Damage and melting of ITER-like flat-type tungsten castellated blocks exposed to long pulse H-mode plasmas.

Abstract Damage and melting of ITER-like tungsten castellated blocks – made of tungsten top layer, copper inter-layer, copper alloy base (CuCrZr) – exposed to long pulse H-mode plasmas were investigated. Since the blocks were not actively cooled, the temperature of blocks was increased rapidly up to melting point of tungsten during H-mode plasmas resulting in severe damage such as cracks and melting of tungsten layer. It is observed that the copper inter-layer located at 5 mm below the surface of the tungsten was also melted indicating that the temperature of the interface had reached the melting point of copper, at least 1200 °C. Melted tungsten material was moved towards j × B direction (high filed side). The melting event was reproduced by 3D transient modeling using COMSOL with 2 MW/m2 heat load and explains the observation quantitatively well. This indicates that failure of cooling system during a long pulse operation with metal walls, especially melting of copper inter-layer will be critical. [ABSTRACT FROM AUTHOR]