Thermal behaviour of bare and coated first walls under severe plasma-disruption conditions

The thermal response of first walls made of bare stainless steel or graphite, and the capability of coatings to prevent stainless steel first walls from melting or from loss of mechanical function under various plasma disruption conditions, have been analysed. Plasma disruptions with energy densities up to 10 MJ/m2 and disruption times ranging from 20 ms to below 1 ms have been considered. In view of their favourable high-melting, thermal-shock resistant properties, coatings of graphite, TiC, and SiC were studied.The parametric numerical analysis shows that bare stainless steel might be seriously eroded and damaged by disruptions with an energy density beyond 2 MJ/m2. To cope with a wide range of disruption times and energy densities, the minimum required coating thickness to prevent stainless steel from melting should be about 0.1 mm per 1 MJ/m2 of expected energy density. However, due to the relatively high value of surface evaporation, the coating thickness should be one order of magnitude larger in order to withstand a proper number of disruptions.