Dynamo quenching due to shear flow

TL;DR

This paper develops a theory showing that shear flow significantly suppresses the alpha effect and turbulent viscosity in magnetohydrodynamics, impacting dynamo action and momentum transport in plasmas like the Sun.

Contribution

It demonstrates for the first time that shear flow reduces the alpha effect even without magnetic fields and explores how magnetic fields further suppress it, providing new insights into dynamo quenching.

Findings

Shear flow severely reduces the alpha effect.

Magnetic fields below equipartition further suppress the alpha effect.

Turbulent viscosity is significantly reduced by shear and magnetic fields.

Abstract

We provide a theory of dynamo ($\alpha$ effect) and momentum transport in three-dimensional magnetohydrodynamics. For the first time, we show that the $\alpha$ effect is severely reduced by the shear even in the absence of magnetic field. The $\alpha$ effect is further suppressed by magnetic fields well below equipartition (with the large-scale flow) with different scalings depending on the relative strength of shear and magnetic field. The turbulent viscosity is also found to be significantly reduced by shear and magnetic fields, with positive value. These results suggest a crucial effect of shear and magnetic field on dynamo quenching and momentum transport reduction, with important implications for laboratory and astrophysical plasmas, in particular for the dynamics of the Sun.