The effect of resonant magnetic perturbation on the electron density threshold of runaway electron generation during disruptions on J-TEXT

Abstract

The generation of runaway electrons (REs) during disruptions is a key issue for the safety operation of large tokamak. For better design a reliable scenario to suppress REs generation, investigation of the REs generation during disruption is highly essential. On J-TEXT, it presents that the REs generation is strongly depend on the pre-disruption electron density, toroidal magnetic fields (BT) and magnetic perturbations. The REs generation can be avoided in discharges with a low BT or a high electron density. For discharges with a high BT, a high density threshold is required to suppress REs generation. However, this threshold is decreased with the application of resonant magnetic perturbation (RMP) which is applied before the thermal quench. The enhancement of magnetic perturbation increases the REs loss during disruption, leading to the robust runaway suppression in the discharges with a relative low electron density. The density threshold required for REs suppression is reduced with the increase of RMP strength and the m/n = 2/1 mode RMP is more efficiency than the m/n = 3/1 mode RMP for the reduction of density threshold, where m and n are the poloidal and toroidal mode number, respectively. The NIMROD simulation indicates that the m/n = 2/1 mode RMP creates stronger magnetic perturbations during disruption and leads to a high loss ratio of RE seeds. The REs loss ratio is significantly related to the magnetic topology and the strength of magnetic perturbation during disruption. All results give an evidence of the significant effect of RMP mode and amplitude on the electron density threshold for REs generation, which might give an insight to the future large reactor tokamaks operating in high electron density.