Enhanced dynamo growth in nonhomogeneous conducting fluids

TL;DR

This paper demonstrates that inhomogeneous electrical conductivity and magnetic permeability can significantly lower the threshold for magnetic-field generation in dynamo systems, with implications for laboratory and astrophysical applications.

Contribution

It shows that inhomogeneities in conductivity and permeability reduce dynamo thresholds and extends a duality argument linking different dynamo configurations beyond mean-field theory.

Findings

Inhomogeneous conductivity or permeability lowers dynamo stability thresholds.

A duality relation connects different dynamo setups with unchanged thresholds.

Potential for observing these effects in laboratory and astrophysical contexts.

Abstract

We address magnetic-field generation by dynamo action in systems with inhomogeneous electrical conductivity and magnetic permeability. More specifically, we first show that the Taylor-Couette kinematic dynamo undergoes a drastic reduction of its stability threshold when a (zero-mean) modulation of the fluid's electrical conductivity or magnetic permeability is introduced. These results are obtained outside the mean-field regime, for which this effect was initially proposed. Beyond this illustrative example, we extend a duality argument put forward by Favier \& Proctor {(2013)} to show that swapping the distributions of conductivity and permeability and changing ${ u}\to -{ u}$ leaves the dynamo threshold unchanged. This allows one to make connections between {\it a priori} unrelated dynamo studies. Finally, we discuss the possibility of observing such an effect both in laboratory and astrophysical settings.