Relativistic Plasmas and Strong B-Fields: New Synergism Between HEA and HEDP Edison Liang
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Transcript of Relativistic Plasmas and Strong B-Fields: New Synergism Between HEA and HEDP Edison Liang
Relativistic Plasmas and Strong B-Fields: New Synergism Between HEA and HEDP
Edison LiangRice University
Collaborators: H. Chen, S.Wilks, B. Remington (LLNL); T. Ditmire, (UTX); W. Liu, H. Li, M. Hegelich, (LANL); A.
Henderson, P. Yepes, E. Dahlstrom (Rice)
Santa Fe, NM, August 4, 2010
LLNL Titan laser
New Revolution:Ultra-intense Short Pulse Lasers
bring about the creation of Relativistic Plasmas in the Lab
Matching high energy astrophysical conditions
TPWTrident
Omega laser
Omega laser facility,Univ. of Rochester
Many kJ-class PW lasers are coming on line in the US, Europe and Asia
The National Ignition Facility LLNL
Omega-EP
ARC
FIREX Gekko
ILE Osaka
RAL Vulcan Laser
e/pe
log<>
100 10 1 0.1 0.01
4
3
2
1
0
GRB
Microquasars
Stellar Black Holes
LASER PLASMAS
Phase space of laser plasmas overlap some relevant high energy astrophysics regimes
solid densitycoronal
density
PulsarWind
Blazar
2x1022Wcm-2
2x1020
2x1018
LWFA
(magnetization)
GRB Afterglow
Relativistic Plasmas and Strong B-Fields
1. Pair Plasma Creation Experiments.2. Strong-B Creation Experiments.3. Applications of Pair Plasmas + Strong B
Most relativistic plasmas are “collisionless”. Need to use kinetic, e.g. Particle-in-Cell (PIC), simulations to capture essential physics.
e+e- pair plasmas are ubiquitous in the universe
Thermal MeV pairs Nonthermal TeV pairs
it is highly desirable to create pair plasmas in the laboratory
Internal shocks:Hydrodynamic
Poynting flux:Electro-
magnetic
Gamma-Ray Bursts: High favors ane+e- plasma outflow?
e+e- e+e-
Woosley & MacFadyen,A&A. Suppl. 138, 499 (1999)
What is primary energy source?How are the e+e- accelerated?
How do they radiate?
e+e-
eTrident
Bethe-Heitler
MeV e-
Ultra-intense Lasers is the most efficient tool to make e+e- pairsIn the laboratory
2.1020W.cm-2
0.42 p s
e+e-
125m Au
Early laser experiments by Cowan et al (1999) first demonstrated e+e- production with Au foils. But e+/e- was low (~10-4) due to off-axis
measurements and thin target.
Cowan et al 1999
Trident process dominates for thin targets. Bethe-Heitler dominates for thick targets.
Can the e+ yield keep increasing if we use very thick targets?
(Nakashima & Takabe 2002)
I=1020Wcm-2
?
linear
quadratic
Liang et al 1998
1
2
Au
Set up of Titan Laser Experiments
11
2
MeV
Monte Carlosimulations
Sample Titan data
e+/e- ~ few %
1.00E-003
1.00E-002
1.00E-001
1.00E+000
0 2 4 6 8 10 12
Thickness (mm)
Emergent positrons/incident electrons (log)
e+/e- (10MeV)
e+/e- (5MeV)
Absolute e+ yield (per incident hot electron or laser energy) peaks around 3 mm and increases with
hot electron temperature
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0 2 4 6 8 10 12
thickness (mm)
emergent positron/emergent electron
e+/e- (10MeV)
e+/e- (experiment)
e+/e- (5MeV)
Only emergent e+/e- ratio can be measured, butdiscrepancy between theory and data for thick
targets remains to be resolved
Omega-EP
Assuming that the conversion of laser energy to hot electronsIs ~ 30 %, and the hot electron temperature is ~ 5 -10MeV, the
above results suggest that the maximum positron yield is
~ 1012 e+ per kJ of laser energywhen the Au target ~ 3-5 mm
The in-situ e+ density should exceed 1018/cm3
The peak e+ current should exceed 1024 /sec
This would be 1010 higher than conventional sourcesusing accumulators and electrostatic traps.
PW laser PW laser
Double-sided irradiation plus sheath focusing may provide astrophysically relevant pair “fireball” in the center ofa thick target cavity: ideal lab for GRB & BH -flares
3-5mm 3-5mm
high density “pure”e+e- due to coulombrepulsion of extra e-’s
diagnostics
diagnostics
Thermal equilibrium pair plasma and BKZS limit may be replicatedif we have multiple ARC beams staged in time sequence.
How are relativistic jets confined and dissipate?
Laser-driven Helmohltz coil can generate MG axial fields (Daido et al 1986). Myatt et al (2007) proposed Omega-EP experiments toconfine pair jets. We proposed similar experiments for TPW.
TPW long pulse to drive B
TPW short pulse to make pairs or proton beam
(courtsey J. Myatt 2007)
Helmholtz coil B-field Scaling Estimates
1. Energy Scaling: EB ~ 10% of absorbed laser energyFor cylindrical volume of 0.1mm radius x 1 mm lengthwe find Bmax ~ 15 MG per kJ of incident laser energy assuming 30% absorption into hot electrons.
