Comoving Acceleration by Relativistic Poynting Flux

Edison Liang Rice University Acknowledgements: Kasumi Nishimura, Koichi Noguchi (Japan); Peter Gary, Hui Li (LANL); Scott Wilks, Bruce Langdon (LLNL)

Krakow, PL 2008

Side Note

Nonlinear collective processes behave very differently in the ultra relativistic regime, due to the v=c limit.

Manifestation of “relativistic phase space squeezing”

Two Distinct Paradigms for the energetics of ultra-relativistic jets/winds

What is primary energy source?

How are the e+e- accelerated?

How do they radiate?

B Internal shocks Hydrodynamic Outflow e+e ions shock g -rays SSC, IC… e+e g -rays Poynting flux Electro-magnetic -dominated outflow

Ez By Jz x EM pulse Entering Plasma

Particle acceleration by relativistic j x B (ponderomotive) force

JxB force snowplows all surface particles upstream: < g > ~ max(B 2 /4 p nm e c 2 , a o ) e.g. intense laser target interactions

(Wilks et al PRL 1992

)

y By Ez Jz JxB

Exiting Plasma

z x k

x 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: < g > >> (B 2 /4 p nm e c 2 , a o Accelerator” .

) “ Comoving Ponderomotive

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

2.5D PIC Poynting flux Is an efficient accelerator

(Liang & Nishimura PRL 91, 175005 2004)

W e / w pe =10 L o =120c/ W e t.

W e =800 t.

W e =10000

Details of early e+e- expansion Momentum gets more and more anisotropic with time

In comoving Poynting flux acceleration, the most energetic particles ~ comoving with local EM field P rad ~ W e 2 g 2 sin 4 a where a is angle between p and Poynting vector k. B y p a k PIC sim results show that a ~ 0.01 - 0.1

E z critical frequency w cr ~ W e g 2 sin 2 a << w crsyn ~ W e g 2

CPA produces Power-Law spectra with low-energy cut-off.

Peak Lorentz factor g m corresponds roughly to the profile/group velocity of the EM pulse a ~0--1.5

Typical GRB spectrum g m E pk ~200 keV logdN /dE  ~-2--2.5

 =(n+1)/2 logE E pk dN/dt time

The power-law index seems remarkably robust, independent of initial plasma size or kT o and only weakly dependent on B o L o =10 5 r ce , 3x10 6 time steps f( g ) L o = 10 4 r ce ~ -3 g

W

e /

w

ep =10

W

e /

w

ep =10 0

f=1.33 C o =27.9

g

m

(t) ~ (2f

W

e

(t)t + C

o first principles

)

1/2

t ≥ L

o

/c f~1

This formula can be derived analytically from

CPA reproduces many GRB signatures: profiles, spectra and spectral evolution

(Liang & Nishimura PRL 91, 175005 2004)

W e / w pe =10 L o =120c/ W e t.

W e =800 t.

W e =10000 magnify

a ~0--1.5

t W e =1000 logdN /dE E pk ~200 keV  ~-2--2.5

5000 logE E pk time dN/dt 10000 18000 hard-to-soft GRB spectral evolution diverse and complex BATSE light curves Fourier peak wavelength scales as ~ c.

g m / w pe

QuickTime™ and a Animation decompressor are needed to see this picture.

(movie by Noguchi 2004)

P rad = 2e 2 (F || where F || and F + 2 + g 2 F + 2 ) /3c is force along v is force orthogonal to v

CPA is stable in 3-D (

Noguchi et al 2005

) QuickTime™ and a TIFF (U ncompressed) decompressor are needed to see this picture.

QuickTime™ and a TIFF (U ncompressed) decompressor are needed to see this picture.

B 2

In pure e-ion plasmas, CPA transfers EM energy mainly to ion component due to charge separation

e+e e-ion

In mixture of e-ion and e+e- plasmas, Poynting flux selectively accelerates only the e+e- component e pure e-ion: ions get most of energy via charge separation ion e+e 10%e-ion, 90%e+e : ions do not get accelerated, e+e gets most energy ion

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

Bulk G from hoop stress compressed toroidal fields loaded with e+e-ion plasma Poynting flux pulse from transient accretion disk or ms magnetar wind small section modeled as cylinder progenitor wind

B ~2x10 f ecB/ G N~ 6x10 51 E n ~1.2x10

pk pair G 5 G (R 14 -1 = e 4 B y 2 G 2 sin 4 a /6m 2 c 3  (f 1/3 (f = h w cr /2 p -1/3 R 14 1/3 R W 4 p -1/2 14 -1/3 E 51 1/2 T 30 -1/2 ) W 4 p 1/6 W 4 p -1/6 ~ 490 keV(f 2/3 (acceleration rate = cooling rate, f~O(1)) E 51 -1/6 T 30 1/6 a .1

-4/3 ) E R = N/( W RR 2 )~ 5x10 10 (f -1/3 51 14 7/6 -1/3 R 14 T 30 1/6 a W 4 p -1/6 -7/3 .1 4/3 ) E 51 1/6 T 30 -1/6 a .1 -2/3 ) W 4 p -1/6 E 51 7/6 T 30 -7/6 a .1

4/3 )

(from Liang and Noguchi 2008)

Can we create a comoving

J x B

force in the lab? B 2 opposing thin slab of e+e or e-ion plasma B EM pulses Use two linearly polarized plane laser pulses irradiating a thin plasma slab from both sides

B y p x E z J z x I=10 21 Wcm -2 n l o =1 m m Initial e+e =15n cr , kT o =2.6keV, thickness=0.5

m m ,

Two colliding 85 fs long, 10 21 Wcm -2 , l =1 m m, Gaussian laser pulses accelerate e+e the maximum e+e- energy to >1 GeV in 1ps or 300 m m B y n/n cr =14 g p x g max ~t 0.8

-637 m m x 637 300 m m

Momentum distribution approaches ~ -1 power-law and continuous increase of maximum energy with time f( g ) -1 t w o =4000 g g

Maximum energy coupling can reach ~ 45% E laser QuickTime™ and a Graphics decompressor are needed to see this picture.

E e

Summary 1. A relativistic Poynting flux can accelerate electrons to g >>1 if W e > w pe and if it can stay comoving. 2. This mechansim can be tested in the laboratory by hitting a thin overdense 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 Poynting flux 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 LPAWG Relativistic Plasma Physics New Applications HED facilities

At the May 2007, WG meeting, the WG tentatively identified the following Five important astrophysics questions that are most pressing and 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 WG Website

(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 .