The impact of resonant magnetic perturbations on runaway electron dynamics

Understanding runaway electron dynamics is among the highest priorities of the fusion roadmap. Dedicated campaigns on tokamak COMPASS with routinely generated runaway electron (RE) beams [1], together with controlled application of a strong magnetic perturbation (up to Bpert/BT0= 0.9*10-2at plasma edge) allowed unique studies of the RE behavior. This work presents a study of impact of externally triggered resonant magnetic perturbation (RMP) on a formation of a layer of stochastic magnetic field lines at the plasma edge, MHD activity, radial transport (combination of diffusion and advection [2]) of RE. The study utilizes both detailed data analysis and modeling. Furthermore, the effect of the mentioned processes on a RE seed formation, dynamics of the fully developed RE population, and on the effectiveness of RE loss processes is evaluated. The RE population has been modeled with the combination of a transport simulation code METIS [3] and a Fokker-Planck code LUKE [4] for plasmas before application of the external perturbation field. Screening of the external perturbation due to plasma response as well as unscreened vacuum approximation have successfully been modeled with a resistive MHD code MARS-F [5]. The magnitude of the perturbed magnetic field has been implemented into an open-source python package for fast manipulation with equilibria PLEQUE [6] (developed at COMPASS) and into a particle tracking code, in order to quantify the degree of induced field line stochasticity as well as the effect of perturbed fields on the RE orbits. A significant impact of the magnetic perturbation on the RE dynamics is reported.