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 mat erial has been considered as one of the candidate plasma-facing materi als 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 te mperature exceeds about 1000 degrees C. In this study the surface of C FC, CX-3002U, was converted to B4C and SiC by using a chemical vapor r eaction, CVR. The thermal response properties of divertor mock-ups mad e by these materials and CFC were examined. These mock-ups were irradi ated by electron beams with heat flux up to 15 MW/m(2). The surface te mperature rise of B4C-converted CFC tile was the highest and that of C FC the lowest. This difference was consistent with the value of the th ermal conductivity e.g. B4C-converted CFC has the lowest thermal condu ctivity, 200 W/m K and CFC has the highest one, 450 W/m K. The heat fl ux that increases the surface temperature to 1000 degrees C was approx imately 8, 10 or 11 MW/m(2) for B4C-converted CFC, SiC-converted CFC o r CFC, respectively. Thermal cycling tests with more than 2000 shots w ere also conducted for these mock-ups. No deterioration in the heat tr ansfer for each mock-up was found for the heat flux which increased th e surface temperature to 1000 degrees C.