Simulation of energy-dependent stochastic transport induced by low-order MHD instabilities for runaway electron mitigation

Matsuyama, Akinobu; Yagi, Masatoshi; Ishii, Yasutomo; Aiba, Nobuyuki; Kagei, Yasuhiro*

Response of the runaway electron (RE) drift orbit to low-order magnetohydrodynamic (MHD) perturbations has been studied in tokamak plasmas. The tearing and resistive-kink like perturbations are taken into account, which is a possible cause of the re-distribution of REs in the inner core region. The onset of stochastic RE drift orbit is shown to depend strongly on the RE energy. This is due to that for highly relativistic REs, drift resonance of the orbit shift with macroscopic modes is much stronger than what is expected for non-relativistic electrons. It is demonstrated that the drift resonance can cause both the enhancement and the suppression of orbit stochasticity at high energy relevant to disruption-induced REs, depending not only on the perturbation amplitude but also on the phase difference between the modes.