Ⅳ. OPERATION RECORDS

RIKEN Accel. Prog. Rep. 53

Operation report of the ring cyclotrons in the RIBF accelerator complex
N. Tsukiori,∗1 K. Ozeki,∗2 T. Dantsuka,∗2 M. Fujimaki,∗2 T. Fujinawa,∗2 N. Fukunishi,∗2 S. Fukuzawa,∗1M. Hamanaka,∗1 H. Hasebe,∗2 Y. Higurashi,∗2 E. Ikezawa,∗2 H. Imao,∗2 S. Ishikawa,∗1 O. Kamigaito,∗2Y. Kanai,∗2 M. Kase,∗2 M. Kidera,∗2 K. Kobayashi,∗1 M. Komiyama,∗2 R. Koyama,∗1 K. Kumagai,∗2 T. Maie,∗2M. Nagase,∗2 T. Nagatomo,∗2 T. Nakagawa,∗2 M. Nakamura,∗2 T. Nakamura,∗1 M. Nishida,∗1 M. Nishimura,∗1J. Ohnishi,∗2 H. Okuno,∗2 N. Sakamoto,∗2 J. Shibata,∗1 K. Suda,∗2 A. Uchiyama,∗2 S. Watanabe,∗2T. Watanabe,∗2 Y. Watanabe,∗2 K. Yadomi,∗1 K. Yamada,∗2 and H. Yamasawa∗2The operation report of the ring cyclotrons in theRIBF accelerator complex from Jan. to Dec. 2019 is presented here. Table 1 presents a summary of the beams
accelerated by these cyclotrons. The availability in thetable is deﬁned by the ratio of the actual beam time tothe scheduled beam time, which is an index of the stable
operation of accelerators. In calculating each availability,
for beam times that were completed earlier than scheduled, the scheduled times are identiﬁed with the actualtimes. Multiple experiments supplying identical beams
are shown as a block.
The total beam supply time (actual beam time) was
1581.8 h. The ratio of beam times between the experiments conducted in the old facility (RARF) and those
conducted in the new facility (RIBF) was 8% and 92%.
In the RARF, the actual beam time was 128.0 h, andthe availability was 105.6%. Beams were stably supplied
as usual. In addition to the beams listed in Table 1,experiments for synthesizing the 119th element using a51
V beam were conducted as a closed beam time under
the Nishina Center Director.
In the RIBF, three beam services were conducted. The
total beam time was 1453.8 h, and the availability was92.2%. For the supply of 238 U beams, a maximum beam
intensity of 94.2 particle nA was achieved, which was1.3 times higher than the value of 72.0 particle nA ina previous beam time in Oct. 2018. A second hightemperature oven1) was added in the 28-GHz superconducting electron cyclotron resonance ion source, which
has contributed to an increase in intensity and the stabilization of the uranium beam. Furthermore, the stabilization of the magnetic ﬁeld of the IRC has also contributed to a stable beam intensity and an improvementin the transmission eﬃciencies for RRC and fRC.2) For

the supply of 124 Xe beams, a maximum beam intensityof 173 particle nA was achieved, which was 1.7 times
higher than the value of 102 particle nA in a previous
beam time in Apr. 2016.
The improvement of the acceleration voltage by theupgrade of the RRC resonators3) performed in 2018 hascontributed to the remarkable enhancement in the intensity of beams delivered to the RIBF. In 18.25-MHz
operations, both resonators were operated with an acceleration voltage of over 138 kV. Owing to an improvement of the shunt impedance, a signiﬁcant reduction wasachieved in the frequencies of the voltage breakdown bydischarge and in the high-voltage trips of the vacuum
tube. After all beam times scheduled in the ﬁrst halfof this ﬁscal year had been ﬁnished, a high-power test
was performed. Both resonators achieved an acceleration voltage of 160 kV, which was twice that before theupgrade.
However, after the resonator upgrade of RRC, waterleakages occurred in cooling water channels of the stems
several times in 2018 and once in 2019. We spent 4–
5 days repairing the leakage point by welding. Water
leakage is a very serious problem that hinders the stable operation of RIBF. Therefore, during this summer
maintenance period, an intensive investigation to ﬁndtiny leaks and the treatment of all the leaks found in theinvestigation were conducted. Since then, no degradations of vacuum occurred due to water leakage from thestems.
References

1) J. Ohnishi et al., RIKEN Accel. Prog. Rep. 52, 109 (2019).
2) R. Koyama et al., in this report.
3) K. Yamada et al., RIKEN Accel. Prog. Rep. 52, 13 (2019).

Table 1. Summary of the accelerated beams in 2019.

∗1∗2

SHI Accelerator Service Ltd.
RIKEN Nishina Center- 218 -