Experimental study of m/n=2/1 mode RMP on the runaway current suppression during disruptions on J-TEXT

Abstract A systematic experimental study of m/n = 2/1 mode resonant magnetic perturbation (RMP) on the runaway current suppression is carried out on J-TEXT. The RMP is applied before disruptions which are deliberately triggered by massive gas injection (MGI). In the experiments, when the RMP amplitude is relatively low, its effect on the suppression of the runaway current is weak. However, when the RMP strength is high enough for mode penetration, the phase of a 2/1 mode island has a significant impact on the runaway current formation. The optimal island phase for avoiding runaway electron (RE) generation has been found, where the island’s O-point is close to the MGI deposition region. In addition, more effective suppression is achieved when the penetration duration exceeds approximately 50 ms. Under a specific island phase, RE suppression can also be achieved even when mode penetration occurs shortly before the disruption. The results suggest that different suppression mechanisms dominate at different penetration durations. For long penetration durations, both pre-disruption profile modification and enhanced magnetic perturbations during disruption contribute to RE suppression, whereas for late penetration the suppression is mainly associated with magnetic perturbations developing during the disruption. These findings demonstrate the important role of plasma response and magnetic island evolution in RE mitigation by high-amplitude RMP.