Post on 23-Jun-2015
Magnetic field amplification and electron acceleration to near ion energy equipartition
from a mildly quasi-parallel relativistic shock Gareth Murphy(1), Mark Dieckmann(2), Luke Drury(1)
1. Dublin Inst for Advanced Studies, 2. Univ. of Linkoping
0 2000 4000 6000 80000
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400log(!), Time = 16000"t
0.0 0.6 1.3 1.9 2.5 3.2 3.8
0 2000 4000 6000 8000-1.0
-0.5
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Ion Phase Space, Time = 16000!t
0.3 1.1 1.9 2.7 3.4 4.2 5.0
Motivation
• Explore the formation of mildly relativistic shocks at kinetic level with PIC simulations
• How is non-thermal radiation produced?
• How does a quasi-parallel field affect shock formation?
GRB internal shock
• When fast blobs meet slow blobs
• Internal shock
• Emission of Gamma rays
• Synchrotron (jitter) radiation implies fast electrons and large magnetic fields
Numerical Method
• Particle In Cell (PIC) Simulations
• Plasma Simulation Code (PSC; Ruhl et al 2003)
• MPI-Parallel
Problem setup
• 0.9c collision speed
• Density ratio of 10
• Ion/electron mass ratio of 250
• Quasi-parallel magnetic field
• 100 CP’s per cell
• 18,000 x400 cells in 2D
1D structure
0 200 400 600 800 10000
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200Electron Phase Space, Time = 25000!t
0.3 0.9 1.5 2.1 2.7 3.3 3.9
Electron phase space
• Gamma of ~ 100 for a tenuous population of electrons 0 2000 4000 6000 8000
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Electron Phase Space, Time = 16000!t
0.3 1.2 2.1 3.0 3.9 4.8 5.7
Ion phase space
• Ions accelerated by longitudinal electric field
• Shock drift acceleration 0 2000 4000 6000 8000-1.0
-0.5
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Ion Phase Space, Time = 16000!t
0.3 1.1 1.9 2.7 3.4 4.2 5.0
Ion density -filamentation
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400log(!), Time = 16000"t
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400log(!), Time = 16000"t
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Filaments
Magnetic bubbles
Integrated density structure
0 2000 4000 6000 80000
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400
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1000Left-moving ionsRight-moving ionsLeft-moving electronsRight-moving electrons
Right Moving Ions
Left Moving Ions
Electron Density
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400log(!), Time = 16000"t
0.0 0.8 1.5 2.3 3.0 3.8 4.5
0 2000 4000 6000 80000
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400log(!), Time = 16000"t
0.0 0.7 1.4 2.1 2.9 3.6 4.3
Magnetic Bubbles
Magnetic Field
• Peak from gradient in convection (u x B) electric field.
• Drift current
• Magnetic bubbles - formation observed in lab plasmas but not in astrophysical context
2D Magnetic Pressure
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log(B2), Time = 16000!t
-3.1 -2.2 -1.2 -0.3 0.6 1.6 2.5
Integrated Magnetic Pressure
B2
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0.5
1.0
1.5
2.0
Peaks at shock frontCompression of magnetic field
Conclusions
• Filamentation at the shock front
• Field amplification in excess of that expected from compression alone.
• Electron acceleration to near energy-equipartition with ions.
• Expect significant synchotron (jitter) radiation
Future Work
• 3D Simulations
• Transient Shock
Obrigado!
0 2000 4000 6000 80000
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log(!), Time = 18000"t
0.0 0.6 1.3 1.9 2.5 3.2 3.8
0 2000 4000 6000 80000
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log(B2), Time = 16000!t
-3.1 -2.2 -1.2 -0.3 0.6 1.6 2.5
0 2000 4000 6000 80000
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Electron Phase Space, Time = 16000!t
0.3 1.2 2.1 3.0 3.9 4.8 5.7
0 2000 4000 6000 8000-1.0
-0.5
0.0
0.5
Ion Phase Space, Time = 16000!t
0.3 1.1 1.9 2.7 3.4 4.2 5.0