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Journal Articles

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

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.

Journal Articles

Consideration of high intensity single bunch acceleration in J-PARC RCS

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

Proceedings of 20th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.64 - 68, 2023/11

The J-PARC 3GeV synchrotron (RCS) provides high intensity proton beams to the Materials and Life Science Experimental Facility (MLF) and the Main Ring (MR). The harmonic number (h) of the RCS is 2 and the RCS normally accelerates two bunches. For some experiments at the MLF, a single bunch is preferred. In this case, one of the rf bucket is filled with protons and the other is empty. Therefore the beam intensity is halved. If the RCS can accelerate with h=1, the intensity per bunch can be doubled, enabling to provide single bunch beams to the MLF with the maximum intensity. This possibly increases the MR beam power by injecting high intensity single bunches eight times. In this presentation, we report mainly on the consideration of h=1 acceleration in the RCS by longitudinal simulations.

Journal Articles

Development of a single-ended magnetic alloy loaded cavity in the Japan Proton Accelerator Research Complex rapid cycling synchrotron

Yamamoto, Masanobu; Nomura, Masahiro; Okita, Hidefumi; Shimada, Taihei; Tamura, Fumihiko; Hara, Keigo*; Hasegawa, Katsushi*; Omori, Chihiro*; Sugiyama, Yasuyuki*; Yoshii, Masahito*

Progress of Theoretical and Experimental Physics (Internet), 2023(7), p.073G01_1 - 073G01_16, 2023/07

 Times Cited Count:0 Percentile:0.01

The Japan Proton Accelerator Research Complex (J-PARC) Rapid Cycling Synchrotron (RCS) employs Magnetic Alloy (MA) loaded cavities. We realize multi-harmonic rf driving and beam loading compensation owing to the broadband characteristics of the MA. The currently installed cavity is the conventional type one which is designed to be driven by tube amplifiers in a push-pull operation. The push-pull operation has some advantages, i.e., suppressing a higher harmonic distortion without the beam acceleration and shortening the cavity length. However, a disadvantage arises at the high intensity beam acceleration where the multi-harmonic rf driving causes a severe imbalance of the anode voltage swing and restricts the tube operation. Although we have achieved an acceleration for the design beam power of 1 MW, the imbalance becomes an issue to further increase the beam power. We have developed a single-ended MA cavity to avoid such difficulty. The cavity has no tube imbalance intrinsically and it is found that the power consumption to drive the cavity can be reduced compared with the conventional one.

Journal Articles

Demonstration of a kicker impedance reduction scheme with diode stack and resistors by operating the 3-GeV rapid cycling synchrotron of the Japan Proton Accelerator Research Complex

Shobuda, Yoshihiro; Harada, Hiroyuki; Saha, P. K.; Takayanagi, Tomohiro; Tamura, Fumihiko; Togashi, Tomohito; Watanabe, Yasuhiro; Yamamoto, Kazami; Yamamoto, Masanobu

Physical Review Accelerators and Beams (Internet), 26(5), p.053501_1 - 053501_45, 2023/05

 Times Cited Count:0 Percentile:0.02(Physics, Nuclear)

At the Rapid Cycling Synchrotron (RCS) in Japan Proton Accelerator Research Complex (J-PARC), theoretical predictions have indicated that the kicker-impedance would excite the beam-instability. A 1 MW beam with large emittance can be delivered to the Material and Life Science Experimental Facility (MLF) through suppression of the beam instabilities by choosing the appropriate machine parameters. However, we require other high-intensity and high-quality smaller emittance beams (than the 1 MW beam) for the Main Ring (MR). Hence, we proposed a scheme for suppressing the kicker-impedance by using prototype diodes and resistors, thereby demonstrating the effect on the kicker impedance reduction. However, the J-PARC RCS must be operated with a repetition rate of 25 Hz, which urged us to consider special diodes that are tolerant to heating. After developments, we have demonstrated that the special diodes with resistors can suppress the beam instability by reducing the kicker impedance. Enhanced durability of the prototype diodes and resistors for the 25 Hz operation was also realized. Moreover, the new diodes and the resistors have negligible effect on the extracted beam from the RCS. From a simulation point of view, the scheme can be employed for at least 5 MW beam operation within the stipulated specifications.

