IPAC2017 - List of Authors (Yamamoto, N.)

Paper	Title	Page
MOPIK011	Electron Beam Generation From InGaN/GaN Superlattice Photocathode	522
	N. Yamamoto KEK, Ibaraki, Japan M. Hosaka, A. Mano, T. Miyauchi, Y. Takashima Nagoya University, Nagoya, Japan M. Katoh UVSOR, Okazaki, Japan
	GaAs-type photocathode (PC) has been used as electron spin polarization (ESP) sources for various applications. Recently, by using a strain-compensated technique for GaAs/GaAsP, the super lattice (SL) thickness of up to 720 nm could be manufactured and the quantum efficiency (QE) improvements with the thickness increases was observed. In the experiments, the ESP degradation was also observed for the thicker thickness samples than 194nm and we considered that electron spin relaxation during diffusion process in the PC caused the degradation. Therefore, we propose developing fcc-GaN based PCs instead of GaAs because a factor of ten longer spin relaxation time compared with GaAs/GaAsP SL was reported. However an fcc-GaN sample with adequate dimensions for PC applications is not available at present due to manufacturing difficulties. Then at the start of GaN-type PC development, an hcp-GaN sample has been studied. In the study, NEA-activation was made for an InGaN/GaN SL sample and QE, surface lifetime and ESP were measured. The QE and ESP values were 1.3% and 2.1% at the pump laser wavelength of 405nm.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-MOPIK011
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MOPVA018	Resonant Coherent Diffraction Radiation System at ERL Test Accelerator in KEK	887
	Y. Honda, A. Aryshev, R. Kato, T. Miyajima, T. Obina, M. Shimada, R. Takai, N. Yamamoto KEK, Ibaraki, Japan
	Funding: This work was supported by JSPS KAKENHI Grant Number 16H05991 An Energy Recovery Linac can produce a low emittance and short bunch beam at a high repetition rate. A test accelerator, compact-ERL, has been operating in KEK for development works of technologies related to ERL and CW-Superconducting accelerators. In a special beam operation mode of bunch compression, a short bunch beam of ~150 fs at the repetition rate of CW 1.3 GHz can be realized in the return-loop. One of the promising applications of such a short bunch beam is a high power THz radiation source produced by a coherent radiation. When a charged particle beam passes close to a conductive target, a radiation called diffraction radiation is produced. If the target mirrors form an optical cavity which fundamental frequency matches the repetition frequency of the beam, the radiation resonates in the cavity, resulting in extracting a huge radiation power determined by the loss of the cavity. We plan to perform an experiment of the resonant coherent diffraction mechanism in the return-loop of the compact-ERL to test the feasibility to be a wide band high power THz source. We report the design of the experimental setup to be installed in the summer of 2017.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-MOPVA018
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WEPAB048	Present Status of Accelerators in Aichi Synchrotron Radiation Center	2691
	M. Hosaka, T. Ishida, A. Mano, A. Mochihashi, Y. Takashima Nagoya University, Nagoya, Japan Y. Hori, N. Yamamoto KEK, Ibaraki, Japan M. Katoh UVSOR, Okazaki, Japan S. Koda SAGA, Tosu, Japan H. Ohkuma, S. Sasaki JASRI/SPring-8, Hyogo, Japan
	Aichi Synchrotron Radiation Center is a synchrotron radiation facility in operation since 2013. The electron energy of the storage ring is 1.2 GeV and the circumference is 72 m. In spite of the compact size of the storage ring, synchrotron radiation up to hard X-ray region (~20 keV) is available from the 5 T super conducting bending magnets. Presently (Dec. 2016), 8 beamlines (5 hard X-ray and 3 soft X-ray) are in operation and 2 new hard X-ray beamlines are under commissioning. This contribution reports on the present status as well as machine studies to improve the performance of the accelerators.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-WEPAB048
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THPIK036	Design Study of Damped Accelerating Cavity Based on the TM020-Mode and HOM Couplers for the KEK Light Source Project	4172
	T. Takahashi, S. Sakanaka, N. Yamamoto KEK, Ibaraki, Japan
	A novel damped-cavity scheme was recently proposed by Ego et al.. In this design, TM020 resonant mode is used for beam acceleration. Power of higher-order (or lower-order) modes are extracted through cylindrical slots which are placed at the position where the magnetic fields of HOMs are strong while that of TM020 mode is zero. Extracted powers are absorbed by lossy ferrites. In this scheme, excellent HOM damping is possible while occupying less space of the straight section in storage rings. We propose in this paper an alternative design which is based on the same TM020 mode but with rod-type HOM couplers. The rod-type HOM couplers are placed where the electric fields of HOMs are strong while that of TM020 mode is zero. In this scheme, openings needed for HOM extraction can be made smaller, which is desirable for stiffening the mechanical structure of the cavity. Potential use of lossy dielectric materials is another merit. We present external Q-values of HOMs that can be achieved in this scheme, as well as an effect of HOM couplers on the TM020 mode. Our current study is directed to a 1.5 GHz higher-harmonic cavity for the proposed KEK Light Source project. H. Ego et al., in Proceedings of the 11-th Annual Meeting of Particle Accelerator Society of Japan, Aug. 9-11, 2014, MOOL14 [in Japanese]. ** K. Harada et al., IPAC2016, THPMB012.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-THPIK036
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THPIK037	Simulation Study of Normal-Conducting Double RF System for the 3-GeV KEK Light Source Project	4176
	N. Yamamoto, S. Sakanaka, T. Takahashi KEK, Ibaraki, Japan
	For the proposed 3-GeV KEK Light Source (KEK-LS) project, a double RF system using 500-MHz accelerating and 1.5-GHz third-harmonic cavities is under consideration. To mitigate intrabeam scattering due to ultra-low emittance, the bunch length will be elongated using the harmonic cavities which is based on the TM020 resonant mode. An accelerating cavity based on this mode was first proposed by Ego et al., and we found it very suitable for the harmonic cavities due to the following reasons: 1) it has high unloaded-Q and high stored electromagnetic energy which result in the reduction of transient beam-loading effect due to bunch gaps, and 2) efficient damping of higher (or lower) order modes is possible. Our investigations based on numerical simulations predicted the bunch elongation by a factor of 3.1 when realistic bunch-gaps were assumed. To improve the bunch elongation further, we also proposed to compensate the transient beam loading with two realistic measures: 1) compensation of rf voltages due to feedforward technique, and 2) compensation using a separate rf cavity. We will present our study on the double rf system based on numerical simulations. K. Harada et al., IPAC2016, THPMB012. ** H. Ego et al., Proceedings of the 11-th Annual Meeting of Particle Accelerator Society of Japan, Aug. 9-11, 2014, MOOL14 [in Japanese].
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-THPIK037
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Paper

