Dynamo efficiency with shear in helical turbulence

TL;DR

This paper investigates how shear flow influences magnetic field generation in helical turbulence, revealing that weak shear enhances turbulence and transport coefficients, while strong shear suppresses them, affecting dynamo efficiency.

Contribution

It introduces a non-perturbative approach to incorporate shear effects in helically forced turbulence, showing differential impacts on turbulence intensity and transport coefficients.

Findings

Weak shear enhances turbulence and transport coefficients.

Strong shear suppresses turbulence and transport coefficients.

Beta effect is more strongly suppressed than alpha effect.

Abstract

To elucidate the influence of shear flow on the generation of magnetic field (the dynamo effect), we study the kinematic limit where the magnetic field does not backreact on the velocity field. By non-perturbatively incorporating the effect of shear in a helically forced turbulence, we show that turbulence intensity and turbulent transport coefficients (turbulent viscosity, $\alpha$ and $\beta$ effect) are enhanced by a weak shear while strongly suppressed for strong shear. In particular, $\beta$ is shown to be much more strongly suppressed than $\alpha$ effect. We discuss its important implications for dynamo efficiency, i.e. on the scaling of the dynamo number with differential rotation.