Dynamo mechanism: Effects of correlations and viscosities

TL;DR

This paper investigates how background velocity, magnetic field correlations, and viscosities influence turbulent dynamo processes, revealing that initial growth and saturation are largely unaffected by these factors and identifying conditions for dynamo suppression.

Contribution

It provides a comprehensive calculation of oefficient dependencies on viscosities and correlations, and explores the hydrodynamic limit and suppression conditions within a renormalization group framework.

Findings

Magnetic field growth is qualitatively independent of initial correlations.

Dynamo growth requires Ekman number M > 1/2 for Kolmogorov spectra.

Suppression of dynamo growth occurs below a critical rotation rate.

Abstract

We analyze the effects of the background velocity and the initial magnetic field correlations, and viscosities on the turbulent dynamo and the \alpha-effect. We calculate the \alpha-coefficients for arbitrary magnetic and fluid viscosities, background velocity and the initial magnetic field correlations. We explicitly demonstrate that the general features of the initial growth and late-time saturation of the magnetic fields due to the non-linear feedback are qualitatively independent of these correlations. We also examine the hydrodynamic limit of the magnetic field growth in a renormalization group framework and discuss the possibilities of suppression of the dynamo growth below a critical rotation. We demonstrate that for Kolmogorov- (K41) type of spectra the Ekman number M >1/2 for dynamo growth to occur.