel bifurcation and self-correction
– Vc is significantly slower than Vg of linear waves
• Since we have examined 1018 and 1020 W/cm2 cases– laser energy tracking (absorption vs reflection)
– density- and intensity-scalings of Vc
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Ion density plot (n0=0.3-1 nc), I=1020 W/cm2, ~6.4 ps
25
0
m
500 m
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50
m
500 m
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Ion density plot (n0=0.3-1 nc), I=1018 W/cm2, ~9.2 ps
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x1
n c
Density at channel center
Define channel as n<nr
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1019 W/cm2
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0.32 0.36 0.4 0.44 0.48 0.52 0.56 0.6 0.64
n_0 / n_c
V_c / c
Simulation 0.2LinearWilksSimulation 0.1Simulation 0.05
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• Longitudinal advancing involves many highly nonlinear processes
– Plasma piling-up– Laser hosing/channel bending– Channel bifurcation– Channel smoothing (self-correcting)
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1018 W/cm21020 W/cm2
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0.52 0.56 0.6 0.64 0.68 0.72 0.76 0.8 0.84 0.88 0.92 0.96 1
n_0/n_c
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Simulation 0.2LinearWilksSimulation 0.1Simulation 0.05
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n_0/n_c
V_c/c
Simulation 0.2LinearpodermotiveSimulation 0.1
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0 5000 10000 15000time (0.53 fs)
fraction of pulse energy
electron absorption rateion absorption rateE3&B2 E1&E2&B1&B3Reflected
Without channeling, most of pulse energy would be absorbed by electrons
1018 W/cm2
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time (fs)
fraction of pulse energy
electron absorption rateion absorption rateE3&B2 E1&E2&B1&B3Reflected
1020 W/cm2
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• Find the optimized intensity for channeling– Density- and intensity-scalings of Vc
– Ignition pulse propagation in a preformed channel– 3D effects
• Other simulations– Circularly-polarized laser heating– Weibel instabilities of an e--beam in rising densities
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• Relativistic SF/Filament
Stages of channeling process
Ela
ser
ne
ni
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• Relativistic SF/Filament• Ponderomotive
SF/Filament
Stages of channeling process
Ela
ser
ne
ni
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• Relativistic SF/Filament• Ponderomotive
SF/Filament• Central filament
widening & shock launching
Stages of channeling process
Ela
ser
ne
ni
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• Regular Transverse expansion– Vt~0.03c ~2Cs (at 500 keV)
– Channel wider than laser width
• Longitudinal advancing involves many highly nonlinear processes
– Plasma piling-up
V 1
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F r a m e 0 0 1 ? 2 5 A u g 2 0 0 6 ?
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F r a m e 0 0 1 ? 2 6 A u g 2 0 0 6 ?
ni/n
c
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• Regular Transverse expansion– Vt~0.03c ~2Cs (at 500 keV)– Channel wider than laser width
• Longitudinal advancing involves many highly nonlinear processes
– Plasma piling-up– Laser hosing/channel bending– Channel bifurcation– Channel smoothing (self-correcting)
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p-pol
s-pol
• The 14m-wide beam shows uneven advancing speed– V0.1c->t=30 ps
– V>(mnc/Mn)1/2a=0.04c (for n=nc)• t<80 ps
• 3D effects (p-pol vs s-pol)– Vs>Vp
– Ws<Wp
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• Hole-boring from 1nc to 10 nc takes >300 ps
• Tripling the frequency of channeling pulse can channel to 1022 cm-3
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