Search

In an emulsion-counter hybrid experiment performed at J-PARC, a Ξ^{-} absorption event was observed which decayed into twin single-Λ hypernuclei. Kinematic calculations enabled a unique identification of the reaction process as Ξ^{-}+^{14}N→_{Λ}^{10}Be+_{Λ}^{5}He. For the binding energy of the Ξ^{-} hyperon in the Ξ^{-}-^{14}N system a value of 1.27±0.21 MeV was deduced. The energy level of Ξ^{-} is likely a nuclear 1p state which indicates a weak ΞN-ΛΛ coupling.

We have developed a new production target at the J-PARC Hadron Experimental Facility. The target is made of gold and is indirectly cooled by water through a copper block. Although this cooling structure is the same as that of the current production target, the cooling efficiency is improved by doubling the copper cooling block. We performed an elastic-plastic analysis for thermal-stress evaluation of the new target, using the tensile-test results of bulk gold. For each type of stress, we compared the results of the analysis to the allowable stress. It turns out that the new target is capable of a primary-proton beam power up to 90 kW for a 5.52-s repetition cycle. In this paper, the design and preparation of the new target are presented.

In the K1.8 beam-line at Hadron Experimental Facility of J-PARC, a new magnetic spectrometer S-2S is being installed. S-2S was designed to achieve a high momentum resolution of Δp/p = 6 × 10−4 in FWHM. Several strangeness-physics programs which require the high resolution will be realized by S-2S. The present article introduces J-PARC E70 (missing-mass spectroscopy of Ξ12Be) and E94 (missing-mass spectroscopy of Λ7Li, Λ10B, and Λ12C) experiments.

J-PARC E07 is the most complex emulsion experiment to date investigating double hypernuclei with a hybrid emulsion method. This experiment aims to detect 104 Ξ− stop events, ten times more events than the past experiments. Thus, an unequivocal identification of several new double hypernuclei is expected. The beam exposure has been completed at the K1.8 beam line of the J-PARC hadron facility in June 2017. The photographic development of all emulsion sheets has also been completed in February 2018. The emulsion sheets are presently being analyzed with dedicated optical microscopes. Current statistics is comparable to that of E373 and so far 10 events of 3-vertices topology have been detected. A typical event of double Λ hypernucleus and a twin Λ hypernucleus are introduced. We plan to complete the main part of the emulsion scanning within a year.

We developed a Lambertson magnet and two septum magnets as the splitting devices for the new beamline at the Hadron Experimental Facility in J-PARC. This new beamline, now under construction, is called high-p/COMET beamline, and the experiments using 30- and 8-GeV proton beams are planned. The required functions of the splitting devices are as follows: to split a small fraction (around 10−4) of the 30-GeV proton beam into the high-p/COMET beamline (30-GeV mode) and to bend all of the 8-GeV proton beam into the high-p/COMET beamline (8-GeV mode). These two requirements are met by adjusting the vertical beam position at the entrance of the Lambertson magnet. In 30-GeV mode, the Lambertson magnet is used to scrape the beam halo of the proton beam and bend the beam into the high-p/COMET beamline. The beam loss at the Lambertson magnet is inevitable; thus, the magnet must be resistant to the radiation and heat caused by the beam loss. The magnet is composed of nonorganic materials only and equipped with two water pipes to remove the heat induced by the beam loss. The branched beam is bent further by two septum magnets at the downstream of the Lambertson magnet. The construction and the magnetic field measurements of these devices were completed in March 2015, and the installation into the beamline is planned for the summer of year 2017.

This paper reports developments of indirectly cooled radiation-resistant magnet coils, which can be loaded with 2000-A dc. This current capacity is required for the most upstream magnets of a new high-momentum beam line to be constructed in the future extension of the J-PARC hadron experimental facility. Indirectly cooled coils using solid-conductor-type mineral insulation cables (MICs) and stainless-steel water pipes were adopted to achieve high radiation hardness. MICs were sandwiched by independent cooling water pipes and stacked in a casing, and the entire coil assembly was filled with solder. However, the maximum load applied to the indirectly cooled MIC coils was limited to 1000-A dc, mainly owing to a heat problem at the end parts of the coils. In pursuit of the required current capability, we have carried out load tests using a test sample of the end parts, which consists of MIC current leads and a copper bus bar connecting the MIC conductors, instead of a whole MIC coil. By improving the structure of the end parts, we have succeeded to operate the test piece stably with 2000-A dc in a vacuum.

