A review on two previous divertor target concepts for DEMO: mutual impact between structural design requirements and materials performance

Development of a diverter target with a sufficient capability of power exhaust is a crucial prerequisite for the realization of a fusion power plant. While the design and technology for divertor target has been successfully developed for ITER, the applicability of this concept is not necessarily assured yet for DEMO mainly because the neutron irradiation dose expected for the DEMO divertor will be an order of magnitude higher than that of the ITER divertor. The possible embrittlement of structural heat sink materials due to irradiation is likely to restrict the structural performance and the operational flexibility of a target component to a considerable extent. For judgment of design feasibility of a target concept a quantitative evaluation of the thermal and structure mechanical performance is needed. In this article, a review on two representative target design concepts considered for the DEMO divertor is presented. Emphasis is put on the mutual impact between the design requirements and the performance of structural materials. Water-cooled and helium-cooled concepts are discussed considering two baseline heat sink materials, CuCrZr alloy and tungsten, respectively. Conclusions are derived from the critical features of the heat sink performance in terms of structural reliability, design/material interface and further R&D needs.