Enhanced fast ion prompt loss due to resonant magnetic perturbations in KSTAR

Abstract

We report a numerical study for the impact of resonant magnetic perturbation (RMP) on fast ion prompt loss in KSTAR using full orbit following simulation. Experimental observation in KSTAR indicates a sudden increase in RMP-induced fast ion prompt loss when the applied RMP field exceeds a threshold amplitude. Full orbit simulation with 3D perturbed equilibrium computed by the ideal plasma response reproduces the experimentally observed feature of RMP-induced prompt loss of fast ions and the existence of threshold RMP amplitude. Simulation with vacuum fields only shows a small increase in the fast ion loss that is insufficient to explain the observation. We show that the conservation of canonical angular momentum is broken due to the RMP during the fast ion transit, which is consistent with the enhanced fast ion loss above the threshold RMP amplitude. Phase space analysis suggests that trapped and intermediate pitch passing particles modified from initial high pitch passing ones are responsible for the threshold behavior of the fast ion loss in the simulation, while the phase space distribution of lost particles depends on the RMP field configuration.