A double-$\Lambda$ hypernucleus, ${}_{\Lambda\Lambda}\mathrm{Be}$, was observed by the J-PARC E07 collaboration in nuclear emulsions tagged by the $(K^{-},K^{+})$ reaction. This event was interpreted as a production and decay of $ {}_{\Lambda\Lambda}^{\;10}\mathrm{Be}$, ${}_{\Lambda\Lambda}^{\;11}\mathrm{Be}$, or ${}_{\Lambda\Lambda}^{\;12}\mathrm{Be}^{*}$ via $\Xi^{-}$ capture in ${}^{16}\mathrm{O}$. By assuming the capture in the atomic 3D state, the binding energy of two $\Lambda$ hyperons$\,$($B_{\Lambda\Lambda}$) of these double-$\Lambda$ hypernuclei are obtained to be $15.05 \pm 0.11\,\mathrm{MeV}$, $19.07 \pm 0.11\,\mathrm{MeV}$, and $13.68 \pm 0.11\,\mathrm{MeV}$, respectively. Based on the kinematic fitting, ${}_{\Lambda\Lambda}^{\;11}\mathrm{Be}$ is the most likely explanation for the observed event., Comment: 11 pages, 3 figures

An electrostatic separator is one of the key elements of a secondary beam line at the Hadron experimental hall of J-PARC. It generates a transverse electric field along the beam axis to separate particles of the same momentum by their mass differences. Two beam lines for charged secondary particles, K1.8 and K1.1BR, are constructed, to provide kaon beams with less contamination of pions. Three experimental areas, K1.8, K1.8BR and K1.1BR are available for nuclear and particle physics experiments. Two 6-m-separators and a 2-m-separator of a Wien filter type are installed for the K1.8 and the K1.1BR beam lines.

The target station in the hadron experimental facility at J-PARC consists of a production target and a huge vacuum chamber in which several secondary-beam-line magnets can work. This vacuum chamber system aims to remove the vacuum beam pipe from the magnet gap, because the cooling of the beam pipe is the most serious problem in the high intensity beam facility. We have developed indirectly cooled radiation-resistant magnets for the hadron target station. Their coils are made of solid-conductor type mineral-insulation cables and stainless-steel water pipes. They have the great advantages that electric circuits can be completely independent of water pass. The mechanical strength and the insulation performance of the coil are significantly improved also because the insulation water pipes can be avoided from the water pass. A C-type sector dipole and a figure-8-type quadrupole magnet have been fabricated by using indirectly cooled radiation-resistant magnet technology, and installed in the vacuum chamber. We have succeeded to operate them in vacuum stably with the current of DC 1000 A by improving the end structure of the MIC coils and increasing their emissivity. These magnets have been used for the real beam operation without any serious problems.

More than 50 radiation-resistant electromagnets were constructed for the primary proton and the secondary particle beam lines of the Hadron Experimental Hall of Japan Proton Accelerator Research Complex (J-PARC). The main radiation-resistant technologies we employed were the Polyimide-resin Insulation conductor for magnets at the relatively low radiation exposure and the Mineral Insulation Cable for magnets at the seriously high radiation environment. The remote handling and maintenance scheme of radiation-resistant magnets for seriously high radiation environment was developed also based on the Chimney magnet technology and applied to magnets near the production target in the Hadron Hall. On January 27th 2009, the first proton beam was successfully introduced to the Hadron Hall from the main accelerator of J-PARC, i.e. 50 GeV Proton Synchrotron. On February 10th, the secondary particles were extracted to the experimental area of the Hadron Hall through the secondary particle beam line. No serious problem happened on magnets of both primary proton and the secondary particle beam lines until the end of the beam operation scheduled on February 26th .

The new electrostatic (ES) separator to select and deliver 1–2 GeV/c kaon beams is made for the secondary beam line at the high intensity proton accelerator facility. The ES separator will generate a 75 kV/cm electrostatic field between parallel electrodes of 10 cm gap and 6 m in length along the beam direction. The K − /π − ratio of the line is expected to have a larger value than 1. It is designed so as to be radiation-proof and to lower spark rate comparing with the present separators.

