Ⅰ. HIGHLIGHTS OF THE YEARRIKEN Accel. Prog. Rep. 53

Calibration of the beam energy position monitor system for the RIKEN
superconducting acceleration cavity†
T. Watanabe,∗1 H. Imao,∗1 O. Kamigaito,∗1 N. Sakamoto,∗1 N. Fukunishi,∗1 M. Fujimaki,∗1 K. Yamada,∗1Y. Watanabe,∗1 T. Toyama,∗2 T. Miyao,∗2 A. Miura,∗3 K. Hanamura,∗4 T. Kawachi,∗4 R. Koyama,∗5
and A. Kamoshida∗1,∗6Upgrades for the RIKEN Heavy-ion Linac that involvea new Superconducting Linac (SRILAC) are currently
underway to promote super-heavy element searches andthe radioactive isotope (RI) production of astatine(211 At) for medical use.1,2) We have developed a beamenergy position monitor (BEPM) system3) that can simultaneously measure not only the beam position but
also the beam energy by measuring the time of ﬂight ofthe beam. By using parabolic-shaped electrodes (Fig. 1),
we realized the ideal linear response of the quadrupole
moments while maintaining good linear position sensitivity. We fabricated 11 BEPMs and a position calibration system employing the wire method that we used toobtain the sensitivity and oﬀset of the BEPMs.
Destructive monitors generate outgassing; if they areused, it becomes diﬃcult to maintain the Q value andsurface resistance of the superconducting radio frequency(SRF) cavities over a long period of time. It is, therefore,
crucial to develop nondestructive beam measurement diagnostics. With the aim of measuring the beam position
at an overall accuracy of ± 0.1 mm, a calibration measurement was performed at the KEK campus in Tokai.
Because there are 3 types of BEPMs for the SRILAC,3)
we designed and fabricated dummy pipes that surroundthe wire and jigs to mechanically ﬁt the calibration device. The calibration device is shown in Fig. 2. The
BEPM to be calibrated is connected to a dummy pipewith an inner diameter equal to that of one of the BEPMs(Fig. 2(a)). The assembly is ﬁxed to an XY stage thatmoves within the measurement region in 2-mm steps. A
wire acting as a signal source is ﬁxed. Round crimp terminals are attached by crimping and soldering at bothCross
SectionElectrodeCeramic
Insulator

SMA
FeedthroughFig. 1. Parabolic-shaped electrodes.
†∗1
∗2
∗3
∗4
∗5
∗6Condensed from the the proceedings in 2019 International
Beam Instrumentation Conference (IBIC 2019)
RIKEN Nishina Center
KEK/J-PARC, Tokai
JAEA/J-PARC, Tokai
Mitsubishi Electric System & Service Co., Ltd., TokaiSHI Accelerator Service Ltd., Wako
National Instruments Japan Corporation, Tokyo

Type Ⅲy(a)xTo NetworkAnalyzer

(b)
(b)

Fig. 2. Photographs of the calibration measurement device,
jigs, and dummy pipes.

ends of a copper-plated piano wire. The dummy duct
has a double-pipe structure that can be expanded andcontracted. When the round-crimp terminals are connected to the electrode on both end plates, the innerdummy pipes are made to slide into the outer dummy
pipe to provide suﬃcient space for the connection of theelectrodes. After that operation is completed, the inner dummy pipes are restored to their original position
and ﬁxed to the double pipe by fastening bands. Adequate tension can be applied by moving one of the end
plates outward with ﬁne adjustment. The dummy pipes
are connected to the end plates with an RF contact ﬁnger and are held to the ground potential (Fig. 2(b)).
When the measurement was repeated, it was found thatboth the required electrical characteristics and ﬂexibility
could be achieved simultaneously by reducing the number of RF contact ﬁngers and applying copper tape tothe end plates. As a result, measurement errors weredrastically reduced.
By using the calibration device, the calibration wascompleted to within ±0.05 mm mechanical accuracy. We
will continue to analyze the measurement results of all
the BEPMs, which will be used to measure the beam
position and energy using the calibration values when
the beam is accelerated at SRILAC.
References

1) N. Sato et al., RIKEN Accel. Prog. Rep. 50, 262 (2017).
2) S. Yano et al., RIKEN Accel. Prog. Rep. 50, 263 (2017).
3) T. Watanabe et al., Proc. 15th Ann. Meet. of Particle
Accel. Soc. Jpn., Nagaoka, Japan, 2018-Aug. (2018), p. 49.

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