Basic study on the plasma facing materials-tritium interactions in the next generation

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The principal aim of the present project is to make investigations on the critically important issues of plasma-material interactions which are expected to play a decisive role in the near-tern devices ; namely, (a) development of high heat flux components (HFFC) for plasma facing surfaces, and (b) utilization of tritium for the realization of tritium fuel cycle. In order to achieve these goals, some basic experimental as well as numerical studies were performed, from which the following results were obtained.(1) Transport of carbon as well as boron-containing species in the steady-state linear plasma was studied by means of optical spectroscopy. It was revealed that under the divertor plasma conditions, these impurity species are expected to be ionized most probably in the state of C^+ or B^+.(2) Numerical calculations were performed to investigate the transport characteristics of the divertor plasma in a real tokamak geometry such as ITER (International Thermonuclear Experimental Reactor). The effects of thermal force and non-local electron heat transport were studied.(3) Ion- and gas-driven permeation behavior of deuterium in niobium was studied. The results indicated that the permeation probability was 0.2-0.3 in the temperature range of 873-1173 K.Then calculation was performed to evaluate the hydrogen permeation and retention properties at higher fluxes, in order to examine the applicability of niobium membrane to selective pumping of hydrogen isotopes in a fusion reactor fuel cycle.(4) A test device for tritium experiment has been constructed. As a preliminary experiment, a gas containing 0.6 GBq of tritium was admitted to the device, and thermal desorption spectra of tritium containing species ; namely, DT and T_2, from nickel were obtained.