Rotation and instability of plasma in fastBzcompression experiments

The phenomena of rotation and subsequent instability of plasma in fast compression (thetapinch) devices is discussed in the light of present stability theory including finite Larmor radius effects (Rosenbluth et al. , 1961). For the rotation to be unstable the plasma must possess an angular momentum exceeding that appropriate to the ion diamagnetic current and it is suggested that this is acquired as a result of a secondary process occurring as the plasma leaves the wall. It is shown that when this process is taken into account the theory is adequate to explain most observed phenomena and suggests others which might be investigated. In the Appendix to this paper the theory of finite Larmor radius stabilization is interpreted in terms of a hydrodynamic picture. This analysis is not rigorous but does suggest that the stability criteria, originally derived for a specific model, might have more general validity.