Noise-Sustained Convective Instability in a Magnetized Taylor-Couette Flow

TL;DR

This study numerically investigates the magnetorotational instability in a magnetized Taylor-Couette flow, revealing that experimental wave patterns are noise-sustained convective instabilities rather than absolute instabilities.

Contribution

It demonstrates that boundary conditions and noise sources influence the observed instabilities, clarifying the nature of experimental wave patterns in magnetized Taylor-Couette flows.

Findings

Distant upstream boundary stabilizes convective instability.

Wave patterns are noise-sustained convective instabilities.

Experiments have not yet achieved absolute instability regime.

Abstract

The helical magnetorotational instability of the magnetized Taylor-Couette flow is studied numerically in a finite cylinder. A distant upstream insulating boundary is shown to stabilize the convective instability entirely while reducing the growth rate of the absolute instability. The reduction is less severe with larger height. After modeling the boundary conditions properly, the wave patterns observed in the experiment turn out to be a noise-sustained convective instability. After the source of the noise resulted from unstable Ekman and Stewartson layers is switched off, a slowly-decaying inertial oscillation is observed in the simulation. We reach the conclusion that the experiments completed to date have not yet reached the regime of absolute instability.