Support of liquid metal surface by alternating magnetic field

The behaviour of liquid metal, when supported over parts of its surface by an alternating magnetic field, has been examined in controlled conditions by an analogue experimental technique based on sodium immersed in an inert oil of slightly lower density. Experiments have been performed over a wide range of frequency, and with various excitation-system geometries. The ultimate purpose of the work is to identify mechanisms that may limit the size of liquid metal charge capable of stable levitation in an ´electro-magnetic crucible´, and that may affect stability in related devices. Various theories are current, and it uncertain which are correct. It has become clear that a particular static stability analysis, based on energy considerations, leads to conclusions which are contradicted by experiment; this matter is now theoretically understood. Dynamic instability of the metal surface is possibly important in practice. Past work on plasma stability is relevant to the subject, but requires extension for the liquld-metal case. This paper briefly reviews the general problem, and then concentrates on the analogue apparatus and experimental results, drawing attention to the main features of observed behaviour.