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laser. X2. X1. Isolated Target. Isolated boundaries- we believe this is essential 100 n c Plasma 20 m radius resistive core particle drag Force = -k p  -2 passes low and high energy particles (<50KeV, >10MeV) Box size 150  x130  5x10 8 cell Grid size: 0.05 c/ 0 , 0.5 c/  p

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Isolated Target

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Isolated target

laser

X2

X1

Isolated Target

  • Isolated boundaries- we believe this is essential

    • 100 nc Plasma

  • 20 m radius resistive core

    • particle drag Force = -k p -2

    • passes low and high energy particles (<50KeV, >10MeV)

  • Box size 150  x130 

    • 5x108 cell

    • Grid size: 0.05 c/0 , 0.5 c/ p

    • 4 electrons per cell, 109 particles

    • Te = 1.0 keV, mI= 3672me

  • Duration 2.5ps +

    • 9104 time steps

    • 1 - 2 months real time

  • 1-laser, W0 = 20 

    • Spot size matches core

41µ

20µ

51µ

130µ

44m

0.8m

150µ

Flux diagnostic planes


Magnetic filamentation and hot region

Magnetic Filamentation and Hot Region

  • Hot spot and magnetic filamentation are spatially correlated.

  • Weibel instability relaxes anisotropic particle distributions as well as filamenting currents.

  • Magnetic fields reach over 100MG for high laser intensity runs - channeling usable 2 MeV energy electrons in x1 direction.

8x1020 W/cm2 @ 1 ps


Plasma modifies energy spectrum of electrons carrying energy forward

Plasma Modifies Energy Spectrum of Electrons Carrying Energy Forward

4

10

5

0

laser

2

AU

MeV

0

Sampled Region

-2

32 95 127

X1 m

Core Edge

Peak energy

reduction

Shock Front

Energy Flux Density (net)

2226 ps, 2x1020 W/cm2


Does ponderomotive scaling work at higher intensity

Does Ponderomotive Scaling Work at Higher Intensity?

Ponderomotive hot = mec2(sqrt(1+I2/1.37x1018)-1)

Hot electron scaling drops to hot/2 at higher intensities

Up to 2x predicted Thot - 85% of energy flux is below 2x predicted Thot

I=1.25x1019

Thot =1.11MeV

I=5x1019

Thot =2.62MeV

I=2x1020

Thot =5.68MeV

I=8x1020

Thot =11.84MeV


Temperature of electron spectrum softens down stream

“Temperature” of Electron spectrum softens down stream

k skin depth

kx2

kx1

E1 k-spectrum 5x1019 W/cm2 at 557 fs

Enhanced electric field fluctuations at skin depth


Well defined simulations of hot tail

Well Defined Simulations of Hot Tail

10

-10

20

MeV

Initial P1 vs P2 (log)

F(Electron Energy)

Periodic Spectral Simulation (Parsec).

Energy and Momentum conserved.

Initialized with no net current.


High intensity laser delivers power to core more efficiently

High Intensity Laser DeliversPower to Core more Efficiently

~ 50x

Scaled

To Laser

Intensity

~ 10x

Laser Intensity

8x1020 W/cm2

2x1020 W/cm2

5x1019 W/cm2

8x1020 W/cm2 laser delivers:

5x the Power of 2x1020 W/cm2 laser

50x the Power of 5x1019 W/cm2 laser


Laser self focusing speeds hole boring

Laser Self Focusing Speeds Hole Boring

Whole boring

Distance* for

Initial Density Profile

I=2x1020 W/cm2

Electron Density

  • Isolated transverse boundaries

  • Thermal boundary at back of target

  • Exponential density profile: max 20 nc

  • Target size 85  x 85 

    • Grid size: 0.05 c/0

    • 4 electrons per cell

    • Te = 0.1keV, mI= 3672me

  • 1-laser, W0 = 5 

I=6x1020 W/cm2

Pointing flux

*Calculated Wilks, prl, 92


Isolated target

PIC Simulation of Electron Transport In Fast Ignition Targetswith Ultra-High Intensity Ignition Laser

J. Tonge, J. May, F.S. Tsung, W. B. Mori

C. Ren*

F. Fíuza, M. Marti**, L. Silva**

UCLA, *Rochester,**Insituto Superior Técnico

Anomalous Absorption 0608

Williamsburg, VA


Coherent waves are weakly damped with k near c

Coherent waves are weakly damped with /k near c

tail

notail

kx=.93 c/pvphase= .86c

= .8 p p=100

53 pe-1

k skin depth

Periodic Spectral Run


Shocks accelerate return current in fast ignition isolated target simulations

Shocks Accelerate return current in Fast Ignition (Isolated Target) Simulations

Return current does not have enough energy to traverse magnetic field.

Electric Field Builds

Return current electrons accelerate and filament moving magnetic field (and shock) forward.

Electric Field

Magnetic Field


Summary

Summary

  • Power Delivered Target Core

    • Higher intensity laser are more efficient for energy transport.

