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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

Development of next-generation timing system for the Japan Proton Accelerator Research Complex

Tamura, Fumihiko; Takahashi, Hiroki; Kamikubota, Norihiko*; Ito, Yuichi*; Hayashi, Naoki

IEEE Transactions on Nuclear Science, 68(8), p.2043 - 2050, 2021/08

 Times Cited Count:0 Percentile:0.01(Engineering, Electrical & Electronic)

A precise and stable timing system is necessary for high intensity proton accelerators such as the J-PARC. The existing timing system, which was developed during the construction period of the-PARC, has been working without major issues since 2006. After a decade of operation, the optical modules, which are key components for signal transfer, were discontinued already. Thus, the next-generation timing system for the J-PARC is under development. The new system is designed to be compatible with the existing system in terms of the operating principle. The new system utilizes modern high speed signal communication for the transfer of the clock, trigger, and type code. We present the system configuration of the next-generation timing system and current status.

Journal Articles

Non-adiabatic longitudinal bunch manipulation at flattop of the J-PARC MR

Tamura, Fumihiko; Omori, Chihiro*; Yoshii, Masahito*; Sugiyama, Yasuyuki*

Proceedings of 12th International Particle Accelerator Conference (IPAC 21) (Internet), p.3023 - 3026, 2021/08

The J-PARC MR delivers the high intensity proton beams for the neutrino experiment. The new Intermediate Water Cherenkov Detector (IWCD) will be constructed for the future neutrino experiment and a low peak time structure is desired by the IWCD. Thus, we consider bunch manipulation at flattop of the MR for reducing the peak current. The manipulation should be quickly done to minimize the loss of the beam power. Also, the beam gap must be kept for the rise time of the extraction kicker. We propose a non-adiabatic bunch manipulation using the multiharmonic rf voltage. By using the neighbor harmonic of the accelerating harmonic, the first and eighth bunches can be decelerated and accelerated, respectively. After a certain period, the rf phase is flipped to $$pi$$ for debunching. Thanks to the initial deceleration and acceleration, the beam gap for the kickers is kept. We present the concept and the longitudinal simulation result.

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:0 Percentile:0.03(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.

Journal Articles

Applying image recognition technology by convolutional neural networks to mountain plot images

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

Proceedings of 17th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.64 - 67, 2020/09

Image recognition using a convolutional neural network (CNN) has been used in a wide range of fields and has produced excellent results. If this image recognition technology is used effectively, it should be possible to obtain information from an image equal to or more than the information that a person can obtain from an image. At J-PARC, researchers with specialized knowledge obtain beam information needed to adjust the equipment from an image called mountain plot. In this study, we applied the image recognition technology by using CNN to this mountain plot image, and tried to obtain the information about the beam necessary for adjustment. As a result, we were able to obtain more information than is currently available by using the image recognition technology. In the future, we plan to adjust the equipment based on the information actually obtained from the image recognition technology and confirm its effectiveness

Journal Articles

Towards widespread use of MTCA in accelerators

Tamura, Fumihiko; Yoshii, Masahito*; Kamikubota, Norihiko*; Takahashi, Hiroki

Proceedings of 17th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.68 - 72, 2020/09

MTCA (MicroTCA) is expected to be the next generation platform for advanced control in accelerators. MTCA has many advantages over the widely used VMEs, such as high speed, large data transfer capacity, and high maintainability with hot-swappable modules. After the application to the LLRF control system at KEK, MTCA has been used in many accelerators around the world, while it takes a long time for MTCA to spread to the accelerators in Japan. Recently, the number of large-scale adoptions such as the LLRF control system, for the J-PARC RCS has been increasing. In this article, we introduce a case study of MTCA adoption and discuss why MTCA has not been widely used in Japan. Also, the efforts for the future promotion of MTCA in Japan are reported.

Journal Articles

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

Yamamoto, Kazami; Yamamoto, Masanobu; Yamazaki, Yoshio; Nomura, Masahiro; Suganuma, Kazuaki; Fujirai, Kosuke; Kamiya, Junichiro; Hatakeyama, Shuichiro; Hotchi, Hideaki; Yoshimoto, Masahiro; et al.

Proceedings of 17th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.209 - 213, 2020/09

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, just before the summer shutdown period, we have been trying continuous supply of 1-MW high-intensity beam, which is the design value, to a neutron target. First trial was 1-hour continuous operation in July 2018, and second trial was 10-hours continuous in July 2019. In both cases, we achieved almost stable operation. Furthermore, in June 2020, we tried to operate continuously for over 40 hours. But in this case, some trouble occurred and the operation was frequently suspended. Through these continuous operation trials, we have identified issues for stable operation of 1 MW. In this presentation, we will report the results of 1-MW continuous operation and issues obtained from these results.

