Thermal properties of redeposition layers in the JT-60U divertor region

Hydrogen isotope retention of JT-60U W-shaped divertor tiles exposed to DD discharges

“…Succeeding discharges would pile up the re-deposited layers with similar D/C, but maybe somewhat different by each discharges depending on the plasma heat load, which enables to distinguish the re-deposited layers piled up by shot as clearly shown by Gotoh for the divertor tiles of JT-60 [14]. With piling-up the re-deposited layers by the following discharges, their thermal contact to the substrate became poor [15] and the temperature of the whole re-deposited layers would rise higher during the shot. When a particular shot with larger heating power was made, the temperature of the redeposited layers would increase uniformly, resulting additional deuterium release to homogenize D/C over the whole re-deposited layers.…”

Deuterium depth profiling in graphite tiles not exposed to hydrogen discharges before air ventilation of JT-60U

“…In the inner divertor region, thick re-deposition layer up to 200 μm was observed [11,15]. Considering that the density of the re-deposition layer was 0.91 g/cm 3 [16], the depth of 14 × 10 23 carbon atoms/m 2 corresponds to a linear depth of 30.7 μm for re-deposition layers on the ID sample.…”

Retention and depth profile of hydrogen isotopes in gaps of the first wall in JT-60U

“…Although first walls are generally thought to be erosion dominated area, the results show that deposition could occur in gap side surface even in first wall area. Assuming the density of the carbon deposition layer was 0.91 g/cm 3 [14] and all hydrogen and deuterium were retained in the carbon deposition layer, the atomic ratio of (H + D)/C was estimated to be approximately 0.15. This value is higher than that of re-deposited layer observed in the inner divertor region of JT-60U [12], probably due to the lower temperature of the first wall.…”