Characteristics of radiation distribution and divertor detachment in impurity seeding on JT-60U

Asakura, Nobuyuki; Nakano, Tomohide; Naito, Osamu; Oyama, Naoyuki

Impurity gas seeding is considered as the primary technique to decrease the heat loading to the divertor. Characteristics of the divertor plasma and radiation was investigated. Distribution of the impurity radiation in the edge and divertor was different depending on the impurity species. For Argon seeding, radiation loss in the main edge increased compared to Neon seeding cases. ELM characteristics changed from Type-I to Type-III for the intense Ar seeding, and detachment was produced. Dynamics of the transition from detachment to re-attachment was investigated. When the Ar gas puff rate was reduced, Type-I ELM activity appeared accompanied by a reduction in the edge radiation loss. Time scale of the re-attachment was short (0.4 s) compared to the transition from attached to detached divertor (1 s), which was affected by change in the edge transport barrier. In-out asymmetries in and ion flux became large in the re-attachment, and influence of the carbon-influx was increased.