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KEK electron positron injector linac initiated the injection operation into Photon Factory (PF) light source in 1982. Since then for 39 years, it has served for multiple projects, namely, TRISTAN, PF-AR, KEKB, and SuperKEKB. Its total operation time has accumulated 200 thousand hours on May 7, 2020. We are extremely proud of the achievement following continuous efforts by our seniors. The construction of the injector linac started in 1978, and it was commissioned for PF with 2.5 GeV electron in 1982. In parallel, the positron generator linac was constructed for the TRISTAN collider project. The slow positron facility was also commissioned in 1992. After the KEKB asymmetric-energy collider project was commissioned in 1998 with direct energy injections, the techniques such as two-bunch acceleration and simultaneous injection were developed. As the soft structure design of the linac was too weak against the great east Japan earthquake, it took three years to recover. Then the construction and commissioning for the SuperKEKB project went on, and the simultaneous top-up injection into four storage rings contributes to the both elementary particle physics and photon science., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

A muon linac is under development for future muon ’’’ 2/EDM experiments at J-PARC. The linac provides a 212 MeV muon beam to an MRI-type compact storage ring. Af- ter the initial acceleration using the electrostatic field created by mesh and cylindrical electrodes, the muons are acceler- ated using four types of radio-frequency accelerators. To validate the linac design as a whole, end-to-end simulations were performed using General Particle Tracer. In addition, error studies is ongoing to investigate the effects on beam and spin dynamics of various errors in the accelerator com- ponents and input beam distribution. This paper describes the preliminary results of the end-to-end simulations and error studies., Proceedings of the 31st International Linear Accelerator Conference, LINAC2022, Liverpool, UK

The muon linac project for the precise measurement of the muon anomalous magnetic and electric dipole moments, which is currently one of the hottest issues of the elementary particle physics, is in progress at J-PARC. The muons from the J-PARC muon facility are once cooled to room temperature, then accelerated up to 212 MeV with a normalized emittance of 1.5 pi mm mrad and a momentum spread of 0.1%. Four types of accelerating structures are adopted to obtain the efficient acceleration with a wide beta range from 0.01 to 0.94. The project is moving into the construction phase. They already demonstrated the re-acceleration scheme of the decelerated muons using a 324-MHz RFQ in 2017. The high-power test of the 324-MHz Interdigital H-mode (IH) DTL using a prototype cavity will be performed in 2021. The fabrication of the first module of 14 modules of the 1296-MHz Disk and Washer (DAW) CCL will be done to confirm the production process. Moreover, the final design of the travelling wave accelerating structure for the high beta region is also proceeding. In this presentation, the recent progress toward the realization of the world first muon linac will be presented., Proceedings of the 31st International Linear Accelerator Conference, LINAC2022, Liverpool, UK

KEK electron positron injector linac has established simultaneous top-up injections in 2019 for 5 rings of SuperKEKB DR, LER, HER, PF ring and PF-AR as a base of the both elementary particle physics and photon science experiments even under a quite short beam lifetime. It improved the injection stabilities while the SuperKEKB broke the world record of the collision luminosity of the previous project KEKB. As the collision performance improves, the beam-beam effect makes the dynamic aperture shrink, and the beam lifetime reduces further. Thus, it became inevitable for the injector to be upgraded in order to resolve the contradictory improvements of higher charge and lower emittance of injection beams regarding beam wakefield till 2025. The upgrade plan is described including pulsed magnets, an energy compression system, accelerating structures, girders, positron generator and so on., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

The disk-loaded structures (DLS) in the muon LINAC are under development for the J-PARC muon g-2/EDM experiment. Four DLSs with an accelerating gradient of 20 MV/m take charge of muon acceleration from 40 MeV to 212 MeV, which corresponds to 70% to 94% of the speed of light. The quasi-constant gradient type TM01-2pi/3 mode DLSs with gradually varying disk spacing was designed and confirmed that the cumulative phase slip due to the mismatch between muon and phase velocity can be suppressed to less than 2 degrees at the frequency of 2592 MHz. In addition, the optimum synchronous phase and the lattice were investigated to satisfy the requirements of the total emittance less than 1.5 pi mm mrad and the momentum spread less than 0.1% in RMS., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

