# Dynamo enhancement and mode selection triggered by high magnetic permeability

## TL;DR

This paper uses numerical simulations to study how high magnetic permeability in impellers can trigger and enhance dynamo action, reproducing experimental observations and revealing an axisymmetric dynamo mode.

## Contribution

It introduces a simulation approach modeling magnetic permeability jumps and demonstrates the emergence of an axisymmetric dynamo mode at high permeability thresholds.

## Key findings

- High magnetic permeability impellers trigger dynamo mode
- Simulation reproduces experimental dynamo observations
- Axisymmetric dynamo mode appears at permeability threshold

## Abstract

We present results from consistent dynamo simulations, where the electrically conducting and incompressible flow inside a cylinder vessel is forced by moving impellers numerically implemented by a penalization method. The numerical scheme models jumps of magnetic permeability for the solid impellers, resembling various configurations tested experimentally in the von-Karman Sodium experiment. The most striking experimental observations are reproduced in our set of simulations. In particular, we report on the existence of an axisymmetric dynamo mode, self-consistently generated when the magnetic permeability of the impellers exceeds a threshold. We describe a possible scenario involving both the turbulent flow in the vicinity of the impellers and the high magnetic permeability of the impellers.