Shear-driven instabilities in Hall-MHD plasmas

TL;DR

This paper investigates how the Hall effect influences plasma instabilities in shear flows, revealing a new Hall magneto-shear instability and analyzing its impact on known phenomena like the magneto-rotational instability.

Contribution

The study introduces the Hall magneto-shear instability, a new instability driven by the Hall effect in shear flows, and assesses its role in the development of the magneto-rotational instability.

Findings

Discovery of the Hall magneto-shear instability.

Quantitative analysis of Hall effect on MRI development.

Identification of the Hall effect's influence on plasma transport.

Abstract

The large-scale dynamics of plasmas is well described within the framework of magnetohydrodynamics (MHD). However, whenever the ion density of the plasma becomes sufficiently low, the Hall effect is likely to become important. The role of the Hall effect has been studied in several astrophysical plasma processes, such as magnetic reconnection, magnetic dynamo, MHD turbulence or MHD instabilities. In particular, the development of small-scale instabilities is essential to understand the transport properties in a number of astrophysical plasmas. The magneto-rotational instability, which takes place in differentially rotating accretion disks embedded in relatively weak magnetic fields, is just one example. The influence of the large-scale velocity flows on small-scale instabilities is often approximated by a linear shear flow. In this paper we quantitatively study the role of the Hall effect on plasmas embedded in large-scale shear flows. More precisely, we show that a new instability develops as long as the Hall effect is present, which we therefore term as the Hall magneto-shear instability. As a particular case, we recover the so-called magneto-rotational instability and quantitatively assess the role of the Hall effect on its development and evolution.