Magnetorotational instability driven dynamos at low magnetic Prandtl numbers

TL;DR

This study investigates how magnetic boundary conditions affect magnetorotational instability-driven dynamos at low magnetic Prandtl numbers, revealing that boundary conditions significantly influence MRI activity and dynamo saturation.

Contribution

It demonstrates that magnetic boundary conditions enable MRI and dynamo action at low Pm, which was not possible in fully periodic systems, highlighting the importance of boundary effects.

Findings

MRI activity depends on boundary conditions.

Dynamo action occurs for 0.1 < Pm < 10 with vertical fields.

Saturation level of MRI is independent of Pm.

Abstract

Numerical simulations of the magnetorotational instability (MRI) with zero initial net flux in a non-stratified isothermal cubic domain are used to demonstrate the importance of magnetic boundary conditions.In fully periodic systems the level of turbulence generated by the MRI strongly decreases as the magnetic Prandtl number (Pm), which is the ratio of kinematic viscosity and magnetic diffusion, is decreased. No MRI or dynamo action below Pm=1 is found, agreeing with earlier investigations. Using vertical field conditions, which allow the generation of a net toroidal flux and magnetic helicity fluxes out of the system, the MRI is found to be excited in the range 0.1 < Pm < 10, and that the saturation level is independent of Pm. In the vertical field runs strong mean-field dynamo develops and helps to sustain the MRI.