Suppression of externally induced magnetic island by plasma current oscillation in HYBTOK-II

Summary form only given, as follows. In several tokamak devices, in order to suppress MHD instabilities, especially classical and neoclassical tearing modes (NTM), the plasma current density profile control have been performed by a ramp-up or ramp-down of plasma current and local plasma heating (or current drive). Recently, the plasma current oscillation experiment has been done to suppress self-generated tearing modes in HT-7 tokamak. The conditions under which the tearing modes were suppressed by the plasma current oscillation are as follows (a) Oscillation amplitude of the plasma current is large enough to move the resonance surface outside the magnetic island, and (b) the oscillation period is faster than the growth time of the tearing modes. In HYBTOK-II tokamak, the magnetic islands are generated by externally applied rotating helical magnetic perturbation (RHMP). We have confirmed that the amplification of RHMP in the plasma is suppressed by the plasma current oscillation. It follows from this result that the growth of magnetic islands is suppressed by the plasma current oscillation.