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Journal Articles

Effects of the longitudinal impedances on non-adiabatic bunch manipulation at flattop of J-PARC MR

Tamura, Fumihiko; Omori, Chihiro*; Yoshii, Masahito*; Tomizawa, Masahito*; Toyama, Takeshi*; Sugiyama, Yasuyuki*; Hasegawa, Katsushi*; Kobayashi, Aine*; Okita, Hidefumi

Proceedings of 19th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.175 - 178, 2023/01

J-PARC MR delivers high intensity proton beams to the neutrino experiment. Eight bunches with high peak currents are extracted from the MR by the extraction kicker, therefore the neutrino beam has the similar structure. Intermediate Water Cherenkov Detector (IWCD) will be installed for the future experiments and the IWCD requires a time structure with low peaks. We consider bunch manipulation at flattop of the MR for reducing the peak current. It should be quickly done to avoid the significant loss of the beam power. The beam gap for the kicker rise time must be kept. We propose a non-adiabatic bunch manipulation using the multiharmonic rf voltage. The longitudinal impedance in the MR can affect the beam stability. The feasibility of the manipulation is discussed by using the longitudinal simulations.

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:81.34(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

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

Vacuum tube operation analysis for 1.2 MW beam acceleration in J-PARC RCS

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

Proceedings of 10th International Particle Accelerator Conference (IPAC '19) (Internet), p.2017 - 2019, 2019/06

J-PARC RCS has successfully accelerated 1 MW proton beam, and we have considered acceleration with the next target being 1.2 MW. An issue for 1.2 MW beam acceleration is the rf system. The present anode power supply is limited by its output current, and the vacuum tube amplifier suffers from an unbalance of the anode voltage swing, arising from the combination of multi-harmonic rf driving and push-pull operation. We have investigated the mitigation of the maximum anode currents and unbalanced tubes by choosing appropriate circuit parameters of the rf cavity with tube amplifier. We describe the analysis results of the vacuum tube operation for 1.2 MW beam acceleration in the RCS.

Journal Articles

Conceptual design of a single-ended MA cavity for J-PARC RCS upgrade

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

Journal of Physics; Conference Series, 1067, p.052014_1 - 052014_6, 2018/10

 Times Cited Count:3 Percentile:81.16

The J-PARC RCS employs Magnetic Alloy (MA) loaded cavities. The RF power is fed by vacuum tubes in push-pull operation. We realize multi-harmonic RF driving and beam loading compensation thanks to the broadband characteristics of the MA. However, the push-pull operation has disadvantages in multi-harmonics. An unbalance of the anode voltage swing remarkably appears at very high intensity beam acceleration. We propose a single-ended MA cavity for the RCS beam power upgrade, where no unbalance arises intrinsically.

Journal Articles

Measurement of thermal deformation of magnetic alloy cores of radio frequency cavities in 3-GeV rapid-cycling synchrotron of Japan Proton Accelerator Research Complex

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

Nuclear Instruments and Methods in Physics Research A, 875, p.92 - 103, 2017/12

 Times Cited Count:0 Percentile:0.02(Instruments & Instrumentation)

Journal Articles

New injection scheme of J-PARC rapid cycling synchrotron

Yamamoto, Kazami; Kamiya, Junichiro; Saha, P. K.; Takayanagi, Tomohiro; Yoshimoto, Masahiro; Hotchi, Hideaki; Harada, Hiroyuki; Takeda, Osamu*; Miki, Nobuharu*

Proceedings of 8th International Particle Accelerator Conference (IPAC '17) (Internet), p.579 - 581, 2017/05

The 3-GeV Rapid Cycling Synchrotron of Japan Proton Accelerator Research Complex aims to deliver 1-MW proton beam to the neutron target and Main Ring synchrotron. Present beam power of the Rapid Cycling Synchrotron is up to 500-kW and the higher radiation doses were concentrated in the injection area. These activations were caused by the interaction between the foil and the beam. To reduce the worker dose near the injection point, we have studied a new design of the injection scheme to secure enough space for radiation shielding and bellows. In the new system, two of four injection pulse bump magnets are replaced and we are able to ensure the additional space around the injection foil chamber. So far, new injection system seems not impossible. However, preliminary study result indicated that temperature of the duct and shielding metals would be slightly higher. The eddy current due to the shift bump magnet field generates heat. Thus we have to study details of above effect.

