High Magnetic Shear Gain in a Liquid Sodium Stable Couette Flow Experiment; A Prelude to an alpha-Omega Dynamo

TL;DR

This study demonstrates a significant magnetic field amplification in a liquid sodium Couette flow experiment, providing insights into astrophysical magnetic field generation with low turbulence conditions.

Contribution

It presents the first experimental evidence of high magnetic shear gain in stable Couette flow, advancing understanding of dynamo mechanisms in low turbulence environments.

Findings

Achieved a toroidal magnetic field approximately 8 times the radial component.

Demonstrated high magnetic shear gain in stable, low turbulence flow.

Contrasted results with higher turbulence shear flows showing smaller gains.

Abstract

The $\Omega$-phase of the liquid sodium $\alpha$-$\Omega$ dynamo experiment at NMIMT in cooperation with LANL has successfully demonstrated the production of a high toroidal field, $B_{\phi} \simeq 8\times B_r$ from the radial component of an applied poloidal magnetic field, $B_r$. This enhanced toroidal field is produced by rotational shear in stable Couette flow within liquid sodium at $Rm \simeq 120$. The small turbulence in stable Taylor-Couette flow is caused by Ekman flow where $ (\delta v/v)^2 \sim 10^{-3} $. This high $\Omega$-gain in low turbulence flow contrasts with a smaller $\Omega$-gain in higher turbulence, Helmholtz-unstable shear flows. This result supports the ansatz that large scale astrophysical magnetic fields are created within semi-coherent large scale motions in which turbulence plays only a smaller diffusive role that enables magnetic flux linkage.