Linear Vlasov Theory in the Shearing Sheet Approximation with Application to the Magneto-Rotational Instability

TL;DR

This paper develops a kinetic theory framework for analyzing the magneto-rotational instability in collisionless, differentially rotating plasmas using the shearing sheet approximation, extending previous models and clarifying stability conditions.

Contribution

It generalizes linear Vlasov theory to shearing sheets, enabling detailed kinetic stability analysis of MRI in collisionless plasmas, including new stability insights.

Findings

Derived the conductivity tensor for shearing sheet plasmas.

Revealed stability of initially unmagnetized cold collisionless plasmas.

Showed reduction to known models like Hall MHD and gyro-viscous limits.

Abstract

We derive the conductivity tensor for axisymmetric perturbations of a hot, collisionless, and charge-neutral plasma in the shearing sheet approximation. Our results generalize the well-known linear Vlasov theory for uniform plasmas to differentially rotating plasmas and can be used for wide range of kinetic stability calculations. We apply these results to the linear theory of the magneto-rotational instability (MRI) in collisionless plasmas. We show analytically and numerically how the general kinetic theory results derived here reduce in appropriate limits to previous results in the literature, including the low frequency guiding center (or "kinetic MHD") approximation, Hall MHD, and the gyro-viscous approximation. We revisit the cold plasma model of the MRI and show that, contrary to previous results, an initially unmagnetized collisionless plasma is linearly stable to axisymmetric perturbations in the cold plasma approximation. In addition to their application to astrophysical plasmas, our results provide a useful framework for assessing the linear stability of differentially rotating plasmas in laboratory experiments.