Thetapinch experiments with trapped antiparallel magnetic fields

Experimental evidence is presented which shows that stability for a cylindrical plasma sheet confined by antiparallel magnetic fields is established for times which are longer than theoretically predicted growth times for tearing instabilities by at least an order of magnitude. It is shown that the enhanced stability is not due to wall effects, inertia effects, too short a pinching coil, finite Larmor radius and viscosity effects. One possible explanation for the stability is shown to be related to the level of initial plasma perturbation. Further the enhanced stability can be explained by the observed plasma rotation. It is shown by simple arguments that the rotation can cancel the tearing mode's growth and that the rotation itself is a result of the diffusion of angular momentum across the neutral surface enclosing the confined plasma.