Helium retention of 316L stainless steel used for the first wall of the large helical device (LHD)

Helium retention of 316L stainless steel used for LHD plasma facing material was evaluated after helium ion irradiation by using a technique of thermal desorption spectroscopy (TDS). After the irradiation with helium energy of a few hundreds eV, most of the retained helium desorbed in the temperature range lower than 550degC. With increase of ion energy, the ratio of helium desorbed in higher temperature range (> 550degC) increased. In the irradiation with a helium energy of 3 keV, the retained helium desorbed only in the higher temperature range. Based upon the obtained results, the desorption behavior of helium in the stainless steel sample exposed to the LHD plasma discharges was discussed. (author)