RIKEN Accel. Prog. Rep. 50 (2017)

Ⅳ. OPERATION RECORDS

Maintenance of vacuum equipment for accelerators
S. Watanabe,*1 Y. Watanabe,*1 E. Ikezawa,*1 N. Sakamoto,*1 N. Yamada,*1M. Kase,*1 K. Oyamada,*2 M. Nishida*2 K. Yadomi,*2 J. Shibata,*2 and A. Yusa*2
We have been maintaining the vacuum equipment of theaccelerators in good condition. We report the maintenanceof the vacuum for the accelerators in 2016.
First, the maintenance of vacuum equipment in RILAC isdescribed. In January, the pressure at the X-re-buncher(X-REB) increased to 5 x 10-5 Pa after a joint for coolingthe inner cylinder was repaired. When the X-REB wassearched, leak points were found downstream of the duct ofbeam. The leak points were found in an O-ring of a Penninggauge, an O-ring of a Pirani gauge, and an O-ring between arotary pump and turbo-molecular pump. These O-rings
were replaced with new ones and no further leaks could befound using a helium leak detector. However, the pressure
did not improve. The cause of the pressure increase layelsewhere and remained unknown until April, when a shaft
on a bottom plate of the outer cylinder was disassembled
and reconstructed. The bolts and screws of this part weretightened and the pressure improved. In February, a leak
was confirmed in cavity No. 5 using a helium leak detector.
However, the leak points could not be identified. Because
the helium leak detector takes some time to respond after
the helium gas has been shot, the leak point could bedifferent from the place where the helium was shot. Toidentify the leak point, a dye penetrant inspection (colorcheck) was used. A color check is a method for searchingscratches and cracks on metal. First, special colored liquid
is sprayed on the metal. Next, the liquid is wiped off.
Finally, the scratches and cracks appear if they exist. Whenthe liquid was sprayed on a welded area of the RF feeders,
red color appeared on the reverse side of the painted area.
This indicated that the liquid had passed though thechamber wall. These scratches were treated with vacuum
sealing agent. However, the vacuum pressure could not beimproved. This indicated other paths that linked outside of
the chamber to its inside. If these paths through the chamber
wall were the cause of the vacuum leak, the chamber wallshould be changed to improve the leak completely. In April,a vacuum leak was found on a part of the welded joint offlanges near cavity No. 6 in an area called e42. However, it
was difficult to repair the leak because the access space wasnarrow. The leak could not be repaired. Because thepressure was kept at the order of 10-5 Pa, the vacuum leak
did not influence the experiments.
In February, the pressure increased in the AVF cyclotron.
The cause of the pressure increase was a vacuum leak.
Vacuum leaks in the AVF cyclotron had occurred previously.
Leak often happened because of a deformation of theflange.
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RIKEN Nishina Center
SHI Accelerator Service LTD- 288 -Hence, the flange was supported by pillars so that it would
not deform. In this case, the cause of the leak was not thecondition of the pillars. Therefore, an O-ring of the flangewas greased and the vacuum leak was fixed. In March, arotary pump used at the AVF cyclotron stopped suddenly.
The rotary pump was replaced with a spare. However, thereduction in pressure obtained by the spare was notsufficient. Hence, the spare pump was replaced with theformer one which worked normally. The cause of thisincident remains unknown.
In March, a cryopump did not work at the SRC. The
cause of this problem was a compressor malfunction. To fix
the compressor, its head unit was replaced. The cryopump
worked normally again.
At the IRC in April, several cryopumps failures occurred.
A cryopump failed to work properly. When the circuit
breaker was turned off and reset, the pump worked again.
However, it soon failed to work again. The pump wasreplaced with a spare one. Another cryopump also failed towork. After the circuit breaker was turned off and on, thepump was restarted.
At the fRC in April, a cryopump failed to work. After aswitch in front of a compressor was turned off and on, thecryopump was restarted.
At the RRC, a bellows connected with RF No. 2 had aleak point. Vacuum leaks from this part occurred frequently.
The leak was treated with a vacuum sealing agent. However,the leak happened repeatedly, especially duringexperimental beam time. In November, the pressure
increased during beam time. The ion beam was stopped andthe leak point was investigated. The cause of the pressure
increase was a leak on the bellows. The leak point wastreated with vacuum sealing agent. Then the pressure
decreased. To solve this problem completely, RF No. 2 haveto be taken apart, and the bellows will need to be replaced.
A large-scale repair is needed to solve this problem. It is noteasy to solve this problem; therefore, the treatment using
vacuum sealing agent will be continued.