Thermal testing of TiC and TiN coating materials for tokamak limiters and walls

Thermal testing of coating materials for tokamak limiters and walls was carried out by means of an electron beam equipment. The materials tested are TiC coated onto POCO graphite and TiC and TiN onto Mo by chemical vapor deposition. All the coating layers survived without exfoliation under 80% of the beam power which eroded the substrate material. This shows good thermal and mechanical contact between coatings and substrates. Allowable heat loads for upset conditions such as plasma disruption were estimated to be about 3.5 kW/cm2 in uniform heating during 1 s for the three coating materials. The heat load limits in usual tokamak operation were also estimated in view of plasma contamination by limiter material evaporation. The limits in uniform heating for 1 s are about 3 kW/cm2 for TiC on Mo, 2.5 kW/cm2 for TiN on Mo, and 2 kW/cm2 for TiC on POCO graphite. The TiC coating on Mo thus appears to be the most interesting choice within the framework of this study. (author)