Thermal response for divertor mock-up using surface-modified CFC tile

It is necessary for the divertor plate to be actively cooled in order to remove the extremely high heat load from the fusion plasma. CFC material has been considered as one of the candidate plasma-facing materials because of its high thermal shock resistance. However, CFC causes several problems, such as the enhancement of hydrogen recycling, large erosion due to oxygen and radiation enhanced sublimation where the temperature exceeds about 1000 degrees C. In this study the surface of CFC, CX-3002U, was converted to B4C and SiC by using a chemical vapor reaction, CVR. The thermal response properties of divertor mock-ups made by these materials and CFC were examined. These mock-ups were irradiated by electron beams with heat flux up to 15 MW/m(2). The surface temperature rise of B4C-converted CFC tile was the highest and that of CFC the lowest. This difference was consistent with the value of the thermal conductivity e.g. B4C-converted CFC has the lowest thermal conductivity, 200 W/m K and CFC has the highest one, 450 W/m K. The heat flux that increases the surface temperature to 1000 degrees C was approximately 8, 10 or 11 MW/m(2) for B4C-converted CFC, SiC-converted CFC or CFC, respectively. Thermal cycling tests with more than 2000 shots were also conducted for these mock-ups. No deterioration in the heat transfer for each mock-up was found for the heat flux which increased the surface temperature to 1000 degrees C.