A Self-Consistent Treatment of the Electromotive Force in Magnetohydrodynamics for Large Diffusivities

TL;DR

This paper extends mean field electrodynamics to include large diffusivities, revealing new coupling effects that can drive large-scale magnetic and velocity field growth even without traditional alpha-effects.

Contribution

It introduces a self-consistent approach accounting for the Lorentz force effects in high-diffusivity MHD flows, generalizing previous models.

Findings

New mean coupling terms identified that influence magnetic and velocity field growth.

Large-scale magnetic and velocity fields can grow without alpha-effects due to these new couplings.

The model extends the understanding of MHD flows in high-diffusivity regimes.

Abstract

The coupled equations that describe the effect of large-scale magnetic and velocity fields on forced high-diffusivity magnetohydrodynamic flows are investigated through an extension of mean field electrodynamics. Our results generalise those of R\"adler & Brandenburg (2010), who consider a similar situation but assume that the effect of the Lorentz force on the momentum equation can be neglected. New mean coupling terms are shown to appear, which can lead to large-scale growth of magnetic and velocity fields even when the usual $\alpha$-effects are absent.