Expansion of a radially symmetric blast shell into a uniformly magnetized plasma

TL;DR

This study uses 2D PIC simulations to explore how a radially symmetric blast shell expands into a magnetized plasma, revealing shock formations similar to MHD predictions and instabilities caused by magnetic field expulsion.

Contribution

It demonstrates that collisionless plasma shocks can resemble magnetohydrodynamic shocks and details the transition of shock types with propagation angles.

Findings

Formation of forward shocks resembling MHD shocks

Transition from ion acoustic to magnetosonic shocks with angle

Magnetic field expulsion triggers electron-cyclotron drift instability

Abstract

The expansion of a thermal pressure-driven radial blast shell into a dilute ambient plasma is examined with two-dimensional PIC simulations. The purpose is to determine if laminar shocks form in a collisionless plasma that resemble their magnetohydrodynamic counterparts. The ambient plasma is composed of electrons with the temperature 2 keV and cool fully ionized nitrogen ions. It is permeated by a spatially uniform magnetic field. A forward shock forms between the shocked ambient medium and the pristine ambient medium, which changes from an ion acoustic one through a slow magnetosonic one to a fast magnetosonic shock with increasing shock propagation angles relative to the magnetic field. The slow magnetosonic shock that propagates obliquely to the magnetic field changes into a tangential discontinuity for a perpendicular propagation direction, which is in line with the magnetohydrodynamic model. The expulsion of the magnetic field by the expanding blast shell triggers an electron-cyclotron drift instability.