Masayuki Shimamoto

Bio: Masayuki Shimamoto is an academic researcher from KEK. The author has contributed to research in topics: Beam (structure) & KEKB. The author has an hindex of 6, co-authored 17 publications receiving 136 citations.

Beam commissioning and operation of the J-PARC main ring synchrotron

Abstract: The slow cycling main ring synchrotron (MR) is located the furthest downstream in the J-PARC accelerator cascade. It became available for user operation in 2009 and provides high-intensity 30 GeV proton beams for various experiments on particle and nuclear physics. The MR has two beam extraction systems: a fast extraction system for beam delivery to the neutrino beam line of the Tokai-to-Kamioka (T2K) experiment and a slow extraction system for beam delivery to the hadron experimental hall. After a nine-month beam shutdown during the recovery from the Great East Japan Earthquake, the J-PARC facility resumed beam operation in December 2011. The MR delivers a 160–200kW beam to the T2K experiment and a 3.5–6kW beam to users in the hadron experimental hall. In this paper, a brief review of the MR and the recent status of beam operation are presented. Near-future plans for a beam intensity upgrade are also discussed.

The vacuum system of KEKB

Abstract: For the KEK B-factory, two rings with a circumference of 3016 m , mainly made of copper, were constructed. A gap between the flanges is filled using Helicoflex as a vacuum seal. The contact force of an RF finger in a bellows is assured by using a spring finger. Pumping slots are backed by crossing bars to prevent the penetration of beam-induced fields. To obtain a pressure of 10 −9 Torr with the beam when the photo-desorption coefficient reaches 10−6, the design of pump layout is aimed to realize 100 l s −1 m −1 . NEG strips are used as the main pump. Chemical polishing is applied to clean the extruded surface of a copper chamber. Almost all chambers were baked before installation. Only ion pumps were baked in situ. The photo-desorption coefficient at the start of commissioning was slightly higher than expected, but a decrease of the coefficient is as expected on the whole. At high currents, some bellows were found to be warmed by the TE mode of beam induced fields. The effect of the electron cloud became evident, especially in the LER. Direct damage by the beam is seen at the surface of the movable mask.

Present status of the KEK B-factory vacuum system

Abstract: The KEK B-Factory (KEKB) is a two-ring electron-positron collider with asymmetric energies to quest the CP violation. The design beam currents are 1.1 A and 2.6 A for 8.0 GeV electron and 3.5 GeV positron ring, respectively. Most of beam chambers are made of oxygen free copper for its ability to withstand the intense heat load and to shield effectively the radiation from the high beam currents. The pumping scheme is a combination of the nonevaporable getter pumps and auxiliary sputter ion pumps. Special care is taken of the inside of beam chambers to avoid excitation of higher-order modes (HOM). The commissioning of KEKB started in December 1998. The vacuum system has been operating almost satisfactorily. The average pressure of about 3×10−7 Pa is achieved now for both rings at the beam current of about 1 A. The coefficient of photon-stimulated gas desorption has been decreasing steadily to less than 1×10−6 molecules photon−1 at the integrated linear photon density of about 7×1025 photons m−1. The presenc...

Human immunoglobulin adsorption investigated by means of quartz crystal microbalance dissipation, atomic force microscopy, surface acoustic wave, and surface plasmon resonance techniques.

Abstract: Time-resolved adsorption behavior of a human immunoglobin G (hIgG) protein on a hydrophobized gold surface is investigated using multitechniques: quartz crystal microbalance/dissipation (QCM-D) technique; combined surface plasmon resonance (SPR) and Love mode surface acoustic wave (SAW) technique; combined QCM-D and atomic force microscopy (AFM) technique. The adsorbed hIgG forms interfacial structures varying in organization from a submonolayer to a multilayer. An "end-on" IgG orientation in the monolayer film, associated with the surface coverage results, does not corroborate with the effective protein thickness determined from SPR/SAW measurements. This inconsistence is interpreted by a deformation effect induced by conformation change. This conformation change is confirmed by QCM-D measurement. Combined SPR/SAW measurements suggest that the adsorbed protein barely contains water after extended contact with the hydrophobic surface. This limited interfacial hydration also contributed to a continuous conformation change in the adsorbed protein layer. The viscoelastic variation associated with interfacial conformation changes induces about 1.5 times overestimation of the mass uptake in the QCM-D measurements. The merit of combined multitechnique measurements is demonstrated.