The muon g-2/EDM experiment is under preparation at Japan Proton Accelerator Research Complex (J-PARC), and the muon linear accelerator for the experiment is being developed. A Disk-and-Washer (DAW) cavity will be used for the medium-velocity part of the accelerator, and muons will be accelerated from v/c=ß=0.3 to 0.7 with the operating frequency of 1.296 GHz. Machining, brazing, and low-power measurements of a prototype cell reflecting the design of the first tank of DAW were performed to identify fabrication problems. Several problems were identified, such as displacement of washers during brazing, and some measures will be taken in the actual tank fabrication. In this paper, the results of the prototype cell fabrication will be reported., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

A muon linac is under development for a new muon g-2/EDM experiment at J-PARC. The muons are cooled to about room temperature and then re-accelerated to 212 MeV by four linear accelerators to produce a low-emittance muon beam. In the low-beta section, a short-range acceleration cavity with high efficiency needs to be developed to suppress the decay of muons. We propose a 324 MHz inter-digital H-mode drift-tube linac (IH-DTL) with high acceleration efficiency. The cavity can be downsized by introducing the alternating phase focusing (APF) method that provides transverse focusing only with an E-field. We have developed a prototype cavity that accelerates muons up to 1.3 MeV to demonstrate the principle. In this paper, the result of the high power test of the APF IH-DTL prototype is reported., Proceedings of the 31st International Linear Accelerator Conference, LINAC2022, Liverpool, UK

The KEK injector Linac feeds beams to four rings. It is called J-Linac. SuperKEKB Main Rings are High-Energy-Ring (HER) and Low-Energy-Ring (LER). The Linac injects a 7.0 GeV electron beam to HER and a 4.0 GeV positron beam to LER. It also injects electron beams into two light source rings. We have successfully performed this simultaneous four-ring injection. We achieve this complex simultaneous injection by using two electron guns, a positron source with a flux concentrator, and pulsed magnets. In SuperKEKB phase 3 operation, 2.0 nC electron and 3.0 nC positron beam injections were achieved., Proceedings of the 65th ICFA Advanced Beam Dynamics Workshop on High Luminosity Circular e+e- Colliders, eeFACT2022, Frascati, Italy

The world’s first disk-loaded structure (DLS) at the high-velocity part of a muon LINAC is under development for the J-PARC muon g-2/EDM experiment. We have simulated the first designed constant impedance DLS to accelerate muons from ß = 0.7 to 0.94 at an operating frequency of 1296 MHz and a phase of -10 degrees to ensure longitudinal acceptance and have shown the quality of the beam meets our requirements. Because the structure needs a high RF power of 80 MW to generate a gradient of 20 MV/m, a constant gradient DLS with the higher acceleration efficiency is being studied for lower operating RF power. In this poster, we will show the cell structure design yielding a gradient of 20 MV/m with lower RF power., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

国内初の高輝度中型放射光施設となる3GeV次世代放射光施設の蓄積リングは、最新の加速器ラティス設計であるMBA(Multi-Bend Achromat)構造を取り入れて低エミッタンス化し、軟X線からテンダーX線領域で高コヒーレンス・高輝度光の提供を目指す。蓄積リングへの入射加速器は、軟X線FELへの拡張性を考慮して3 GeVの線型加速器とし、SACLAで用いられた常伝導高勾配C-band加速システムを採用した。また、電子ビームの安定性や加速器運転の信頼性が、光源の実効性能や利用者の利便性に大きく影響するとの視点に立ち、機器性能の確保、運転の信頼性とメインテナンス性を最大限考慮した加速器設計を進めている。 蓄積リングは周長約350mで16セル、4BAを採用し、SPring-8 II計画のR&Dを最大限活用して機器の性能保証、コストの合理化を図っている。自然水平エミッタンス1.1nmrad、蓄積電流400mAを目指す。SACLAをベースに設計された3GeV線形加速器は、蓄積リングへの入射器としての運転を前提としているが、蓄積リング外側に配置しており、将来の軟X線FELへの拡張を視野に入れている。 本発表では、3GeV次世代放射光施設の加速器の特徴と進展状況を報告する。, 第16回日本加速器学会年会

