Transverse electron-scale instability in relativistic shear flows

TL;DR

This paper demonstrates that electron-scale surface waves in relativistic shear flows are unstable in the transverse plane, leading to significant microscopic and macroscopic phenomena relevant for astrophysical plasma processes.

Contribution

It reveals the instability of electron-scale surface waves in relativistic shear flows and verifies results with simulations, highlighting their role in plasma dynamics and field generation.

Findings

Unstable electron-scale surface waves in relativistic shear flows.

Higher growth rates than Kelvin-Helmholtz instability.

Formation of mushroom-like electron density structures.

Abstract

Electron-scale surface waves are shown to be unstable in the transverse plane of a shear flow in an initially unmagnetized plasma, unlike in the (magneto)hydrodynamics case. It is found that these unstable modes have a higher growth rate than the closely related electron-scale Kelvin-Helmholtz instability in relativistic shears. Multidimensional particle-in-cell simulations verify the analytic results and further reveal the emergence of mushroom-like electron density structures in the nonlinear phase of the instability, similar to those observed in the Rayleigh Taylor instability despite the great disparity in scales and different underlying physics. Macroscopic ($\gg c/\omega_{pe}$) fields are shown to be generated by these microscopic shear instabilities, which are relevant for particle acceleration, radiation emission and to seed MHD processes at long time-scales.