Title

Page

Electron Beam Generation From InGaN/GaN Superlattice Photocathode

522

N. Yamamoto
KEK, Ibaraki, Japan
M. Hosaka, A. Mano, T. Miyauchi, Y. Takashima
Nagoya University, Nagoya, Japan
M. Katoh
UVSOR, Okazaki, Japan

GaAs-type photocathode (PC) has been used as electron spin polarization (ESP) sources for various applications. Recently, by using a strain-compensated technique for GaAs/GaAsP, the super lattice (SL) thickness of up to 720 nm could be manufactured and the quantum efficiency (QE) improvements with the thickness increases was observed. In the experiments, the ESP degradation was also observed for the thicker thickness samples than 194nm and we considered that electron spin relaxation during diffusion process in the PC caused the degradation. Therefore, we propose developing fcc-GaN based PCs instead of GaAs because a factor of ten longer spin relaxation time compared with GaAs/GaAsP SL was reported. However an fcc-GaN sample with adequate dimensions for PC applications is not available at present due to manufacturing difficulties. Then at the start of GaN-type PC development, an hcp-GaN sample has been studied. In the study, NEA-activation was made for an InGaN/GaN SL sample and QE, surface lifetime and ESP were measured. The QE and ESP values were 1.3% and 2.1% at the pump laser wavelength of 405nm.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-MOPIK011

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reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

MOPVA018

Resonant Coherent Diffraction Radiation System at ERL Test Accelerator in KEK

887

Y. Honda, A. Aryshev, R. Kato, T. Miyajima, T. Obina, M. Shimada, R. Takai, N. Yamamoto
KEK, Ibaraki, Japan

Funding: This work was supported by JSPS KAKENHI Grant Number 16H05991
An Energy Recovery Linac can produce a low emittance and short bunch beam at a high repetition rate. A test accelerator, compact-ERL, has been operating in KEK for development works of technologies related to ERL and CW-Superconducting accelerators. In a special beam operation mode of bunch compression, a short bunch beam of ~150 fs at the repetition rate of CW 1.3 GHz can be realized in the return-loop. One of the promising applications of such a short bunch beam is a high power THz radiation source produced by a coherent radiation. When a charged particle beam passes close to a conductive target, a radiation called diffraction radiation is produced. If the target mirrors form an optical cavity which fundamental frequency matches the repetition frequency of the beam, the radiation resonates in the cavity, resulting in extracting a huge radiation power determined by the loss of the cavity. We plan to perform an experiment of the resonant coherent diffraction mechanism in the return-loop of the compact-ERL to test the feasibility to be a wide band high power THz source. We report the design of the experimental setup to be installed in the summer of 2017.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-MOPVA018

