Ⅰ. HIGHLIGHTS OF THE YEARRIKEN Accel. Prog. Rep. 56 (2023)
RIKEN
Accel. Prog. Rep. 56 (2023)

Operation test of kicker system with new PFN capacitors
Y. Yamaguchi,∗1 T. Ohnishi,∗1 G. Hudson-Chang,∗1,∗2 M. Kanda,∗3 Y. Koizumi,∗3 D. Nagae,∗1,∗4 K. Okubo,∗3K. Sasaki,∗3 N. Shinozaki,∗3 A. Yano,∗5 A. Ozawa,∗1,∗5 T. Yamaguchi,∗1,∗3,∗5 and M. Wakasugi∗1,∗6
In the rare-RI ring (R3) facility, the kicker system
is a key device for injecting and extracting particles
one-by-one. Recently, we have succeeded in magnetic
ﬁeld ﬂattening during injection duration and extending the extraction duration, thereby improving the experimental eﬃciency.1) However, the ceramic capacitors used in the pulse forming network (PFN) of thekicker power supply were broken several times due toinsulation breakdown after 1 day of operation with acharging voltage of 45 kV to 55 kV in the 2021 massmeasurement experiments.2,3) This failure, which interferes with the execution of the experiment, must berepaired quickly. We report the progress of the repair
work.
The PFN, consisting of sixteen capacitor and inductor sections, forms a high-voltage unit together witha thyratron and other components.4) The high-voltage
unit is installed in a tank ﬁlled with insulating oil.
The capacitor HP40-H132-00 we have used so far ismade by the former AVX corporation (Kyocera AVX
now). It has a three-layer structure and is insulatedwith molded resin. The outer diameter is 38 mm, thelength is 47 mm, the rated voltage is 80 kV, and thecapacitance is 375 pF.
A failure analysis was performed by Kyocera. The
central part of the three-layer structure was found tobe particularly damaged (see Fig. 1(b)). The damage was so severe that it is diﬃcult to pinpoint thecause, but the following are possible causes: 1) due
to the part of dielectric layer is slightly weak, 2) due
to the stacked element structure, the central element
overheated, and then the increase in dielectric loss andfurther overheating caused an electron avalanche, orFig. 1. (a) shows broken AVX capacitor, and (b) showsinternal damage revealed by Kyocera.
∗1∗2∗3∗4∗5∗6RIKEN Nishina Center
Department of Physics, University of Surrey
Department of Physics, Saitama University
Laboratory for Zero-Carbon Energy, Tokyo Institute ofTechnology
Institute of Physics, University of Tsukuba
Institute for Chemical Research, Kyoto University- S26 -3) due to electric ﬁeld concentration on the washer
between the elements. Thus, it is thought that thestacked elements structure could not withstand our useof the repetition of the high-voltage charging within
200 µs and the instantaneous discharging by thyratron. Then we decided to replace it with a single-layer
structure capacitor, a commercially available productwith proven track record.
Figure 2(a) shows a new capacitor FHV-10AN madeby TDK corporation. The outer diameter is 38 mm,
the length is 33 mm, the rated voltage is 50 kV, andthe capacitance is 700 pF. Two TDK capacitors areconnected in series to make almost the same capacitance as the AVX one. Figure 2(b) indicates the output currents when operated at a charging voltage of55 kV. It can be seen that the waveform (blue-line)
obtained with TDK capacitors is almost the same asthat (black-line) obtained with AVX capacitors.

Fig. 2. (a) shows installed new capacitors. (b) indicates
output signals from current monitor (details in text).

There are eight high-voltage units in total. Currently, the two high-voltage units for one twin-type
kicker magnet have been replaced with TDK capacitors. Recently, we conducted 5-days continuous operation test for all units with a charging voltage ofaround 50 kV. As a result, ﬁve of the six units with
AVX capacitors failed again. On the other hand, thetwo units with TDK capacitors had no problems. We
concluded that the use of TDK capacitors would solve
the above three concerns and enable stable continuous
operation. Therefore, the remaining six high-voltage
units will also be replaced with new capacitors soon.
References
1) Y. Yamaguchi et al., RIKEN Accel. Prog. Rep. 54, 100(2021).
2) A. Ozawa et al., RIKEN Accel. Prog. Rep. 55, 13(2022).
3) S. Naimi et al., RIKEN Accel. Prog. Rep. 55, 14 (2022).
4) Y. Yamaguchi et al., Phys. Scr. T166, 014056 (2015).