Energy oscillations and a possible route to chaos in a modified Riga dynamo

TL;DR

This paper investigates how modifications to the Riga dynamo setup, specifically increasing azimuthal flow, can lead to energy oscillations and chaos, revealing magneto-inertial waves and complex dynamical transitions.

Contribution

It introduces a modified Riga dynamo model with increased azimuthal flow, demonstrating the emergence of energy oscillations and routes to chaos not present in the original configuration.

Findings

Energy oscillations occur with increased azimuthal flow.

Magneto-inertial waves are identified as a new dynamic regime.

Transitions to chaos are observed at higher magnetic Reynolds numbers.

Abstract

Starting from the present version of the Riga dynamo experiment with its rotating magnetic eigenfield dominated by a single frequency we ask for those modifications of this set-up that would allow for a non-trivial magnetic field behaviour in the saturation regime. Assuming an increased ratio of azimuthal to axial flow velocity, we obtain energy oscillations with a frequency below the eigenfrequency of the magnetic field. These new oscillations are identified as magneto-inertial waves that result from a slight imbalance of Lorentz and inertial forces. Increasing the azimuthal velocity further, or increasing the total magnetic Reynolds number, we find transitions to a chaotic behaviour of the dynamo.