IV. OPERATION RECORDS

RIKEN Accel. Prog. Rep. 55 (2022)

RIKEN Accel. Prog. Rep. 55 (2022)

Impurity concentration in recovered helium gas of liquid-helium
supply and recovery system
M. Nakamura,∗1 T. Dantsuka,∗1 H. Okuno,∗1 S. Turuma,∗1 M. Kuroiwa,∗1 M. Ohshima,∗2 H. Hirai,∗2H. Shiraki,∗2 H. Shiba,∗2 K. Kimura,∗2 S. Okada,∗2 A. Mikami,∗2 H. Hazama,∗2 M. Nagano,∗2 andM. Nakayama∗2We use recovered helium gas for a liquid-helium supply system. However 1–2 ppm hydrogen gas, for example, was intermixed with the recovered helium gas, andwe had to stop the operation of our system for a few
month in 2004.1) To cope with such serious troubles, weintroduced gas chromatography equipment and havebeen analyzing the recovered helium gas. Then, wecould observe the concentration of impurity gas andthe condition of the recovered helium gas for eﬀectiveoperation. In this paper, we report the change in concentration of impurity gases in 2021.
The recovered helium was analyzed using SHIMADZ
2014 every day except Saturdays and holidays. The results from January 4 to December 28 in 2021 are shownin Fig. 1. The left axis shows the concentration of N2and O2 , and the right axis shows that of H2 , CO2 , andCO. The results for CO2 and CO are presented in a bar
chart because we could rarely observe these gases andthe results are diﬃcult to plot using polygonal lines.
The black, gray, and red lines show the N2 , O2 , and H2concentration, respectively. The blue and green bars
show the CO2 and CO concentration, respectively.
The concentration changes of N2 and O2 were almostin exact correspondence. The N2 and O2 concentrations changed from 1300 to 2000 ppm and from 900 to
1300 ppm, respectively. From April to September, theN2 and O2 concentrations reduced to approximately
1300 and 900 ppm, respectively. We presume that N2and O2 from air intermixed into the helium gas when
helium was recovered. However, the ratio of N2 andO2 of our result is approximately 0.7 and not the sameas that of the air (0.25). The cause of this diﬀerence
cannot be explicated at present.
The ﬂuctuation of the H2 concentration was fairlyradical. Ordinarily, the H2 concentration settled
around 0.1 ppm. However, the concentration suddenly
increased to 0.3–0.7 ppm at several instances. The
correlation of H2 concentration change with that of N2and O2 is not so clear. We presume that the H2 impurity intermixed into the recovered helium gas througha mechanism diﬀerent from that of N2 and O2 .
We cannot estimate the CO2 and CO impurity concentrations because these gases were observed only afew times in this year.
In January, some parts included in the helium liqueﬁer were blocked, and we could not operate the heliumliqueﬁer. In the term of this trouble, we could observe
CO2 and CO several times, and H2 concentration increased to 0.7 ppm. The N2 and O2 concentrations
also increased. Hence, we can presume that this serious trouble was caused by impurity gases. However,the cause of this trouble could not be clariﬁed.
To keep the purity of liquid helium, we have to analyze the impurity gases in the recovered helium gas.
Reference1) K. Ikegami et al., RIKEN Accel. Prog. Rep. 38, 286(2005).

Fig. 1.
∗1∗2

Impurity concentration in the recovered helium gas in 2021.

RIKEN Nishina Center
Nippon Air Conditioning Service Co., Ltd.

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