The high intensity proton accelerator facility J-PARC is now in its final stage of construction. Soon intense primary proton beams will be slowly extracted to an experimental hall (HD-hall) and transported to a production target. Since the radiation level around the target will be very high, the beam line tunnel needs to be surrounded by 2.5 m-5 m thick concrete shields in the HD-hall. Radiation resistant magnets for handling high intensity beams are buried inside these thick concrete shields. This structure, however, brought us a problem of leading electric power lines to the magnets. For a solution to this problem, we have developed water cooled bus ducts penetrating radiation shield. These bus ducts enable us to connect the power supplies placed outside the shields to the magnets in the shortest power line length without any deterioration of protection ability of radiation shielding. The maximum power capacity of the bus duct is over 5000 A. The bus ducts plays an important part in our radiation resistant magnet system.

In a high-intensity proton beam facility, beam line elements downstream of a production target are exposed to a huge amount of radiation and heat. Beam pipes are closer to the beam than the magnet poles and more difficult to cool sufficiently without tritium production. Therefore, the magnets are placed in a large vacuum chamber, instead of using vacuum pipes located within the pole gaps. We have adopted indirect-cooling mineral-insulation-cable (MIC) coils for these magnets. They have a great advantage that the mechanical strength and the insulation performance can be significantly improved by avoiding the use of ceramic insulation pipes, because electric circuits are completely separated from water passages. We have made coils using 1000-A-class solid-conductor MICs and stainless-steel pipes, and tested magnet operation in vacuum. By improving the structure of end parts of MICs and increasing their emissivity, we have successfully fed the current of DC 1000 A to the solid-conductor MIC coils in vacuum.

In a high-intensity proton beam facility, beam line elements downstream of a production target are exposed to a huge amount of radiation and heat. A water-cooled beam collimator must be located between the target and the magnets, and the iron yokes of the magnets also have to be cooled by water. Moreover, beam pipes are closer to the beam than the magnet poles and more difficult to cool sufficiently without tritium production. Therefore, the magnets are placed in a large vacuum chamber, instead of using vacuum pipes located within the pole gaps. In order to reduce the residual radiation dose during maintenance, the chamber lid and feedthroughs are 4 meter above the beam line, and radiation-shielding blocks are also stacked in the chamber. We have tested magnet operation in vacuum using a dipole magnet with mineral-insulation-cable (MIC) coils and a nickel-coated yoke. A magnet with 2500-A-class hollow-conductor MIC coils has worked successfully with the current of DC 3000 A. The stability of operation in vacuum was confirmed by measuring the temperature with thermocouples and the magnetic field with a NMR probe. We have also succeeded in operating a 1000-A-class solid-conductor MIC coil in vacuum

Several species of radiation-resistant magnets were developed for J-PARC, a Japanese brand-new high-intensity accelerator complex, whose maximum beam power reaches 1 MW. The first development was polyimide insulation magnets. The ordinal epoxy resin was replaced by polyimide resin in order to improve its radiation lifetime up to $4 \times 10^8$ Gy. Most accelerator magnets of J-PARC were assembled with polyimide insulation coils. Peripherals of polyimide insulation magnets, such as insulation water tubes, water valves, water gaskets, etc., were replaced also by ones made of inorganic materials. The second development was mineral insulation magnets. Magnet excitation coils were made of “Mineral Insulation Cable (MIC).” The copper conductor of MIC was surrounded by a thin MgO insulation layer, and the MgO layer was covered by a copper sheath. Several sizes of MIC cross section were developed for large and small magnets with various maximum currents from 1000 to 3000 A. Peripherals of magnets assembled with MIC coils were also made of completely inorganic materials. These MIC magnets were used at the downstream part of beam loss points such as the secondary particle production target of Hadron Experimental Facility. The R&D stories of the radiation-resistant magnets, including the present status of the magnet operation, are briefly summarized.

