Electron Surfing and Drift Accelerations in a Weibel-dominated High-Mach-number Shock

TL;DR

This study uses 3D particle-in-cell simulations to reveal how electrons are accelerated to relativistic energies in high-Mach-number shocks through a combination of shock-surfing and stochastic drift mechanisms facilitated by ion-Weibel turbulence.

Contribution

It demonstrates the coexistence of electrostatic and magnetic turbulence in strong shocks and identifies ion-Weibel turbulence as crucial for efficient nonthermal electron acceleration.

Findings

Electrons gain energy via shock-surfing and drift accelerations.

Ion-Weibel turbulence is essential for nonthermal electron acceleration.

Energetic electrons undergo pitch-angle diffusion and continuous acceleration.

Abstract

How electrons get accelerated to relativistic energies in a high-Mach-number quasi-perpendicular shock is presented by means of ab initio particle-in-cell simulations in three dimensions. We found that coherent electrostatic Buneman waves and ion-Weibel magnetic turbulence coexist in a strong-shock structure whereby particles gain energy during shock-surfing and subsequent stochastic drift accelerations. Energetic electrons that initially experienced the surfing acceleration undergo pitch-angle diffusion by interacting with magnetic turbulence and continuous acceleration during confinement in the shock transition region. The ion-Weibel turbulence is the key to the efficient nonthermal electron acceleration.