Locking of kink modes in a reversed-field pinch

Experiments have been performed on the Reversatron II [IEEE Trans. Plasma Sci. PS-16, 667 (1988)] reversed-field pinch to study phase locking of kink modes in discharges with thick and thin shells. In the thick shell discharges, internal modes which are resonant or nearly resonant on axis are found to phase lock at random locations in toroidal angle. Externally nonresonant modes which lock tend to do so at the shell gap. In the thin shell discharges, the internally resonant modes and the externally nonresonant modes both tend to lock at the shell gap. Phase locking is not observed in every shot and the duration of the locking varies. The position of locking does not rotate