Electron Kelvin-Helmholtz Instability at Quasi-perpendicular Shocks

Electron-scale instabilities at collisionless shocks are central to plasma dissipation and particle energization, yet their physical origin and nonlinear consequences remain poorly constrained. In this presentation, we investigate the development and impact of electron Kelvin–Helmholtz instability (EKHI) at quasi-perpendicular shocks, which reveals a new pathway for electron acceleration and electron-scale structure formation.

High-resolution particle-in-cell simulations show that intense electron velocity shear naturally forms along the shock surface due to drift motion. When the shear layer thickness approaches electron kinetic scales, it becomes unstable to EKHI. This instability is localized within the shock transition, evolves on electron timescales, and is fundamentally distinct from ion-scale KH modes commonly observed at planetary boundaries.

In the nonlinear stage, the EKHI generates coherent electron vortices embedded within the shock ramp. These vortices are accompanied by strong bipolar parallel electric fields and pronounced charge separation, which effectively generate field-aligned electron beams therein. Interestingly, we further demonstrate that EKHI between the reforming shock fronts can produce electron vortex magnetic holes, which are electron-scale coherent structures frequently observed in turbulent plasma. This indicates a possible generation mechanism for electron-scale magnetic holes in Earth's magnetosheath.

These results identify EKHI as a key mechanism linking shock-surface shear flows, electron vortices, magnetic holes, and electron energization at quasi-perpendicular shocks. This process provides a viable pre-acceleration channel for electrons and has broad implications for kinetic-scale energy conversion at collisionless shocks.