Journal Articles

Benchmarking of longitudinal calculation code BLonD for Application to 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 17th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.674 - 678, 2020/09

Longitudinal beam simulation code BLonD (Beam Longitudinal Dynamics), which has been developed by CERN in recent years, is being used accelerator facilities around the world. BLonD can simulate longitudinal beam motion considering with wake voltage and space charge effect and is written by Python, which makes it highly readable and general-purpose code. We are currently conducting a benchmark of BLonD aiming at studying for further improvements of acceleration technology and stable operation of the J-PARC 3GeV synchrotron (RCS). The bunching factor, which express the longitudinal beam charge distribution, calculated by BLonD simulation reflected by the current 1MW beam operation parameters reproduce the experimental results well and the validity of BLonD for RCS longitudinal beam simulation was confirmed.

Journal Articles

First measurement and online monitoring of the stripper foil thinning and pinhole formation to achieve a longer foil lifetime in high-intensity accelerators

Saha, P. K.; Yoshimoto, Masahiro; Hatakeyama, Shuichiro; Hotchi, Hideaki; Harada, Hiroyuki; Tamura, Fumihiko; Yamamoto, Kazami; Yamazaki, Yoshio; Kinsho, Michikazu; Irie, Yoshiro*

Physical Review Accelerators and Beams (Internet), 23(8), p.082801_1 - 082801_13, 2020/08

 Times Cited Count:1 Percentile:35.83(Physics, Nuclear)

Journal Articles

J-PARC 3-GeV RCS; 1-MW beam operation and beyond

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:1 Percentile:27.17(Instruments & Instrumentation)

no abstracts in English

Journal Articles

Simulations of beam loading compensation in a wideband accelerating cavity using a circuit simulator including a LLRF feedback control

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

Journal of Physics; Conference Series, 1350(1), p.012189_1 - 012189_7, 2019/12

 Times Cited Count:0 Percentile:0.07

Magnetic alloy cavities are employed in the J-PARC RCS to generate high accelerating voltages. The cavity, which is driven by a vacuum tube amplifier, has a wideband frequency response and the beam loading in the cavity is multiharmonic. Therefore, the tube must generate a multiharmonic output current. An LTspice circuit model is developed to analyze the vacuum tube operation and the compensation of the multiharmonic beam loading. The model includes the cavity, tube amplifier, beam current, and LLRF feedback control. The feedback control consists of the I/Q demodulator including low pass filters, PI control, and I/Q modulator. In this presentation, we present the implementation of the LLRF functions in the LTspice simulations. The preliminary simulation results are also presented. The simulations fairly agree with the beam test results.

Journal Articles

Multiharmonic vector rf voltage control for wideband cavities driven by vacuum tube amplifiers in a rapid cycling synchrotron

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

Physical Review Accelerators and Beams (Internet), 22(9), p.092001_1 - 092001_22, 2019/09

 Times Cited Count:2 Percentile:39.22(Physics, Nuclear)

Beam loading compensation in the rf cavities is a key for acceleration of high intensity beams in 3 GeV RCS of the J-PARC. Since we employ wideband magnetic alloy rf cavities for the J-PARC RCS and the wake voltage contains several harmonics, a multiharmonic beam loading compensation is required. The multiharmonic rf feedforward for the most important six harmonics is implemented in the existing low level rf (LLRF) control system, which has been working fairly well for acceleration of high intensity beams of up to 1 MW. However, we found the degradation of the performance for compensation of the feedforward with very high intensity beams. Therefore, a multiharmonic vector rf voltage control has been developed. The detail of system configuration, commissioning methodology, and beam test results using very high intensity beams are described. The beam loading by the 1 MW equivalent beam in the cavity is successfully compensated.

Journal Articles

Development of next-generation LLRF control system for J-PARC rapid cycling synchrotron

Tamura, Fumihiko; Sugiyama, Yasuyuki*; Yoshii, Masahito*; Ryoshi, Masatsugu*

IEEE Transactions on Nuclear Science, 66(7), p.1242 - 1248, 2019/07

 Times Cited Count:3 Percentile:57.07(Engineering, Electrical & Electronic)

The LLRF control system for the rapid cycling synchrotron of the J-PARC started its operation in 2007. The key functions of the LLRF control system are the dual harmonic auto voltage control and the multiharmonic rf feedforward to compensate the beam loading in the MA cavity caused by high intensity beams. The system has been working well without major problems for more than ten years. However, the old FPGAs are discontinued and not supported by the current development environment. It will be difficult to maintain the system in near future. Thus, we are planning to replace the existing VME-based LLRF control system with a new MicroTCA.4 based system. In this presentation, we present the configuration of the system under development, the implemented functions, and preliminary test results.

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