Performance degradation of helium refrigerator for liquid hydrogen circulation system of J-PARC high intensity neutron source; Investigation of performance degradation

Teshigawara, Makoto   ; Aso, Tomokazu ; Hasegawa, Shoichi   ; Muto, Hideki*; Aoyagi, Katsuhiro*; Takada, Hiroshi   ; Ikeda, Yujiro

Performance degradation of helium refrigerator was occurred for liquid hydrogen circulation system of J-PARC high intensity neutron source since 2015. In order to find the cause of performance degradation of helium refrigerator, we investigated the impurities in helium gas and accumulated oil in inside cold box components by quadrupole mass spectrometer and organic solvent extraction. The measured impurities and accumulated oil were less than design value. We collected 143g of total amount of accumulated oil from heat exchanger and adosorber, which was corresponded to estimated value from 10 ppb of oil contamination in helium and accumulated operation period. However, we only could find out that accumulated oil like coating film on top surface of felt, which was used to hold the active charcoal in adsorber. We report detailed measurement results of impurities, accumulated oil, etc., to find the cause of performance degradation.