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, 10 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, Bomega , has to be greater than a certain critical value, Bomega crit, for the rotamak discharge to be maintained. Provided Bomega >or=Bomega crit, the properties of the discharge are then determined by the behaviour of the circuit used to couple the RF generators to the plasma load. The conditions necessary for the production of a compact toroidal magnetic configuration are presented.