Relativistic Plasmas in Astrophysics

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

• 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 0
High-b
Blazar
logltggt
INTENSE LASERS
Low-b
Galactic Black Holes
100 10 1 0.1
0.01
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
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Relativistic interaction with underdense plasma
applications for laboratory astrophysics
Victor Malka LOA, ENSTA CNRS - École
Polytechnique,91761 Palaiseau cedex, France
(courtesy of Victor Malka)
6th International Conference on High Energy
Density Laboratory Astrophysics at Rice
University in Houston, Texas, March 11-14, 2006.
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Particle acceleration by relativistic j x B force
EM pulse
Entering
By
Plasma
JxB force snowplows all surface particles
upstream ltggt max(B2/4pnmec2, ao) Leading
Poynting Accelerator (LPA)
Ez
Jz
x
Exiting
Plasma
JxB force pulls out surface particles. Loaded EM
pulse (speed lt c) stays in-phase with the fastest
particles, but gets lighter as slower particles
fall behind. It accelerates indefinitely over
time ltggt gtgt B2 /4pnmec2, ao Trailing Poynting
Accelerator(TPA). (Liang et al. PRL 90, 085001,
2003)
x
8
t.We800
t.We10000
TPA reproduces many GRB signatures
profiles, spectra and spectral Evolution (Liang
Nishimura PRL 91, 175005 2004)
magnify
We/wpe 10 Lo120c/We
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Details of early ee- expansion
Momentum gets more and more anisotropic with time
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In pure e-ion plasmas,TPA transfersEM
energymainly to ioncomponent dueto charge
separation
ee-
e-ion
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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
Lo105rce
Lo 104rce
f(g)
-3.5
g
13
When a single intense EM pulse irradiates an
ee- plasma, it snowplows all upstream
particles without penetrating
LLNL PW-laser striking target
px
px
By
By
two10p
two40p
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How to create comoving J x B TPA
acceleration in the laboratory?
B
B
thin slab of ee- plasma
EM pulses
2 opposite
It turns out that it can be achieved with two
colliding linearly polarized EM pulses
irradiating a central thin ee- plasma slab
15
By
Jz
Ez
px
x
I1021Wcm-2 l1mm Initial ee- n15ncr,
kT2.6keV, thickness0.5mm,
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Acceleration by colliding laser pulses appears
almost identical to that generated by
EM-dominated outflow
two40p
Poynting Jet
Colliding laser pulses
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Two colliding 85 fs long, 1021Wcm-2, l1mm,
Gaussian laser pulse trains can accelerate the
ee- energy to gt1 GeV in 1ps or 300mm (Liang, POP
13, 064506, 2006)
px
By
g
Gev
slope0.8
x
637mm
-637mm
x
18
Details of the inter-passage of the two pulse
trains
Ez
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
two4800
By
By/100
n/ncr
Px/100
20
Momentum distribution approaches -1 power-law
and continuous increase of maximum energy with
time
f(g)
two4000
-1
g
21
Highest energy particles are narrowly beamed at
specific angle from forward direction of Poynting
vector, providing excellent energy-angle
selectivity
two4800
g
1GeV
degree
22
Both the maximum energy and fraction of particles
accelerated increase with laser intensity
two141
I1023Wcm-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
two2400
n/ncr9
0.1
0.01
24
Maximum energy coupling reaches 42
Elaser
Eee-
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Maximum particle energy increases with total
laser pulse fluence (FI.Dt), but asymptotic
power-law slope stays constant at -1
two141
f(g)
F32MJ/cm2
8
-1
3.3
1.65
g
26
Initial plasma temperature have little effect on
the asymptotic momentum distribution.
po0.5
po0.1
two40p
27
If left and right pulses have unequal
intensities, acceleration becomes asymmetric and
sensitive to plasma density, Here
Ilt--8.1020Wcm-2 I--gt1021Wcm-2
n0.025
n9
Pulses transmitted at max. compression
Pulses totally reflected at max. compression
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2D studies with finite laser spot size D8 mm

Bz
y
y
y
x
x
x
px
g
Eem
x
E ee-
x
a(degrees)
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Compression Acceleration of overdense 0.5 mm
thick e-ion plasma slab by 2-side irradiation of
I1021 Wcm-2 laser pulses
10pi
pe
30
Acceleration of e-ion plasma by CLPA is sensitive
to the plasma density
n9
n1
10pi
10pi
100Ex
100Ex
pe
n0.001
n0.01
10pi
10pi
1000Ex
10000Ex
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Electron energy spectrum is similar in ee- and
e-ion cases
ee-
e-ion
f
g
g
32
2D e-ion interaction with laser spot size D8 mm
e-
px
y
y
ion
x
x
x
100gi
ge
Eem
Ee
Ei
a(degrees)
33
Conceptual experiment to study the CPA mechanism
with Three PW lasers
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The National Ignition Facility LLNL
LLNL PW-laser
RAL PW-laser
10kJ 2008
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Comparison of Acceleration Gradients
Existing Accelerators GeV/m Other
Underdense Proposals GeV/mm CPA
GeV/0.1mm (_at_1021W.cm-2) Max. potential in
comoving laser E-field eED 6
GeV(I/1021W.cm-2)1/2(D/0.1mm)
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• 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 ee- 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.