Collisionless shock formation, spontaneous electromagnetic fluctuations, and streaming instabilities

Collisionless shocks are ubiquitous in astrophysics and in the lab. Recent numerical simulations and experiments have shown how they can arise from the encounter of two collisionless plasma shells. When the shells interpenetrate, the overlapping region turns unstable, triggering the shock formation....

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Bibliographic Details
Published in:Physics of plasmas 2013-04, Vol.20 (4)
Main Authors: Bret, A., Stockem, A., Fiuza, F., Ruyer, C., Gremillet, L., Narayan, R., Silva, L. O.
Format: Article
Language:English
Subjects:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY
ASTROPHYSICS
CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS
COLLISIONLESS PLASMA
COMPUTERIZED SIMULATION
FLUCTUATIONS
NUMERICAL ANALYSIS
PLASMA INSTABILITY
PLASMA SIMULATION
RELATIVISTIC PLASMA
RELATIVISTIC RANGE
SHOCK WAVES
TWO-DIMENSIONAL CALCULATIONS
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Summary:Collisionless shocks are ubiquitous in astrophysics and in the lab. Recent numerical simulations and experiments have shown how they can arise from the encounter of two collisionless plasma shells. When the shells interpenetrate, the overlapping region turns unstable, triggering the shock formation. As a first step towards a microscopic understanding of the process, we analyze here in detail the initial instability phase. On the one hand, 2D relativistic Particle-In-Cell simulations are performed where two symmetric initially cold pair plasmas collide. On the other hand, the instabilities at work are analyzed, as well as the field at saturation and the seed field which gets amplified. For mildly relativistic motions and onward, Weibel modes govern the linear phase. We derive an expression for the duration of the linear phase in good agreement with the simulations. This saturation time constitutes indeed a lower-bound for the shock formation time.
ISSN:1070-664X
1089-7674
DOI:10.1063/1.4798541