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

Abstract Radiation distribution and divertor detachment in argon impurity seeding discharges were investigated in JT-60U. A large peak in the radiation power profile was observed at the edge. A radiation power in the core plasma ( ρ / a  ⩽ 0.93–0.95) and power flux to the edge pedestal were evaluated, and transition of ELM characteristics from Type-I to Type-III was seen at an exhaust power of 1.5–1.8 times larger than the L–H threshold power scaling. In the Type-III ELM plasma, the outer divertor plasma became partially detached. Intrinsic carbon impurity rather than the seeding argon dominated the radiated power in the divertor, which was decreased in the detached divertor due to a reduction in carbon influx. During re-attachment, ion saturation current and electron temperature at the outer divertor plasma increased with similar time scales (0.3–0.4 s) of decreasing Ar impurity at the edge and the changing ELM activity.