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.

arXiv comment10 pages, 6 figures, to appear in Journal of Plasma Physics

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