Particle balance under global wall saturation in long-pulse discharges of JT-60U

During 30s-ELMy H-mode discharges, the wall-pumping rate decreases with a decay constant of several seconds and then becomes constant. During the constant wall-pumping phase, in discharges with a density of 65% of the Greenwald density, the wall-pumping rate is negative, in other words, outgassing. It has been found that this outgassing rate correlates with an increase in the tile temperature around the outer strike point. In discharges with a density of 80% of the Greenwald density, the wall-pumping rate is positive. Unless a high net deposition rate (>60%) of hydrocarbon is assumed, the positive wall-pumping rate cannot be explained only by the co-deposition of deuterium with carbon even if the outgassing rate is assumed to be zero. The vessel deuterium inventory decreases by 1.1 × 1024 on one experimental day with 17 long discharges. The main chamber wall is suggested as the deuterium source for the decrease of the inventory.