Comoving Acceleration by Relativistic Poynting Flux

Edison LiangRice University

Acknowledgements: Kasumi Nishimura, Koichi Noguchi (Japan); Peter Gary, Hui Li (LANL);

Scott Wilks, Bruce Langdon (LLNL)

Krakow, PL 2008

Side Note

Nonlinear collective processesbehave very differently in the ultra-

relativistic regime, due to the v=c limit.

Manifestation of “relativistic phasespace squeezing”

Internal shocksHydrodynamic Outflow

Poynting fluxElectro-magnetic-dominated outflow

Two Distinct Paradigms for the energeticsof ultra-relativistic jets/winds

e+e-ions

e+e-

What is primary energy source?How are the e+e- accelerated? How do they radiate?

shock-raysSSC, IC… -rays

B

By

Ez

Jz

Plasma

JxB force snowplows all surface particles upstream:<> ~ max(B2/4nmec2, ao)e.g. intense laser target interactions(Wilks et al PRL 1992)

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 The pulse accelerates indefinitely over time: <> >> (B2 /4nmec2, ao ) “Comoving Ponderomotive Accelerator”.

(Liang et al. PRL 90, 085001, 2003)

Entering

Exiting

Particle acceleration by relativisticj x B (ponderomotive) force

x

x

EM pulse

By

x

y

z

Ez

Jz JxB

k

t.e=800 t.e=10000

e/pe =10 Lo=120c/e

2.5D PICPoynting

fluxIs an

efficient accelerator(Liang &

NishimuraPRL 91,175005 2004)

Momentum gets more and more anisotropic with time

Details of early e+e- expansion

p

By

Ez

k

In comoving Poynting flux acceleration, the mostenergetic particles ~ comoving with local EM field

Prad ~ e22sin4

where is angle between p and Poynting vector k.

critical frequencycr ~ e2sin2crsyn~ e2

PIC sim results show that ~ 0.01 - 0.1

CPA produces Power-Law spectra with low-energy cut-off.Peak Lorentz factor mcorresponds roughly to the

profile/group velocity of the EM pulse

logdN/dE

logE

Epk~200 keV

~0--1.5

β~-2--2.5

time

Epk

dN/dt

m

Typical GRB spectrum

β=(n+1)/2

The power-law index seems remarkably robust, independent of initial plasma size or kTo

and only weakly dependent on Bo

f()

~ -3

Lo=105rce, 3x106 time steps

Lo= 104rce

m(t) ~ (2fe(t)t + Co)1/2 t ≥ Lo/c f~1This formula can be derived analytically from

first principles

f=1.33 Co=27.9

e/ep=10e/ep=100

t.e=800 t.e=10000

magnify

e/pe =10 Lo=120c/e

CPAreproducesmany GRB signatures:

profiles,spectra

and spectralevolution(Liang &

NishimuraPRL 91,175005 2004)

te=1000

5000

10000

18000

Fourier peak wavelength scales as ~ c.m/ pe

logdN/dE

logE

Epk~200 keV

~0--1.5

β~-2--2.5

time

Epk

dN/dthard-to-soft GRB spectralevolution

diverseandcomplexBATSElightcurves

(movie by Noguchi 2004)

QuickTime™ and aAnimation decompressor

are needed to see this picture.

Prad = 2e2(F|| 2+ 2F+2) /3c

where F|| is force along vand F+ is force orthogonal to v

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

CPA is stablein 3-D

(Noguchi et al2005)

B2

In pure e-ion plasmas,

CPA transfersEM energy

mainly to ioncomponent due

to charge separation

e+e-

e-ion

pure e-ion: ions get most of

energy via charge separation

10%e-ion, 90%e+e-: ions do

not get accelerated, e+e- gets most

energy

e ion

e+e- ion

In mixture of e-ion and e+e- plasmas, Poynting flux selectively accelerates only the e+e- component

A ms magnetar collapsing into a BH may give rise to an intense Poynting-flux pulse ?

