Large scale fluctuations and dynamics of the Bullard - von K\'arm\'an dynamo

TL;DR

This study investigates a synthetic fluid dynamo inspired by the Bullard device, focusing on how flow modifications influence dynamo behavior and the role of large-scale fluctuations in magnetic field reversals.

Contribution

It introduces a two-step dynamo model combining turbulence and alpha effect, analyzing the impact of flow modifications on dynamo dynamics and reversals.

Findings

On-off intermittency at dynamo onset is robust.

Large-scale fluctuations significantly influence magnetic reversals.

Flow modifications alter dynamo behavior and stability.

Abstract

A synthetic fluid dynamo built in the spirit of the Bullard device [E. C. Bullard, Proc. Camb. Phil. Soc., 51, 744 (1955)] is investigated. It is a two-step dynamo in which one process stems from the fluid turbulence, while the other part is an alpha effect achieved by a linear amplification of currents in external coils [M. Bourgoin et al., New J. Phys., 8, 329 (2006)]. Modifications in the forcing are introduced in order to change the dynamics of the flow, and hence the dynamo behavior. Some features, such as on-off intermittency at onset of dynamo action, are very robust. Large scales fluctuations have a significant impact on the resulting dynamo, in particular in the observation of magnetic field reversals.