Performance degradation of helium refrigerator for liquid hydrogen circulation system of J-PARC high intensity neutron source; Element test related to increasing differential pressure, which might cause performance degradation

Teshigawara, Makoto   ; Aso, Tomokazu ; 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. During cause investigation of performance degradation of helium refrigerator, we found out that accumulated oil like coating film on top surface of felt, which was used to hold the active charcoal in adsorber, might cause pressure difference in adsorber. We performed cold nitrogen gas flow test in the felt accumulated oil and found out that frozen oil under cold nitrogen flow caused the pressure difference.