FSC Channeling in the Corona of Fast Ignition Targets G. Li, R. Yan, and C. Ren, UR/LLE T. Wang, J. Tonge, and W. B. Mori, UCLA.

FSC

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

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

FSC


are needed to see this picture.Channeling makes ignition pulse more effective

• 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

FSC



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)

FSC


are needed to see this picture.New results in the last 6 months

• 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

FSC


are needed to see this picture.Channeling process at different intensities is similar

Ion density plot (n0=0.3-1 nc), I=1020 W/cm2, ~6.4 ps

25

0

m

500 m

QuickTime™ and aMicrosoft Video 1 decompressorare needed to see this picture.

FSC


are needed to see this picture.At I=1018 W/cm2, channeling is much slower2

50

m

500 m


Ion density plot (n0=0.3-1 nc), I=1018 W/cm2, ~9.2 ps

FSC


are needed to see this picture.How do we measure Vc?




x1

n c

Density at channel center

Define channel as n<nr

FSC


are needed to see this picture.Vc decreases as n0 increases

1019 W/cm2

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

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

FSC


are needed to see this picture.Channel advancing is stochastic

• Longitudinal advancing involves many highly nonlinear processes

– Plasma piling-up– Laser hosing/channel bending– Channel bifurcation– Channel smoothing (self-correcting)

FSC


are needed to see this picture.Vc decreases as IL decreases

1018 W/cm21020 W/cm2

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

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

V_c/c

Simulation 0.2LinearWilksSimulation 0.1Simulation 0.05

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0.3 0.35 0.4 0.45 0.5

n_0/n_c

V_c/c

Simulation 0.2LinearpodermotiveSimulation 0.1

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0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

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

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 2000 4000 6000 8000 10000 12000

time (fs)

fraction of pulse energy

electron absorption rateion absorption rateE3&B2 E1&E2&B1&B3Reflected

1020 W/cm2

FSC


are needed to see this picture.Work underway

• 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

FSC



• Relativistic SF/Filament

Stages of channeling process

Ela

ser

ne

ni

FSC



• Relativistic SF/Filament• Ponderomotive

SF/Filament


Ela

ser

ne

ni

FSC



• Relativistic SF/Filament• Ponderomotive

SF/Filament• Central filament

widening & shock launching


Ela

ser

ne

ni

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• Regular Transverse expansion– Vt~0.03c ~2Cs (at 500 keV)

– Channel wider than laser width


– Plasma piling-up

V 1

V

2

0 1 0 0 0 2 0 0 0

0

0 . 0 5

0 . 1

0 . 1 5

0 . 2

0 . 2 5

0 . 3

0 . 3 5

0 . 4

0 . 4 5

0 . 5

F r a m e 0 0 1 ? 2 5 A u g 2 0 0 6 ?

V 1

V

2

0 1 0 0 0 2 0 0 0 3 0 0 0

0

0 . 1

0 . 2

0 . 3

0 . 4

0 . 5

0 . 6

0 . 7

0 . 8

0 . 9

1

F r a m e 0 0 1 ? 2 6 A u g 2 0 0 6 ?

ni/n

c

FSC



• Regular Transverse expansion– Vt~0.03c ~2Cs (at 500 keV)– Channel wider than laser width


– Plasma piling-up– Laser hosing/channel bending– Channel bifurcation– Channel smoothing (self-correcting)

FSC


are needed to see this picture.How long does it to take to get to 1nc?

QuickTime™ and aVideo decompressor


QuickTime™ and aVideo decompressor


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

FSC


are needed to see this picture.It will take blue light to channel to 1022 cm-3

• Hole-boring from 1nc to 10 nc takes >300 ps

• Tripling the frequency of channeling pulse can channel to 1022 cm-3



FSC


are needed to see this picture.Summary

• Clean channel can be created for I=1019 W/cm2

• Channel advancing is stochastic but self-correcting• Channeling to n=1022 cm-3 requires 0.35-m light

FSC Channeling in the Corona of Fast Ignition Targets G. Li, R. Yan, and C. Ren, UR/LLE T. Wang, J. Tonge, and W. B. Mori, UCLA.

Documents

v c slide

fsc channeling process

n c tv p w s fsc

frequency of channeling

ps slide

threshold pp c

ppw nn c

pulse energy