Electron Beams Generated by the Electron Kelvin‐Helmholtz Instability at a Quasi‐Perpendicular Shock

Abstract Electron beams are considered to be important free energy sources for the excitation of various plasma waves at quasi‐perpendicular shocks. In this article, we perform a two‐dimensional particle‐in‐cell simulation of a low‐plasma‐ β quasi‐perpendicular shock. The magnetic field at the shock ramp has a large gradient, where upstream electrons and ions are separated due to their different gyro‐radius. This charge separation induces a sub‐ion scale electric field at the shock ramp. The electric drift of electrons in this field can induce an electron shear flow, resulting in the excitation of Kelvin‐Helmholtz instability and the generation of electron vortices. These vortices further cause charge separation at their centers, resulting in a large electrostatic field. The electrons trapped in these vortices can gain energy from the parallel component of the electric field, which eventually leads to field‐aligned electron beams. Our results provide a novel process for generating electron beams at low‐plasma‐ β quasi‐perpendicular shocks.