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Saha, P. K.; Okabe, Kota; Nakanoya, Takamitsu; Shobuda, Yoshihiro; Harada, Hiroyuki; Tamura, Fumihiko; Okita, Hidefumi; Yoshimoto, Masahiro; Hotchi, Hideaki*
Journal of Physics; Conference Series, 2420, p.012040_1 - 012040_7, 2023/01
Shobuda, Yoshihiro
Proceedings of 19th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.28 - 32, 2023/01
Two-dimensional resistive-wall impedance of cylindrical chambers with a finite thickness decreases proportionally to the frequency when the skin depth is greater than the chamber thickness. The phenomenon is typically interpreted that the electro-magnetic fields leak out of the chamber over the frequency range. However, the relation among the resistive-wall impedance, the space charge impedance, and the leakage fields from the chamber is not clear. This study provides a more comprehensive picture of dealing with them simultaneously.
Yamamoto, Kazami; Yamamoto, Masanobu; Yamazaki, Yoshio; Nomura, Masahiro; Suganuma, Kazuaki; Fujirai, Kosuke; Kamiya, Junichiro; Nakanoya, Takamitsu; Hatakeyama, Shuichiro; Yoshimoto, Masahiro; et al.
Proceedings of 19th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.277 - 281, 2023/01
The J-PARC 3GeV Rapid Cycling Synchrotron (RCS) is aiming to provide the proton beam of very high power for neutron experiments and the main ring synchrotron. We have continued the beam commissioning and the output power from RCS have been increasing. In recent years, we have been trying continuous supply of 1-MW high-intensity beam, which is the design value, to a neutron target. We tried to operate continuously for over 40 hours in June 2020. However, some trouble occurred and the operation was frequently suspended. In June 2021, we tried again 1-MW operation but it was suspended due to deterioration of the cooling water performance. Last summer shutdown period, we recovered performance of the cooling water system and retried in this June. In the final case, the outside temperature became extremely high. We could not keep 1-MW power, whereas 600 kW beam was delivered in stable.
Saha, P. K.; Okabe, Kota; Nakanoya, Takamitsu; Yoshimoto, Masahiro; Shobuda, Yoshihiro; Harada, Hiroyuki; Tamura, Fumihiko; Okita, Hidefumi; Hatakeyama, Shuichiro; Moriya, Katsuhiro; et al.
Proceedings of 19th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.1 - 5, 2023/01
Yoshimura, Nobuyuki*; Toyama, Takeshi*; Kobayashi, Aine*; Nakamura, Takeshi*; Okada, Masashi*; Shobuda, Yoshihiro; Nakaya, Tsuyoshi*
Proceedings of 19th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.936 - 941, 2023/01
no abstracts in English
Kobayashi, Aine*; Toyama, Takeshi*; Nakamura, Takeshi*; Shobuda, Yoshihiro; Ishii, Koji*; Tomizawa, Masahito*; Takeuchi, Yasunao*; Sato, Yoichi*
Proceedings of 19th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.19 - 23, 2023/01
In the J-PARC main ring, density modulation due to longitudinal beam instability occurs during the debunching process of coasting beams. This leads to the generation of an electron cloud, which in turn causes transverse beam instabilities. The transverse beam instability causes beam loss and the electron cloud is assumed to cause vacuum degradation, both of which hinder the beam intensity enhancement, so it is essential to clarify the causes and countermeasures. In particular, the longitudinal impedance of several hundred MHz has been investigated as relevant, and measures to reduce the impedance of individual devices are underway. The Eddy-current type septum magnet, newly installed this year, was found to have a large impedance by simulation. Therefore, we are investigating a method to reduce the impedance by a flange loaded with SiC radio wave absorber, which can be applied to locations where there is no spatial margin to install a taper. In this report, we will discuss the characterization of SiC to be used in actual devices, impedance simulation reflecting the results of SiC evaluation, and evaluation of the effect of impedance countermeasures by impedance measurement using the wire method, and progress in evaluating the effect on the beam by beam simulation and beam study.
Yamamoto, Kazami; Kinsho, Michikazu; Hayashi, Naoki; Saha, P. K.; Tamura, Fumihiko; Yamamoto, Masanobu; Tani, Norio; Takayanagi, Tomohiro; Kamiya, Junichiro; Shobuda, Yoshihiro; et al.
