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Journal Articles

Simulation of phase modulation for longitudinal emittance blow-up in J-PARC MR

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.

Journal Articles

Simulation of controlled longitudinal emittance blow-up in J-PARC RCS

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.

Journal Articles

Condition of MA cut cores in the RF cavities of J-PARC main ring after several years of operation

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.

Journal Articles

Condition of MA cores in the RF cavities of J-PARC synchrotrons after several years of operation

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.

Journal Articles

Simulation of longitudinal emittance control in J-PARC RCS

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.

Journal Articles

Core buckling position measurement for J-PARC RCS cavity

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

Journal Articles

Measurement of thermal deformation of magnetic alloys cores for RF cavities

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.

Journal Articles

Higher harmonic voltages in J-PARC RCS operation

Schnase, A.; Tamura, Fumihiko; Yamamoto, Masanobu; Nomura, Masahiro; Hasegawa, Katsushi; Shimada, Taihei; Suzuki, Hiromitsu; Omori, Chihiro*; Yoshii, Masahito*; Ezura, Eiji*; et al.

Proceedings of 2009 Particle Accelerator Conference (PAC '09) (DVD-ROM), p.1988 - 1990, 2009/05

Journal Articles

Acceleration voltage pattern for J-PARC RCS

Yamamoto, Masanobu; Hasegawa, Katsushi; Nomura, Masahiro; Schnase, A.; Tamura, Fumihiko; Anami, Shozo*; Ezura, Eiji*; Hara, Keigo*; Omori, Chihiro*; Takagi, Akira*; et al.

Proceedings of 11th European Particle Accelerator Conference (EPAC '08) (CD-ROM), p.379 - 381, 2008/06

The calculation code for the acceleration voltage pattern is usually based on the differential equation of the longitudinal synchrotron motion. We have developed the code based on the forward-difference equation which satisfies the synchronization with the bending magnetic field ramping accurately. This is very useful especially at the rapid cycling synchrotron where the ramping rate is high.

Journal Articles

Beam acceleration with full-digital LLRF control system in the J-PARC RCS

Tamura, Fumihiko; Schnase, A.; Nomura, Masahiro; Yamamoto, Masanobu; Hasegawa, Katsushi; Haga, Koichi; Yoshii, Masahito*; Omori, Chihiro*; Toda, Makoto*; Hara, Keigo*; et al.

Proceedings of 11th European Particle Accelerator Conference (EPAC '08) (CD-ROM), p.364 - 366, 2008/06

In the J-PARC RCS (Rapid Cycling Synchrotron) we employ a full-digital LLRF control system to accelerate an ultra-high intensity proton beam. The key feature is the multi-harmonic RF signal generation by using direct digital synthesis (DDS) technology. By employing a full-digital system, highly accurate, stable and reproductive RF voltages are generated in the wide-band RF cavities loaded by magneticalloy (MA) cores. The beam commissioning of the J-PARC RCS has been started in October 2007. The accelerators, the linac and the RCS, show good stability. The beam orbit and the longitudinal beam shape and phase are reproductive from cycle to cycle especially thanks to the stability of the linac energy, the RCS bending field and the frequency and voltage of the RCS RF. This reproductivity makes the beam commissioning efficient. We present the examples of the orbit signals and the longitudinal currentsignals. Also, we discuss the longitudinal beam control performance and future plans.

Journal Articles

J-PARC RCS non-linear frequency sweep analysis

Schnase, A.; Anami, Shozo*; Ezura, Eiji*; Haga, Kaiichi*; Hara, Keigo*; Hasegawa, Katsushi; Nomura, Masahiro; Omori, Chihiro*; Takagi, Akira*; Tamura, Fumihiko; et al.

Proceedings of 11th European Particle Accelerator Conference (EPAC '08) (CD-ROM), p.346 - 348, 2008/06

Journal Articles

Cavity voltage calibration for J-PARC Ring RF

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

Journal Articles

Commissioning of beam acceleration in J-PARC RCS and MR

Tamura, Fumihiko; Schnase, A.; Nomura, Masahiro; Yamamoto, Masanobu; Suzuki, Hiromitsu; Shimada, Taihei; Hasegawa, Katsushi; Yoshii, Masahito*; Omori, Chihiro*; Toda, Makoto*; et al.

