Controlled carbon deposit removal by oxygen radicals

Amorphous hydrogenated carbon deposits are a present problem in fusion devices with carbon walls. They act as an unpredictable source of hydrogen retention and thus have to be regularly removed. In our experiment we studied removal of hard carbon deposits in an atmosphere of partially dissociated room temperature oxygen. The source of oxygen atoms was a radiofrequency glow discharge in oxygen at pressures in the vicinity of 100 Pa. The etching efficiency was observed as surface emissivity variations. Etchings rates are compared to those measured in the discharge region in presence of charged particles. Etching rates in the discharge region are of the order of 1 nm/s, etching rates in a neutral oxygen atmosphere were found to be strongly temperature dependent and reached the value of 10 nm/s at 300 °C.