Buneman instability in a magnetized current-carrying plasma with velocity shear

TL;DR

This study investigates how velocity shear influences the Buneman instability in magnetized plasmas, revealing that shear broadens unstable modes and affects wave coupling, with implications for magnetic reconnection turbulence.

Contribution

It combines Mathieu-equation analysis and Vlasov simulations to explore shear effects on Buneman instability, a novel approach in this context.

Findings

Shear enhances coupling between oblique waves and electron beams.

Wider range of unstable eigenmodes with lower growth rates due to shear.

Lower hybrid instabilities are unaffected by shear.

Abstract

Buneman instability is often driven in magnetic reconnection. Understanding how velocity shear in the beams driving the Buneman instability affects the growth and saturation of waves is relevant to turbulence, heating, and diffusion in magnetic reconnection. Using a Mathieu-equation analysis for weak cosine velocity shear together with Vlasov simulations, the effects of shear on the kinetic Buneman instability are studied in a plasma consisting of strongly magnetized electrons and cold unmagnetized ions. In the linearly unstable phase, shear enhances the coupling between oblique waves and the sheared electron beam, resulting in a wider range of unstable eigenmodes with common lower growth rates. The wave couplings generate new features of the electric fields in space, which can persist into the nonlinear phase when electron holes form. Lower hybrid instabilities simultaneously occur at $k_{\shortparallel}/k_{\perp} \sim \sqrt{m_e/m_i}$ with a much lower growth rate, and are not affected by the velocity shear.