Journal Articles

Vacuum tube operation analysis under multi-harmonic driving and heavy beam loading effect in J-PARC RCS

Yamamoto, Masanobu; Nomura, Masahiro; Shimada, Taihei; Tamura, Fumihiko; Hara, Keigo*; Hasegawa, Katsushi*; Omori, Chihiro*; Toda, Makoto*; Yoshii, Masahito*; Schnase, A.*

Nuclear Instruments and Methods in Physics Research A, 835, p.119 - 135, 2016/11

 Times Cited Count:5 Percentile:44.88(Instruments & Instrumentation)

A magnetic alloy loaded cavity is used to generate multi-harmonic rf voltage in J-PARC RCS. However, a vacuum tube operation analysis under the multi-harmonic driving is very complicated because many variables should be solved with a self consistency. At the conventional operation analysis, a hand work by tracing the constant current curve of the tube was performed, or an appropriate single harmonic wave form was assumed. We have developed a numerical analysis code which calculates the vacuum tube operation automatically and it realizes the multi-harmonic vacuum tube operation analysis. The code is verified at the high power beam acceleration test and we confirm the calculation results are consistent with the measurement ones. We can calculate the vacuum tube operation precisely by using the code, and it will contribute to improving the quality of the beam in the high intensity proton synchrotron.

Journal Articles

Longitudinal particle tracking code for a high intensity proton synchrotron

Yamamoto, Masanobu

Proceedings of 57th ICFA Advanced Beam Dynamics Workshop on High-Intensity and High-Brightness Hadron Beams (HB 2016) (Internet), p.110 - 114, 2016/08

We have been developing a longitudinal particle tracking code for a high intensity proton synchrotron, especially for the J-PARC Synchrotron. Although some longitudinal particle tracking codes exist, our code can track the particles with a wake voltage and a space charge effect, and also can calculate a beam emittance and a momentum filling factor under a multi-harmonics to evaluate the margin of a rf bucket. Furthermore, we originally have developed the calculation method of a synchronous particle, which realizes the simulation in the case that the revolution frequency of the synchronous particle is not proportional to an acceleration frequency pattern. This is useful to check an adiabaticity. We have achieved 1 MW-eq. beam acceleration at J-PARC RCS by using the code because we can calculate the optimum acceleration conditions for the high intensity beam. We will describe the basic design of the code and the simulation results for the J-PARC RCS and MR.

Journal Articles

Simulation of beam behavior caused by odd harmonics of beam loading in J-PARC RCS

Yamamoto, Masanobu; Nomura, Masahiro; Shimada, Taihei; Tamura, Fumihiko; Hara, Keigo*; Hasegawa, Katsushi*; Omori, Chihiro*; Toda, Makoto*; Yoshii, Masahito*

Proceedings of 7th International Particle Accelerator Conference (IPAC '16) (Internet), p.3443 - 3445, 2016/06

The J-PARC RCS accelerates 2 bunches at the harmonic number 2. The major Fourier component of the beam current is even harmonics. However, the odd harmonics grow under some conditions even though they are very small amplitude at the beginning. Particle tracking simulation suggests that the displacement and the deformation of the bunch are caused by the odd harmonics, it is synchronized with the potential distortion, and it results in the beam instability. We describe the particle tracking simulation results for the odd harmonic beam loading effect in the RCS.

Journal Articles

Simulation of phase modulation for longitudinal emittance blow-up in J-PARC MR

Yamamoto, Masanobu; Ezura, Eiji*; Hara, Keigo*; Hasegawa, Katsushi*; Nomura, Masahiro; Omori, Chihiro*; Schnase, A.*; Shimada, Taihei; Takagi, Akira*; Takata, Koji*; et al.

