RIKEN Accel. Prog. Rep. 50 (2017)

Ⅳ. OPERATION RECORDS

Operation of the BigRIPS cryogenic plant
K. Kusaka,1 M. Ohtake,1 K. Yoshida,1 M. Ohshima,2 A. Mikami,2 H. Hazama,2H. Miura,2 H. Shiraki,2 H. Hirai,2 M. Haneda,2 R. Sasaki,2 and M. Nakayama2In 2016, we have operated the BigRIPS cryogenic plantaccording to the RIBF beam time schedule. We started
continuous operation in March, and, after about 100 days ofsteady state operation, the main compressor was stopped inJuly. After the summer maintenance,1) we restarted thecryogenic plant in September and stopped the compressor inDecember. The total operation time of the compressor unit
was 59,276 h.
During these continuous operations, we faced threesignificant incidents. One incident was the sudden stop of
the compressor unit on Oct. 12 that was caused by a power
outage. This large power outage in the Tokyo metropolitan
area was caused by a power transmission cable of the Tokyo
Electric Power Co. (TEPCO) that caught on fire. Although
the power of all the cryogenic plants and most of the watercooling system in the RIBF facility is supplied by the
independent RIBF co-generation system (CGS), a
momentary voltage drop arose from the power switchingsystem interlock between the TEPCO- and the CGS-powerlines. The momentary voltage drop stopped some coolingwater pumps and our compressor unit stopped at the sametime. The reason for the failure of the mechanicalcomponents caused by the momentary voltage drop is underinvestigation.
Another incident consisted of the sudden stops of theexpansion turbines in the refrigerator, which were false
interlock stops caused by the failure of the temperaturetransducer for the helium gas at the exit of the second
turbine, T2. We replaced the temperature transducer andcontinued the operation. The temperature at the T2 exit isone of the most important parameters for the refrigerator
system and is usually set to 11.6 K for optimum cooling
capacity. However, we had to change the T2 temperatureparameter to 10.5 K for optimum cooling capacity during
the 48Ca beam time. At this parameter setting, we operated
the cryogenic system with a beam heat load fluctuation of
more than 100 W. We calibrate the T2 temperaturetransducer and test the cooling capacity using the standalone operation of the TCF200 cold-box in 2017.
The third incident was an unusual noise that wasproduced by the main motor of the compressor unit. We
first noticed the noise in mid-November and the noise level
gradually increased daily, even though we had greased themotor unit. Since 2015, we have regularly measured thevibrations of the main compressor unit using an OH-580A
hand-held vibration tester.4) The vibration acceleration in
the vertical and horizontal directions as a function of thetotal operation time is shown in Fig. 1. Measurements wereperformed both at the high-pressure and low-pressure sidesof the compressor. It is clear that the vibration acceleration
increased drastically after hour 58,630 of operation, whichcorresponds to Nov. 14. On Dec. 5, the acceleration
exceeded more than 20 m/s2 and the noise level became
dangerously large, so we decided to cancel the beam timeand stop the compressor unit on Dec. 6. After a 6-hrecovery operation after the expansion turbines werestopped, the compressor was safely stopped. Using atemporary recovery line, evaporated helium gas from theSTQ cryostats was successfully transferred to the RIKEN
liquid-helium supply and recovery system.
The main motor unit was disassembled on site toinvestigate the origin of the unusual vibrations. In a baring
unit on the anti-coupling side, damage was found on asurface of its inner ring (Fig. 2). The motor unit wasreassembled with a new bearing unit. After carefulmechanical and electrical checks of the whole compressor
unit, the test operation was successfully performed and thevibration acceleration was measured to be less than 8 m/s2.
The origin of the bearing damage is under investigation.

Fig. 1. Vibration acceleration of the compressor unit.

Fig. 2. Damaged bearing unit, disassembled from theanti-coupling side of the motor unit.
References
1) K. Kusaka et al.: RIKEN Accel. Prog. Rep. 49, 330 (2016).
2) http://www.testo.jp.

1

RIKEN Nishina Center2
Nippon Kucho Service Co., Ltd.

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