The facility of the long baseline neutrino oscillation experiment using the J-PARC's 50 GeV-0.75 MW proton beam is now under way. The primary proton beam line consists of three sections, i.e. the first preparation (PP) section with normal conducting magnets, the second arc (ARC) section with superconducting magnets and the third final focus (FF) section with normal conducting magnets. In the PP section, we have to clean the primary proton beam extracted from the 50 GeV-PS and transport halo-less pure beam only to the ARC section. In the FF section the magnets have to be placed very close to the pion production target and horns. Therefore the normal conducting magnets have to work in the very high radioactive environment. The R&D works on the radiation resistant magnets for handling a high-intensity proton beam have already been continued at KEK as reported in . Another important point regarding high-intensity beam handling is to realize easy maintenance of the beam line. Any magnet experiencing trouble can be easily removed from beam line and repaired remotely. For this purpose, we developed new tools for the magnet maintenance. These are automatic sling apparatus, quick alignment and installation guide, and the quick disconnect devices of cooling water and electric power. In this paper, we will report the beam line maintenance scheme developed for the neutrino beam line, as well as the design of normal conducting magnet sections

At the Japan Proton Accelerator Research Complex (J-PARC), the world highest intensity secondary beams of kaons, pions, anti-protons, muons, and neutrinos will be produced by irradiating a target with the 50 GeV primary proton beam of 0.75 MW. Utilizing such high intensity secondary beams, various unique and interesting experimental studies in nuclear and particle physics can be carried out. We will describe the current R&D status of the target systems to be constructed in the Nuclear and Particle Physics Experimental Hall (NP-Hall) and the neutrino beam line of J-PARC. Some experimental studies proposed there will be also introduced.

A series of the R&D works on the radiation resistant magnets for the Japan Hadron Facility (JHF) project has been continued at the High Energy Accelerator Research Organization (KEK). The JHF is a high-energy part of the Japanese high intensity Particle Accelerator Research Complex (J-PARC), which is Japanese next-generation high-intensity accelerator project. The main JHF accelerator is the 50 GeV proton synchrotron and will provide high intensity 15/spl mu/A proton beam for various nuclear and particle physics experiments. This time, the actual sized completely-inorganic radiation-resistant quadrupole magnet, designed for the 50 GeV proton beam transportation, was manufactured successfully by using mineral insulation magnet cable (MIC). The assembling procedure and the test results are presented in this issue.

High-resolution spectrometers for both incident beams and scattered particles have been constructed at the K1.8 beam line of the Hadron Experimental Facility at J-PARC. A point-to-point optics is realized between the entrance and exit of QQDQQ magnets for the beam spectrometer. Fine-pitch wire chamber trackers and hodoscope counters are installed in the beam spectrometer to accept a high rate beam up to 107 Hz. The superconducting kaon spectrometer for scattered particles was transferred from KEK with modifications to the cryogenic system and detectors. A missing-mass resolution of 1.9 ± 0.1 MeV/c2 (FWHM) was achieved for the ∑ peaks of (π±, K+) reactions on a proton target in the first physics run of E19 in 2010.

A brief description of the primary beam line at the hadron experimental facility at the Japan Proton Accelerator Research Complex (J-PARC) is presented. The facility has been constructed in Tokai, Japan, and the first beam was successfully introduced into the experimental hall in January 2009. The facility utilizes a high-intensity proton beam with an energy of 50 GeV and a power of 750 kW and provides various secondary beams such as pions, kaons, and antiprotons for nuclear and particle physics experiments. We have developed beam-line components with sufficient radiation hardness and heat resistance to handle the high-power proton beam.

J‐PARC Hadron Experimental Facility is designed as a multi‐purpose experimental facility for particle and nuclear physics experiments using high‐intensity secondary particles (Kaons, pions, and so on) produced by 50 GeV‐15 μA (750 kW) primary proton beams. Currently, three secondary beam lines (K 1.8 BR, K 1.8, and KL) have been constructed. The first beam extraction from 50 GeV proton synchrotron was on January 27th, 2009, and the beam commissioning of the primary and secondary beam lines are on going. The present article reports construction status and beam commissioning of Hadron Experimental Facility in detail.

