Investigation of carbon dust accumulation in the JT-60U tokamak vacuum vessel

Asakura, Nobuyuki; Hayashi, Takao; Ashikawa, Naoko*; Fukumoto, Masakatsu

Dust generated by the plasma-wall interaction is a potential source of the tritium retention in a fusion reactor. Dust samples were collected at 3, 5 and 3 different toroidal locations of the first wall, divertor surface and exhaust route under the divertor, respectively. On the tile surface, large number of dust was found, in particular, at the inner divertor rather upper area of the deposition layers, where recycling neutrals are increased during discharges. On the other hand, significant amount of dust (20-50 times larger) was generally accumulated at the bottom divertor, in particular, the plasma-unexposed area (remote area). It was found that the poloidal distribution is relatively symmetrical in the toroidal direction within a factor of three. Recently, analysis of dust spatial and size distributions, and evaluation of fuel retention in dust have been progressed. The total amount of the hydrogen isotope contained in the dust was estimated.