Post on 24-Jan-2016
description
transcript
Highlights of talk :
1. e+e- pair laser production
1. Collisionless shocks
1. Colliding laser pulses accelerator
e+e- plasmas can be created by irradiating high-Z targets with ultra-intense lasers
Fast ionsLaser
Au foil
1020 W/cm2
for 10 p Wilks et al., Phys. Plasmas 8, 542 (2001), Liang and Wilks, PRL (1998)
e+e-
Thot=[(1+I2/1.4.1018)1/2-1]mc2
Thot > mc2 when I2 >1018 Wcm-2
(<==> eE/m > c)
LLNL PW-laser striking target
Au
e+e-
e
(Liang & Wilks 1998)
Sample Laser Numbers
1 PW = 1 kJ / 1 ps
1 PW / (30 μm)2 = 1020 W/cm2
1020 W/cm2/ c~ 3.1016 er /gcm3 ~ 2.1022 e+ - /e cm3
S olidA u ion dens ity~ 6.1022 /cm3
n+/ne ~ 4.10-3
Bequipartition ~ 9.108 G
PAIR PRODUCTION BY SUPERTHERMALS ON HIGH-ZTARGET:
dN+/dt = (dN+/dt)eion + (dN+/dt)γion + (dN+/dt)γγ1 > 2 3
f or thi (n << 20 μm) lase r targe . ts HencedN+/ = dt (N+ + N-) < Nion (f(γ) vσeion )>
f(γ) is normalize dsupertherma l distr ibutionfunc tionandσeion ~ 1.4 10x –30 cm2 Z2 ( lnγ)3 f orγ >> 1
istride nt pai r produc tionc rosssec tion( +e ionË e+ion+γγ):Solving above equation:N+ = Z Nion {exp(Γt) – 1}/2 ~ ZNionΓt/2 for Γt << 1Ë N+/Ne ~ Γt/2 ~ 2 x 10–3 for t ~ 10 ps, I = 1020 Wcm-2
For Au: N+ ~ 1022 cm-3
e+e-)
B-H pair-production has larger cross-section than trident, but it depends on bremsstrahlung photon flux and optical
depth of the high-Z target
B-H
trident
(Nakashima & Takabe 2002 PoP)
20 40
Pair Creation Rate Rises Rapidly then plateaus above ~1020Wcm-2
1019W/cm2
1020W/cm2
Liang et al 1998
Nakashima & Takabe 2002f(E) approximates a truncated Maxwellian
2.1020W.cm-2
0.42 p s
e+e-
125μm Au
LLNL PW laser experiments confirm copious e+e-production
Cowan et al 2002
Trident dominates at early times and thin targets, but B-H dominates at late times and thick targetsdue to increasing bremsstrahlung photon density
Nakashima & Takabe 2002
(Wilks & Liang 2002Unpublished)
Nakashima & Takabe 2002
(Nakashima & Takabe 2002)
Two-Sided PW Irradiation may create a pair fireball
After lasers are turned off, e+e- plasmas expands relativistically, leaving the e-ion plasma behind.Charge-separation E-field is localized in the e-ionplasma region. It does not act on the e+e- plasma
(Liang & Wilks 2003)
e+e-
e-ion
ux
x
Ex
x
Phase plot of e+e-component
Weibel Instability in 3D using Quicksilver (Hastings & Liang 2007)e+e- colliding with e+e- at 0.9c head-on
Px vs x
By vs x
QuickTime™ and a decompressor
are needed to see this picture.
B
3D Simulations of Radiative Relativistic Collisionless Shocks
Movie by Noguchi
Psyn
Ppic
Calibration of PIC calculation again analytic formula
px
By*100
f(γ)
γ
Interaction of e+e- Poynting jet with cold ambient e+e- shows broad
(>> c/e, c/pe) transition region with 3-phase “Poynting shock”
ejecta
ambient
ejectaspectralevolution
ambientspectral evolution
γ
ejecta e- shocked ambient e-
Prad of “shocked” ambient electron is lower than ejecta electron
Propagation of e+e- Poynting jet into cold e-ion plasma: acceleration stalls after “swept-up” mass > few times ejecta mass. Poynting flux decays via mode conversion and particle acceleration
ejecta e+ ambient e- ambient ion
px/mc
By
x
By*100
pi*10
pi
ejecta e+
ejecta e-
ambient ion
ambient e-
γ
f(γ)-10pxe-10pxej
100pxi
100Ex
100By
Prad
Poynting shock in e-ion plasma is very complex with 5 phases and broad transition region(>> c/i, c/pe). Swept-up electrons are
accelerated by ponderomotive force. Swept-up ions are accelerated by charge separation electric fields.
