Modulated toroidal current suppression of MHD activity on the HT-7 superconducting tokamak

Modulation of the plasma current has been used successfully to suppress MHD activity. This was achieved in discharges near the density limit where lar ge MHD m = 2 tearing modes were suppressed by sufficiently large plasma cur rent oscillations. The modulation of the plasma current must be large enoug h to move the resonance q = 2 surface outside the island width on a timesca le faster than the growth time of the instability. These observations resem ble those predicted in a previous study of non-linear effects on the m = 1 mode.