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.