Journal Articles

Design studies on a high-power wide-band RF combiner for consolidation of the driver amplifier of the J-PARC RCS

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

Journal of Physics; Conference Series, 2420, p.012092_1 - 012092_6, 2023/01

A power upgrade of existing 8 kW solid-state driver amplifier is required for the acceleration of high intensity proton beams on the J-PARC 3 GeV rapid cycling synchrotron. The development of a 25 kW amplifier with gallium nitride (GaN) HEMTs, based on 6.4 kW modules is on going. The combiner is a key component to achieve such a high output power over the wide bandwidth required for multi-harmonic rf operation. This paper presents preliminary design of the combiner. The circuit simulation setup and results, including the realistic magnetic core characteristics and frequency response of the cable are reported.

Journal Articles

Evaluation of higher harmonics generated in acceleration gaps during the high power beam acceleration at J-PARC RCS

Okita, Hidefumi; Tamura, Fumihiko; Yamamoto, Masanobu; Nomura, Masahiro; Shimada, Taihei; Yoshii, Masahito*; Omori, Chihiro*; Hara, Keigo*; Hasegawa, Katsushi*; Sugiyama, Yasuyuki*

Proceedings of 19th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.262 - 266, 2023/01

no abstracts in English

Journal Articles

Image recognition technology is used to obtain momentum distribution and longitudinal beam shape from mountain plot image

Nomura, Masahiro; Okita, Hidefumi; Shimada, Taihei; Tamura, Fumihiko; Yamamoto, Masanobu; Sugiyama, Yasuyuki*; Hasegawa, Katsushi*; Hara, Keigo*; Omori, Chihiro*; Yoshii, Masahito*

Proceedings of 19th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.215 - 217, 2023/01

no abstracts in English

Journal Articles

Results of 1-MW operation in J-PARC 3 GeV rapid cycling synchrotron, 2

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.

Journal Articles

Improvement of longitudinal beam tracking simulation considering the frequency response of the cavity gap voltage monitor

Okita, Hidefumi; Tamura, Fumihiko; Yamamoto, Masanobu; Nomura, Masahiro; Shimada, Taihei; Yoshii, Masahito*; Omori, Chihiro*; Hara, Keigo*; Hasegawa, Katsushi*; Sugiyama, Yasuyuki*

Nuclear Instruments and Methods in Physics Research A, 1041, p.167361_1 - 167361_7, 2022/10

 Times Cited Count:0 Percentile:34.54(Instruments & Instrumentation)

Wideband RF cavities are employed in the Rapid Cycling Synchrotron of the Japan Proton Accelerator Research Complex. RF gap voltage generated during the high power beam acceleration includes the wake voltage and distortion derived from the tube amplifier. The signal from RF gap voltage monitors, which measure the RF gap voltage during the acceleration, includes these effects. We developed the longitudinal beam tracking simulation using the measurement of the RF gap voltage monitors. To apply the measurement of the RF gap voltage monitors to the simulation, the theoretical frequency response models of the voltage divider and the coaxial cable, which are the primary components of the cavity gap voltage monitor, are developed. By taking the frequency response into account, the tracking simulation well reproduces the measured bunch shape at 1 MW.

Journal Articles

Design and actual performance of J-PARC 3 GeV rapid cycling synchrotron for high-intensity operation

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:3 Percentile:80.29(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.

Journal Articles

Influence of a positive grid biasing on RF system in J-PARC RCS

Yamamoto, Masanobu; Nomura, Masahiro; Okita, Hidefumi; Shimada, Taihei; Tamura, Fumihiko; Hara, Keigo*; Hasegawa, Katsushi*; Omori, Chihiro*; Sugiyama, Yasuyuki*; Yoshii, Masahito*

Proceedings of 13th International Particle Accelerator Conference (IPAC 22) (Internet), p.1336 - 1338, 2022/06

In order to accelerate a high intensity beam in the RCS, a large amplitude of the rf current is provided by a tube amplifier to compensate a heavy beam loading. Tetrode vacuum tubes are used in the RCS, and the control grid voltage enters into a positive region to feed such a large rf current. The positive grid biasing affects the waveform of the control grid voltage; it is deformed due to the induced control grid current under the condition of the multi-harmonic rf driving. Furthermore, the DC bias voltage drop on the control grid is observed because of the exceeding the capability for the control grid power supply. We describe the influence of the positive grid biasing in the RCS.

