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Shobuda, Yoshihiro; Chin, Y. H.*; Takata, Koji*; Toyama, Takeshi*; Nakamura, Keigo*
Proceedings of 57th ICFA Advanced Beam Dynamics Workshop on High-Intensity and High-Brightness Hadron Beams (HB 2016) (Internet), p.523 - 528, 2016/08
In J-PARC MR, there is a concern that electron cloud instabilities may appear and limit the beam current at future higher power operations. For the case, we have developed a wider-band beam position monitor by deforming the electrode shapes. The modification of the electrode can be done without significant enhancement of the beam coupling impedance. For typical electrode shapes, we show the coupling impedances as well as the frequency responses of the electrodes.
Shobuda, Yoshihiro; Chin, Y. H.*; Takata, Koji*; Toyama, Takeshi*; Nakamura, Keigo*
Physical Review Accelerators and Beams (Internet), 19(2), p.021003_1 - 021003_15, 2016/02
Times Cited Count：1 Percentile：11.14(Physics, Nuclear)The frequency domain performance of a stripline beam position monitor depends largely on the longitudinal shape of its electrode. To attain a good impedance matching along the electrode, it needs to be precisely bent down toward its downstream in proportion to its width. In this report, we first propose a triangle electrode for easy fabrication and set-up. Theoretical and simulation results show that the simple triangle electrode has a remarkably flatter frequency response than the rectangle one. The frequency response, in particular at high frequencies, can be further improved by attaching an "apron" plate, perpendicular to the upstream edge of the electrode. The overshooting of the frequency response at low frequency can be eliminated by replacing the straight sidelines of the triangle by three-point polylines. We found that the concave pentagon electrode achieves a wide and flat frequency response up to about 
GHz for the J-PARC Main Ring.
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.
Shobuda, Yoshihiro; Toyama, Takeshi*; Chin, Y. H.*; Takata, Koji*
Proceedings of 54th ICFA Advanced Beam Dynamics Workshop on High-Intensity, High Brightness and High Power Hadron Beams (HB 2014) (Internet), p.74 - 78, 2015/03
Shobuda, Yoshihiro; Chin, Y. H.*; Takata, Koji*
Physical Review Special Topics; Accelerators and Beams, 17(9), p.091001_1 - 091001_41, 2014/09
Times Cited Count：8 Percentile：50.96(Physics, Nuclear)Nomura, Masahiro; Shimada, Taihei; Tamura, Fumihiko; Yamamoto, Masanobu; Hara, Keigo*; Hasegawa, Katsushi*; Omori, Chihiro*; Takata, Koji*; Toda, Makoto*; Yoshii, Masahito*; et al.
Nuclear Instruments and Methods in Physics Research A, 749, p.84 - 89, 2014/06
Times Cited Count：2 Percentile：19.23(Instruments & Instrumentation)We have been developing high shunt impedance Magnetic Alloy (MA) cores. The MA core shunt impedance is a key parameter to achieve a higher field gradient for increasing a beam power. We increase the MA core shunt impedance by two different ways. One way is applying an external magnetic field during annealing to increase the MA core magnetic properties. The other way is using thinner ribbons to reduce the eddy current. In this paper, we discuss the latter way.
Ao, Hiroyuki; Asano, Hiroyuki; Tamura, Jun; Ouchi, Nobuo; Takata, Koji*; Naito, Fujio*
Proceedings of 9th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.1124 - 1126, 2013/08
In the case of the RF window operated with the standing-wave cavity coupled to waveguides using coupling apertures, the reflection of the RF window affects the total coupling factor (voltage standing wave ratio, VSWR) consisted of the RF window and the cavity. Hence, the reflection (VSWR) of the RF window should be minimized not to change the cavity VSWR optimized separately, and to prevent standing waves between the RF window and the cavity. For minimizing the VSWR of the pillbox-type RF window, this report proposes that the dielectric constant of the ceramic is measured directly using the resonant frequency in the fabrication process of the RF window. In this work, three RF windows are fabricated additionally using the same type ceramic (NTK HA95), the small VSWR 
could be achieved using this procedure. This result also shows that the dielectric constant increases linearly with increasing the density.
Yamamoto, Masanobu; Nomura, Masahiro; Schnase, A.; Shimada, Taihei; Tamura, Fumihiko; Ezura, Eiji*; Hara, Keigo*; Hasegawa, Katsushi*; Omori, Chihiro*; Takagi, Akira*; et al.