ejecta e- shocked ambient e-
Prad of shocked ambient electron is comparable to the e+e- case
Examples of collisionless shocks: e+e- running into B=0 e+e- cold plasma ejecta hi-B, hi-γ weak-B, moderate γ B=0, low γ
swept-up
swept-up
swept-up
100By
ejecta
swept-up100By
100Ex
100By100Ex
-px swept-up
-pxswrpt-up
ejecta
When a single intense EM pulse irradiates an e+e- plasma,
it snowplows all upstream particles without penetrating
to=10 to=40
LLNL PW-laser striking target
By
px
By
px
thin slab of e+e-
plasma2 opposite EM pulses
It turns out that it can be achieved with two colliding linearly polarized EM pulses
irradiating a central thin e+e- plasma slab
How to create comoving J x B acceleration in the laboratory?
B B
I=1021Wcm-2
=1μmInitial e+e- n=15ncr,
kT=2.6keV,thickness=0.5μm,
px
x
By
Ez
Jz
Acceleration by colliding laser pulses appears almost identical to that generated by EM-dominated outflow
Poynting Jet Colliding laser pulses
to=40
x
Two colliding 85 fs long, 1021Wcm-2, =1μm, Gaussian laser pulse trains can accelerate
the e+e- energy to >1 GeV in 1ps or 300μm(Liang, POP 13, 064506, 2006)
637μm-637μm
Bypx
slope=0.8γ
x
Gev
QuickTime™ and aGraphics decompressor
are needed to see this picture.
QuickTime™ and aGraphics decompressor
are needed to see this picture.
to = 40 to = 80™ QuickTime and a Graphics decompressor
.are needed to see this picture
™ QuickTime and a Graphics decompressor
.are needed to see this picture
t o = 120 to = 160
Details of the inter-passage of the two pulse trains
ByEz
By
Particles are trapped and accelerated by multiple ponderomotive traps, EM energy is continuously transferred to particle energy
Notice decay of magnetic energy in pulse tail
to=4800
Px/100
By/100n/ncr
Momentum distribution approaches ~ -1 power-law and continuous increase of maximum energy with time
f(γ)
γ
-1
to=4000
degree
γ
1GeV
Highest energy particles are narrowly beamed at specificangle from forward direction of Poynting vector,
providing excellent energy-angle selectivity
to=4800
QuickTime™ and aGraphics decompressor
are needed to see this picture.
QuickTime™ and aGraphics decompressor
are needed to see this picture.
Elaser
Ee+e-
Maximum energy coupling reaches ~ 42%
n=0.025 n=9
If left and right pulses have unequal intensities,acceleration becomes asymmetric and sensitive to
plasma density, Here I<--=8.1020Wcm-2; I-->=1021Wcm-2
Pulses transmittedat max. compression
Pulses totally reflectedat max. compression
2D studies with finite laser spot size: D=8 μm
y
x
x
Bz
y
x
Eem
E e+e-
γ
(degrees)
y
x
px
x
Compression & Acceleration of overdense 0.5 μm thick e-ion plasma slab by 2-side irradiation of I=1021 Wcm-2 laser pulses
10*pi
pe
Acceleration of e-ion plasma by CLPA is sensitive to the plasma densityn=9 n=1
n=0.01 n=0.001
10pi
pe
100Ex 100Ex
1000Ex 10000Ex
10pi
10pi10pi
e+e- e-ion
f
γ γ
Electron energy spectrum is similar in e+e- and e-ion cases
y
x
y
x
px
x
Eem
Ee
Ei
γe 100γi
(degrees)
2D e-ion interaction with laser spot size D=8 μm
ion
e-
Conceptual experiment to study the CPA mechanism withThree PW lasers
e/pe
log<γ>
100 10 1 0.1 0.01
4
3
2
1
0
GRB
Galactic Black Holes
INTENSE LASERS
Phase space of laser plasmas overlaps most of relevant high energy astrophysics regimes
High-
Low-
PulsarWind
Blazar
Rpe/c
mi/me