Pumping velocity in homogeneous helical turbulence with shear

TL;DR

This paper develops a comprehensive mean-field theory for magnetic field pumping in homogeneous helical turbulence with shear, combining analytical methods and numerical simulations to validate the theoretical predictions.

Contribution

It introduces a new mean-field theory for magnetic pumping in shear flows, integrating multiple analytical approaches with numerical validation.

Findings

Effective pumping velocity is proportional to alpha effect and vorticity.

Numerical simulations agree with theoretical predictions.

Pumping causes separation of magnetic field components along vorticity.

Abstract

Using different analytical methods (the quasi-linear approach, the path-integral technique and tau-relaxation approximation) we develop a comprehensive mean-field theory for a pumping effect of the mean magnetic field in homogeneous non-rotating helical turbulence with imposed large-scale shear. The effective pumping velocity is proportional to the product of alpha effect and large-scale vorticity associated with the shear, and causes a separation of the toroidal and poloidal components of the mean magnetic field along the direction of the mean vorticity. We also perform direct numerical simulations of sheared turbulence in different ranges of hydrodynamic and magnetic Reynolds numbers and use a kinematic test-field method to determine the effective pumping velocity. The results of the numerical simulations are in agreement with the theoretical predictions.