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Lam, T.-N.*; Chin, H.-H.*; Zhang, X.*; Feng, R.*; Wang, H.*; Chiang, C.-Y.*; Lee, S. Y.*; Kawasaki, Takuro; Harjo, S.; Liaw, P. K.*; et al.
Acta Materialia, 245, p.118585_1 - 118585_9, 2023/02
Times Cited Count：1 Percentile：44.11(Materials Science, Multidisciplinary)Nakayoshi, Akira; Journeau, C.*; Rempe, J.*; Barrachin, M.*; Bottomley, D.; Nauchi, Y.*; Song, J. H.*
Proceedings of 2019 International Workshop on Post-Fukushima Challenges on Severe Accident Mitigation and Research Collaboration (SAMRC 2019) (USB Flash Drive), 6 Pages, 2019/11
Shobuda, Yoshihiro; Chin, Y. H.*
Scientific Reports (Internet), 8, p.12805_1 - 12805_19, 2018/08
Times Cited Count：4 Percentile：26.4(Multidisciplinary Sciences)In typical numerical simulations, the space-charge force is calculated by slicing a beam into manylongitudinal segments and by solving the two-dimensional Poisson equation in each segment. Thismethod neglects longitudinal leakage of the space-charge force to nearby segments owing to itslongitudinal spread over 1/Lorentz-
. By contrast, the space-charge impedance, which is the Fourier transformof the wake function, is typically calculated directly in the frequency-domain. So long as we followthese approaches, the longitudinal leakage effect of the wake function will remain to be unclear. In thepresent report, the space-charge wake function is calculated directly in the time domain by solving thethree-dimensional Poisson equation for a longitudinally Gaussian beam. We find that the leakage effectis insignificant for a bunch that is considerably longer than the chamber radius so long as the segmentlength satisfies a certain condition. We present a criterion for how finely a bunch should be sliced so thatthe two-dimensional slicing approach can provide a good approximation of the three-dimensional exactsolution.
Shobuda, Yoshihiro; Chin, Y. H.*; Hayashi, Naoki; Irie, Yoshiro*; Takayanagi, Tomohiro; Togashi, Tomohito; Toyama, Takeshi*; Yamamoto, Kazami; Yamamoto, Masanobu
Physical Review Accelerators and Beams (Internet), 21(6), p.061003_1 - 161003_15, 2018/06
Times Cited Count：3 Percentile：32.07(Physics, Nuclear)no abstracts in English
Saha, P. K.; Shobuda, Yoshihiro; Hotchi, Hideaki; Harada, Hiroyuki; Hayashi, Naoki; Kinsho, Michikazu; Tamura, Fumihiko; Tani, Norio; Yamamoto, Masanobu; Watanabe, Yasuhiro; et al.
Physical Review Accelerators and Beams (Internet), 21(2), p.024203_1 - 024203_20, 2018/02
Times Cited Count：8 Percentile：62.44(Physics, Nuclear)Shobuda, Yoshihiro; Chin, Y. H.*
Progress of Theoretical and Experimental Physics (Internet), 2017(12), p.123G01_1 - 123G01_22, 2017/12
Times Cited Count：7 Percentile：52.81(Physics, Multidisciplinary)no abstracts in English
Chin, Y. H.*; Chao, A. W.*; Blaskiewicz, M. M.*; Shobuda, Yoshihiro
Physical Review Accelerators and Beams (Internet), 20(7), p.071003_1 - 071003_18, 2017/07
Times Cited Count：4 Percentile：37.82(Physics, Nuclear)no abstracts in English
Shobuda, Yoshihiro; Saha, P. K.; Hotchi, Hideaki; Harada, Hiroyuki; Takayanagi, Tomohiro; Tamura, Fumihiko; Tani, Norio; Togashi, Tomohito; Toyama, Takeshi*; Watanabe, Yasuhiro; et al.
