NONLINEAR EVOLUTION OF M=1 INTERNAL-MODE IN A CURRENT-CARRYING FINITE-BETA PLASMA OF HELIOTRON TORSATRON

Nonlinear behaviour of the m = 1 internal mode is studied in a straigh t Heliotron E configuration with net plasma current for both a peaked and a broad current profile case. In the former case the (m, n) = (1, 1) internal kink mode is destabilized in the neighbourhood of the inne r iota = 1 surface for low beta plasmas, although two iota = 1 surface s exist in the plasma column, where iota is a total rotational transfo rm. When the beta value is increased, the internal kink mode is combin ed with the interchange mode and the linear mode structure covers the two iota = 1 resonant surfaces, since Heliotron E has a large magnetic hill. Nonlinear evolution shows two stages: the first one is similar to the nonlinear internal kink mode and the second one to the nonlinea r interchange mode. For the broad current profile case only the m = 1 interchange mode is destabilized even in the current-carrying plasma a nd beta limit appears. Nonlinear behaviour is the same as that in curr entless plasmas.