Role of soft-iron impellers on the mode selection in the VKS dynamo experiment

TL;DR

This paper uses numerical simulations to demonstrate that soft-iron impellers significantly influence the mode selection in the VKS dynamo experiment, highlighting their crucial role in the magnetic field generation process.

Contribution

The study introduces a localized permeability model to simulate soft-iron impellers, revealing their essential impact on the dynamo mechanism in the VKS experiment.

Findings

Soft-iron impellers determine the dominant magnetic mode.

An axisymmetric magnetic field mode is explained by the combined effects of soft-iron and small-scale flow.

Permeability distribution influences the dynamo process significantly.

Abstract

A crucial point for the understanding of the von-K\'arm\'an-Sodium (VKS) dynamo experiment is the influence of soft-iron impellers. We present numerical simulations of a VKS-like dynamo with a localized permeability distribution that resembles the shape of the flow driving impellers. It is shown that the presence of soft-iron material essentially determines the dynamo process in the VKS experiment. % An axisymmetric magnetic field mode can be explained by the combined action of the soft-iron disk and a rather small $\alpha$-effect parametrizing the induction effects of unresolved small scale flow fluctuations.