Flip instability of plasma in the theta pinch

Recent experiments on the behaviour of plasma in the theta pinch have shown that, although the plasma in reversed-field discharges is normally unstable, there are some cases in which the plasma is stable and contained. The present paper considers the following hypothesis: (a) that the mode of instability commonly encountered is that observed by Clark and Wuerker (in which the axis of the magnetic moment of the current supporting the trapped reversed field appears to rotate from its initial state of alignment with the field axis) and (b) that there exists a class of configurations of the plasma enclosed by the field lines that are stable against this rotation of the plasma axis.