Thermoelectric Precession in Turbulent Magnetoconvection

TL;DR

This study investigates thermoelectric effects on turbulent magnetoconvection in liquid gallium, revealing that thermoelectric currents induce a precession of large-scale circulation, with a model predicting the dynamics accurately.

Contribution

The paper introduces a thermoelectric magnetoconvection model that explains the precession of large-scale circulation driven by thermoelectric currents in turbulent magnetoconvection.

Findings

Large-scale circulation precesses only with electrically conducting boundaries.

Precession direction reverses with magnetic field reversal.

Model accurately predicts precession frequency and dynamics.

Abstract

We present laboratory measurements of the interaction between thermoelectric currents and turbulent magnetoconvection. In a cylindrical volume of liquid gallium heated from below and cooled from above and subject to a vertical magnetic field, it is found that the large scale circulation (LSC) can undergo a slow axial precession. Our experiments demonstrate that this LSC precession occurs only when electrically conducting boundary conditions are employed, and that the precession direction reverses when the axial magnetic field direction is flipped. A thermoelectric magnetoconvection (TEMC) model is developed that successfully predicts the zeroth-order magnetoprecession dynamics. Our TEMC magnetoprecession model hinges on thermoelectric current loops at the top and bottom boundaries, which create Lorentz forces that generate horizontal torques on the overturning large-scale circulatory flow. The thermoelectric torques in our model act to drive a precessional motion of the LSC. This model yields precession frequency predictions that are in good agreement with the experimental observations. We postulate that thermoelectric effects in convective flows, long argued to be relevant in liquid metal heat transfer and mixing processes, may also have applications in planetary interior magnetohydrodynamics.