Japanese universitiesʹ activities for PFC development and PMI studies

Development of reliable plasma facing components (PFC) with active cooling structures is required for divertor plates of fusion devices in order to remove a large heat flow to the divertor. It is also known that plasma material interactions (PMIs), i.e. fuel hydrogen recycling and erosion of plasma facing material (PFM) determine the energy confinement characteristics. The lifetime of PFCs is limited by the erosion of PFMs. In Japanese universities, studies concerning PFCs and PMIs have been carried out so far for LHD and ITER. For the LHD divertor, both graphite/copper brazed components and mechanical joint components have been developed, and the heat load performance has been examined. For the particle control in LHD, a localized divertor called LID has been designed, the preliminary experiment was conducted in a small helical device, the CHS. In order to reduce the oxygen impurity level, boronization experiments have been conducted systematically, and properties such as oxygen gettering and hydrogen retention were clarified. In the TRIAM-1M tokamak, the damage of PFMs has been investigated using a surface probe. Data on hydrogen retention, which determines the degree of hydrogen recycling, have been accumulated for graphite, Li, B, B4C, SiC and W. Conditioning methods are also suggested. In this paper, the problems associated with PFCs and PMIs are pointed out and data recently obtained in Japanese universities and NIFS are briefly introduced.