    • Higher intensity delivers much more energy density

  • Electron Energy Transport

    • Most (80-90%) of the energy is transported in the hot bulk

  • Enhanced Fluctuations

    • Turbulent electric field causes relaxation of energetic tail electrons

  • Electromagnetic Shock

    • Energy of energy flux spectrum is reduced at shock

  • Ponderomotive Scaling

    • At higher intensity (>=5x1019W/cm2) Thot is 50% predicted below 2x predicted Thot

    • 85% of energy flux is below 2x predicted Thot (p-polarized 2D)


How does laser accelerate electrons poster tonight josh may

How Does Laser Accelerate Electrons?Poster Tonight: Josh May

Electrons are pulled out into vacuum and accelerated by lasers electric field

and rotated back into plasma by lasers magnetic field

30nc, I=5x1019 W/cm2, Plane Wave, ~2 0 target width


Electrons accelerate in vacuum

Electrons Accelerate in Vacuum


Relativistic shock simulation setup

Relativistic Shock Simulation Setup

Physical Parameters

Laser

50 nc

Ignition laser

  • λ0 = 1μm

  • I0 = 1.25x1019 - 5x1021 W/cm2

  • p-polarization & s-polarization

Plasma

Numerical Parameters

  • 60 μm x 17 μm

  • ne0 = 5x1022 - 1023 cm-3

  • mi/me = 3672 (D+)

  • Ti0 = Te0 = 1 keV

  • Dx⊥ kp = 0.4

  • Dz kp = 0.4

  • Particles per cell = 4


Dynamics in front surface of target

Dynamics in Front Surface of Target

Filamentation @ target

Mass build up/compression & strong electric field

t ~ 350 fs

Weibel

instability

Return currents


Relativistic shock is launched

Relativistic Shock is Launched

Ion phase space & electron density

Pressure behind front drives shock

Ions reflected @ shock front with 2 vsh

vsh ~ 0.1 c

Plateau in electron density due to reflected ions

vhb ~ 0.075 c

Relativistic shock is mediated by Weibel driven magnetic fields

≠ high Mach number ion acoustic shocks

≈ relativistic shocks in astrophysics


Outline

Outline

  • Describe Isolated Target

  • Power Delivered Target Core

  • Energy Transport in Isolated Target

  • Energy Transport Across Density Gradient

  • Enhanced Fluctuations (Turbulence)

  • Electromagnetic Shock

  • Ponderomotive Scaling


Can we use higher intensity ignition lasers how will fast ignition without cone targets work

Can we use higher intensity ignition lasers?How will fast ignition without cone targets work?

  • Concerns:

    • If ponderomotive scaling* holds then e- spectrum is too hot.

    • Electrons are generated too far from core.

  • Advantages:

    • Smaller spot sizes & more hole boring

    • Simplicity of target design

  • 3 Simulations to examine laser intensity

*Wilks et al. prl, aug 92


Net electron energy flux spectrum peaks at low energy

Net Electron Energy Flux Spectrum Peaks at Low Energy*

Through plane 0.8 mm in front of core

Intensity

8x1020 W/cm2

2x1020 W/cm2

5x1019 W/cm2

.25 MeV

.9 MeV

2.6 MeV

*compared to ponderomotive

scaling

MeV

Scaled to laser power @ 2.5 ps


Energy is transported in hot bulk

Energy is Transported in Hot Bulk

80% - 90%

of NET energy flux

laser

Peaks at -0.1 mec

Sample Region

6

F

(log(n))

P2

(mec)

-10

0

20

-6

P1 (mec)

-6

0

10

Hot Bulk

Tail

P1 (mec)

Distribution at 1.5 ps


Does peak in net electron energy flux spectrum move lower at higher density

Does Peak in net Electron Energy Flux Spectrum move lower at higher density?

As energy flux carrying electrons move up the density ramp in a real target return current will be carried by more lower energy electrons. This will “uncover” more of the energy distribution of the forward energy flux causing the peak of the net flux to move lower in energy.

Electron Energy Flux SpectrumI = 8x1020 W/cm2 @ 1 ps

.8 in front of core


Density gradient simulation shows lower peak in electron energy flux spectrum at higher density

Density Gradient Simulation Shows Lower Peak in Electron Energy Flux Spectrum at Higher Density

Flux planes

100 nc

300 nc

800 nc

Target Density Profile

Energy Flux

  • Isolated transverse boundaries

  • Thermal boundary at back of target

  • Exponential density profile: max 1000 nc

  • Target size 15  x13 

    • Grid size: 0.5 c/ p at 1000nc

    • 4 electrons per cell

    • Te = 0.1keV, mI= 3672me

  • 1-laser, W0 = 3 

  • 27 times the computational cost of isolated target simulation

Energy Spectrum of

Net Energy Flux at 1ps


Addition of monte carlo collisions doesn t change results in density gradient simulation

Addition of Monte Carlo Collisions Doesn’t Change Results in Density Gradient Simulation

No collisions

Collisions


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