We developed beam diagnosis devices, a residual gas ionization beam profile monitor (RGIPM) and an optical transition radiation (OTR) monitor, for a high power proton beam transfer line at the 50-GeV proton synchrotron (PS) of the Japan Proton Accelerator Research Complex (J-PARC). The RGIPM collects electrons produced by beam ionizing a residual gas in the vacuum beam pipe. Since the RGIPM is operated at a vacuum level of 1 Pa, a magnetic field is required to confine electrons around the magnetic field against the diffusion effect due to interactions of drift electrons to residual gas molecules. We, therefore, developed a magnet-built-in type of RGIPM. The OTR monitor observes OTR photons emitted at beam particles crossing a screen with a video camera. We demonstrated that the OTR can be measured even at the KEK 12-GeV proton synchrotron. In order to maintain radiation doses to imaging devices small, the devices are located at a distance of 5 m from the beam line. The OTR photons are collected by a Newtonian reflecting telescope.

Nondestructive beam profile monitor utilizing ionizations of residual gas has been developed for continuous monitoring of 3/spl times/10/sup 14/ protons at Japan Proton Accelerator Research Complex (J-PARC). Knock-on electrons produced in the ionizations of residual gas vacuumed to 1 Pa are collected with a uniform electric field applied between electrodes. Applying a uniform electric field parallel to the electric field is essential to reduce diffusion of electrons crossing over magnetic flux. A prototype monitor has been constructed and installed in EP2-C beam line at KEK 12 GeV proton synchrotron (12 GeV-PS). The profiles measured with the present monitor agree with the ones measured with the existing destructive profile monitor. The present monitor shows sufficient performances as a candidate of the profile monitor at J-PARC. In the present article, the working principle of the present monitor, the results of test experiments, and further developments are described in detail.

We developed the optical transition radiation (OTR) monitor as a profile monitor for a high intensity (750 kW) slow-extraction beam line at the Japan Proton Accelerator Research Complex (J-PARC). The OTR monitor is considered to be one of good candidates for such a profile monitor, because the OTR light intensity only depends on the reflectivity of an OTR screen. We performed an experiment to test a prototype OTR monitor at the slow-extraction beam line of the KEK 12 GeV-PS. We succeeded to observe a beam profile clearly under the conditions of a low gamma factor of about 13.8, a low beam intensity of 4E11 protons per pulse, and a large beam loss of 1 W/m or more. We also checked a beam response, a background level, and a resistance to radiation of the monitor. We designed and developed two types of the image detecting system such as an optical fiber system and a optical system to enhance the S/N and reduce a radiation damage to the system.

In order to handle high intensity primary proton beam provided by Japan Proton Accelerator Research Complex (J-PARC), radiation-resistant beam lines have been constructed at Hadron Experimental Hall of J-PARC. The key technology of the radiation-resistant beam line is the radiation-resistant magnets. However all the peripheral devices of the magnets were designed and assembled as radiation-resistant ones since peripherals as well as magnets should be operated in very high radiation environment. In addition a safe operation and maintenance scheme of high intensity beam lines has been established based on the Chimney technology of radiation-resistant magnets including their peripherals. Then the beam lines in the Hadron Experimental Hall have been constructed with “radiation-resistant magnet system”.

The construction of the facility of the long baseline neutrino oscillation experiment using the J-PARC's 50 GeV-0.75 MW proton beam [1] was completed at the end of 2008. The number of radiation-resistant magnets we have prepared for the neutrino beamline of J-PARC were 15 with Polyimide resin Insulation (PI) against up to 108 Gy, and 4 magnets with completely Mineral Insulation Cable (MIC) for higher radiation dose up to 1011 Gy, and 2 magnets with Epoxy resin Insulation. All magnets were equipped with remote handling system, i.e. automated magnet lifts, quick alignment guides, water connectors, electric power connectors and interlock-signal connectors. On April 23rd 2009, the first proton beam was successfully introduced to the neutrino beamline from the main accelerator of J-PARC and the long baseline oscillation experiment, T2K, started. Now the beamline is operated with 135 kW (30 GeV-4.5 ) primary proton beam. No serious problem happened on magnets until the great East Japan earthquake on March 11th.

J-PARC Hadron Experimental Facility is designed to carry out a variety of particle and nuclear physics experiments with intense secondary particles generated by 750 kW proton beams. The first construction stage including the experimental hall, the primary beam line, and one secondary beam line (K1.8BR) has been completed at the end of December 2008. In order to handle the high intensity primary beam safely, we have developed many special devices working under severe radiation environment. The present article reports the current status of the Hadron Experimental Facility in detail.