Tritium inventory of carbon dust in ITER

In order to estimate tritium inventory of carbon dust in ITER, deuterium absorption amounts of carbon dust after D2 gas absorption and deuterium ion irradiation were measured. In a case of D2 gas absorption, the amount of retained deuterium was very low, D/C∼10−3 in the atomic ratio of D/C, when the gas pressure was 1 Pa and the temperature 573 K. In a case of the deuterium ion irradiation, the amount of retained deuterium was very similar to the case for graphite. Thus, at a divertor wall temperature higher than 1073 K, the amount of retained deuterium can be regarded negligible small, D/C∼0. During the plasma discharge, carbon eroded at a divertor trace by both plasma irradiation and high heat flux co-deposits on the vacuum vessel with fuel hydrogen atoms. In order to estimate the amount of retained fuel hydrogen in the co-deposited carbon dust, D2 arc discharge with carbon electrodes was conducted and the amount of retained deuterium in the co-deposited dust was measured. In a case that the D2 gas pressure was approximately 1 Pa and the wall temperature approximately 400 K, the amount of retained deuterium was low, D/C∼0.06. Above results showed that fuel hydrogen inventory of the co-deposited carbon dust was largest. In a DT plasma, the corresponding tritium inventory becomes a half, T/C∼0.03, which is approximately one order of magnitude smaller than the value estimated so far.