Hydrogen isotope behavior and its interaction with post irradiated energetic helium in SiC

Silicon carbide (SiC) is thought to be one of the primary candidates for the first wall and structural materials of future fusion reactors due to its minimal activation, good thermal conductivity, low radiation loss and high chemical stability. In a D-T fusion reactor, deuterium and tritium are proposed as a fuel and first wall materials are exposed to the D-T plasma. By the fusion reaction, high energy neutron and helium are produced and they are also irradiated to the materials. Therefore, it is important to elucidate the helium ion irradiation effect on the hydrogen isotope retention in SiC. In the previous study, the hydrogen retention and hydrogen isotope replacement were studied by the elastic recoil detection (ERD) technique. Trapping and detrapping mechanisms of hydrogen isotope in SiC have been also discussed with taking account of the damaged structure produced by helium ion pre-irradiation. For the evaluation of the hydrogen isotope retention, it is important to irradiate helium ion after deuterium ion irradiation to understand the hot atom effect between trapped deuterium and energetic helium. Therefore, in this study, deuterium ion was implanted into SiC almost up to the saturation and thereafter, helium ion was also irradiated, The chemical states of Si and C were evaluated by X-ray photoelectron spectroscopy (XPS) and the hydrogen isotope retention was also estimated by Thermal Desorption Spectroscopy (TDS). The dynamics of the hydrogen isotope behavior interacting with energetic helium in SiC was discussed with taking account of hot atom reaction. It was found that the deuterium was trapped by Si and C with forming Si-D and C-D bonds. By the helium ion irradiation, the deuterium retention was decreased, indicating the interaction between trapped deuterium and energetic helium. In the presentation, the interaction mechanism will be discussed in detail.