Magnetic field reversals in an experimental turbulent dynamo

TL;DR

This paper reports the first laboratory observation of magnetic field reversals in a turbulent liquid sodium dynamo, showing random switching between two symmetric states and similarities to Earth's magnetic behavior.

Contribution

It provides the first experimental evidence of magnetic field reversals in a turbulent dynamo, highlighting the role of flow parameters and revealing a hierarchy of time scales.

Findings

Magnetic field randomly switches between two symmetric states.

Reversal durations are much longer than switching times.

Reversals and excursions correlate with minima in mechanical power.

Abstract

We report the first experimental observation of reversals of a dynamo field generated in a laboratory experiment based on a turbulent flow of liquid sodium. The magnetic field randomly switches between two symmetric solutions B and -B. We observe a hierarchy of time scales similar to the Earth's magnetic field: the duration of the steady phases is widely distributed, but is always much longer than the time needed to switch polarity. In addition to reversals we report excursions. Both coincide with minima of the mechanical power driving the flow. Small changes in the flow driving parameters also reveal a large variety of dynamo regimes.