Hall current effects in mean-field dynamo theory

Abstract

The role of the Hall term on large scale dynamo action is investigated by means of the First Order Smoothing Approximation. It is shown that the standard $\alpha$ coefficient is altered, and is zero when a specific double Beltrami state is attained, in contrast to the Alfvénic state for MHD dynamos. The $\beta$ coefficient is no longer positive definite, and thereby enables dynamo action even if $\alpha$-quenching were to operate. The similarities and differences with the (magnetic) shear-current effect are pointed out, and a mechanism that may be potentially responsible for $\beta <0$ is advanced. The results are compared against previous studies, and their astrophysical relevance is also highlighted.

7 pages; 0 figures

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• Hall MHD waves: A fundamental departure from their MHD counterparts
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• A new and alternative look at NonLinear Alfvénic States
• Discrete Symmetries in Dynamo Reversals