Two-dimensional PIC simulations of ion-beam instabilities in Supernova-driven plasma flows

TL;DR

This study uses 2D PIC simulations to explore ion-beam instabilities in supernova remnant plasma flows, revealing how different collision scenarios generate waves and fields that accelerate particles and influence shock formation.

Contribution

It provides new insights into the nonlinear interactions of ion-beam driven waves in supernova remnant shocks through detailed PIC simulations.

Findings

Upper-hybrid waves accelerate electrons to ~10 keV.

Asymmetric collisions produce large-scale electric fields.

Large-scale fields disrupt electron phase space holes and accelerate ions.

Abstract

Supernova remnant (SNR) blast shells can reach the flow speed $v_s = 0.1 c$ and shocks form at its front. Instabilities driven by shock-reflected ion beams heat the plasma in the foreshock, which may inject particles into diffusive acceleration. The ion beams can have the speed $v_b \approx v_s$. For $v_b \ll v_s$ the Buneman or upper-hybrid instabilities dominate, while for $v_b \gg v_s$ the filamentation and mixed modes grow faster. Here the relevant waves for $v_b \approx v_s$ are examined and how they interact nonlinearly with the particles. The collision of two plasma clouds at the speed $v_s$ is modelled with particle-in-cell (PIC) simulations, which convect with them magnetic fields oriented perpendicular to their flow velocity vector. One simulation models equally dense clouds and the other one uses a density ratio of 2. Both simulations show upper-hybrid waves that are planar over large spatial intervals and that accelerate electrons to $\sim$ 10 keV. The symmetric collision yields only short oscillatory wave pulses, while the asymmetric collision also produces large-scale electric fields, probably through a magnetic pressure gradient. The large-scale fields destroy the electron phase space holes and they accelerate the ions, which facilitates the formation of a precursor shock.