compressedtoroidal fieldsloaded withe+e-ion plasma

Poynting flux pulse from transient accretion disk or ms

magnetar wind

smallsection

modeledas cylinder

Bulk from hoop stress

progenitorwind

B ~2x105 G (R14-1 4

-1/2 E511/2T30

-1/2)f ecB/ = e4By

22sin4/6m2c3 (acceleration rate = cooling rate, f~O(1))~1.2x105 (f 1/3 R14

1/3 41/6 E51

-1/6T301/6.1

-4/3)N~ 6x1051 (f -1/3 R14

-1/3 4-1/6 E51

7/6T301/6 .1

4/3) Epk = hcr/2 ~ 490 keV(f 2/3 R14

-1/3 4-1/6 E51

1/6T30-1/6 .1

-2/3)

npair = N/(RR2)~ 5x1010(f -1/3 R14-7/3 4

-1/6 E517/6T30

-7/6 .14/3)

(from Liang and Noguchi 2008)

thin slab of e+e-or

e-ionplasma

2 opposing EM pulses

Use two linearly polarized plane laser pulses irradiating a thin plasma slab from both sides

Can we create a comoving J x B force in the lab?

B B

I=1021Wcm-2

=1mInitial e+e- no=15ncr,

kTo=2.6keV,thickness=0.5m,

px

x

By

Ez

Jz

x

Two colliding 85 fs long, 1021Wcm-2, =1m, Gaussian laser pulses accelerate e+e-

the maximum e+e- energy to >1 GeV in 1ps or 300m

637m-637m

Bypxn/ncr=14

max~t0.8

300m

Momentum distribution approaches ~ -1 power-law and continuous increase of maximum energy with time

f()

-1

to=4000

QuickTime™ and aGraphics decompressor

are needed to see this picture.

Elaser

Ee

Maximum energy coupling can reach ~ 45%

Summary

1. A relativistic Poynting flux can accelerate electrons to >>1 if e > pe and if it can stay comoving.

2. This mechansim can be tested in the laboratory by hitting a thinoverdense target with two opposing ultra-intense lasers.

3. Maximum energy coupling from EM to particles > 40%.

4. Acceleration is only limited by the transverse size of the Poyntingflux or dephasing.

5. Application of CPA to GRB and other astrophysical sources remains to be investigated.

Laboratory Plasma Astrophysics Working Group

(LPAWG)

Status Report

At a meeting in May 2007 at Rice University, a Laboratory Plasma Astrophysics Working Group (LPAWG) was formed to explore emerging opportunities of studying physics problems at the interface of High Energy/Relativistic Astrophysics and Collisionless Plasmas, using High Energy Density (HED) facilities such as intense lasers, pulse power machines and other plasma facilities such as those at UCLA,Wisconsin, Caltech, MIT, LANL and others.

The goal was to have a unified voice in the formulation of upcoming science policies of the new USDOE program in HED Physics and other related interagency programs.

Currently the WG has ~ 30 international members on the mailing list.

High Energy Astrophysics

HED facilities

Relativistic Plasma Physics

LPAWG

New Applications

At the May 2007, WG meeting,the WG tentatively identified the followingFive important astrophysics questions that are most pressingand potentially relevant to laboratory plasma experiments. The five astrophysics questions are:1. What is the role of e+e- pairs in the most energetic phenomena of the universe such as gamma-ray bursts, AGN jets and pulsar wind dynamics?2. Why are astrophysical jets spectacularly collimated over

enormous distances?3. How does tenuous plasma stop and dissipate ultra-relativistic

particle outflows such as pulsar winds and gamma-ray bursts?4. How do shock waves produce ultra-high energy cosmic rays?5. How does magnetic turbulence dissipate energy in astrophysical

plasmas?

A “white paper” addressing these five questions is currently under construction. We hope to have a preliminary draft completed by November 2008 to be commented, refined and improved on by all WG members plus outside reviewers. The Preliminary Draft and later revisions will be posted on the WGWebsite (only first drafts of Ch.1,2,4,5 of “white paper” have been written):

http://spacibm.rice.edu/~liang/plasma_group

Next WG meeting: to be hosted by L. Silva in Lisbon, in 2009, date and details to be determined and posted on the WG website and emailed to members.