Proceedings of 8th International Particle Accelerator Conference (IPAC '17) (Internet), p.2946 - 2949, 2017/05
no abstracts in English
Shobuda, Yoshihiro; Chin, Y. H.*; Saha, P. K.; Hotchi, Hideaki; Harada, Hiroyuki; Irie, Yoshiro*; Tamura, Fumihiko; Tani, Norio; Toyama, Takeshi*; Watanabe, Yasuhiro; et al.
Progress of Theoretical and Experimental Physics (Internet), 2017(1), p.013G01_1 - 013G01_39, 2017/01
Times Cited Count：12 Percentile：66.82(Physics, Multidisciplinary)The Rapid Cycling Synchrotron (RCS), whose beam energy ranges from 400 MeV to 3 GeV and which is located in the Japan Proton Accelerator Research Complex, is a kicker-impedance dominant machine, which violates the impedance budget from a classical viewpoint. Contrary to conventional understanding, we have succeeded to accelerate a 1-MW equivalent beam. The machine has some interesting features: for instance, the beam tends to be unstable for the smaller transverse beam size, the beam is stabilized by increasing the peak current 
. Space charge effects play an important role in the beam instability at the RCS. In this study, a new theory has been developed to calculate the beam growth rate with the head-tail and coupled-bunch modes (
) while taking space charge effects into account. The theory sufficiently explains the distinctive features of the beam instabilities at the RCS.
Shobuda, Yoshihiro; Chin, Y. H.*
Physical Review Accelerators and Beams (Internet), 19(9), p.094201_1 - 094201_24, 2016/09
Times Cited Count：5 Percentile：41.5(Physics, Nuclear)In a so-called waveguide FEL for THz radiations, an extremely small aperture (
mm) waveguide is used to confine angularly wide spread radiation fields from a low energy electron beam into a small area. This confinement increases the interaction between the electron beam and the radiation fields to achieve a much higher FEL gain. The radiation fields propagate inside the waveguide as waveguide modes, not like a light flux in a free space FEL. This characteristic behavior of the radiation fields makes intuitive understanding of the waveguide FEL difficult. We developed a three-dimensional waveguide FEL theory to calculate a gain of THz waveguide FEL including the effects of the energy spread, the beam size and the beta Tron oscillations of an electron beam, and effects of a rectangular waveguide. The FEL gain can be calculated as a function of frequency by solving the dispersion relation. Theoretical gains are compared with simulation results for a waveguide FEL with a planar undulator similar to the KAERI one. Good agreements are obtained.
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：11.94(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.
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; Saha, P. K.; Toyama, Takeshi*; Yamamoto, Masanobu; Chin, Y. H.*; Irie, Yoshiro*
Proceedings of 54th ICFA Advanced Beam Dynamics Workshop on High-Intensity, High Brightness and High Power Hadron Beams (HB 2014) (Internet), p.369 - 373, 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：48.72(Physics, Nuclear)Shobuda, Yoshihiro; Chin, Y. H.*
Physical Review Special Topics; Accelerators and Beams, 17(9), p.092801_1 - 092801_8, 2014/09
Times Cited Count：2 Percentile：20.13(Physics, Nuclear)Shobuda, Yoshihiro; Tamura, Fumihiko; Yamamoto, Masanobu; Chin, Y. H.*
Proceedings of 2nd International Particle Accelerator Conference (IPAC 2011) (Internet), p.595 - 597, 2011/09
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
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：54.31(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.*; Toyama, Takeshi*; Ikegami, Masanori*
Proceedings of 2009 Particle Accelerator Conference (PAC '09) (DVD-ROM), p.4701 - 4703, 2009/05
The kicker magnet is one of dominant sources of impedances with 3 GeV RCS at J-PARC. It has been considered that this impedance gives us the significant constraint to increase the beam intensity. Recently, the 300 kW beam was accomplished at 3 GeV RCS, while no instability is found. We discuss the space charge effect to stabilize the beam instability.
