Thermo-oxidation to remove re-deposited layers and to release trapped hydrogen isotopes in HT-7 superconducting tokamak

Thermo-oxidation between 0.7 Pa and 32 Pa at wall temperatures of 400–470 K has been investigated in the HT-7 superconducting tokamak. During the oxidation process, deposited carbon layers were removed by the formation of CO and CO2 and the incorporated hydrogen was released in the form of water molecules. A significant fraction of the injected oxygen was also absorbed on the walls. The overall amount of adsorbed oxygen is nearly linear with the filling pressure. The results of the thermo-oxidation experiment in HT-7 were similar to those in TEXTOR. High wall temperature and high oxygen pressure are helpful in removing carbon co-deposits and releasing trapped hydrogen.