Journal of Nuclear Science and Technology, 59(9), p.1174 - 1205, 2022/09
Times Cited Count：1 Percentile：58.67(Nuclear Science & Technology)In the Japan Proton Accelerator Research Complex, the purpose of the 3 GeV rapid cycling synchrotron (RCS) is to accelerate a 1 MW, high-intensity proton beam. To achieve beam operation at a repetition rate of 25 Hz at high intensities, the RCS was elaborately designed. After starting the RCS operation, we carefully verified the validity of its design and made certain improvements to establish a reliable operation at higher power as possible. Consequently, we demonstrated beam operation at a high power, namely, 1 MW. We then summarized the design, actual performance, and improvements of the RCS to achieve a 1 MW beam.
Shobuda, Yoshihiro; Toyama, Takeshi*; Yoshimoto, Masahiro; Hatakeyama, Shuichiro
Proceedings of 13th International Particle Accelerator Conference (IPAC 22) (Internet), p.1663 - 1666, 2022/07
Ceramic breaks are used in synchrotrons for many purposes. For example, they are inserted between the Multi-Wire Profile Monitors (MWPMs) on the injection line at the rapid cycling synchrotron (RCS) in J-PARC to completely prevent the wall currents accompanying beams from affecting the MWPMs. On the other hand, from the viewpoint of suppressing beam impedances and the radiation fields from the ceramic breaks, it would be preferable that the inner surface of the ceramic break is coated with titanium nitride (TiN), or covered over capacitors. In this report, we measure the radiation fields from the ceramic break with and without capacitors as well as the beam profile and investigate the effect of the ceramic break on the measurements.
Kobayashi, Aine*; Toyama, Takeshi*; Nakamura, Takeshi*; Shobuda, Yoshihiro; Ishi, Koji*
Nuclear Instruments and Methods in Physics Research A, 1031, p.166515_1 - 166515_12, 2022/05
Times Cited Count：0 Percentile：0.02(Instruments & Instrumentation)The beam power of the main ring of the Japan Proton Accelerator Research Complex (J-PARC) is currently being increased. For high-power beam realization, it is essential to suppress the beam instability that limits the beam power and to estimate and enact countermeasures against the beam coupling impedance of individual devices. The fast-extraction (FX) septum magnet will be replaced with another magnet that copes with higher numbers of repetition cycles. Despite their different structures, both septa demonstrated a large impedance in estimates performed by the CST studio suite wake-field solver. The widely used taper impedance-reduction method would be effective but receives spatial constraints. By attaching a copper plate and SiC to the flange of the septum magnet, we could effectively reduce the impedance. The copper plate on the flange reduces the impedance below the cut-off frequency. Moreover, when SiC was loaded, the remaining impedance was three times lower than when using the copper plate alone. After applying this method to the new septum magnet, the maximum longitudinal impedance was reduced to 1% of the value without countermeasures, largely improving the beam stability condition. We also estimated the required thickness of SiC and the calorific value. This method saves space and is installed by simple attachment to the flange, regardless of the shape of the beam pipe. Therefore, it is also applicable to other devices.
Shobuda, Yoshihiro
Progress of Theoretical and Experimental Physics (Internet), 2022(5), p.053G01_1 - 053G01_44, 2022/05
Times Cited Count：0 Percentile：0.01(Physics, Multidisciplinary)When the skin depth is greater than the chamber thickness for relativistic beams, the two-dimensional longitudinal resistive-wall impedance of a cylindrical chamber with a finite thickness decreases proportionally to the frequency. The phenomenon is commonly interpreted as electro-magnetic fields leaking out of the chamber over a frequency range. However, the relationship between the wall current on the chamber and the leakage fields from the chamber is unclear because the naive resistive-wall impedance formula does not dynamically express how the wall current converts to the leakage fields when the skin depth exceeds the chamber thickness. A prestigious textbook {Kheifets} re-expressed the resistive-wall impedance via a parallel circuit model with the resistive-wall and inductive terms to provide a dynamic picture of the phenomenon. However, there are some flaws in the formula. From a fundamental standpoint, this study highlights them and provides a more appropriate and rigorous picture of the longitudinal resistive-wall impedance with finite thickness. To demonstrate their physical meaning, we re-express the longitudinal impedance for non-relativistic beams, as well as the transverse resistive-wall impedance including space charge impedance based on a parallel circuit model.
Shobuda, Yoshihiro; Toyama, Takeshi*
Proceedings of 18th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.75 - 79, 2021/10
The beam impedance of a ceramic break with thin titanium nitride coating (TiN) consists of resistive wall term caused by TiN, radiation term, and capacitive term made by the ceramic itself in parallel. The entire wall current continues to run in TiN even when the skin depth is much larger than the chamber thickness, except for the extremely thin TiN. This characteristic is useful in developing a wall current monitor with an improved frequency response.