Proceedings of 5th Annual Meeting of Particle Accelerator Society of Japan and 33rd Linear Accelerator Meeting in Japan (CD-ROM), p.337 - 339, 2008/00

The beam commissioning of the J-PARC RCS was started in October 2007 and acceleration of $$1.07times10^{13}$$ protons has been successfully achieved in February 2008. Also, the beam commissioning of MR began in May 2008. The RF capture of the beam and the extraction at the injection energy of 3 GeV was successfully performed. In both of the RCS and MR, MA (magnetic alloy) cavities are employed to achieve high accelerating voltages which are necessary to accelerate the high intensity proton beams. We employ full-digital LLRF control systems to realize precise and reproducible control of RF frequencies, voltages and phases. We present the status of the RF acceleration with examples of the beam signals. Also we discuss the future plans.

Journal Articles

Development of MA core for J-PARC Ring RF Cavity

Nomura, Masahiro; Tamura, Fumihiko; Schnase, A.; Yamamoto, Masanobu; Hasegawa, Katsushi; Shimada, Taihei; Suzuki, Hiromitsu; Ezura, Eiji*; Hara, Keigo*; Toda, Makoto*; et al.

Proceedings of 5th Annual Meeting of Particle Accelerator Society of Japan and 33rd Linear Accelerator Meeting in Japan (CD-ROM), p.246 - 248, 2008/00

We have been developing MA core for J-PARC Ring RF Cavity. From long run tests, we found that poor electrical isolation between layers caused damages to the cores. We improved the electrical isolation mainly by introducing a smooth tension control system to the winding process. The degree of the each core's electrical isolation was evaluated by the results of DC resistance and radial RF impedance measurements. After long run tests of all of the cores, we installed 10 RF cavities in a tunnel in May 2007 and beam commissioning was started from October 2007. Until now, total operation time of the RF cavities in the tunnel is about 1500 hours. To check the condition of the cores, we measured the RF cavity impedance at intervals of beam operations. The result of impedance measurements shows that no impedance reduction related to core damage was observed.

Journal Articles

Longitudinal particle simulation for J-PARC RCS

Yamamoto, Masanobu; Anami, Shozo*; Ezura, Eiji*; Hasegawa, Katsushi; Hara, Keigo*; Horino, Mitsuyoshi*; Nomura, Masahiro; Omori, Chihiro*; Schnase, A.; Shimada, Taihei; et al.

Proceedings of 5th Annual Meeting of Particle Accelerator Society of Japan and 33rd Linear Accelerator Meeting in Japan (CD-ROM), p.358 - 360, 2008/00

The beam commissioning has been started at the J-PARC RCS in October 2007, and the beam acceleration and the extraction at 3 GeV has been succeeded. Some longitudinal bunch gymnastics has been tested toward the high intensity operation, one of the issues is arriviating the space charge effect at the injeciton. Since the multi-turn injection scheme is employed at the RCS, the electric charge density of the bunch near the center of the RF bucket tends to be high with only normal fundamental RF capture. Some schemes such as adding 2nd higher harmonic RF, the momentum offset and the phase offset of the 2nd one are simulated by longitudinal particle tracking code to make the bunching factor low. The comparison between the beam test result and the particle tracking simulation is described.

Journal Articles

MA cavities for J-PARC with controlled Q-value by external inductor

Schnase, A.; Hasegawa, Katsushi; Nomura, Masahiro; Tamura, Fumihiko; Yamamoto, Masanobu; Anami, Shozo*; Ezura, Eiji*; Hara, Keigo*; Omori, Chihiro*; Takagi, Akira*; et al.