Journal Articles

Evaluation of the frequency response of the RF gap voltage monitor of the J-PARC RCS

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

Proceedings of 18th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.840 - 844, 2021/10

The J-PARC RCS employs the dual-harmonic operation, in which the fundamental and the second harmonic RF voltages are used for the beam acceleration. The each harmonic voltage and phase applied for the acceleration gaps are controlled by the multiharmonic vector RF voltage control system using the signal from the cavity gap voltage monitor equipped with the one of the acceleration gaps of the each RF cavity. Since the bunch shape varies depending on the relative phase of each harmonic, it is important to evaluate the frequency response of the cavity gap voltage monitor. The measurements of frequency response of the cavity gap voltage monitor and beam tracking simulation considering the measurement were carried out. As a result, it was confirmed that the bunch shape of the beam tracking simulation reproduces the one measured at the 1MW beam operation well. The details of the frequency response measurement, the beam tracking simulation and the discussion of the cavity gap voltage monitor circuit are reported.

Journal Articles

Performance of the next-generation LLRF control system for the J-PARC RCS

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

Proceedings of 18th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.170 - 174, 2021/10

A stable and precise LLRF (Low Level RF) control system is indispensable for acceleration of high intensity proton beam in the J-PARC RCS. The original LLRF control system had been operated without major problems for more than ten years since the start of operation of the RCS, while maintenance of the system became difficult due to the obsolesce of the old FPGAs in the modules. We developed and installed the next-generation LLRF control system based on MTCA.4. The key function of the system is the multiharmonic vector rf voltage control feedback. We describe the system overview and the commissioning results. The performance of the beam loading compensation is significantly improved.

Journal Articles

Evaluations with autoencoder whether the image used for image recognition is appropriate

Nomura, Masahiro; Okita, Hidefumi; Shimada, Taihei; Tamura, Fumihiko; Yamamoto, Masanobu; Furusawa, Masashi*; Sugiyama, Yasuyuki*; Hasegawa, Katsushi*; Hara, Keigo*; Omori, Chihiro*; et al.

Proceedings of 18th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.80 - 82, 2021/10

no abstracts in English

Journal Articles

Consideration of triple-harmonic operation for the J-PARC RCS

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

Proceedings of 12th International Particle Accelerator Conference (IPAC 21) (Internet), p.3020 - 3022, 2021/08

In the J-PARC RCS, the dual-harmonic operation, in which each RF cavity is driven by superposition of the fundamental accelerating voltage and the second harmonic voltage, are employed. The dual-harmonic-operation significantly improves the bunching factor and is indispensable for acceleration of the high intensity beams. The original LLRF control system was replaced with the new system in 2019, which can control the amplitudes of the higher harmonics as well as the fundamental and second harmonics. Therefore we consider to use additionally the third harmonic voltage for further improvement of the bunching factor during acceleration. By the triple-harmonic operation, the flat RF bucket can be realized and beam simulation results indicate that the bunching factor can be improved about 30% at maximum. In this presentation, we describe the longitudinal simulation studies of the triple-harmonic operation. Also the preliminary test results are presented.

Journal Articles

Vacuum tube operation tuning for a high intensity beam acceleration in J-PARC RCS

Yamamoto, Masanobu; Okita, Hidefumi; Nomura, Masahiro; Shimada, Taihei; Tamura, Fumihiko; Furusawa, Masashi*; Hara, Keigo*; Hasegawa, Katsushi*; Omori, Chihiro*; Sugiyama, Yasuyuki*; et al.

Proceedings of 12th International Particle Accelerator Conference (IPAC 21) (Internet), p.1884 - 1886, 2021/08

Tetrode vacuum tubes in J-PARC RCS are used under a reduced filament voltage condition compared with the rating value to prolong the tube lifetime. For the first time after 60,000 hour of operation in the RCS, one tube has reached the end of its life in 2020. Therefore, the reduced filament voltage works well because the tube has been running beyond an expected lifetime suggested by the tube manufacturer. However, the reduced filament voltage decreased the electron emission from the filament. Although the large amplitude of the anode current is necessary for the high intensity beam acceleration to compensate a wake voltage, a solid-state amplifier to drive a control grid circuit almost reaches the output power limit owing to the poor electron emission from the filament. We changed the filament voltage reduction rate from 15% to 5%. The required power of the solid-state amplifier was fairly reduced, whereas the accelerated beam power remained the same. We describe the measurement results of the vacuum tube parameters in terms of the filament voltage tuning.

