Kelvin-Helmholtz versus Hall Magneto-shear instability in astrophysical flows

TL;DR

This paper compares Kelvin-Helmholtz and Hall magneto-shear instabilities in astrophysical plasma flows, revealing that under intense shear conditions, the microscopic Hall instability can dominate over the macroscopic Kelvin-Helmholtz instability.

Contribution

The study provides a comparative analysis of both instabilities using 3D simulations, highlighting conditions where the Hall magneto-shear instability surpasses Kelvin-Helmholtz growth rates.

Findings

Hall magneto-shear instability becomes dominant at high shear intensities.

Growth rates of Hall instability can exceed Kelvin-Helmholtz under certain conditions.

Microscopic instabilities are significant in low-density astrophysical plasmas.

Abstract

We study the stability of shear flows in a fully ionized plasma. Kelvin-Helmholtz is a well known, macroscopic and ideal shear-driven instability. In sufficiently low density plasmas, also the microscopic Hall magneto-shear instability can take place. We performed three-dimensional simulations of the Hall-MHD equations where these two instabilities are present, and carried out a comparative study. We find that when the shear flow is so intense that its vorticity surpasses the ion-cyclotron frequency of the plasma, the Hall magneto-shear instability is not only non-negligible, but it actually displays growth rates larger than those of the Kelvin-Helmholtz instability.