Particle-in-cell simulation study of a lower-hybrid shock

TL;DR

This study uses particle-in-cell simulations to analyze how a magnetized high-pressure plasma expands into a low-pressure medium, forming a lower-hybrid shock and revealing the effects of magnetic fields and electron drift on shock dynamics.

Contribution

It provides new insights into the formation and evolution of lower-hybrid shocks in magnetized plasmas through detailed PIC simulation analysis.

Findings

LH shock transforms into nonlinear LH wave due to ion acceleration.

Magnetic field pile-up modifies shock structure and oscillations.

Electron drift causes energy loss and shock slowdown.

Abstract

The expansion of a magnetized high-pressure plasma into a low-pressure ambient medium is examined with particle-in-cell (PIC) simulations. The magnetic field points perpendicularly to the plasma's expansion direction and binary collisions between particles are absent. The expanding plasma steepens into a quasi-electrostatic shock that is sustained by the lower-hybrid (LH) wave. The ambipolar electric field points in the expansion direction and it induces together with the background magnetic field a fast E cross B drift of electrons. The drifting electrons modify the background magnetic field, resulting in its pile-up by the LH shock. The magnetic pressure gradient force accelerates the ambient ions ahead of the LH shock, reducing the relative velocity between the ambient plasma and the LH shock to about the phase speed of the shocked LH wave, transforming the LH shock into a nonlinear LH wave. The oscillations of the electrostatic potential have a larger amplitude and wavelength in the magnetized plasma than in an unmagnetized one with otherwise identical conditions. The energy loss to the drifting electrons leads to a noticable slowdown of the LH shock compared to that in an unmagnetized plasma.