Particle Acceleration in Kinetic Plasma Processes

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Particle Acceleration in Kinetic Plasma Processes

• Masahiro HOSHINO
• University of Tokyo

Collaboration with S. Zenitani, K. Nagata, C.
Jaroschek
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Cosmic Ray Accelerator

• Relativistic Shock and Reconnection in
  Astrophysics
• Pulsars Winds (g 106-7)
• Extragalactic radio source (g 10)
• Gamma ray bursts (g gt 100)
• Sources for UHE CR?

3
Open Issues in Particle Acceleration

• Structure of Collisionless Shock Reconnection
• Acceleration Mechanisms
• Fermi acceleration (slow process)
• Injection Problem Particles need
  pre-acceleration to leave the thermal pool and
  enter Fermi acceleration engine.This mechanism
  remains unknown.
• Acceleration Efficiency How large fraction of
  the accelerated particles?
• This fraction remains unknown.
• Something else in kinetic plasma process
• (fast process) ?
• There are many possible mechanisms, but they
  remains unknown.
• Efficiency of Nonthermal Particles

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Shock Numerical Experiment
Modeling on Collisionless Shock
Particle-in-Cell (PIC) Simulation
Bz
z
Ey
wall
y
e,e-
x
injection
reflection
108 particles
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Shock Heating for s0.1
shock front
injection
relativistic Maxwellian
wall
upstream
downstream
EM waves are strong No nonthermal Acceleration
Langdon et al. PRL 1988, Gallant et al. ApJ 1992
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How are nonthermal particles generated?

• (1) Low s Shock with Surfing Acceleration,
• (2) Pair plasmas ion Shock,
• (3) Striped Wind Shock.

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Shock Acceleration for s10-4
relativistic Maxwellian
injection
shock front
wall
upstream
downstream
nonthermal particles

• EM waves are very strong
• Strong Acceleration occurs at the shock front

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s dependence
s10-1
s10-2
s10-4
s10-3
Nonthermal
slt 10-3 ? strong non-thermal acceleration s
10-2 ? marginal
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Shock Surfing Acceleration
z
Sagdeev and Shapiro (1973), Katsouleas and
Dawson (1983)
y
Bz
Ey
? charge
Current Sheet Shock Surfing
? charged particles
?
Near the Shock Front
x
? -charge
shock surface
This can provide unlimited acceleration
Hoshino PTP 2001, Nagata 2005
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Weibel Instability in 3D Shocks

• Magnetic Fields by Weibel Instability

Weibel 1959
Hededal et al. ApJ 2004
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Perpendicular shock
Parallel shock
upstream
upstream
downstream
downstream
magnetic field
magnetic field
Fermi acceleration
Surfing acceleration, ..
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Surfing Acceleration with Turbulent Fields
Kolmogolov Turbulence Test Particle
Simulation
This Talk
Electrostatic Potential (particle trapping
force)
Trajectory around Shock
Niemiec and Ostrowski, ApJ 2004
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Fermi Surfing Accelerationin Oblique Shock
Fermi
Fermi Surfing
along shock
N(cos q)
N(cos q)
cos j
cos j
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How are nonthermal particles generated?

• (1) Low s Shock with Surfing Acceleration,
• (2) Pair plasmas ion Shock,
• (3) Striped Wind Shock.

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Composition pair ion plasmas
(Upstream) Kinetic energy of p dominates
(Downstream) Strong turbulence by p
synchrotron maser inst.? energy transfer to e
shock front
Ion synchrotron maser instability
Hoshino et al. ApJ 1992
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Efficiency of pairion Shock
Nonthermal Efficiency
Power-Law Index
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How are nonthermal particles generated?

• (1) Low s Shock with Surfing Acceleration,
• (2) Pair plasmas ion Shock,
• (3) Striped Wind Shock.

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Striped Wind
neutron star
Equatorial plane
Meridional plane
equator
Coroniti, ApJ 1990 Kirk et al. PRL 2003
rotation axis
magnetic axis
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1D Relativistic Shock Simulation
Vx
Vx,ele
Vy
Shock-Current Sheet Interaction
Vy,ele
Energy
Eele
Ey
Ey/E0
Current Sheet
s1 ?10
Bz
Bz/B0
Upstream
Downstream
X
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Bz
BEFORE
TD (Current Sheet)
FS (Shock)
upstream
downstream
X
Bz
AFTER
upstream
downstream
X
TD (Current Sheet)
FS (Shock)
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Bz
BEFORE
TD (Current Sheet)
FS (Shock)
upstream
downstream
X
FW (Magnetosonic Wave)
Bz
AFTER
upstream
downstream
Thick CS
X
TD (Current Sheet)
FS (Shock)
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Multi-Current Sheet Interaction with Shock
Vx,ele
Vx,ele
Vy,ele
Vy,ele
Multi-current sheets
Bz/B0
nonthermal particles
Bz/B0
Ey/E0
Ey/E0
Upstream
Downstream
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How are nonthermal particles generated?

• (1) Low s Shock with Surfing Acceleration,
• (2) Pair plasmas ion Shock,
• (3) Striped Wind Shock,
• (4) Magnetic Reconnection

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Flares
Magnetic Reconnection
Solar Stellar Flares, Magnetosphere, Accretion
Disks, Pulsar Wind-Nebula,
YOHKOH, SOHO, Trace, RHESSI
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Relativistic Magnetic Reconnection(Particle-in-Ce
ll simulation)
Zenitani Hoshino, ApJ 2001
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Nonthermal Acceleration in MRX
Jaroschek et al. ApJ 2004
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Power-Law Spectrum in Reconnection

• Acceleration rate
• Loss rate
• Energy Spectrum

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3D Reconnection with Guide Field
t/tc 160
t/tc 160
t/tc 200
t/tc 200
Zenitani Hoshino, PRL 2005
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Summary
Direct Acceleration

• Surfing Acceleration (low s),
• Pair Ion Shock/Synchrotron Inst. (low s),
• Surfing Fermi Acceleration (low s),
• Striped Wind Shock (medium s),
• Reconnection (high s).

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Acceleration Mechanisms
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Acceleration Mechanisms