Cold boronisation in TCA

Boronisation of the TCA vacuum vessel was performed at ambient temperature. The paper presents detailed surface analysis of the coating and a description of the tokamak performance after boronisation. The obtained coatings showed a film composition close to the feed gas composition although a high oxygen content was measured. Apart from the dominating carbidic B-C bonds, the existence of at least two non-equivalent carbon bonding sites were found. Boronisation gave an immediate and long-term improvement of many plasma parameters in TCA with a strong reduction of both low and high-Z impurities in the plasma. In particular oxygen was reduced by over 20 despite a high level oxygen contamination in the coating. The gas retention in the film has been shown to be temporarily reduced by glow discharge cleaning. With these techniques we are able to obtain nearly isotopically pure discharges. Boronisation has been shown to be a very efficient wall conditioning procedure in TCA.