Characteristics of post-disruption runaway electrons with impurity pellet injection

Kawano, Yasunori; Nakano, Tomohide; Isayama, Akihiko; Asakura, Nobuyuki; Tamai, Hiroshi ; Kubo, Hirotaka; Takenaga, Hidenobu; Bakhtiari, M.; Ide, Shunsuke; Kondoh, Takashi; Hatae, Takaki

An experiment to investigate mitigation effects of impurity pellet injection on disruption generated runaway electrons was carried out in the JT-60U tokamak device. Deposition of impurity neon pellets into a post-disruption runaway plasma was observed with increment of bulk electron density. At the impurity pellet injection, decay time of runaway current became shorter as factor of 2. There was an approximately linear relationship between changes in decay rate of runaway current and a photo-neutron signal which indicated loss of runaway electrons from the plasma. Consequently, enhanced loss of runaway electrons from a tokamak plasma, hence mitigation effect on them, by injection of impurity neon pellets was found.