Single bunch injection scheme for doubling the beam intensity of J-PARC Main Ring

Tamura, Fumihiko; Okita, Hidefumi; Hotchi, Hideaki*; Saha, P. K.; Sato, Yoichi*; Yoshii, Masahito*; Omori, Chihiro*; Yamamoto, Masanobu; Seiya, Kiyomi*; Sugiyama, Yasuyuki*; et al.

JPS Conference Proceedings (Internet), 45, p.011129_1 - 011129_7, 2026/06

https://doi.org/10.7566/JPSCP.45.011129

The current goal of the J-PARC Main Ring (MR) is an output beam power of 1.3 MW, with a beam intensity is 3.3e14 protons per pulse (ppp) at a repetition period is 1.16 s. The Rapid Cycling Synchrotron (RCS) delivers two bunches to the MR in each injection and eight bunches are accumulated in the MR with four injections. The harmonic number of the RCS is 2 and the maximum nunch intensity of the RCS is 4.2e13 protons per bunch (ppb). If the harmonic number of the RCS is set to 1 and the RCS can accelerate a single bunch with the same intensity of 8.3e13 ppp/ppb, the bunch intensity in the MR can be doubled to 8.3e13 ppb, which corresponds to the accumulated beam intensity of 6.6e14 ppp with eight bunches. In this presentation, the feasibility of single bunch acceleration in the RCS is discussed based on the longitudinal beam simulations.

Upgrade activities toward beyond 1 MW beam at J-PARC Rapid Cycling Synchrotron

Okita, Hidefumi; Moriya, Katsuhiro; Yamada, Ippei; Chimura, Motoki; Saha, P. K.; Harada, Hiroyuki; Shobuda, Yoshihiro; Yoshimoto, Masahiro; Tamura, Fumihiko; Yamamoto, Masanobu; et al.

JPS Conference Proceedings (Internet), 45, p.011130_1 - 011130_8, 2026/06

https://doi.org/10.7566/JPSCP.45.011130

no abstracts in English

Operational experience of single-ended magnetic alloy cavities at J-PARC RCS

Tamura, Fumihiko; Okita, Hidefumi; Yamamoto, Masanobu; Yoshii, Masahito*; Omori, Chihiro*; Seiya, Kiyomi*; Sugiyama, Yasuyuki*; Nomura, Masahiro; Shimada, Taihei; Hasegawa, Katsushi*; et al.

Proceedings of 22nd Annual Meeting of Particle Accelerator Society of Japan (Internet), p.269 - 273, 2026/03

https://www.pasj.jp/web_publish/pasj2025/proceedings/PDF/WEP0/WEP032.pdf

The replacement project for the Magnetic Alloy (MA) cavities of the 3GeV RCS at J-PARC has been underway for several years. The original cavities are the push-pull (PP) configuration, where rf current is supplied alternately from a pair of tetrode tubes to the electrodes on the upstream and downstream sides of the acceleration gap. All cavities are to be replaced with newly developed single-ended (SE) cavities. In PP cavities, significant unbalance in the operation of the upstream and downstream tetrodes due to multiharmonic rf occurs. This unbalance has been one of the limiting factor of beam intensity. This unbalance does not occur essentially in SE cavities. Currently, six of the twelve cavities have been replaced. The SE cavity does not have a configuration to cancel even-order higher harmonics, therefore the harmonic components are different from those of the original PP cavity. We report on the operational experience with the single-ended cavity at the J-PARC RCS.

Beam loss mitigation for operation beyond 1 MW beam power of the J-PARC RCS

Saha, P. K.; Harada, Hiroyuki; Tamura, Fumihiko; Shobuda, Yoshihiro; Kojima, Kunihiro; Yoshimoto, Masahiro; Okita, Hidefumi; Okabe, Kota; Hatakeyama, Shuichiro; Nakanoya, Takamitsu; et al.

Proceedings of 22nd Annual Meeting of Particle Accelerator Society of Japan (Internet), p.549 - 553, 2026/03

https://www.pasj.jp/web_publish/pasj2025/proceedings/PDF/THP0/THP028.pdf

Consideration for improving the longitudinal beam matching between RCS and MR at the J-PARC

Okita, Hidefumi; Adachi, Kyosuke; Tamura, Fumihiko; Nomura, Masahiro; Shimada, Taihei; Yoshii, Masahito*; Omori, Chihiro*; Seiya, Kiyomi*; Sugiyama, Yasuyuki*; Hasegawa, Katsushi*; et al.

Journal of Physics; Conference Series, 3094(1), p.012027_1 - 012027_7, 2025/09

https://doi.org/10.1088/1742-6596/3094/1/012027

no abstracts in English

Half-integer random resonance compensation for further beam power ramp-up in the 3-GeV rapid cycling synchrotron of the Japan Proton Accelerator Research Complex

Kojima, Kunihiro; Harada, Hiroyuki; Tamura, Fumihiko; Okita, Hidefumi; Chimura, Motoki; Saha, P. K.

