[en] A compact silica aerogel Cherenkov counter with fine-mesh type photo-multiplier tubes has been developed to reject e⁺e^- pair created events at a trigger level. The silica aerogel is covered with a highly reflective material to lead emitted Cherenkov photons into the photo-cathodes. The efficiency of e⁺e^- event identification is obtained to be more than 97%. (author)

[en] A large-acceptance spectrometer, Neutral Kaon Spectrometer 2 (NKS2), was newly constructed to explore various photoproduction reactions in the gigaelectronvolt region at the Laboratory of Nuclear Science (LNS, currently ELPH), Tohoku University. The spectrometer consisted of a dipole magnet, drift chambers, and plastic scintillation counters. NKS2 was designed to separate pions and protons in a momentum range of less than 1 GeV/$c$, and was placed in a tagged photon beamline. A cryogenic H₂/D₂ target fitted to the spectrometer were designed. The design and performance of the detectors are described. The results of the NKS2 experiment on analyzing strangeness photoproduction data using a 0.8–1.1 GeV tagged photon beam are also presented.

[en] At Ibaraki Neutron Medical Research Center, an 8-MeV proton linear accelerator is being developed for iBNCT (Ibaraki - Boron Neutron Capture Therapy), with the aim of achieving the highest possible performance at a low cost. In this accelerator, there are two RF cavities driven by only one high-power klystron as the RF source. A digital low-level RF system has been successfully implemented for the iBNCT accelerator, with very good RF field regulation. An effective multipurpose and smart tuner controller was also developed. Finally, a novel auto-startup technology for two cavities with one RF source was successfully developed. The time required for the RF startup process is greatly reduced from the conventional time of 30 min, to less than 1 min. The good stability and fast response achieved by using this technology make it suitable for the medical use of iBNCT accelerators. This technology will be extremely useful in the development of similar accelerators.

[en] For the proton linear accelerator (LINAC) at the Japan Proton Accelerator Research Complex (J-PARC), the RF fields at acceleration RF cavities are controlled by an FPGA (Field-Programmable Gate Array)-based digital feedback (FB) control system installed in a compact PCI (cPCI). Recently, the software of DSP and FPGA programs for the low-level RF (LLRF) control systems of the J-PARC LINAC is upgraded. Firstly, a function of inspecting cavity pickup and cavity reflection signals is added to the LLRF control systems so that any of instabilities could be monitored in real-time, and an interlock due to larger RF cavity reflection amplitude will be applied to the fast interlock system. Secondly, an intelligent sag compensation and automatic FPGA calibration are programmed so that the RF waveforms in case of FB OFF and FB ON can be almost the same. Furthermore, a new function of separating the chopped beam automatically to two scrapers is being developed using FPAG control systems. The details on the software upgrade of the DSP and FPGA programs will be reported in this paper. (author)

[en] The Japan Proton Accelerator Research Complex (J-PARC) linac is operated with design peak current of 50 mA from 2018. For operation with such a high beam current, it is important to understand transverse and longitudinal beam properties especially in low-velocity region. A medium energy beam transport (MEBT1) line between the 3-MeV radio-frequency quadrupole linac (RFQ) and the 50-MeV drift-tube linac (DTL) is a 3-m-long transport line to match the beam to the DTL and produces a macro pulse configuration for a 3-GeV rapid-cycling synchrotron (RCS). In this paper, recent measurements and beam tuning results in MEBT1 will be presented. (paper)

[en] We have developed a drift-tube linac (DTL) design for a muon linac, in order to measure the anomalous magnetic moment and electric dipole moment (EDM) of muons at J-PARC. The DTL accelerates muons from β=v/c=0.08 to 0.27 at an operational frequency of 324 MHz. The output beam emittances are calculated as 0.30 π and 0.17 πmm mrad in the horizontal and vertical directions, respectively, which satisfies the experimental requirement. The design, results, and comparisons to other acceleration structures are described in this paper. (author)

[en] It is extremely important to diagnose beams in accelerators to improve accelerator operation. In the low velocity section of a proton or heavy ion linac, the diagnostic method for longitudinal beam properties is less established compared to that for transverse properties. We have developed a new diagnostic method for the longitudinal bunch size by utilizing an RF deflector. We evaluated the uncertainty in bunch size measurement through simulation, and it was obtained as 0.5°. In addition, we measured longitudinal beam emittance through bunch size measurements at several RF amplitudes of an upstream buncher. The measured emittance was $0.13\pm 0.01\pi$ deg.MeV, which was consistent with the simulation result.

[en] We have measured the longitudinal bunch size of beams from the radio-frequency quadrupole linac (RFQ) at the Japan Proton Accelerator Research Complex (J-PARC). The radio-frequency deflector (RFD) is installed in the medium-energy beam transport section (MEBT1) between the RFQ and the drift-tube linac (DTL). The RFD, which is usually used to produce a macro pulse configuration for the 3-GeV rapid-cycling synchrotron, is utilized to produce a different deflecting angle depending on the bunch arrival phase. Transverse beam profiles were measured after the RFD with and without deflection to extract the longitudinal bunch size. The Courant-Snyder parameters in the longitudinal direction were estimated by measurements for different strength of the upstream buncher. These measurements are one of the important steps to understand the longitudinal beam properties at a high beam current. (paper)

[en] The low level RF (LLRF) control systems have been successfully improved for the J-PARC LINAC upgrade. After the installation of 972-MHz high-β acceleration section behind the 324-MHz low-β section beginning in the summer of 2013, the proton beam was successfully accelerated to 400 MeV in January 2014. Many improvements in the LLRF control systems have been carried out to facilitate the operation of the J-PARC LINAC at 400 MeV. The reference 12-MHz signal delay settings for the feedback control systems have been optimized using 12-MHz delay modules. The stability performances of the 972-MHz RF and CLK (Clock) and Mixer and IQ (Mixer and IQ-modulator) boards have been improved using temperature-compensation techniques. By improving the hardware of the feedback control systems, very good stability of the RF systems has been achieved. (author)

[en] In order to study the photoproduction of neutral kaons and charged pions, a liquid H₂/D₂ target system was developed for the neutral kaon spectrometer at the Laboratory of Nuclear Science, Tohoku University. The target system was designed to maximize the production yield, to minimize the background events, and easy to operate safely. According to the experimental test, the position settlement uncertainty of the target is found to be about 1.1 mm, the uncertainty of the target nucleon number is about 0.63%, and the target system can work stably over 3 weeks. This liquid H₂/D₂ target system fully meets the experiment requirement. (authors)