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

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.