Electrostatic and electromagnetic instabilities associated with electrostatic shocks: two-dimensional particle-in-cell simulation

TL;DR

This study uses two-dimensional particle-in-cell simulations to explore how electrostatic and electromagnetic instabilities influence the structure and evolution of high-speed collisionless shocks in plasma, revealing the roles of ion-ion and beam-Weibel instabilities.

Contribution

It demonstrates the development and impact of electrostatic and electromagnetic instabilities on shock dynamics using realistic ion-to-electron mass ratio simulations.

Findings

Electrostatic ion-ion instability can destroy shock structure.

Beam-Weibel instability leads to magnetic field growth and long-term shock evolution.

Secondary electrostatic shocks can form in reflected ions.

Abstract

A two-dimensional electromagnetic particle-in-cell simulation with the realistic ion-to-electron mass ratio of 1836 is carried out to investigate the electrostatic collisionless shocks in relatively high-speed (~3000 km s^-1) plasma flows and also the influence of both electrostatic and electromagnetic instabilities, which can develop around the shocks, on the shock dynamics. It is shown that the electrostatic ion-ion instability can develop in front of the shocks, where the plasma is under counter-streaming condition, with highly oblique wave vectors as was shown previously. The electrostatic potential generated by the electrostatic ion-ion instability propagating obliquely to the shock surface becomes comparable with the shock potential and finally the shock structure is destroyed. It is also shown that in front of the shock the beam-Weibel instability gradually grows as well, consequently suggesting that the magnetic field generated by the beam-Weibel instability becomes important in long-term evolution of the shock and the Weibel-mediated shock forms long after the electrostatic shock vanished. It is also observed that the secondary electrostatic shock forms in the reflected ions in front of the primary electrostatic shock.