Investigation of the trapped helium and hydrogen ions in plasma facing materials for LHD using thermal desorption spectrometer and alternating glow discharge cleanings

Preliminary experiment to evaluate, analyze, and reduce the gas accumulation of materials used in LHD as plasma facing components has been carried out using a test devices ACT and a thermal desorption spectrometer. As the test materials, stainless steel (SUS316L) and iso-graphite (IG-430U) are selected and installed inside the vacuum vessel of ACT as linings, which are near the same kinds as the first wall material and armor tile material of the divertor plate used in LHD, respectively. Each material is exposed to alternating glow discharge plasma with He and H2 gasses. Qualitative measurement using a quadruple mass filter indicates that the He gas amount released from the stainless steel wall during H2 glow discharge cleaning is several times as much as that released from the graphite wall, which is an unexpected result. This result does not contradict that of the thermal desorption spectrometer measurement for small samples exposed to He glow discharge plasma for 7 h.