Proceedings of 3rd International Particle Accelerator Conference (IPAC '12) (Internet), p.2952 - 2954, 2012/05
In J-PARC RCS, the high intensity beam is delivered to the MR. The longitudinal beam emittance at the RCS extraction should be optimized to avoid the beam loss after the MR injection. In order to match the longitudinal emittance shape between the RCS and the MR, it is desirable to enlarge the longitudinal emittance during the RCS acceleration. We have performed the particle tracking simulation for the controlled longitudinal emittance blow up in the RCS.
Nomura, Masahiro; Schnase, A.; Shimada, Taihei; Tamura, Fumihiko; Yamamoto, Masanobu; Sato, Tomonori; Yamamoto, Masahiro; Ezura, Eiji*; Hara, Keigo*; Hasegawa, Katsushi*; et al.
Proceedings of 2nd International Particle Accelerator Conference (IPAC 2011) (Internet), p.107 - 109, 2011/09
J-PARC 3 GeV Rapid Cycling Synchrotron (RCS) and 50 GeV Synchrotron (MR) employ the Magnetic Alloy (MA) loaded RF cavities. We observed the impedance reductions of MR RF cavities. Opening the RF cavities, we found that the impedance reductions were caused by the corrosion on the core cutting surfaces. The copper ions in the cooling water from hollow conductors of main magnets might accelerate the corrosion process.
Ao, Hiroyuki; Asano, Hiroyuki; Tamura, Jun; Ouchi, Nobuo; Hasegawa, Kazuo; Morishita, Takatoshi; Takata, Koji*; Naito, Fujio*; Yamazaki, Yoshishige
Proceedings of 8th Annual Meeting of Particle Accelerator Society of Japan (Internet), 3 Pages, 2011/08
An annular-ring coupled structure (ACS) for J-PARC linac has been in mass-production since March 2009. It was planned to fabricate 18 ACS accelerating modules and two debuncher modules for the three years. At present, they are progressing on schedule. The past achievements include: ten accelerating modules were completed on schedule; the frequency tuning of the most accelerating modules was finished except two debencher modules; and 14 accelerating modules have been brazed. One of the mass-produced modules was conditioned up to 1.6 MW, which corresponds to the accelerating field by 15% higher than the designed value of 4.2 MV/m.
Shobuda, Yoshihiro; Chin, Y. H.*; Takata, Koji*
Proceedings of 46th ICFA Advanced Beam Dynamics Workshop on High-Intensity and High-Brightness Hadron Beams (HB 2010) (Internet), p.348 - 352, 2010/09
no abstracts in English
Ao, Hiroyuki; Asano, Hiroyuki; Ouchi, Nobuo; Tsubota, Naoaki; Hasegawa, Kazuo; Hirano, Koichiro; Morishita, Takatoshi; Takata, Koji*; Naito, Fujio*; Yamazaki, Yoshishige
Proceedings of 7th Annual Meeting of Particle Accelerator Society of Japan (DVD-ROM), p.552 - 554, 2010/08
The energy upgrade of the J-PARC linac was started from March 2009. In this project 20 Annular Coupled Structure (ACS) modules will be fabricated. The resonant frequency of the ACS module has to be tuned with mechanical machining before the final brazing. Therefore the test cells were fabricated to accumulate frequency tuning parameters. We fixed the final dimensions and the machining amount of the frequency tuning using these results. So far, the cell parts for the five ACS modules were tuned within 71.93 
0.05 MHz. At the moment the first ACS module is being assembled and it will be completed in autumn 2010.
Nomura, Masahiro; Schnase, A.; Shimada, Taihei; Suzuki, Hiromitsu; Tamura, Fumihiko; Yamamoto, Masanobu; Ezura, Eiji*; Omori, Chihiro*; Hara, Keigo*; Hasegawa, Katsushi*; et al.
Proceedings of 1st International Particle Accelerator Conference (IPAC '10) (Internet), p.3723 - 3725, 2010/05
We have been operating the RF cavities loaded with MA cores with a high field gradient of more than 20 kV/m since October 2007. We have been measuring the RF cavity impedance at the shutdown periods, and we detected the impedance reductions of RCS RF cavities on January and June 2009. Taking out the RF cavities from the beam line and opening them, we found that many of cores showed a buckling at the inner radius. We report the detail of condition of MA cores and the relation between the impedance reduction and core condition.
