Comoving Acceleration by Relativistic Poynting Flux

1
Comoving Acceleration by Relativistic Poynting
Flux Edison Liang Rice University Acknowledgeme
nts Kasumi Nishimura, Koichi Noguchi (Japan)
Peter Gary, Hui Li (LANL) Scott Wilks, Bruce
Langdon (LLNL) Krakow, PL 2008
2

• Side Note
• Nonlinear collective processes
• behave very differently in the ultra-
• relativistic regime, due to the vc limit.
• Manifestation of relativistic phase
• space squeezing

3
Two Distinct Paradigms for the energetics of
ultra-relativistic jets/winds
What is primary energy source? How are the ee-
accelerated? How do they radiate?
B
ee- ions
ee-
shock
g-rays SSC, IC
g-rays
Internal shocks Hydrodynamic Outflow
Poynting flux Electro-magnetic -dominated
outflow
4
Particle acceleration by relativistic j x B
(ponderomotive) force
EM pulse
Entering
By
Plasma
JxB force snowplows all surface particles
upstream ltggt max(B2/4pnmec2, ao) e.g. intense
laser target interactions (Wilks et al PRL 1992)
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 The pulse accelerates indefinitely
over time ltggt gtgt (B2 /4pnmec2, ao ) Comoving
Ponderomotive Accelerator. (Liang et al. PRL 90,
085001, 2003)
x
5
t.We800
t.We10000
2.5D PIC Poynting flux Is an efficient
accelerator (Liang Nishimura PRL 91, 175005
2004)
We/wpe 10 Lo120c/We
6
Details of early ee- expansion
Momentum gets more and more anisotropic with time
7
In comoving Poynting flux acceleration, the
most energetic particles comoving with local EM
field Prad We2g2sin4a where a is angle
between p and Poynting vector k.
By
p
a
k
PIC sim results show that a 0.01 - 0.1
Ez
critical frequency wcr Weg2sin2a ltlt
wcrsyn Weg2
8
CPA produces Power-Law spectra with low-energy
cut-off. Peak Lorentz factor gmcorresponds
roughly to the profile/group velocity of the EM
pulse
Typical GRB spectrum
gm
b(n1)/2
9
The power-law index seems remarkably robust,
independent of initial plasma size or kTo and
only weakly dependent on Bo
Lo105rce, 3x106 time steps
Lo 104rce
f(g)
-3
g
10
?e/wep10
?e/wep100
f1.33 Co27.9
?m(t) (2f?e(t)t Co)1/2 t Lo/c f1 This
formula can be derived analytically from first
principles
11
t.We800
t.We10000
CPA reproduces many GRB signatures
profiles, spectra and spectral evolution (Liang
Nishimura PRL 91, 175005 2004)
magnify
We/wpe 10 Lo120c/We
12
tWe1000
hard-to-soft GRB spectral evolution
5000
10000
diverse and complex BATSE light curves
18000
Fourier peak wavelength scales as c.gm/ wpe
13
Prad 2e2(F 2 g2F2) /3c where F is force
along v and F is force orthogonal to v
(movie by Noguchi 2004)
14
CPA is stable in 3-D (Noguchi et al 2005)
B2
15
In pure e-ion plasmas,CPA transfersEM
energymainly to ioncomponent dueto charge
separation
ee-
e-ion
16
In mixture of e-ion and ee- plasmas, Poynting
flux selectively accelerates only the ee-
component
e
ion
pure e-ion ions get most of energy via charge
separation
ee-
10e-ion, 90ee- ions do not get accelerated,
ee- gets most energy
ion
17
A ms magnetar collapsing into a BH may
give rise to an intense Poynting-flux
pulse ?
compressed toroidal fields loaded with ee-ion
plasma
Bulk G from hoop stress
small section modeled as cylinder
Poynting flux pulse from transient accretion disk
or ms magnetar wind
progenitor wind
18

• B 2x105 G (R14-1 ?4?-1/2 E511/2T30-1/2)
• f ecB/? e4By2?2sin4?/6m2c3 (acceleration rate
  cooling rate, fO(1))
• 1.2x10? (f 1/3 R141/3 ?4?1/6 E51-1/6T301/6?.1-4/3
  )
• N 6x1051 (f -1/3 R14-1/3 ?4?-1/6 E517/6T301/6
  ?.1 4/3)
• Epk h?cr/2? 490 keV(f 2/3 R14-1/3 ?4?-1/6
  E511/6T30-1/6 ?.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)
19
Can we create a comoving J x B force in the
lab?
thin slab of ee- or e-ion plasma
B
B
EM pulses
2 opposing
Use two linearly polarized plane laser pulses
irradiating a thin plasma slab from both sides
20
By
Jz
Ez
px
x
I1021Wcm-2 l1mm Initial ee- no15ncr,
kTo2.6keV, thickness0.5mm,
21
Two colliding 85 fs long, 1021Wcm-2, l1mm,
Gaussian laser pulses accelerate ee- the
maximum ee- energy to gt1 GeV in 1ps or 300mm
px
By
n/ncr14
g
gmaxt0.8
x
637mm
-637mm
300mm
22
Momentum distribution approaches -1 power-law
and continuous increase of maximum energy with
time
f(g)
two4000
-1
g
g
23
Maximum energy coupling can reach 45
Elaser
Ee
24

• Summary
• 1. A relativistic Poynting flux can accelerate
  electrons to
• g gtgt1 if We gt wpe 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
  gt 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.

25
Laboratory Plasma Astrophysics
Working Group (LPAWG) Status
Report
26
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.
27
Relativistic Plasma Physics
High Energy Astrophysics
LPAWG
New Applications
HED facilities
28

• 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
• What is the role of ee- 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?

29
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_g
roup 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.