Particles trajectories in Weibel magnetic filaments with a flow-aligned magnetic field

TL;DR

This paper investigates how an external magnetic field influences the formation of Weibel magnetic filaments and shock initiation in plasma collisions, revealing that sufficiently strong guiding fields prevent filament blocking of incoming flows.

Contribution

It demonstrates that an external magnetic field modifies filament behavior and shock formation conditions, extending understanding of plasma dynamics in magnetized environments.

Findings

External magnetic fields affect filament size and shock formation.

Filaments cannot block particles when external field exceeds half the peak filament field.

Shock formation depends on the ratio of external to filament magnetic fields.

Abstract

For a Weibel shock to form, two plasma shells have to collide and trigger the Weibel instability. At saturation, this instability generates in the overlapping region magnetic filaments with peak field $B_f$. In the absence of an external guiding magnetic field, these filaments can block the incoming flow, initiating the shock formation, if their size is larger than the Larmor radius of the incoming particles in the peak field. Here we show that this results still holds in the presence of an external magnetic field $B_0$, provided it is not too high. Yet, for $B_0 \gtrsim B_f/2$, the filaments become unable to stop any particle, regardless of its initially velocity.