IV. OPERATION RECORDS

RIKEN Accel. Prog. Rep. 55 (2022)

RIKEN Accel. Prog. Rep. 55 (2022)

Operation of the BigRIPS cryogenic plant
K. Kusaka,∗1 M. Ohtake,∗1 K. Yoshida,∗1 M. Ohshima,∗2 A. Mikami,∗2 H. Hazama,∗2 H. Shiraki,∗2 H. Hirai,∗2K. Kimura,∗2 M. Nagano,∗2 H. Shiba,∗2 and S. Okada∗2   

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    Fig. 1. Oil contamination at the entrance of the third coalescer vessel.
∗1∗2RIKEN Nishina Center
Nippon Air Conditioning Services Co., Ltd.

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Since the total operation time of the helium compressor unit has reached to 77,680 h in August 2021, the maincompressor was shipped to the manufacturer’s factory formaintenance. The compressor unit was disassembled,
and its interior was cleaned. All the components werechecked carefully, and no signiﬁcant mechanical damage
was found.
In addition to maintaining the mechanical componentsof the compressor unit, we replaced the activated charcoal and molecular sieves in the adsorbent vessel in August 2021. We measured the operation interval of thedrain valves of the coalescer vessels in the compressor
unit, to evaluate the oil contamination level. We replaced coalescer ﬁlter elements ﬁve times since 2008. The
operation periods of replaced ﬁlter elements are fromAug. 2008 to July 2010, Sept. 2010 to July 2012, Sept.
2012 to July 2014, Sept. 2014 to July 2016, and Sept.
2016 to June 2019. Figure 1 shows an estimate of the oil
contamination level at the entrance of the third coalescer
vessel as a function of the coalescer ﬁlter operation time.
The navy blue, green, and yellow diamonds represent
the estimates for the ﬁrst, the second, and the third elements, respectively. The fourth, the ﬁfth and the sixth
elements are shown with pink, red, and purple diamonds,respectively. The oil contamination values measured using the oil check kit are also shown. The open triangles,
squares, and circles represent the results for the ﬁrst,
the second, and the third elements. The results for thefourth and the ﬁfth elements are indicated by the open
diamonds and circles, respectively. The cross represents
the results of the sixth elements. Both estimations of theoil contamination level are consistent with each other,and the performance eﬃciency of the sixth ﬁlter element
is apparently better than that of the others.
At the end of October 2021, we started continuous



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Fig. 2. Vibration acceleration of the compressor unit.

operation of the BigRIPS cryogenic plant after summer
maintenance. This operation was terminated by an incident in the 2021 winter beam time. At 7:35 on December 3, the ﬁre alarm of the RI-Beam Factory (RIBF)
building rang, and the cryogenic plant operator foundsmoke emanating from the compressor unit of the BigRIPS cryogenic plant. After having made necessary
emergency contacts, the plant operator stopped the compressor unit safely at 7:50. Evaporated helium gas fromthe STQ cryostats was transferred to the RIKEN liquidhelium supply and recovery system using a temporary
recovery line. We inferred that the smoke was emitted
from the coupling side baring unit of the main motor of
the compressor unit, since burnt grease was found aroundthe coupling. A sudden increase in the operation currentof the motor unit from 30.6 A to 33.6 A, which was measured at 7:28, also indicates a breakdown of the mainmotor.
We noticed an unusual noise produced by the main
motor of the compressor unit since November 2021. We
measured the vibrations of the compressor at the highpressure and low-pressure sides since 2015. Figure 2
shows the vibration acceleration in the vertical and horizontal directions as a function of the total operation
time. Continuous operation started with a total operation time of 77,683 h and the acceleration increased
rapidly. The ﬁnal measurement of the vibrations wasperformed on Dec. 1. Two additional rapid increases inthe vibration acceleration at operation times of 59,000 h
and 71,000 h were caused by damage to the bearing unit
occurred in Dec. 20161) and in June 2019.2)
The main motor unit was dismounted from the compressor unit and shipped to the manufacturer’s factoryfor repairs in January 2022. The origin of the unusual
vibrations is under investigation.
References
1) K. Kusaka et al., RIKEN Accel. Prog. Rep. 50, 285 (2017).
2) K. Kusaka et al., RIKEN Accel. Prog. Rep. 53, 222 (2019).

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