Full suppression of runaway electron generation by the mode penetration of resonant
magnetic perturbations during disruptions on J-TEXT
Lin, Z. F.; Chen, Z. Y.; Huang, D. W.; Huang, J.; Tong, R. H.; Wei, Y. N.; Yan, W.; Li, D.; Hu, Q. M.; Huang, Y.; Yang, H. Y.; Li, Y.; Zhang, X. Q.; Rao, B.; Yang, Z. J.; Gao, L.; Ding, Y. H.; Wang, Z. J.; Zhang, M.; Liang, Y.; Pan, Y.; Jiang, Z. H.
The avoidance and suppression of runaway electron (RE) generation during disruptions
is of great importance for the safe operation of tokamaks. Massive gas injection is
used to suppress the generation of REs, but the poor gas mixing efficiency and extremely
high density required to suppress RE generation make the full RE suppression unreliable.
The magnetic perturbations provide an alternative RE suppression during disruptions.
The use of mode penetration induced by resonant magnetic perturbations (RMPs) to suppress
RE generation has been investigated on the J-TEXT tokamak For a sufficiently long
mode penetration duration, robust runaway suppression has been reached during the
disruptions. The m/n = 2/1 mode RMP with high amplitude excites large magnetic islands
inside the plasma and leads to the large-scale destruction of magnetic surfaces during
disruptions, which results in RE loss and runaway-free disruptions. The critical island
width required for runaway suppression is estimated to be larger than 0.16 as the
minor radius. This value might be slightly underestimated because of the misalignment
between the electron cyclotron emission diagnostic and the island O-point. NIMROD
simulations are used to investigate the effect of magnetic islands on RE generation
during disruption, showing that the large magnetic islands have the ability to enhance
RE seed loss during disruptions. RMP can excite large magnetic islands in the target
plasma without tearing mode and might be a way to prevent RE generation during disruptions.