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reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPAB048

Present Status of Accelerators in Aichi Synchrotron Radiation Center

2691

M. Hosaka, T. Ishida, A. Mano, A. Mochihashi, Y. Takashima
Nagoya University, Nagoya, Japan
Y. Hori, N. Yamamoto
KEK, Ibaraki, Japan
M. Katoh
UVSOR, Okazaki, Japan
S. Koda
SAGA, Tosu, Japan
H. Ohkuma, S. Sasaki
JASRI/SPring-8, Hyogo, Japan

Aichi Synchrotron Radiation Center is a synchrotron radiation facility in operation since 2013. The electron energy of the storage ring is 1.2 GeV and the circumference is 72 m. In spite of the compact size of the storage ring, synchrotron radiation up to hard X-ray region (~20 keV) is available from the 5 T super conducting bending magnets. Presently (Dec. 2016), 8 beamlines (5 hard X-ray and 3 soft X-ray) are in operation and 2 new hard X-ray beamlines are under commissioning. This contribution reports on the present status as well as machine studies to improve the performance of the accelerators.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-WEPAB048

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THPIK036

Design Study of Damped Accelerating Cavity Based on the TM020-Mode and HOM Couplers for the KEK Light Source Project

4172

T. Takahashi, S. Sakanaka, N. Yamamoto
KEK, Ibaraki, Japan

A novel damped-cavity scheme was recently proposed by Ego et al.*. In this design, TM020 resonant mode is used for beam acceleration. Power of higher-order (or lower-order) modes are extracted through cylindrical slots which are placed at the position where the magnetic fields of HOMs are strong while that of TM020 mode is zero. Extracted powers are absorbed by lossy ferrites. In this scheme, excellent HOM damping is possible while occupying less space of the straight section in storage rings. We propose in this paper an alternative design which is based on the same TM020 mode but with rod-type HOM couplers. The rod-type HOM couplers are placed where the electric fields of HOMs are strong while that of TM020 mode is zero. In this scheme, openings needed for HOM extraction can be made smaller, which is desirable for stiffening the mechanical structure of the cavity. Potential use of lossy dielectric materials is another merit. We present external Q-values of HOMs that can be achieved in this scheme, as well as an effect of HOM couplers on the TM020 mode. Our current study is directed to a 1.5 GHz higher-harmonic cavity for the proposed KEK Light Source project**.
* H. Ego et al., in Proceedings of the 11-th Annual Meeting of Particle Accelerator Society of Japan, Aug. 9-11, 2014, MOOL14 [in Japanese].
** K. Harada et al., IPAC2016, THPMB012.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-THPIK036

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THPIK037

Simulation Study of Normal-Conducting Double RF System for the 3-GeV KEK Light Source Project

4176

N. Yamamoto, S. Sakanaka, T. Takahashi
KEK, Ibaraki, Japan

For the proposed 3-GeV KEK Light Source (KEK-LS) project*, a double RF system using 500-MHz accelerating and 1.5-GHz third-harmonic cavities is under consideration. To mitigate intrabeam scattering due to ultra-low emittance, the bunch length will be elongated using the harmonic cavities which is based on the TM020 resonant mode. An accelerating cavity based on this mode was first proposed by Ego et al.**, and we found it very suitable for the harmonic cavities due to the following reasons: 1) it has high unloaded-Q and high stored electromagnetic energy which result in the reduction of transient beam-loading effect due to bunch gaps, and 2) efficient damping of higher (or lower) order modes is possible. Our investigations based on numerical simulations predicted the bunch elongation by a factor of 3.1 when realistic bunch-gaps were assumed. To improve the bunch elongation further, we also proposed to compensate the transient beam loading with two realistic measures: 1) compensation of rf voltages due to feedforward technique, and 2) compensation using a separate rf cavity. We will present our study on the double rf system based on numerical simulations.
* K. Harada et al., IPAC2016, THPMB012.
** H. Ego et al., Proceedings of the 11-th Annual Meeting of Particle Accelerator Society of Japan, Aug. 9-11, 2014, MOOL14 [in Japanese].

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-THPIK037

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