Alpha-effect dynamos with zero kinetic helicity

TL;DR

This paper presents a Roberts-type dynamo model demonstrating that the alpha-effect can occur without kinetic helicity, challenging the traditional assumption that non-zero helicity is necessary for dynamo action.

Contribution

It provides the first explicit example of a dynamo with zero kinetic helicity and develops a mean-field theory within the second-order correlation approximation.

Findings

Dynamo action occurs despite zero kinetic helicity.

Theoretical and numerical results agree on the possibility of alpha-effect dynamos without helicity.

The model challenges previous assumptions about the necessity of helicity in dynamo processes.

Abstract

A simple explicit example of a Roberts-type dynamo is given in which the alpha-effect of mean-field electrodynamics exists in spite of point-wise vanishing kinetic helicity of the fluid flow. In this way it is shown that alpha-effect dynamos do not necessarily require non-zero kinetic helicity. A mean-field theory of Roberts-type dynamos is established within the framework of the second-order correlation approximation. In addition numerical solutions of the original dynamo equations are given, that are independent of any approximation of that kind. Both theory and numerical results demonstrate the possibility of dynamo action in the absence of kinetic helicity.