ON CURRENT TERMINATION IN ROTAMAK DISCHARGES

A new series of rotamak experiments conducted in a 50 litre spherical pyrex discharge vessel is described. An analysis of the results, together with that of previous results from a smaller, IO litre vessel, provides an explanation for the current termination phenomenon which is such a noteworthy and characteristic feature of all rotamak discharges studied to date. It is shown that the amplitude of the applied rotating magnetic field, B-omega, has to be greater than a certain critical value, B-omega(crit), for the rotamak discharge to be maintained. Provided B omega greater than or equal to B-omega(crit), the properties of the discharge are then determined by the behaviour of the circuit used to couple the RF generators to the plasma lo;id. The conditions necessary for the production of a compact toroidal magnetic configuration are presented.