Electron-scale Kelvin-Helmholtz instability in magnetized shear flows

TL;DR

This paper derives a generalized dispersion relation for electron-scale Kelvin-Helmholtz instabilities in relativistic magnetized shear flows, providing insights into how magnetic fields influence instability growth rates and modes, validated by PIC simulations.

Contribution

It presents the first analytical dispersion relation for ESKHI in relativistic magnetized flows and numerically calculates growth rates under various magnetic field conditions.

Findings

Magnetic fields generally decrease ESKHI growth rates.

High shear velocities can slightly increase growth rates with magnetic fields.

PIC simulations confirm the suppression of magnetic field generation due to external magnetic fields.

Abstract

Electron-scale Kelvin-Helmholtz instabilities (ESKHI) are found in several astrophysical scenarios. Naturally ESKHI is subject to a background magnetic field, but an analytical dispersion relation and an accurate growth rate of ESKHI under this circumstance are long absent, as former MHD derivations are not applicable in the relativistic regime. We present a generalized dispersion relation of ESKHI in relativistic magnetized shear flows, with few assumptions. ESKHI linear growth rates in certain cases are numerically calculated. We conclude that the presence of an external magnetic field decreases the maximum instability growth rate in most cases, but can slightly increase it when the shear velocity is sufficiently high. Also, the external magnetic field results in a larger cutoff wavenumber of the unstable band and increases the wavenumber of the most unstable mode. PIC simulations are carried out to verify our conclusions, where we also observe the suppressing of kinetic DC magnetic field generation, resulting from electron gyration induced by the external magnetic field.