Turbulence Reduces Magnetic Diffusivity in a Liquid Sodium Experiment

TL;DR

This study demonstrates that turbulence in a liquid sodium experiment can reduce magnetic diffusivity, potentially aiding the self-generation of large-scale magnetic fields, supported by experimental and numerical evidence.

Contribution

It provides the first detailed measurement of turbulence effects on magnetic diffusivity in a liquid sodium spherical Couette setup.

Findings

Turbulence acts as a negative contribution to magnetic diffusivity in the interior.

Numerical simulations support the experimental results.

Reduced magnetic diffusivity due to turbulence can facilitate magnetic field self-generation.

Abstract

The contribution of small scale turbulent fluctuations to the induction of mean magnetic field is investigated in our liquid sodium spherical Couette experiment with an imposed magnetic field.An inversion technique is applied to a large number of measurements at $Rm \approx 100$ to obtain radial profiles of the $\alpha$ and $\beta$ effects and maps of the mean flow.It appears that the small scale turbulent fluctuations can be modeled as a strong contribution to the magnetic diffusivity that is negative in the interior region and positive close to the outer shell.Direct numerical simulations of our experiment support these results.The lowering of the effective magnetic diffusivity by small scale fluctuations implies that turbulence can actually help to achieve self-generation of large scale magnetic fields.