Magnetic field in a decaying spin-down flow of liquid sodium

P. Frick¹ - S. Denisov¹ - V. Noskov¹ - A. Pavlinov¹ - R. Stepanov^{1, 2}

¹ Institute of Continuous Media Mechanics, 1 Acad.Korolyov str., Perm 614013, Russia
² State National Research Polytechnical University of Perm, 29 Komsomolskii ave., 614990 Perm, Russia

Abstract
The expulsion of magnetic field by strong turbulence is studied experimentally in a nonstationary turbulent flow of liquid sodium generated in a toroidal channel at a moderate magnetic Reynolds number Rm > 10. The applied toroidal magnetic field is mainly collinear with the streamline of a large-scale flow, which reduces the induction effects caused by the mean flow and makes it possible to isolate the contribution of turbulent effects. It is shown that at the highly turbulent stage of flow evolution the mean magnetic field along the channel axis decreases by 30%. The observed effect can be explained as the result of turbulent diamagnetism described by the term \bvecγ∇×(\bvecg ×\bvecB) of the mean field induction equation, where \bvecg is the normalized gradient of the energy of turbulent fluctuations and \bvecB is the mean magnetic field. Figs 9, Refs 13.