Progress of Theoretical and Experimental Physics (Internet), 2025(1), p.013G01_1 - 013G01_19, 2025/01

https://doi.org/10.1093/ptep/ptae185

A comprehensive study on the random resonances was conducted to mitigate beam losses and ensure sufficient tunability of the operating point for further beam power ramp-up in the 3-GeV rapid cycling synchrotron of the Japan Proton Accelerator Research Complex. Low-intensity beam studies revealed considerable excitation of the half-integer random resonance. This half-integer random resonance was successfully compensated using trim quadrupole magnets without exciting other higher-order resonances. By implementing a conventional theoretical procedure based on resonance driving terms, we identified the leakage field from extraction magnets as the primary source of the error field driving the random resonance. High-intensity beam studies confirmed that our resonance compensation approach substantially mitigated beam loss in higher-tune regions, making it highly effective in improving operating point tunability.

Benchmarking GPU backend of longitudinal simulation code BLonD

Adachi, Kyosuke; Tamura, Fumihiko; Nomura, Masahiro; Shimada, Taihei; Miyakoshi, Ryosuke*; Okita, Hidefumi; Yoshii, Masahito*; Omori, Chihiro*; Seiya, Kiyomi*; Hara, Keigo*; et al.

Proceedings of 21st Annual Meeting of Particle Accelerator Society of Japan (Internet), p.543 - 546, 2024/10

https://www.pasj.jp/web_publish/pasj2024/proceedings/PDF/THP0/THP003.pdf

no abstracts in English

Applying a deep generative model to mountain plot images

Nomura, Masahiro; Shimada, Taihei; Tamura, Fumihiko; Okita, Hidefumi; Miyakoshi, Ryosuke*; Seiya, Kiyomi*; Yoshii, Masahito*; Omori, Chihiro*; Hara, Keigo*; Hasegawa, Katsushi*; et al.

Proceedings of 21st Annual Meeting of Particle Accelerator Society of Japan (Internet), p.85 - 88, 2024/10

https://www.pasj.jp/web_publish/pasj2024/proceedings/PDF/THOT/THOT02.pdf

no abstracts in English

J-PARC Linac and RCS; Operational status and upgrade plan to 2 MW

Yamamoto, Kazami; Moriya, Katsuhiro; Okita, Hidefumi; Yamada, Ippei; Chimura, Motoki; Saha, P. K.; Shobuda, Yoshihiro; Tamura, Fumihiko; Yamamoto, Masanobu; Morishita, Takatoshi; et al.

Journal of Neutron Research, 26(2-3), p.59 - 67, 2024/01

https://doi.org/10.3233/JNR-240003

The linac and 3 GeV rapid cycling synchrotron at the Japan Proton Accelerator Research Complex was designed to provide 1-MW proton beams to the following facilities. Thanks to the improvement works of the accelerator system, we successfully accelerate 1-MW beam with quite small beam loss. Currently, the beam power of RCS is limited by the lack of anode current in the RF cavity system rather than the beam loss. Recently we developed a new acceleration cavity that can accelerate a beam with less anode current. This new cavity enables us not only to reduce requirement of the anode power supply but also to accelerate more than 1-MW beam. We have started to consider the way to achieve beyond 1-MW beam acceleration. So far, it is expected that up to 1.5-MW beam can be accelerated after replacement of the RF cavity. We have also been continuing study to achieve up to 2 MW beam in J-PARC RCS.

Improvement of the longitudinal phase space tomography at the J-PARC synchrotrons

Okita, Hidefumi; Tamura, Fumihiko; Yamamoto, Masanobu; Nomura, Masahiro; Shimada, Taihei; Saha, P. K.; Yoshii, Masahito*; Omori, Chihiro*; Sugiyama, Yasuyuki*; Hasegawa, Katsushi*; et al.

Journal of Physics; Conference Series, 2687(7), p.072005_1 - 072005_7, 2024/01

https://doi.org/10.1088/1742-6596/2687/7/072005

Longitudinal phase space tomography is an effective measurement tool for acquiring the longitudinal phase space distribution. For the J-PARC synchrotrons, tomography, which can take into account the beam dynamics such as longitudinal space charge effect and nonlinearity, is desired, as the beam power increases. In this study, for the J-PARC synchrotron, the CERN's tomography, which employs the hybrid algorithm that can consider the beam dynamics for reconstruction, is introduced and benchmarked. The benchmark results show that the CERN's tomography has the ability to measure the longitudinal phase space distribution accurately, in the high-power beam operation at the J-PARC synchrotrons.