Experimental review of hypernuclear physics: recent achievements and future perspectives

Abstract: Since the shutdown of several old proton synchrotrons, which played a fundamental role in the second generation experiments in hypernuclear physics performed in Europe, USA and Japan, some new experimental setups aiming to achieve sub-MeV energy resolution have been operating for a long time. Over the last decade the hypernuclear physics community has been committed to carrying out several third generation experiments by exploiting the potential offered by new accelerators, such as a continuous electron beam machine and a ϕ-factory. Large data samples were collected on specific items thanks to dedicated facilities and experimental apparatuses. The attention was mainly focused on both high-resolution spectroscopy and the decay mode study of single Λ-hypernuclei. Nowadays this phase is over but, until recently, important and, to some extent, unexpected results were achieved. An updated review of selected experimental results is presented, as well as a survey of perspectives for future studies.

Continuing study on the photoelectron and secondary electron yield of TiN coating and NEG (Ti–Zr–V) coating under intense photon irradiation at the KEKB positron ring

Abstract: In order to investigate a way to suppress the electron-cloud instability (ECI), the secondary electron and photoelectron yields (SEY and PEY) of a TiN coating were studied with an intense positron beam at the KEK B-Factory (KEKB), following up our previous study on a NEG (Ti–Zr–V) coating. A TiN-coated chamber was installed at an arc section of the KEKB positron ring, where photons with a line density of 6.5×1014 photons m−1 s−1 mA−1 were directly irradiated. The number of electrons around the positron bunches was measured by a special electron-current monitor, up to a stored beam current of about 1700 mA (1284 bunches). The electron current of the TiN-coated chamber was clearly smaller than those of the NEG-coated and the non-coated copper chambers by a factor of 2 for all beam currents. Using the previous results of the NEG-coated and the non-coated copper chambers as well as the TiN-coated one here, the maximum SEY (δmax) and the PEY (ηe) of the TiN coating, the NEG coating and the copper were again estimated based on a simulation. The evaluated δmax values for these three surfaces were 0.8–1.0, 0.9–1.1 and 1.1–1.3, and the ηe values were 0.13–0.15, 0.22–0.27 and 0.28–0.31, respectively. It was found that the TiN coating had an SEY (δmax∼0.9) as low as the NEG coating (δmax∼1.0), but the electron current was clearly smaller than that of the NEG coating, due to its lower photoelectron yield (ηe∼0.14). This study again indicated that the suppression of photoelectrons is required to make effective use of a surface with a low SEY, such as a TiN or a NEG coating. As an application of the simulation code, the electron current of a beam duct with an antechamber was calculated for the case of a NEG coating or a TiN coating ( δ max = 0.9 – 1.0 ). The calculated electron current for a copper duct with an antechamber was about 1/4 of that of a simple circular copper duct ( δ max = 1.2 for both cases) at a high current (∼1700 mA, 1284 bunches), which was in good agreement with the measurement. By combining with a surface with a low SEY ( δ max = 1.0 – 0.9 ), that is, a TiN coating or a NEG coating, a further reduction of the electron current by a factor of about 2 was obtained.

Materials and Life Science Experimental Facility at the Japan Proton Accelerator Research Complex I: Pulsed Spallation Neutron Source

Abstract: At the Japan Proton Accelerator Research Complex (J-PARC), a pulsed spallation neutron source provides neutrons with high intensity and narrow pulse width pulse to promote researches on a variety of science in the Materials and Life Science Experimental Facility (MLF). It was designed to be driven by a proton beam with an energy of 3 GeV, a power of 1 MW at a repetition rate of 25 Hz, that is world’s highest power level. It is still on the way towards the goal to accomplish the operation with a 1 MW proton beam. In this review, distinctive features of the target-moderator-reflector system of the pulsed spallation neutron source are presented.