Effect of electromagnetic boundary conditions on the onset of small-scale dynamos driven by convection

TL;DR

This study investigates how different electromagnetic boundary conditions influence the onset of small-scale dynamos in convective flows, revealing that conducting boundaries significantly promote dynamo action and that certain boundary conditions lead to Ra-independent critical magnetic Reynolds numbers.

Contribution

It provides a high-order numerical analysis of the impact of electromagnetic boundary conditions on dynamo onset in convective flows, highlighting the role of boundary types in dynamo efficiency.

Findings

Conducting boundaries facilitate dynamo action.

Mixed boundary conditions lead to Ra-independent critical magnetic Reynolds number.

The numerical method achieves near-spectral accuracy.

Abstract

We present a high-order numerical study of the dependence of the dynamo onset on different electromagnetic boundary conditions, in convecting Boussinesq flows forced by a temperature gradient. Perfectly conducting boundaries, vacuum, and mixed electromagnetic boundary conditions are considered, using a method that treats fields and boundary conditions with close to spectral accuracy. Having one or two conducting boundaries greatly facilitates dynamo action. For the mixed case it is shown that the critical magnetic Reynolds number becomes independent of the Rayleigh number, Ra, for sufficiently large Ra.