JPS Conference Proceedings (Internet), 8, p.012015_1 - 012015_6, 2015/09

The J-PARC MR provides a coasting proton beam for nuclear physics experiments by slow extraction. The longitudinal emittance should be enlarged until the MR flat top to mitigate the microwave instability. We have investigated a Phase Modulation (PM) method by using a High Frequency Cavity (HFC) to increase the emittance. We have performed extensive simulation studies to find the appropriate parameters of the PM through the particle tracking simulation. We found that the effective HFC frequency has linear dependence with the PM frequency, where the emittance is smoothly enlarged. Furthermore, we found that the required HFC voltage is inverse proportional to the square root of the duration time of the PM. These PM properties will be used for the design of the HFC. We describe the particle tracking simulation results of controlled emittance blow-up by the PM.

Journal Articles

Progress and status of the J-PARC 3 GeV RCS

Kinsho, Michikazu

Proceedings of 5th International Particle Accelerator Conference (IPAC '14) (Internet), p.3382 - 3384, 2014/07

Big issue for the J-PARC rapid cycling synchrotron (RCS) was displacement of main magnets caused by last big earthquake because this made beam loss more than 400 kW beam power. Since realignment of main magnets and other components was essential to realize higher beam power and stable operation, this work has been done during maintenance period in 2013. To achieve the nominal performance 1MW beam power at the RCS and 0.75 MW at the MR, beam energy of linac was increased from 181 MeV to 400 MeV with a new accelerating structure ACS (Annular-ring Coupled Structure) linac from this January. It was successful 400 MeV beam injection and 3 GeV beam extraction at the RCS, and user operation has been performed with beam power of 300 kW. An equivalent beam power of 560 kW with a beam loss of only 0.3% could be achieved during short time for high intensity beam study.

JAEA Reports

Design report on the 3-GeV proton beam transport facility (3NBT) of High Intensity Proton Accelerator facility (J-PARC)

Sakamoto, Shinichi; Meigo, Shinichiro; Konno, Chikara; Kai, Tetsuya; Kasugai, Yoshimi; Harada, Masahide; Fujimori, Hiroshi*; Kaneko, Naokatsu*; Muto, Suguru*; Ono, Takehiro*; et al.

JAERI-Tech 2004-020, 332 Pages, 2004/03


One of the experimental facilities in Japan Proton Accelerator Research Complex (J-PARC) is the Materials and Life Science Experimental Facility (MLF), where high-intensity neutron beams and muon beams are used as powerful probes for materials science, life science and related engineering. The neutrons and muons are generated with high-intensity proton beam from 3-GeV rapid cycling synchrotron (RCS). The high-intensity proton beam has to be effectively transported, and a neutron production target and a muon production target have to be also properly irradiated. The principal design of the 3-GeV proton beam transport facility (3NBT) is systematized.

Journal Articles

Roundness and straightness measurement of ceramic beam ducts for the 3GeV-synchrotron of Japan-proton accelerator research complex

Nishizawa, Daiji*; Kinsho, Michikazu; Kanazawa, Kenichiro; Ogiwara, Norio; Saito, Yoshio*; Kubo, Tomio*; Sato, Yoshihiro*

Shinku, 47(4), p.339 - 343, 2004/02

Large aperture cylindrical beam ducts consisting of alumina ceramics will be used for the first time in the 3GeV-synchrotron of High Intensity Proton Accelerator Facility. It is necessary to evaluate roundness and straightness of ceramic ducts because we have to compensate contact area of the connected beam duct large as well as we have to compensate large enough beam aperture. We developed an apparatus of measuring roundness and straightness, and we completed data analysis method as well as measuring method. Then we are measuring and evaluating roundness and straightness of ceramic beam ducts. Now, we have newly made an ellipse ceramic duct for the 3GeV-synchrotron BM. This duct has ellipse cross-sections to satisfy with larger aperture that the beam dynamics requires. In this conference, we are going to present taken data and findings regarding form accuracy including roundness and straightness of the ellipse ceramic duct.

Journal Articles

Rapid cycling synchrotron of J-PARC

Suzuki, Hiromitsu

Proceedings of 3rd Asian Particle Accelerator Conference (APAC 2004), p.499 - 501, 2004/00

JAERI and KEK are constrting J-PARC. The accelerator complex consists of a 400 MeV linac, a 3 GeV rapid cycling synchrotron ring (RCS) and a 50 GeV synchrotron ring (MR). The RCS ring accelerates a 400 MeV proton beam from the linac up to 3 GeV and supplies the beam to the MR and a MLF (material and life science facility). The MLF has a neutron production target in order to produce a high intensity neutron beam. For this purpose, the RCS aims to generate a high power proton beam of 1 MW. The construction of the RCS started in 2002. All the components were ordered in the fiscal year of 2002 and 2003. The budged is started in the fiscal year of 2002 and finished in that of 2006. The building will be accomplished in April 2005, and many components of RCS will be installed and tested from May 2005 to April 2007. The beam commissioning of RCS will be started in May 2007. This paper presents the design and status of RCS.

Journal Articles

The JAERI-KEK joint project for the high-intensity proton accelerator, J-PARC

Yamazaki, Yoshishige

Proceedings of 2003 Particle Accelerator Conference (PAC 2003) (CD-ROM), p.576 - 580, 2003/00

The JAERI-KEK Joint Project for the High Intensity Proton Accelerator, now referred to as the J-PARC Project (Japan Proton Accelerator Research Complex), comprises a 400-MeV linac, a 3-GeV, 25-Hz Rapid-Cycling Synchrotron (RCS), and a 50-GeV Main Synchrotron (MR). In contrast to the SNS or the ESS, the J-PARC makes use of the RCS in order to produce MW-class pulsed spallation neutrons rather than a combination of the full-energy linac and the compressor ring.

Journal Articles

Longitudinal beam dynamincs on 3 GeV PS in JAERI-KEK joint project

Yamamoto, Masanobu; Tamura, Fumihiko; Ezura, Eiji*; Hashimoto, Yoshinori*; Mori, Yoshiharu*; Omori, Chihiro*; Schnase, A.*; Takagi, Akira*; Uesugi, Tomonori*; Yoshii, Masahito*

Proceedings of 8th European Particle Accelerator Conference (EPAC 2002), p.1073 - 1075, 2002/00

Longitudinal beam emittance should be controlled to alleviate space charge effects by rf manipulations at 3 GeV proton synchrotrons in JAERI-KEK Joint High Intensity Proton Accelerator Project. At injection, bunching factor of 0.4 will be achived by controlled longitudinal beam painting and multiplying 2nd higher harmonics. Furthermore, heavy beam loading is a severe problem, and it should be compensated by feedforward method for stable acceleration. About these themes, the scenario will be described with particle tracking simulations.

Journal Articles

Design of a dipole magnet for the 3-GeV proton synchrotron of the JAERI/KEK joint project

Tani, Norio; Kanazawa, Kenichiro; Shimada, Taihei; Suzuki, Hiromitsu; Watanabe, Yasuhiro; Adachi, Toshikazu*; Someya, Hirohiko*

Proceedings of 8th European Particle Accelerator Conference (EPAC 2002), p.2376 - 2378, 2002/00

The 3-GeV synchrotron proposed in the JAERI/KEK Joint Project is a rapid-cycling synchrotron (RCS), which accelerates a high-intensity proton beam from 400 MeV to 3 GeV at a repetition rate of 25 Hz. The 3-GeV synchrotron is used to produce pulsed spallation neutrons and muons. It also works as an injector for a 50-GeV synchrotron. Since the magnets for the 3-GeV synchrotron are required to have a large aperture in order to realize the large beam power of 1 MW, there is a large leakage field at an end part than a usual synchrotron magnet. In addition, 25-Hz ac field induces an eddy current in magnet components: e.g. a coil, magnet end plates and etc. We intend to use a stranded conductor as a coil conductor so that the eddy current induced in the coil can be reduced. On the other hand, the eddy current induced in the end plates is expected to be large. Therefore, it is important to investigate an effect of the large leakage field and the eddy current to the beam motion around the magnet end part. We have constructed a prototype dipole magnet and field measurement system for this purpose. This paper reports the results of the design and the preliminary test about this magnet.

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