Magnetic dynamo action at low magnetic Prandtl numbers

TL;DR

This paper investigates magnetic dynamo amplification at low magnetic Prandtl numbers, highlighting the influence of kinetic helicity on dynamo efficiency in turbulent flows relevant to planetary, stellar, and laboratory contexts.

Contribution

It provides a comprehensive analysis using the Kazantsev-Kraichnan model to determine dynamo thresholds and growth rates, emphasizing the role of kinetic helicity at low magnetic Prandtl numbers.

Findings

Kinematic dynamo action is significantly affected by kinetic helicity at low magnetic Prandtl numbers.

Dynamo thresholds and growth rates depend on the helicity spectrum.

Properly chosen helicity spectra can enhance dynamo efficiency.

Abstract

Amplification of magnetic field due to kinematic turbulent dynamo action is studied in the regime of small magnetic Prandtl numbers. Such a regime is relevant for planets and stars interiors, as well as for liquid metal laboratory experiments. A comprehensive analysis based on the Kazantsev-Kraichnan model is reported, which establishes the dynamo threshold and the dynamo growth rates for varying kinetic helicity of turbulent fluctuations. It is proposed that in contrast with the case of large magnetic Prandtl numbers, the kinematic dynamo action at small magnetic Prandtl numbers is significantly affected by kinetic helicity, and it can be made quite efficient with an appropriate choice of the helicity spectrum.