Saturation of Magnetorotational Instability through Magnetic Field Generation

TL;DR

This paper investigates how the Magnetorotational Instability (MRI) saturates in astrophysical plasmas, showing that magnetic field generation via the alpha effect plays a key role in limiting MRI growth.

Contribution

It provides an analytical and computational study revealing the magnetic field generation as the primary saturation mechanism of MRI in astrophysical contexts.

Findings

Large-scale magnetic fields are generated through the alpha effect.

MRI mode saturates via magnetic field growth when flow relaxation is constrained.

Flow relaxation can also cause saturation if the plasma flow is allowed to evolve.

Abstract

The saturation mechanism of Magneto-Rotational Instability (MRI) is examined through analytical quasilinear theory and through nonlinear computation of a single mode in a rotating disk. We find that large-scale magnetic field is generated through the alpha effect (the correlated product of velocity and magnetic field fluctuations) and causes the MRI mode to saturate. If the large-scale plasma flow is allowed to evolve, the mode can also saturate through its flow relaxation. In astrophysical plasmas, for which the flow cannot relax because of gravitational constraints, the mode saturates through field generation only.