Particle trajectories in Weibel filaments: influence of external field obliquity and chaos

Abstract

When two collisionless plasma shells collide, they interpenetrate and the overlapping region may turn Weibel unstable for some values of the collision parameters. This instability grows magnetic filaments which, at saturation, have to block the incoming flow if a Weibel shock is to form. In a recent paper [J. Plasma Phys. (2016), vol. 82, 905820403], it was found implementing a toy model for the incoming particles trajectories in the filaments, that a strong enough external magnetic field ${\mathbf{B}}_0$ can prevent the filaments to block the flow if it is aligned with. Denoting $B_f$ the peak value of the field in the magnetic filaments, all test particles stream through them if $\alpha =B_0/B_f>1/2$. Here, this result is extended to the case of an oblique external field $B_0$ making an angle $\theta$ with the flow. The result, numerically found, is simply $\alpha >\kappa (\theta )/\cos \theta$, where $\kappa (\theta )$ is of order unity. Noteworthily, test particles exhibit chaotic trajectories.

10 pages, 6 figures, to appear in Journal of Plasma Physics

References in corpus (8)

• Particle acceleration in relativistic collisionless shocks: Fermi process at last?
• Relativistic Collisionless Shocks in Unmagnetized Electron-Positron Plasmas
• Physics of Weibel-mediated relativistic collisionless shocks
• Collisionless Weibel shocks: full formation mechanism and timing
• Simulation study of the formation of a non-relativistic pair shock
• Density jump as a function of magnetic field for collisionless shocks in pair plasmas: the perpendicular case
• Hierarchy of instabilities for two counter-streaming magnetized pair beams: influence of field obliquity
• Particles trajectories in Weibel magnetic filaments with a flow-aligned magnetic field