KEK injector linac has delivered electrons and positrons for particle physics and photon science experiments for more than 30 years. It was upgraded for the SuperKEKB project, which aims at a 40-fold increase in luminosity over the previous project KEKB, in order to increase our understanding of flavor physics beyond the standard model of elementary particle physics. SuperKEKB energy-asymmetric electron-positron collider with its extremely high luminosity requires a high current, low emittance and low energy spread injection beam from the injector. The electron beam is generated by a new type of RF gun, that provides a much higher beam current to correspond to a large stored beam current and a short lifetime in the ring. The positron source is another major challenge that enhances the positron bunch intensity from 1 to 4 nC by increasing the positron capture efficiency, and the positron beam emittance is reduced from 2000 μm to 10 μm in the vertical plane by introducing a damping ring, followed by the bunch compressor and energy compressor. The summary of the rejuvenation is reported., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

SPring-8 is a 3rd generation synchrotron radiation facility, which has been operated since 1997. The analog-circuit-based rf modules now in use at the storage ring are obsolete and hard to be maintained. The renewal of them with modern digital ones is underway and the developed LLRF system will be used for the operation of SPring-8-II. We built an amplitude and phase stabilizing system with commercial MicroTCA.4 modules. A motor driver controlled through EtherCAT was newly adapted to the cavity tuner. The system was implemented to the high power rf test stand which consists of a 1 MW klystron, a circulator, and a 508.58 MHz cavity. The rf power was successfully regulated to keep the cavity voltage with an amplitude deviation of less than 0.1% and a phase stability of less than 0.1 degree in rms. We are also developing new MTCA.4 modules: a digitizer AMC having sampling rate of 370 MHz and 16bit resolution, and a signal conditioning RTM. These modules are used for under-sampling rf detection achieving simple composition and more robustness to the ambient parameter changes. We will start installation of the digital system to one of four rf stations in the storage ring in summer 2017., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

The RF system of the SPring-8 storage ring has stably generated an accelerating voltage of 16 MV at a frequency of 508.58 MHz since 1997. In the upgrade of the SPring-8, a beam energy is lowered from 8 to 6 GeV and a needed voltage is 7 MV. The upgrade employs multi-bending optics, and shortens the straight sections available for RF accelerating cavities by 30%. On account of the space, the RF system is to be so rearranged that the number of cavities can be reduced to half. The analog low-level RF (LLRF) system in use controls the voltage with sufficiently small deviations of less than 0.1 % in amplitude and less than 0.1 degree in phase, but becomes out-of-dates and hard to be maintained. We plan to replace them with a compact digital LLRF system in the MTCA.4 standard and based on under-sampling scheme. The SACLA linac is used for injecting a low-emittance beam to the ring. Because we have to balance the FEL operation and the beam injection on demand, pulse-by-pulse control of beam parameters is going to be implemented to the SACLA LLRF modules. Furthermore, we build a timing system for injection to a target bucket-position in the ring within a time deviation of 3 ps., Proceedings of the 7th Int. Particle Accelerator Conf., IPAC2016, Busan, Korea

TOSHIBA is manufacturing the L-band acceleration system for the SPring-8 Joint Project for XFEL. We have developed a new type duct-shaped SiC dummy load for its power distribution system. The load terminates a WR650 waveguide and can absorb the maximum mean power of 10kW. In order to reduce VSWR less than 1.1 in the frequency range of 1.428GHz, we shaped the SiC absorber into a 35cm long tapered cylinder and mounted matching stubs in the waveguide near the inlet of the load. The SiC absorber was fit into a cylindrical copper with efficient water-cooling channels. The design and manufacture and the low-power tests of our original dummy load are described in this paper., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

