1. Relativistic Plasmas in Astrophysics and in Laser Experiments II:
PIC Simulations of Intense Laser
Interactions
Edison Liang, Koichi Noguchi
Rice University
Acknowledgements: Scott Wilks, Bruce Langdon
Lecture Series at LANL July 2006
(Work supported by LLNL, LANL, NASA, NSF)

2. acceleration via intense laser plasma interactions.
This talk will focus on particle
acceleration via intense laser
plasma interactions.

3. Relativistic
Plasma Physics
High Energy
Astrophysics
Particle
Acceleration
New
Technologies
Ultra-Intense
Lasers

4. Phase space of laser plasmas overlaps most of relevant high energy astrophysics regimes
PulsarWind
GRB 4 3 2 1
High-b
Blazar
log<g>
INTENSE LASERS
Low-b
Galactic Black Holes
We/wpe

5. Most conventional laser-plasma acceleration mechanisms (e.g.
LWFA, PWFA, PBWA, FWA)
involve propagation of lasers in
UNDERDENSE plasmas
The mechanism proposed here
utilizes OVERDENSE plasmas

6. LOA, ENSTA – CNRS - École Polytechnique, 91761 Palaiseau cedex, France
Relativistic interaction with underdense
plasma : applications for laboratory astrophysics
Victor Malka
LOA, ENSTA – CNRS - École Polytechnique, Palaiseau cedex, France
(courtesy of Victor Malka)
Laser beam
Electron beam
1 mm
ions
neutrons
6th International Conference on High Energy Density Laboratory Astrophysics at Rice University in Houston, Texas, March 11-14, 2006.

7. Particle acceleration by relativistic
j x B force
EM pulse
Entering By
Plasma
JxB force snowplows all surface particles upstream:
<g> ~ max(B2/4pnmec2, ao)
“Leading Poynting
Accelerator” (LPA) By x y z Ez Jz
JxB k Ez Jz x
Exiting
Plasma
JxB force pulls out surface particles. Loaded EM pulse (speed < c) stays in-phase with the fastest particles, but gets “lighter” as slower particles fall behind. It accelerates indefinitely over time:
<g> >> B2 /4pnmec2, ao “Trailing Poynting Accelerator”(TPA).
(Liang et al. PRL 90, , 2003) x

8. We/wpe =10 Lo=120c/We t.We=800 t.We=10000 TPA reproduces many GRB
signatures:
profiles,
spectra
and spectral
Evolution
(Liang &
Nishimura
PRL 91, )
magnify
We/wpe =10
Lo=120c/We

9. Details of early e+e- expansion
E+e- slab run
Momentum gets more and
more anisotropic with time

10. e+e-
In pure e-ion plasmas, TPA transfers EM energy mainly to ion component due to charge separation
e-ion

11. Pure e-ion run e
ion

12. The power-law index seems remarkably robust
independent of initial plasma size or temperature
and only weakly dependent on B
Lo=105rce
f(g)
Lo= 104rce
-3.5 g

13. When a single intense EM pulse irradiates an e+e- plasma,
it snowplows all upstream particles without penetrating
LLNL PW-laser striking target px px By By
two=10p
two=40p

14. How to create comoving J x B TPA acceleration in the laboratory?
thin slab of e+e-
plasma
EM pulses
2 opposite
It turns out that it can be achieved with two colliding linearly polarized EM pulses irradiating a central thin e+e- plasma slab

15. I=1021Wcm-2 l=1mm Initial e+e- n=15ncr, kT=2.6keV, thickness=0.5mm, ByJz Ez px x
I=1021Wcm-2
l=1mm
Initial e+e-
n=15ncr,
kT=2.6keV,
thickness=0.5mm,

16. Acceleration by colliding laser pulses appears almost identical to that generated by EM-dominated outflow
two=40p
Poynting Jet
Colliding laser pulses

17. Two colliding 85 fs long, 1021Wcm-2, l=1mm,
Gaussian laser pulse trains can accelerate
the e+e- energy to >1 GeV in 1ps or 300mm
(Liang, POP 13, , 2006) px By g
Gev
slope=0.8
-637mm x
637mm x

18. Details of the inter-passage of the two pulse trainsEz By

19. Particles are trapped and accelerated by multiple ponderomotive traps,
EM energy is continuously transferred to particle energy
Notice decay of magnetic energy in pulse tail By
two=4800
By/100
n/ncr
Px/100

20. Momentum distribution approaches ~ -1 power-law
and continuous increase of maximum energy with time
f(g)
two=4000 -1 g

21. Highest energy particles are narrowly beamed at specific
angle from forward direction of Poynting vector,
providing excellent energy-angle selectivity
two=4800 g
1GeV
degree

22. Both the maximum energy and fraction of particles accelerated
increase with laser intensity
two=141
I=1023Wcm-2
f(g)
1021
1019 g

23. Higher plasma density leads to higher fraction of particles
eventually captured and accelerated into the power-law.
But it takes slightly longer to reach the same maximum energy
two=2400
n/ncr=9
0.1
0.01

24. Maximum energy coupling reaches ~ 42%
Elaser
Ee+e-

25. Maximum particle energy increases with total laser pulse fluence
(F=I.Dt), but asymptotic power-law slope stays constant at ~ -1
two=141
f(g)
F=32MJ/cm2 8 -1
3.3
1.65 g

26. Initial plasma temperature have little effect on the asymptotic
momentum distribution.
po=0.5
po=0.1
two=40p

27. If left and right pulses have unequal intensities,
acceleration becomes asymmetric and sensitive to
plasma density, Here I<--=8.1020Wcm-2; I-->=1021Wcm-2
n=0.025
n=9
Pulses transmitted
at max. compression
Pulses totally reflected
at max. compression

28. 2D studies with finite laser spot size: D=8 mmBz y y y x x x px g
Eem x
E e+e- x
a(degrees)

29. Compression & Acceleration of overdense 0.5 mm thick e-ion
plasma slab by 2-side irradiation of I=1021 Wcm-2 laser pulses
10*pi pe

30. Acceleration of e-ion plasma by CLPA is sensitive to the plasma density
10pi
10pi
100Ex
100Ex pe
n=0.01
n=0.001
10pi
10pi
1000Ex
10000Ex

31. Electron energy spectrum is similar in e+e- and e-ion casesf g g

32. 2D e-ion interaction with laser spot size D=8 mmpx y y
ion x x x ge
100gi
Eem Ee Ei
a(degrees)

33. Conceptual experiment to study the CPA mechanism with
Three PW lasers

34. The National Ignition Facility
LLNL
LLNL PW-laser
RAL PW-laser
10kJ |

35. Comparison of Acceleration Gradients:
Existing Accelerators: ~ GeV/m
Other Underdense Proposals: ~ GeV/mm
CPA : ~ GeV/0.1mm
Max. potential in comoving laser E-field
~ eED= 6 GeV(I/1021W.cm-2)1/2(D/0.1mm)

36. SUMMARY ON COLLIDING LASERS CONCEPT
1. Collision of counter-propagating linearly polarized laser pulses
with a central thin over-dense plasma slab can achieve robust trapping and comoving acceleration of the surface electrons.
2. For an e+e- plasma irradiated by two 1021 Wcm-2 pulse trains,
the accelerated particles can exceed GeV in a few hundred mm.
3. Acceleration is only limited by the transverse size of the
laser beams as particles drift transversely at speed c.
4. This acceleration mechanism may be demonstrated using three
PW lasers.
5. CPA may also work for sufficiently thin slabs of e-ion plasmas.