Energy and fluence dependences of helium retention in stainless steel

Abstract Helium retention behavior of 316L stainless steel (316L SS) used for the first wall of the large helical device (LHD) was investigated by using an ECR plasma/ion apparatus and thermal desorption spectroscopy. Samples of 316L SS were irradiated by helium ions with different energy. After helium ion irradiation with 100s eV energy, the desorption temperature of the retained helium was below 800 K. As increasing ion energy, the fraction of helium desorbed temperatures >800 K gradually increased. The retained amount of helium saturated for ion fluences above 1.0 × 1017 He/cm2. The retained amount of He was similar to that observed in other plasma facing materials. For irradiation fluences >1.0 × 1017 He/cm2, blister formation was observed. The present results are consistent with the desorption behavior of 316L SS samples exposed to LHD plasmas.