XFEL/SPring-8 is under construction, which is aiming at generating coherent, high brilliance, ultra-short femto-second X-ray pulse at wavelength of 1Å or shorter. The injector consists of a 500kV thermionic gun (CeB6), a beam deflecting system, multi-stage RF structures and ten magnetic lenses. The multi-stage RF structures (238MHz, 476MHz, 1428MHz) are used for bunching and accelerating the beam gradually to maintain the initial beam emittance. In addition, in order to realize linearizing the energy chirp of the beam bunch at three magnetic bunch compression systems after the injector system, we prepared extra RF structures of 1428MHz and 5712MHz. It is important to stabilize the gap voltage of those RF structures because the intensity of X-ray pulse is more sensitive for a slight variation of the RF system in the injector. We developed some stable amplifiers for those RF structures, and confirmed the amplitude and phase stability of an RF signal outputted from the amplifiers. The measurement results achieved nearly the requirement of design parameters. In this paper, we describe the development status and the achieved performances of RF equipment of the injector section., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

The injector of the 8 GeV linac generates an electron beam of 1 nC, accelerates it up to 30 MeV, and compresses its bunch length down to 20 ps. Even slight RF instability in its multi-stage bunching section fluctuates the bunch width and the peak current of an electron beam and it accordingly results in unstable laser oscillation in the undulator section. The acceptable instabilities of the RF fields in the cavities, which permit 10% rms variation of the peak beam current, are only about 0.01% rms in amplitude and 120 fs rms in phase according to beam simulation. The long-term RF variations can be compensated by feedback control of the RF amplitude and phase, the short-term or pulse-to-pulse variations, however, have to be reduced as much as possible by improving RF equipment such as amplifiers. Thus we have carefully designed and manufactured the RF cavities, amplifiers and control systems, giving the highest priority to the stabilization of the short-term variations. Components of the injector will be completed by the end of the April 2010, and the injector will be perfected in the summer 2010. We will present the performance of the completed devices in the conference., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

We report the design, performance, and installation of the beam diagnostic system of XFEL/SPring-8. The electron beam bunches of an XFEL accelerator are compressed from 1 ns to 30 fs by bunch compressors without emittance growth and peak-current fluctuation which directly cause SASE fluctuation. To maintain the stable bunch compression process, the accelerator requires rf caivty beam position monitors (BPM) with 100 nm resolution, OTR screen monitors (SCM) with a few micro-meter resolution, fast beam current monitors (CT) and temporal structure measurement systems with resolution under picosecond. The performance of the developed monitor instruments, such as the BPM, the SCM, and the CT, was tested at the SCSS test accelerator and satisfied with the requirements. To measure the temporal structure of the electron bunch, three type measurement systems, which are a streak camera, an EO sampling measurement, and a transverse deflecting cavity with a resolution of few-tens femtosecond, are being prepared. The streak camera and EO sampling shows the resolution of sub-picosecond. The installation of these beam diagnostic systems is going on smoothly., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

KEK injector linac has delivered electrons and positrons for particle physics and photon science experiments for more than 30 years. It is being upgraded for the SuperKEKB project, which aims at a 40-fold increase in luminosity over the previous project KEKB, in order to increase our understanding of new physics beyond the standard model of elementary particle physics. SuperKEKB asymmetric electron and positron collider with its extremely high luminosity requires a high current, low emittance and low energy spread injection beam from the injector. Electron beams will be generated by a new type of RF gun, that will provide a much higher beam current to correspond to a large stored beam current and a short lifetime in the ring. The positron source is another major challenge that enhances the positron bunch intensity from 1 to 4 nC by increasing the positron capture efficiency, and the positron beam emittance is reduced from 2000 micron to 20 micron in the vertical plane by introducing a damping ring, followed by the bunch compressor and energy compressor. The recent status of the upgrade and beam commissioning is reported., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark