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Yee-Rendon, B.; Kondo, Yasuhiro; Maekawa, Fujio; Meigo, Shinichiro; Tamura, Jun
Proceedings of 12th International Particle Accelerator Conference (IPAC 21) (Internet), p.790 - 792, 2021/08
The Medium Energy Beam Transport (MEBT) will transport a CW proton beam with a current of 20 mA and energy of 2.5 MeV from the exit of the normal conducting Radiofrequency Quadrupole (RFQ) to the superconducting Half-Wave resonator (HWR) section. The MEBT must provide a good matching between the RFQ and HWR, effective control of the emittance growth and the halo formation, enough space for all the beam diagnostics devices, among others. This work reports the first lattice design and the beam dynamics studies for the MEBT of the JAEA-ADS.
Yee-Rendon, B.; Kondo, Yasuhiro; Maekawa, Fujio; Meigo, Shinichiro; Tamura, Jun; Cicek, E.*
Proceedings of 12th International Particle Accelerator Conference (IPAC 21) (Internet), p.793 - 795, 2021/08
The Five-cell Elliptical Superconducting Radio-Frequency Cavities (SRFC) provide the final acceleration in the JAEA-ADS linac (from 600 MeV to 1.5 GeV); thus, their performance is essential for the success of the JAEA-ADS project. After their optimization of the cavity geometry to achieve a high-acceleration gradient with lower electromagnetic peaks, the next step in the R&D strategy is the accurate estimation of beam-cavity effects which can affect the performance of the cavities. To this end, multipacting studies were developed to investigate its effect in the cavity operation regimen and find countermeasures. The results of this study will help in the development of the SRFC models and in the consolidation of the JAEA-ADS project.
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 
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.
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.
Kamiya, Junichiro; Takano, Kazuhiro; Yuza, Hiromu*; Wada, Kaoru
Proceedings of 12th International Particle Accelerator Conference (IPAC 21) (Internet), p.3471 - 3474, 2021/08
The NEG coating, which has been developed in CERN, is a revolutionary technique that can make a beam pipe act as a vacuum pump by coating the getter materials with the ability to adsorb/absorb gas molecules on the beam pipe surface. The NEG materials are alloys of titanium, zirconium, and vanadium. Titanium is one of the getter materials. In high-power beam accelerators, titanium has been used as the beam pipe chamber material due to its low radioactivation characteristics. The ordinal titanium surface has no getter function because it is covered with titanium-oxide film. The new technique, which removes the titanium-oxide surface by the sputtering and makes the titanium vacuum chamber itself the vacuum pump like NEG coated chamber, has been developed. After sputtering the inner surface of the titanium chamber, we obtained clear evidence that shows the chamber acts as a vacuum pump. We have also tried to make a titanium chamber with a getter function only by baking. Dependence of the getter characteristics on the baking temperature will also be reported.
Yamamoto, Kazami
Proceedings of 12th International Particle Accelerator Conference (IPAC 21) (Internet), p.3027 - 3030, 2021/08
The 3 GeV rapid cycling synchrotron (RCS) at the Japan Proton Accelerator Research Complex (J-PARC) provides more than 700 kW beams to the Material and Life Science Facility (MLF) and Main Ring (MR). In such a high-intensity hadron accelerator, even losing less than 0.1% of the beam can cause many problems. Such lost protons can cause serious radio-activation and accelerator component malfunctions. Therefore, we have been continuing a beam study to achieve high-power operation. In addition, we have also improved and maintained the accelerator components to establish a stable operation. This paper reports the status of the J-PARC RCS over the last two years.
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.
Saha, P. K.; Yoshimoto, Masahiro; Okabe, Kota; Harada, Hiroyuki; Tamura, Fumihiko; Hotchi, Hideaki*
Proceedings of 12th International Particle Accelerator Conference (IPAC 21) (Internet), p.590 - 593, 2021/08
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.
Gatera, A.*; Belmans, J.*; Davin, F.*; De Cock, W.*; Doucet, F.*; Parez, L.*; Pompon, F.*; Ponton, A.*; Vandeplassche, D.*; Bouly, F.*; et al.
Proceedings of 12th International Particle Accelerator Conference (IPAC 21) (Internet), p.675 - 678, 2021/08