2. Current Scaling: I scales linearly with foil gap d. For d~ 1 mm, Imax ~ 1.2x105 A. Hence we estimate Bmax ~10 MG per kJ of incident laser energy
3. Capacitance Scaling: Assuming 5 x1013 hot electrons perkJ of laser energy with 50% into capacitor, and d ~1 mm, we find maximum voltage V ~ 2 x106 V. Using L (inductance) ~14 nH for copper circuit, we find Bmax ~ 10 MG per kJ of incident laser energy.
A Novel Application of Relativistic Pairs + Strong B:Laser Cooling of “Landau Atom” to make dense Ps
Key advantages of laser produced positrons are short pulse (~ps), high density (>1017/cc) and high yield efficiency (~10-3).
To convert these >> MeV positrons to slow positrons using conventional techniques, such as moderation with solid noble gas,
loses the above inherent advantages.
We are exploring intense laser cooling, using photons as “opticalmolasses” similar to atomic laser cooling, to rapidly slow/cool
MeV pairs down to keV or eV energies.
e+/e- o
2o
In a strong B field, resonant scattering cross-section can becomemuch larger than Thomson cross-section, allowing for efficient
laser cooling: analogy to atomic laser cooling
To Compton cool an unmagnetized >>MeV electron, needs laser fluence
~mc2/T ~ 1011J.cm-2 = 8MJ for ____~ 100m diameter laserBut resonant scattering cross
section peaks at fT, f>103, isreduced to 8MJ/f < kJ.
As in atomic laser cooling, we need to“tune” the laser frequency
as the electron cools to stay in ________resonance. How?_________
. For B=108G, hcyc=1eV
cyc=1m
T
f>103T
B~100MG
e+/e-
t3
t2
t1
to
cyc = laser(1-vcos)
Idea: we can tune the effective laser frequency as seen by the e+/e- beams by changing the laser incident angle to match
the resonant frequency as the positron slows.
B~100MG
e+/e-
to
t1
t2
t3
cyc = laser(1-vcos)
Idea: change the incident angle by using a mirror and multiple beams phased in time
We are developing a Monte Carlo code to model this in full 3-D. Initial results seem promising
(Liang et al 2010 in preparation)
High density slow positron source can be used To make BEC of Ps at cryogenic temperatures
(from Liang and Dermer 1988).
Ground state of ortho-Ps has long live, but it can be spin-flipped into para-Ps using 204 GHz microwaves.
Since para-Ps annihilates into 2-’s, there is no recoil shift.The 511 keV line has only natural broadening if the Ps
is in the condensed phase.
A Ps column density of1021 cm-2 could inprinciple achievea gain-length of 10for gamma-rayamplification viastimulated annihilationradiation (GRASAR). (from Liang and Dermer 1988). Such a column wouldrequire ~1013 Ps for a cross-section of(1 micron)2. 1014 e+ is achievablewith 10kJ ARC beamsof NIF.
Ps annihilation cross-section with only natural broadening
1 micron diameter cavity
10 ps pulse of 1014 e+
1021cm-2
Ps column density
Porous silica matrix at 10oK
sweep with 204 GHzmicrowavepulse
Artist conception of a GRASAR (gL=10) experimental set-up
Solid target
B-field
laser
radi
atio
n
high energyprotons
B-field
B-
field
ab
sorp
tionablation
energytransport
ionization
fast particlegeneration
& trajectories
(Courtesy of Tony Bell)
Short pulse laser plasma interactionsShort pulse laser plasma interactionsnaturally generate superstrong B in laser plasmas
X-Wave cutoffsX-Wave cutoffs
1019
1020
1021
1022
1023
0 200 400 600 800 1000
Magnetic field (MG)
Region of harmonic generationnc
nc
2 3 4 5 6 7 8 9
µm
(courtesy of Krushelnick et al)
100
1000
10
17
10
18
10
19
10
20
10
21
Magnetic field (MegaGauss)
Intensity (Wcm
-2
)
2nd harmonic
cut-off
3rd harmonic
cut-off
4th harmonic
cut-off
Experimental results are in agreement with Experimental results are in agreement with “ “ponderomotive” source for fieldsponderomotive” source for fields
can create reconnection layer
shows thin current sheet
Summary: New Synergism between HEA and HEDP
1. Titan laser experiments and numerical simulationspoint towards copious production of e+e- pairs using lasers with I > 1020 Wcm-2.
2. Maximum e+ yield can exceed 1012 per kJ of laserenergy (emergent e+/hot e- ~ few %).
3. The in-situ e+ density can exceed 1018 cm-3.4. Laser-driven Helmholtz coil can create B > 107G4. Dense pair plasmas and jets, coupled with > 107G magnetic
fields, can simulate many astrophysics phenomena, from black hole flares, pulsar winds, blazar jets to -ray bursts.
• Collisionless shocks, reconnection, and shear layers mayalso be studied in the laboratory with HEA applications.