Ⅳ. OPERATION RECORDS
RIKEN
Accel. Prog. Rep. 56 (2023)

RIKEN Accel. Prog. Rep. 56 (2023)

Variation of impurity gas in recovered helium gas for liquid-helium
supply and recovery system
M. Nakamura,∗1 T. Dantsuka,∗1 H. Okuno,∗1 S. Turuma,∗1 M. Ohshima,∗2 H. Hirai,∗2 H. Shiraki,∗2 H. Shiba,∗2K. Kimura,∗2 S. Okada,∗2 A. Mikami,∗2 H. Hazama,∗2 M. Nagano,∗2 and M. Nakayama∗2
We use recovered helium gas for the liquid-helium
supply system. To measure the purity of the recovered
helium gas, we introduce a gas chromatography equipment and monitor the recovered gas. We observed theimpurities concentration and the recovered helium gas
condition for eﬀective operation.1) In this study, we report the changes in the concentration of the impurity
gases observed in 2022.
The recovered helium was analyzed by SHIMADZU
2014, except on Saturdays and holidays. The datafrom January 4 to December 28, 2022, is shown inFig. 1. The left-side axis shows the concentration ofN2 and O2 , and the right-side axis shows that of H2 ,CO2 , and CO. The black, gray, red, blue, and green
lines correspond to the N2 , O2 , H2 , CO2 , and CO concentrations, respectively.
The ﬂuctuation N2 concentration was mostly between 1600 to 1800 and O2 concentration was between
1200 to 1400, almost co-varying with each other. TheN2 concentration is at the same level as that of O2 from
October to December in 2021. The O2 concentration
seems to be slightly higher than that of N2 2021. We
hypothesize that the presence of N2 and O2 is due toair entrainment during the recovery process.1) However, the ratio of N2 and O2 in our analysis is about
0.7 and not the same as 0.25 of the air. The reason forthis discrepancy cannot be explicated.
The ﬂuctuation of H2 concentration was signiﬁcant.
Typically, H2 concentration stabilized at between 0.1
to 0.2 ppm. The H2 concentration suddenly increased
to 0.5–1.5 ppm on several occasions. However, such aFig. 1.
∗1∗2

sudden increase in concentration was limited to a single
day, and the liquid-helium supply and recovery system
was not damaged. The correlation of H2 concentration
ﬂuctuation with that of N2 and O2 is unclear. We presume that H2 impurity intermixed into the recovered
helium gas by a diﬀerent mechanism for N2 and O2 .
CO2 was detected almost daily from July to September. CO2 concentration suddenly increased to 1.2–
10 ppm on several occasions. It seems that CO2 wasdetected before and after the sudden increase in H2
concentration. The reason for this phenomenon cannot
be explicated. However, CO2 can be eliminated immediately from the system because the melting point ofCO2 is much higher than that of N2 and O2 . Therefore,
no problem occurred during the operation because ofCO2 .
We cannot estimate the concentration of CO impurity because these gases were observed only a few times
in this year.
In 2022, we had no serious troubles in the liquidhelium supply and recovery system operations. Especially, our system was not damaged by impurity gases.
However, the concentration of impurity gases continued to exhibit chronic elevation. The concentrationsof N2 and O2 annually become slightly higher. Dealing with such issues will be a critical topic in the nearfuture. Coping with such problems is an important
subject in near future.
Reference1) M. Nakamura et al., RIKEN Accel. Prog. Rep. 55, 181(2022).

Impurity concentration in recovered helium gas in 2022.

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