Convective, absolute and global azimuthal magnetorotational instabilities

TL;DR

This paper investigates the different forms of azimuthal magnetorotational instability in Taylor-Couette flow, emphasizing the importance of absolute instability for experimental detection and analyzing the global structure through DNS and linear stability analysis.

Contribution

It provides a comprehensive analysis of convective, absolute, and global AMRI in Taylor-Couette flow, highlighting the significance of absolute instability for experiments and linking global patterns to linear modes.

Findings

Absolute AMRI is more relevant for experiments than convective AMRI.

Global AMRI exhibits a butterfly pattern consistent with linear stability modes.

DNS confirms the presence of two dominant absolute AMRI modes.

Abstract

We study the convective and absolute forms of azimuthal magnetorotational instability (AMRI) in a Taylor-Couette (TC) flow with an imposed azimuthal magnetic field. We show that the domain of the convective AMRI is wider than that of the absolute AMRI. Actually, it is the absolute instability which is the most relevant and important for magnetic TC flow experiments. The absolute AMRI, unlike the convective one, stays in the device, displaying a sustained growth that can be experimentally detected. We also study the global AMRI in a TC flow of finite height using DNS and find that its emerging butterfly-type structure -- a spatio-temporal variation in the form of upward and downward traveling waves -- is in a very good agreement with the linear stability analysis, which indicates the presence of two dominant absolute AMRI modes in the flow giving rise to this global butterfly pattern.