Deuterium Removal from W-Doped Carbon Films by Thermo-Oxidation

If both carbon and tungsten were to be part of the plasma-facing armor in a future fusion reactor, it is inevitable that carbon co-deposits containing tungsten impurities will form. This work examines the effectiveness of thermo-oxidation in removing hydrogen from W-containing carbon co-deposits. Amorphous deuterated hydrocarbon (a-C:D) films were created with a CD₄/Ar direct-current glow discharge and doped with W sputtered from a W mesh in front of the specimen. The W concentration in the specimens ranged from 0 to 35 at. % W/(W + C). The films were oxidized at 350°C, in 2 Torr pure O₂ for time increments totaling 8 h. The D content of the films was measured before and at various stages of the oxidation exposure using laser thermal desorption spectroscopy. Essentially all deuterium was removed from films containing very little or no W doping [<0.1% W/(W + C)]. For films with more W [few percent W/(W + C)], oxidation was less effective at removing D. For two specimens with 2.4% and 35% W/(W + C), oxidation was completely ineffective at removing D.