Journal Articles

Commissioning of the next-generation LLRF control system for the Rapid Cycling Synchrotron of the Japan Proton Accelerator Research Complex

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

Nuclear Instruments and Methods in Physics Research A, 999, p.165211_1 - 165211_11, 2021/05

 Times Cited Count:3 Percentile:58.42(Instruments & Instrumentation)

The low level rf (LLRF) control system has key roles for the stable acceleration of the high intensity beam. The original LLRF control system for the RCS of J-PARC has been working nicely without major issues for more than ten years since the operation of the RCS started in 2007. Due to the obsolescence of the key digital devices, it is difficult to maintain the original system for a longer period, therefore we developed the next-generation LLRF control system. All of the LLRF functions of the new system were tested and commissioned. In this article, we describe the commissioning of two key functions, the phase feedback and the multiharmonic vector rf voltage control feedback for twelve cavities. The commissioning methodologies and beam test results are presented. The stable acceleration of the high intensity beam at the design intensity of $$8.3times 10^{13}$$ ppp is achieved. The next-generation LLRF control system has been successfully deployed and commissioned.

Journal Articles

1.2-MW-equivalent high-intensity beam tests in J-PARC 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

Journal Articles

Flexible chopper gate pulse generation for the J-PARC RCS

Tamura, Fumihiko; Yamamoto, Masanobu; Yoshii, Masahito*; Sugiyama, Yasuyuki*; Hotchi, Hideaki; Saha, P. K.; Yoshimoto, Masahiro; Harada, Hiroyuki

JPS Conference Proceedings (Internet), 33, p.011021_1 - 011021_6, 2021/03

Chopped beam injection is employed in the J-PARC RCS to avoid the longitudinal beam losses. A fast beam chopper is installed in the MEBT section of the linac. The chopper is driven by the gate pulses sent from the LLRF control system of the RCS. The delay from the zero crossing of the RCS rf and the width are set so that the beam pulse is injected into the proper phase position of the rf bucket. A unique feature of the J-PARC chopper gate pulse generation is thinning of the pulses. The thinning is useful to control the beam intensity without changing much the condition of the longitudinal painting. Also, the beam macro pulse can be trimmed down to a single intermediate pulse by setting the parameters. In this poster, we present the overview of the generation of the chopper gate pulse in the LLRF control system and various beam commissioning results utilizing the flexibility of it. Also, we discuss the upgrade of the chopper gate pulse generation.

Journal Articles

Operation experience of Tetrode vacuum tubes in J-PARC Ring RF system

Yamamoto, Masanobu; Furusawa, Masashi*; Hara, Keigo*; Hasegawa, Katsushi*; Nomura, Masahiro; Omori, Chihiro*; Shimada, Taihei; Sugiyama, Yasuyuki*; Tamura, Fumihiko; Yoshii, Masahito*

JPS Conference Proceedings (Internet), 33, p.011022_1 - 011022_6, 2021/03

A Tetrode vacuum tubes (Thales TH589) are used in the J-PARC ring rf system. The operation has started in 2007, and the total operation time is more than 50,000 hours. There is no tube which reaches the end of life except an initial failure in the 3 GeV synchrotron. TH589 has a thoriated tungsten filament and it is carburized to suppress an evaporation of the thorium. The resistance of the filament decreases through the decarburization process after the filament operation has started. The tube constructor suggests that reduced filament voltage up to 10% compared with the rated value is effective to suppress the decarburization. However, the filament current increases even though the voltage is kept constant due to the resistance reduction, and it is observed that an increment of the power dissipation promotes the decarburization. This means that keeping the filament voltage constant is not enough; keeping the power dissipation constant is necessary to prolong the tube life time, and we employ a procedure to decrease the current regularly.

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