Particle simulation study of electron heating by counterstreaming ion beams ahead of supernova remnant shocks

TL;DR

This study uses particle-in-cell simulations to investigate electron heating mechanisms and magnetic field growth caused by Buneman-type instabilities in the foreshock region of supernova remnant shocks, revealing saturation via phase space holes.

Contribution

It identifies the nonlinear saturation mechanisms and electron heating processes in Buneman-type instabilities specific to supernova remnant shock conditions.

Findings

Instabilities saturate through phase space hole formation.

Electrons develop two distinct velocity distributions.

Magnetic field growth occurs but remains weak.

Abstract

The growth and saturation of Buneman-type instabilities is examined with a particle-in-cell (PIC) simulation for parameters that are representative for the foreshock region of fast supernova remnant (SNR) shocks. A dense ion beam and the electrons correspond to the upstream plasma and a fast ion beam to the shock-reflected ions. The purpose of the 2D simulation is to identify the nonlinear saturation mechanisms, the electron heating and potential secondary instabilities that arise from anisotropic electron heating and result in the growth of magnetic fields. We confirm that the instabilities between both ion beams and the electrons saturate by the formation of phase space holes by the beam-aligned modes. The slower oblique modes accelerate some electrons, but they can not heat up the electrons significantly before they are trapped by the faster beam-aligned modes. Two circular electron velocity distributions develop, which are centred around the velocity of each ion beam. They develop due to the scattering of the electrons by the electrostatic wave potentials. The growth of magnetic fields is observed, but their amplitude remains low.