Investigations of impurity seeding and radiation control for long-pulse and high-density H-mode plasmas in JT-60U

Asakura, Nobuyuki; Nakano, Tomohide; Oyama, Naoyuki; Sakamoto, Yoshiteru; Matsunaga, Go; Itami, Kiyoshi

Impurity gas seeding is one of techniques to decrease peak heat flux to the divertor both in steady-state and transient phases. Power handling by large radiation power loss has been studied in the ELMy H-mode plasmas on JT-60U with argon (Ar) gas seeding since good confinement ( 0.85) was obtained up to high density (/ = 0.8-0.9, is the Greenwald density). On the other hand, it was not clearly understood to sustain the good confinement plasma with the large radiation power under the wall saturated condition where particle recycling flux changes during the long discharge. In this paper, control of the large radiation in the good energy confinement plasma was, for the first time, investigated. Total radiation fraction of / = 0.7-0.95 was maintained for the cases of Ar gas puffing and combination of Ar and Ne puffing. Control of radiation power in the main plasma has been investigated using feedback control of gas puff rate during outgasing condition from the PFCs.