Ⅳ. OPERATION RECORDS

RIKEN Accel. Prog. Rep. 49 (2016)

Present status
status ofof thethe BigRIPSBigRIPS cryogenic
cryogenic plant
Presentplant
K. Kusaka,䠆1 M. Ohtake,䠆1 T. Kubo,䠆1 K. Yoshida,䠆1 M. Ohshima,䠆2 A. Mikami,䠆2 H. Shiba,䠆2 H. Hazama,䠆2H. Miura,䠆2 H. Shiraki,䠆2 H. Hirai,䠆2 M. Haneda,䠆2 M. Kubota,䠆2 M. Noguchi,䠆3 and N. Suzuki䠆3Periodic maintenance of the helium compressor unit is
crucial to ensure long-term continuous operations ofBigRIPS1). Since the total operation time of the helium
compressor unit has reached to 52,060 h in July 2015, themain compressor and the motor unit were shipped to themanufacturer’s factory for maintenance. The compressor
unit was disassembled and its interior was cleaned. All thecomponents were checked carefully and no significant
mechanical damage was found. They were reassembled
with new mechanical seals and bearings.
The main motor unit was also disassembled. The rotor
and the stator coils were cleaned and varnished. The
abrasion of the size of +30–50 Pm was found at theanti-coupling side bearing bracket. The bracket wasrepaired by the bushing method, so that its surface became
highly smooth (+7–10 Pm) and a new motor bearing could
be installed. In addition to mechanical checks electricalproperties of the motor unit were successfully tested. The
rebuilt compressor and main motor unit were installed onsite in September.
In September 2014 we have started the continuous
operation of the BigRIPS cryogenic plant and stopped themain compressor in July 2015. After the summer
maintenance, we started the cryogenic plant in
midSeptember and stopped the compressor in December
2015. During these continuous operations, we faced sometroubles on the compressor unit. One is an unusual noisethat was produced by the main motor unit in May 2015. We
greased the motor unit and maintained the continuousoperation. In other incidents, the compressor unit suddenly
stopped that happened twice in May 2015. The failure of
the temperature transducer for the discharge helium gas
caused false interlock stops. We replaced the temperaturetransducer and continued the operation. After theseincidents, we have started measuring the vibrations of themain compressor unit for sound operations.
Figure 1 shows the vibration velocities in the axial andvertical directions as a function of the total operation time.
We measured vibrations both at the high-pressure (HP) andlow-pressure (LP) sides of the main compressor unit using
the handy vibration tester OH-580A4). It is clearly seen thatthe vibration velocity changed drastically before and after
the maintenance.
In addition to maintaining the mechanical components ofthe compressor unit, we replaced the activated charcoal andmolecular sieves in the adsorbent vessel in August 2015.
We observed the oil contamination level of the oil-removal
RIKEN Nishina Center
Nippon Kucho Service Co., Ltd.
䠆3Mayekawa Mfg. Co., Ltd.
䠆1
䠆2

module using an oil check kit.
Figure 2 shows an estimate of the oil contamination levelat the entrance of the third coalescer vessel as a function ofthe coalescer filter operation time. As stated by Kusaka
et al.2), the amount of oil drain from the vessel is directly
related to the oil contamination level. The navy blue, green,
and, yellow diamonds represent the estimates for the2008-2009, 2010-2011, and 2012-2013 operations,respectively. The coalescer filters used in those periods
were discontinued3). The estimate for the 2014-2015
operation with successive new coalescer filters is shown aspink diamonds. The oil contamination measurement values
using the oil check kit are also shown. The open triangles,
squares, circles, and diamonds represent the results for the2008-2009, 2010-2011, 2012-2013, and 2014-2015
operations, respectively. The performance efficiency of thenew filter elements seems to be similar to or better than thatof the discontinued ones.

Fig. 1. Vibration velocity of the compressor unit.

Fig. 2. Oil contamination at the entrance of the thirdcoalescer vessel.
References

1) K. Kusaka et al.: RIKEN Accel. Prog. Rep. 41, 244 (2008).
2) K. Kusaka et al.: RIKEN Accel. Prog. Rep. 43, 309 (2010).
3) K. Kusaka et al.: RIKEN Accel. Prog. Rep. 48, 330 (2015).
4)http://www.testo.jp.

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