Kobayashi, Aine*; Toyama, Takeshi*; Nakamura, Takeshi*; Shobuda, Yoshihiro; Ishii, Koji*
Proceedings of 18th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.287 - 291, 2021/10
no abstracts in English
Toyama, Takeshi*; Kobayashi, Aine*; Shobuda, Yoshihiro
Proceedings of 18th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.666 - 669, 2021/10
no abstracts in English
Shobuda, Yoshihiro; Kamiya, Junichiro; Takayanagi, Tomohiro; Horino, Koki*; Ueno, Tomoaki*; Yanagibashi, Toru*; Kotoku, Hirofumi*
Proceedings of 12th International Particle Accelerator Conference (IPAC 21) (Internet), p.3205 - 3208, 2021/08
At the injection area of the RCS in J-PARC, the interaction between the copper stripes (RF-shields) on the ceramic chambers and the external magnetic fields modulatesthe magnetic fields in the chamber, causing beam losses for a special tune. A ceramic chamber spirally covered by the stripes is a candidate to mitigate the modulations. In this report, we numerically and experimentally investigate how the interaction is suppressed, while sustaining the beam impedance enhancement within tolerable at the RCS.
Hotchi, Hideaki; Harada, Hiroyuki; Hayashi, Naoki; Kinsho, Michikazu; Okabe, Kota; Saha, P. K.; Shobuda, Yoshihiro; Tamura, Fumihiko; Yamamoto, Kazami; Yamamoto, Masanobu; et al.
JPS Conference Proceedings (Internet), 33, p.011018_1 - 011018_6, 2021/03
no abstracts in English
Shobuda, Yoshihiro; Toyama, Takeshi*
Physical Review Accelerators and Beams (Internet), 23(9), p.092801_1 - 092801_18, 2020/09
Times Cited Count：1 Percentile：17.19(Physics, Nuclear)The beam impedance of a ceramic break with titanium nitride (TiN) coating consists of three electric components in parallel: resistive wall term caused by TiN, radiation term, and capacitive term made by the ceramic itself. The entire wall current continues to run in the thin TiN even when the skin depth is much larger than the chamber thickness, except for the extremely thin TiN satisfying the condition that the radiation loss from the ceramic break becomes lower than the energy loss due to the DC-current on the thin TiN. This characteristic is useful in developing a wall current monitor with an improved frequency response. This study demonstrates the feature of the "ceramic break" monitor up to a few GHz from the theoretical and measurement points of view.
Kobayashi, Aine*; Toyama, Takeshi*; Shobuda, Yoshihiro; Nakamura, Takeshi*; Sato, Yoichi*
Proceedings of 17th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.684 - 688, 2020/09
no abstracts in English
Toyama, Takeshi*; Kobayashi, Aine*; Nakamura, Takeshi*; Shobuda, Yoshihiro
Proceedings of 17th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.689 - 692, 2020/09
no abstracts in English
Hotchi, Hideaki; Harada, Hiroyuki; Hayashi, Naoki; Kinsho, Michikazu; Okabe, Kota; Saha, P. K.; Shobuda, Yoshihiro; Tamura, Fumihiko; Yamamoto, Kazami; Yamamoto, Masanobu; et al.
Journal of Instrumentation (Internet), 15(7), p.P07022_1 - P07022_16, 2020/07
Times Cited Count：3 Percentile：27.92(Instruments & Instrumentation)no abstracts in English
Kamiya, Junichiro; Kotoku, Hirofumi; Shobuda, Yoshihiro; Takayanagi, Tomohiro; Yamamoto, Kazami; Yanagibashi, Toru*; Horino, Koki*; Miki, Nobuharu*
Journal of Physics; Conference Series, 1350, p.012172_1 - 012172_7, 2019/12
Times Cited Count：0 Percentile：0.07One of the issues in the J-PARC 3 GeV rapid cycling synchrotron is the high residual radiation dose around the beam injection point. A radiation shield is necessary to reduce radiation exposure of workers when maintenance is performed there. A space to install the radiation shield should be secured by newly designing a structure of the vacuum chamber at the injection point and the alumina ceramics beam pipes for the shift bump magnets. To make the space for the shield, the chamber is lengthened along the beam line and the cross-sectional shape is changed from circle to rectangle. The displacement and inner stress of the vacuum chamber due to atmospheric pressure were evaluated to be enough small by the calculation. For the ceramics beam pipe's rf-shield, the damping resistor was effective to reduce the induced modulation voltages by the pulsed magnetic field.
