Modelling of LHW-induced helical current filaments on EAST: Study of an alternative method of applying RMPs

The lower hybrid wave (LHW) heating experiments at the Experimental Advanced Superconducting Tokamak (EAST) show a wide range of similarities to effects known from applied resonant magnetic perturbations (RMPs) by in-vessel or external magnetic perturbation coils. These observations suggest a current flow understood to be along scrape-off layer (SOL) field lines; here called helical current filaments (HCFs). For a better understanding of the experimental observations, a model to incorporate the magnetic perturbation of HCFs in the magnetic topology has been developed. Modelled SOL field lines, starting in front of the LHW antenna, show agreement in position and pitch-angle with the experimentally observed radiation belts. The comparison of the pick-up coil signals and the modelled HCFs' perturbation allows for determination of the current strength depending on the filaments' distance from the plasma edge. Agreement of predicted footprint structures with experimentally observed heat load and particle flux profiles at different toroidal angles in the divertor region is found. Based on the modelling results, the idea of LHW-induced RMPs, originating from the experimental observations, is strongly supported.