High heat flux experiment on B4C-converted carbon based materials for plasma facing materials of JT-60U

High heat flux experiments have been previously carried out on three kinds, namely low pressure plasma spray (LPPS), chemical vapor deposition (CVD) and conversion (CVR) methods, of B4C-overlaid CFCs using the JAERI electron beam irradiation system (JEBIS). As a result, it turned out that CVR method has the best adhesion property between B4C layer and bulk carbon. However, thicker B4C layer is necessary to use in long period as the divertor tiles of JT-60U. The purpose of this experiment is to investigate the thermal property of B4C-converted carbon based materials which have thicker B4C layer than the previous experiments. Irradiations were performed under two different heating conditions, namely in the normal condition (5-20 MW/m2, 5 s) and in the disruption conditions (1100-1600 MW/m2, 2-3 ms). The dimensions of the samples were 25 mm x 25 mm x 25 mm, and B4C-converted layers were made on the three kinds of CFCs and fifth kinds of isotropic graphites. The thickness of B4C layer was 150-1300 μm. Measurements were made with respect to the weight loss, changes of the surface morphology and the surface temperature. In the normal condition, the damages such as surface melting and exfoliation were not observed on the samples which have B4C layer below 600 μm in thickness. In the disruption condition, melting and exfoliation were observed on the surfaces of the samples whose substrates were PD-330S, PD-600S and HCB-5S, and melting was observed on the surfaces of the samples whose substrates were PCC-2S, MFC-1, MCI-felt, ETP-10 and STP-60. It is considered that the porous layer in the B4C layer caused the severe exfoliation from the measurement of the surface composition. (author)