Ao, Hiroyuki; Asano, Hiroyuki; Ouchi, Nobuo; Tsubota, Naoaki; Hasegawa, Kazuo; Hirano, Koichiro; Morishita, Takatoshi; Takata, Koji*; Naito, Fujio*; Yamazaki, Yoshishige
Proceedings of 1st International Particle Accelerator Conference (IPAC '10) (Internet), p.618 - 620, 2010/05
The mass production of the ACS (Annular-ring Coupled Structure) cavity started from March 2009 for the J-PARC linac energy upgrade from 181 MeV to 400 MeV. This upgrade project requires 18 ACS accelerating modules and two debunchers additionally within three years. The schedule is so tight that we have to optimize the fabrication process. Thus the test cells were fabricated for the all geometrical beta before the mass production to confirm the initial design and the frequency tuning procedure. This paper describes our approach for the mass production and the current status.
Yamamoto, Masanobu; Nomura, Masahiro; Schnase, A.; Shimada, Taihei; Tamura, Fumihiko; Ezura, Eiji*; Hara, Keigo*; Hasegawa, Katsushi*; Omori, Chihiro*; Takagi, Akira*; et al.
Proceedings of 1st International Particle Accelerator Conference (IPAC '10) (Internet), p.1940 - 1942, 2010/05
The beam commissioning and user operation have been going at the J-PARC RCS. Some Longitudinal beam gymnastics and the acceleration has been successfully performed under the high intensity operation. We have developed the longitudinal particle tracking code with the beam loading and the space charge effects to evaluate the longitudinal beam emittance. We describe the relation between the acceleration voltage pattern and the beam emittance in the dual harmonic rf and the high intensity operation.
Schnase, A.; Omori, Chihiro*; Tamura, Fumihiko; Ezura, Eiji*; Hara, Keigo*; Hasegawa, Katsushi*; Nomura, Masahiro; Shimada, Taihei; Suzuki, Hiromitsu; Takagi, Akira*; et al.
Proceedings of 6th Annual Meeting of Particle Accelerator Society of Japan (CD-ROM), p.1077 - 1079, 2010/03
Shimada, Taihei; Yamamoto, Masanobu; Suzuki, Hiromitsu; Toda, Makoto*; Hasegawa, Katsushi*; Omori, Chihiro*; Tamura, Fumihiko; Schnase, A.; Hara, Keigo*; Nomura, Masahiro; et al.
Proceedings of 6th Annual Meeting of Particle Accelerator Society of Japan (CD-ROM), p.1080 - 1082, 2010/03
Few magnetic alloys cores of the RF cavities which are installed in the 3 GeV rapid cycling synchrotron of the J-PARC have buckled after the operation of about two years. We heated cores in the air and measured thermal deformation in order to get information about the buckling process. We report the results.
Shobuda, Yoshihiro; Chin, Y. H.*; Takata, Koji*
Physical Review Special Topics; Accelerators and Beams, 12(9), p.094401_1 - 094401_19, 2009/09
Times Cited Count：10 Percentile：56.46(Physics, Nuclear)We have developed a theory to calculate both longitudinal and transverse impedances of a resistive short (typically shorter than the chamber radius) insert with cylindrical symmetry, sandwiched by perfectly conductive chambers on both sides. It is found that unless the insert becomes extremely thin (typically a few nm for a metallic insert) the entire image current runs on the thin insert, even in the frequency range where the skin depth exceeds the insert thickness, and therefore the impedance increases drastically from the conventional resistive-wall impedance. In other words, the wake fields do not leak out of the insert unless it is extremely thin. Formulae of the impedance valid for various cases of the insert are categorized in summary.
Shobuda, Yoshihiro; Chin, Y. H.*; Takata, Koji*
Physical Review Special Topics; Accelerators and Beams, 11(1), p.011003_1 - 011003_11, 2008/01
Times Cited Count：0 Percentile：0.01(Physics, Nuclear)Schnase, A.; Ezura, Eiji*; Hara, Keigo*; Hasegawa, Katsushi; Nomura, Masahiro; Omori, Chihiro*; Shimada, Taihei; Suzuki, Hiromitsu; Takagi, Akira*; Tamura, Fumihiko; et al.
Proceedings of 5th Annual Meeting of Particle Accelerator Society of Japan and 33rd Linear Accelerator Meeting in Japan (CD-ROM), p.340 - 342, 2008/00
