Experimental Confirmation of the Standard Magnetorotational Instability Mechanism with a Spring-Mass Analogue

TL;DR

This paper presents the first direct laboratory demonstration of the standard magnetorotational instability (MRI) using a spring-mass analogue, confirming the theory that weak springs enable outward angular momentum transport in rotating flows.

Contribution

It introduces a novel experimental method to replicate MRI using a spring-mass system, bridging solid mechanics and plasma astrophysics.

Findings

Efficient outward angular momentum transport occurs only with weak springs.

The spring-mass analogue accurately replicates MRI behavior.

The experiment confirms theoretical predictions of MRI mechanisms.

Abstract

The Magnetorotational Instability (MRI) has long been considered a plausibly ubiquitous mechanism to destabilize otherwise stable Keplerian flows to support radially outward transport of angular momentum. Such an efficient transport process would allow fast accretion in astrophysical objects such as stars and black holes to release copious kinetic energy that powers many of the most luminous sources in the universe. But the standard MRI under a purely vertical magnetic field has heretofore never been directly measured despite numerous efforts over more than a decade. Here we report an unambiguous laboratory demonstration of the spring-mass analogue to the standard MRI by comparing motion of a spring-tethered ball within different rotating flows. The experiment corroborates the theory: efficient outward angular momentum transport manifests only for cases with a weak spring in quasi-Keperian flow. Our experimental method accomplishes this in a new way, thereby connecting solid and fluid mechanics to plasma astrophysics.