IV. OPERATION RECORDS

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

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. Miura,∗2 H. Shiraki,∗2H. Hirai,∗2 K. Kimura,∗2 M. Nagano,∗2 H. Shiba,∗2 and S. Okada∗2
We operated the BigRIPS cryogenic plant for only
2,838 h in 2020 because the spring beam time was cancelled due to the declaration of state of emergency over
COVID-19. The operation periods were from March 4to April 24 and from September 25 to December 21. After the long shutdown of the RIBF facility, we started
cooling down the warmed-up superconducting triplet
quadrupole (STQ) magnets on October 2.
After successful cooldown operation, we excited STQ1
magnet with stepwise ramping. The STQ1 magnet isan air-core-type superconducting magnet and consistsof three quadrupole coils, P1, P2, and P3, and one
hexapole coil, SX.1) In contrast to the other STQ’s case,
we excite the coils P1, P2, and P3 separately after cooling down. Before simultaneous excitation of all coils, thecoils P1, P3, and SX coils were excited up to their nominal current of 740 A, 628 A, and 32.5 A, respectively.
However, when we ramped P2 from 610 A to 620 A, it
quenched with a current of 620 A, which is 8 A less than
the nominal current. This was the fourth quench of P2,and we consider that it a training quench.
Except for the quenching of P2, we operated the cryogenic system without any trouble. We measured thevibrations of the compressor unit and observed low oil
contamination in helium gas during operations. The total operation time of the compressor unit was 75,060 h.
Figure 1 shows the vibration acceleration in the vertical and horizontal directions as a function of the total operation time. We have been measuring the vibrations of the compressor at the high-pressure and lowpressure sides since 2015. Two rapid increases of the vibration acceleration at operation times of 59,000 h and71,000 h are indicated by arrows. They were causedby the damage of the bearing unit in December 20162)
and June 2019.3) The vibration acceleration mostly remained below 8 m/s2 during the operation period. WeFig. 1. Vibration acceleration of the compressor unit. The
operation period in 2020 is indicated.
∗1∗2

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

Fig. 2. Oil contamination at the entrance of the third coalescer vessel.

consider that the exceptionally large value of 10.3 m/s2
at 74,883 h in the vertical direction at the high-pressure
side is due to measurement error.
We measured the operation interval of the drain valvesof the coalescer vessels in the compressor unit in order toevaluate the oil contamination level. We have replaced
coalescer ﬁlter elements 5 times since 2008. The operation periods of the replaced ﬁlter elements were fromAugust 2008 to July 2010, from September 2010 to July
2012, from September 2012 to July 2014, from September 2014 to July 2016, and from September 2016 to June
2019. Figure 2 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, second, and third elements, respectively. The fourth and the ﬁfth elements are shown withpink and red diamonds, respectively. The oil contamination values measured using the oil check kit are alsoshown. The open triangles, squares, and circles represent the results for the ﬁrst, second, and third elements,respectively. The results for the fourth and the ﬁfth elements are indicated by the open diamonds and circles,respectively. The drain valve of the coalescer vessel operated only once in 2020 after the last maintenance in2019. The operation time and the estimate of the oilcontamination level for the current coalescer are 3550 hand 0.05 wt.ppm, respectively, as shown by the brown
diamond in Fig. 2.
Both estimations of the oil contamination level areconsistent with each other, and the performance eﬃciency of the ﬁfth set of ﬁlter elements seems to be better
than that of the others.
References

1) K. Kusaka et al., IEEE Trans. Appl. Supercond. 18, 240(2008).
2) K. Kusaka et al., RIKEN Accel. Prog. Rep. 50, 285 (2017).
3) K. Kusaka et al., RIKEN Accel. Prog. Rep. 53, 222 (2019).

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