Reduction of eddy currents induced by resonant magnetic perturbation coils by inserting high permeability materials

On the J-TEXT tokamak, a set of dynamic resonant magnetic perturbation (RMP) coils is installed inside the vacuum vessel to investigate the interactions between rotating RMP and the plasma. The coils are designed operating at a frequency up to several kilohertz. Enormous amount of eddy current will be induced in the vessel wall and will bring about a strong attenuation of the magnetic field of the coils. Hence, in order to reduce the screening effect of the eddy current on the magnetic field, a proposal of inserting soft magnetic material blocks with high permeability between RMP coils and the vacuum vessel wall is put forward. Experiments to verify the proposal have been carried out, and the preliminary results indicate that the proposal is realistic.