Compensation of the pick-up fluxes on the plasma position control system when resonant magnetic perturbations are applied in J-TEXT.

In the J-TEXT tokamak the displacement coils, which serve as sensors for feedback control of plasma position, are significantly affected by the resonant magnetic perturbation (RMP) coils. To eliminate the deviation of plasma position caused by the RMP, the responses of the displacement coils to the RMP are studied with a view to compensate for the pick-up fluxes. Both the linear and eddy responses on the displacement coils are taken into account and adjusted accordingly. It was found that positional correction in the vertical direction was required when the RMP was operated in the poloidal mode m = 1 and horizontal positional correction was required when the RMP was operated in the m = 2 mode. When compensation was applied to the position control system, correction of plasma position was successfully achieved, as observed from soft X-ray imaging, as well as from the evolution of the current of the horizontal and vertical fields.