Fuel removal from plasma-facing components by oxidation-based techniques. An overview of surface conditions after oxidation

Oxygen-assisted fuel removal is reported for laboratory-prepared a-C:D films and for layers obtained by boronisation in a tokamak and then exposed to a helium–oxygen glow discharge in TEXTOR. Oxidation of thick mixed-material co-deposits under laboratory conditions is also presented. The essential results are following: (i) laboratory-prepared amorphous deuterated carbon (a-C:D) layers are decomposed efficiently by the He–O2 glow: D and C contents are decreased by a factor of 45–220 and 25–60, respectively; (ii) the same treatment of the boronised films leads to the release of D but no removal of carbon is observed; (iii) the thermal oxidation (at 300 °C in air under laboratory conditions) of co-deposits on PFC and probes exposed to the SOL reduces the D content by a factor of 4–5 after 2 h, whereas nearly complete fuel removal (98%) occurs after 10 h at 300 °C. The study shows that the fuel removal efficiency is dependent on the overall composition of the mixed layer. It is high from pure a-C:D films but distinctly less efficient from real co-deposits.