Proceedings of 2007 Particle Accelerator Conference (PAC '07) (Internet), p.2131 - 2133, 2007/08

Journal Articles

Development of the beam chopper timing system for multi-turn injection to the J-PARC RCS

Tamura, Fumihiko; Schnase, A.; Nomura, Masahiro; Yamamoto, Masanobu; Hasegawa, Katsushi; Yoshii, Masahito*; Anami, Shozo*; Ezura, Eiji*; Hara, Keigo*; Omori, Chihiro*; et al.

Proceedings of 2007 Particle Accelerator Conference (PAC '07) (Internet), p.2125 - 2127, 2007/06

Multi-turn injection using charge exchange is employed for the J-PARC Rapid Cycling Synchrotron (RCS). To reduce space charge effects, the bunching factor of the beam in the ring should be increased. Therefore the momentum-offset injection scheme is used. In each turn, the bunch trains from the linac are injected into the RF buckets with a momentum offset. The bunch train is called the "intermediatepulse". The intermediate pulses are generated in the low energy section of the linac by the RF chopper and pre-chopper. Since the pulses must be synchronized to the RF voltage in the ring, the timing signals for the choppers are generated by the low-level RF (LLRF) system of the RCS. The chopper pulses are sent via optical cables. We developed the chopper timingmodule. We describe the details of the hardware.

Journal Articles

Status of J-PARC ring RF systems

Schnase, A.; Nomura, Masahiro; Tamura, Fumihiko; Yamamoto, Masanobu; Haga, Koichi; Hasegawa, Katsushi; Yoshii, Masahito*; Omori, Chihiro*; Hara, Keigo*; Toda, Makoto*; et al.

Proceedings of 4th Annual Meeting of Particle Accelerator Society of Japan and 32nd Linear Accelerator Meeting in Japan (CD-ROM), p.212 - 214, 2007/00

Journal Articles

Development of the feedforward system for beam loading compensation in the J-PARC RCS

Tamura, Fumihiko; Schnase, A.; Nomura, Masahiro; Yamamoto, Masanobu; Yoshii, Masahito*; Anami, Shozo*; Ezura, Eiji*; Hara, Keigo*; Omori, Chihiro*; Takagi, Akira*

Proceedings of 10th European Particle Accelerator Conference (EPAC 2006) (CD-ROM), p.1319 - 1321, 2006/00

In the J-PARC Rapid Cycling Synchrotron (RCS), the heavy beam loading effects due to the high intensity proton beam must be compensated for stable acceleration. The beam feedforward technique is used to compensate the beam loading in the RCS. We present the development of the feedforward system. We designed and built the full-digital system. Because of the low Q value of each accelerating cavity, the wake voltage consists of not only the accelerating harmonic component but also higher harmonics. Thus, the system is designed to compensate the beam loading at several harmonics. The vector components of the selected harmonic are detected from the beam signal picked up by a wall current monitor. The compensation RF signal is generated from the vector components with proper gain and phase in the latter part. The gain and phase are set individually for each harmonic and each cavity of the twelve cavities. We also present the preliminary test results of the newly developed modules.

Journal Articles

Synchronization system for the J-PARC RCS

Tamura, Fumihiko; Schnase, A.; Nomura, Masahiro; Yamamoto, Masanobu; Hasegawa, Katsushi; Yoshii, Masahito*; Omori, Chihiro*; Hara, Keigo*; Toda, Makoto*; Takagi, Akira*; et al.

Proceedings of 3rd Annual Meeting of Particle Accelerator Society of Japan and 31st Linear Accelerator Meeting in Japan (CD-ROM), p.460 - 462, 2006/00

The beam in the J-PARC RCS has to be extracted with the proper timingand phase to the MR (main ring) and the neutron target in the MLF (material and life science facility). The neutron beamfrom the neutron target is led to the group of spectrometers, such asthe fermi chopper. The choppers and the beam must be precisely synchronized to achieve high energy resolution. Also, the MR injection requires the proper RF bucket selection andprecise beam phase control to avoid the longitudinal dipole oscillations. In this presentation we describe the requirements of the beamsynchronization, the operational principle, and the newly developedmodules for the synchronization.

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