Finite Larmor Radius Effects on Weakly Magnetized, Dilute Plasmas

TL;DR

This paper studies how finite Larmor radius effects influence the stability of weakly magnetized, dilute plasmas, revealing that gyroviscosity can induce a strong instability surpassing the magnetorotational instability in growth rate.

Contribution

It introduces the impact of gyroviscosity and magnetic field pitch angles on plasma stability, highlighting a dominant gyroviscous instability in dilute astrophysical plasmas.

Findings

Gyroviscosity causes a powerful instability.

Most dilute plasmas are unstable under these effects.

Growth rates exceed those of standard magnetorotational instability.

Abstract

We investigate the stability properties of a hot, dilute and differentially rotating weakly magnetized plasma which is believed to be found in the interstellar medium of galaxies and protogalaxies and in the low-density accretion flows around some giant black holes like the one in the Galactic center. In the linear MHD regime, we consider the combined effects of gyroviscosity and parallel viscosity on the magnetorotational instability. The helical magnetic field is considered in the investigation. We show that the gyroviscous effect and the pitch angles cause a powerful gyroviscous instability. Furthermore, in most of the cases, plasma with the above mentioned properties is unstable and the growth rates of the unstable modes are larger than that of the magnetorotational instability.