An unstable motion of plasma in toroidal z-pinch discharge

The MHD instabilities in a z-pinch discharge have experimentally investigated with a toroidal plasma device. The investigations are mainly made by measuring poloidal magnetic fields with a poloidal array of small coils. Especially, the motions of the center of plasma column are observed in relation to m=1 poloidal mode. The experimental results in the unstable case of the low bias magnetic field show that the plasma column experiences a large toroidal drift in the initially rising stage of plasma current and oscillates after that stage. The experimental values for the periods of the oscillatory motions of plasma column are in good accordance with the theoretical values given by MHD theory. (author)