Prospects for observing the magnetorotational instability in the Plasma Couette Experiment

TL;DR

This paper explores the potential to observe magnetorotational instability in plasma experiments, highlighting the effects of plasma-specific physics and proposing flow drive methods to achieve MRI conditions.

Contribution

It develops a stability analysis including plasma effects and suggests electrically driven flow as a feasible way to observe MRI in plasma experiments.

Findings

Ion-neutral collisions limit boundary-driven flows from reaching MRI conditions.

Electrically driven flows can achieve MRI-relevant parameters more easily.

Hardware upgrades are necessary for experimental realization.

Abstract

Many astrophysical disks, such as protoplanetary disks, are in a regime where non-ideal, plasma-specific magnetohydrodynamic (MHD) effects can significantly influence the behavior of the magnetorotational instability (MRI). The possibility of studying these effects in the Plasma Couette Experiment (PCX) is discussed. An incompressible, dissipative global stability analysis is developed to include plasma-specific two-fluid effects and neutral collisions, which are inherently absent in analyses of Taylor-Couette flows (TCFs) in liquid metal experiments. It is shown that with boundary driven flows, a ion-neutral collision drag body force significantly affects the azimuthal velocity profile, thus limiting the flows to regime where the MRI is not present. Electrically driven flow (EDF) is proposed as an alternative body force flow drive in which the MRI can destabilize at more easily achievable plasma parameters. Scenarios for reaching MRI relevant parameter space and necessary hardware upgrades are described.