Influence of He and W-ion irradiation on deuterium retention in tungsten

W samples were irradiated with MeV-energy ions of He and tungsten (W) under various temperatures to examine effects of He-vacancy complexes (HVc) and other defects on deuterium retention in W. The deuterium retention was observed by a nuclear reaction analysis (NRA) during continuous D-plasma exposure to the samples. As a result, D concentration in the sample irradiated at room temperature (RT-irr) became larger than that irradiated at higher temperature (HT-irr). In the HT-irr samples large vacancy clusters would be produced due to migration of atomic vacancies and formation of secondary defects. In contrast, the vacancies in the RT-irr samples were considered to be relatively small in size, and the difference of the D retention in the two samples was seen after additional He irradiation. This was caused by the decrease in the trapping energy of HVc due to the increase in the vacancy size. (author)