The penetration process of a rotating magnetic perturbation into a rotating tokamak plasmahas been investigated, taking account of the mode structure of the perturbations, and using a smallmagnetic probe in the small research tokamak CSTN-IV. It was observed that the radial component of the perturbation was amplified in theplasma when magnetic islands are formed, while the poloidal component was attenuated but,deep inside the plasma, amplified. Using a resistive MHD code, such modifications ofexternal perturbation were found to be caused by a redistribution of plasma current due to the formation of magnetic islands. Considering the phase velocity of both the perturbation and theintrinsic plasma rotation, it was also found that the sideband component substantially affectsthe penetration process with magnetic islands forming. Therefore, in dynamicergodic divertor operation, it is necessary to put the emphasis not only on the frequency ofthe perturbation fields but also on their direction, mode structure and the radial profile of theintrinsic plasma rotation at the same time.
Dynamics of resonant magnetic field penetration and plasma rotation