[in Japanese]

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The construction of the J-PARC Project started in April of 2001. After 8 years of construction period, the project was completed in the spring of 2009. Three accelerator elements (Linac, 3 GeV proton synchrotron and 50 GeV proton synchrotron) are now working. Also, three experimental halls (materials and life experimental hall, hadron experimental hall, and neutrino experimental hall) are in operation. In this article I review all these facilities and their scientific goals. In addition, I would like to overview the current and future scope of this J-PARC facility.

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Recently the investigations on the local stress/strains and related properties in the engineered superconducting composites have been extensively carried out by using the pulsed neutron facilities, J-PARC TAKUMI. Firstly the key concepts are described in order to understand their mechanical-electromagnetic properties after the performance of TAKUMI is briefly introduced. Unique and important results have been obtained by the present diffraction studies. Highlights of the present review are the three dimensional description of strains in Nb₃Sn filaments, the determination of force free strains at RT and 77 K for BSCCO and YBCO tapes, and of T_o for the BSCCO tape and Nb₃Sn wires, which is the initiation temperature of thermally induced residual strains. Typically the local axial strain exerted on Nb₃Sn filaments has been firstly measured along the TF coil used for ITER project in the world.

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The construction of the 1st phase Japan Proton Accelerator Research Complex (J-PARC) has been completed, and experimental facilities, (Materials and Life Science/Hadron/Neutrino) have been utilized for the users. Four major cryogenic systems (three of which are also superconducting magnet systems) have already been installed at J-PARC. There are also several further cryogenics/superconducting systems proposed as part of future J-PARC projects. This article introduces these new projects and briefly describes the cryogenics and superconducting technologies proposed for the projects.

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A helium cryogenic system has been constructed to circulate 300 g/s of Supercritical Helium (SHe) at 4.5 K through a series of superconducting magnets for a neutrino beam line at J-PARC. The conceptual cryogenic system design, considering the cooling characteristics of the magnets, was defined in 2005. The engineering design was subsequently carried out by Taiyo Nippon Sanso Corp. The main elements are a screw compressor with a capacity of 160 g/s at 1.4 MPa, a refrigerator with a capacity of 1.5 kW at 4.5 K and a centrifugal SHe pump with a flow rate of 300 g/s. After system integration in 2008, performance tests were conducted. In a preliminary cooling test to confirm the cryogenic capacity, the cryogenic system successfully performed to the required specifications by circulating a supercritical helium flow of 300 g/s at 0.4 MPa and 4.5 K through a bypass line with a simulated heat load of 520 W and simulated pressure drop of 0.85 MPa. Following this, a full system test with the magnets was carried out. The magnets were pre-cooled from the ambient temperature for eight days and were kept below 4.8 K by circulating pumped SHe. The measured heat leakage at the magnets during these tests, including SHe transfer lines, was 210 W. Since the maximum beam loss predicted is 150 W, the cooling capacity of the cryogenic system is large enough to manage beam operations expected in the future.

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Superconducting combined-function magnets have been utilized for the 50-GeV, 750-kW proton beam line in the J-PARC neutrino experiment. The magnets are designed to provide a dipole field of 2.6 T combined with a quadrupole field of 19 T/m in a coil aperture of 173.4 mm at a nominal current of 7,345 A. Following the success of a prototype R&D project, a superconducting magnet system for the J-PARC neutrino beam line has been constructed since 2005. Using a new conceptual beam line with the superconducting combined-function magnets has demonstrated successful beam transport to the target neutrino production.

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The Muon Science Laboratory at the Materials and Life Science Experimental Facility at J-PARC is now operating stably. In the first stage, a conventional superconducting muon channel was installed, which can extract low-energy positive muons (30 MeV/c) and medium-energy positive (or negative) muons up to 120 MeV/c. The established muon yield is several 10⁷/s for 60 MeV/c (both positive and negative muons) at a proton beam power of 1 MW. This channel is used for various experiments such as muon spin spectroscopy, muon-catalyzed fusion and nondestructive elemental analysis. The superconducting solenoid is the key element of this beam line. We briefly present the construction and operation of this solenoid and cryogenics.

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Material or biological structures are analyzed through cold neutron beam scattering experiments at the Materials and Life Science Experimental Facility (MLF) at J-PARC. The high-energy MeV-order neutrons, which are produced via a spallation reaction between 3-GeV protons and the mercury nucleus, are moderated to cold neutrons with MeV-order energy by passing them through a supercritical hydrogen moderator. The cryogenic hydrogen system provides the supercritical hydrogen to a pressure of 1.5 MPa and temperature of approximately 20 K and removes the energy (nuclear heating), which is estimated to be 3.75 kW for a proton beam power of 1 MW. A kW-order heat load such as this is applied to the cryogenic hydrogen system as a step load. Therefore, to mitigate pressure fluctuation caused by the load, a pressure control system is a necessary requirement. Accordingly, a control system was designed and installed, using a heater as an active controller for thermal compensation and an accumulator as a passive volume controller. During operations at J-PARC, changes in pressure caused by operation of a 120-kW and a 302-kW proton beam were studied. When the proton beam was supplied, the pressure continuously increased until the heater control started, after which the accumulator spontaneously constricted. The heater control maintained a constant temperature downstream of the heater without any thermal disturbance. It was confirmed that the pressure control system was effective in mitigating the pressure fluctuation caused by the load. A simulation code was also developed and the pressure rise behavior and the accumulator variation were studied. The simulation results indicated good agreement with the experimental data within 10%. The pressure rise behavior and the accumulator variation were proportional to the proton beam power. The pressure fluctuation for a 1-MW proton beam was predicted to be 33.9 kPa, which was lower than the allowable pressure rise of 0.1 MPa, and produced an accumulator variation of 11.35 mm. We believe that the pressure control system is effective for use with the operation of a 1-MW proton beam.

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The Superconducting Kaon Spectrometer (SKS) magnet, which was in operation at the K6 beamline in the North Counter Hall of the KEK 12-GeV proton synchrotron from 1991 to 2005, was modified and moved to the newly constructed K1.8 beamline in the Hadron Hall at the Japan Proton Accelerator Research Complex (J-PARC). We reused the original coil assembly which includes coils and vessels, with a Gifford-MacMahon (GM) cryocooler for shield cooling. We used three Gifford-MacMahon/Joule-Thomson (GM/JT) cryocoolers instead of the previous 300-W helium refrigerator. The cooling power of a GM/JT cryocooler is 3.5 W at 4.5 K and 50 Hz. We also installed a new GM cryocooler to cool the GM/JT insert ports. Conventional copper current leads were replaced with Bi2223 high-temperature-superconductor (HTC) leads. We also required a new GM cryocooler to cool the HTC current leads. In total, we installed three GM/JT and three GM cryocoolers. We cooled the reconstructed SKS superconducting magnet at the K1.8 beamline from room temperature to 4.3 K over 1.5 months, applying LN₂ and LHe directly. We confirmed that the three GM/JT cryocooles maintained the LHe level in the steady state. Helium gas pressure within the helium vessel was 113 kPa absolute and the condenser temperatures of the three GM/JT cryocoolers were 4.35 K, 4.46 K, and 4.35 K, respectively. We also measured the rise in temperature of the HTC leads when the magnet was continuously excited at a current of 400 A. The temperature of the HTC leads rose to 41 K and attained saturation after 5 hours. This was sufficiently safe for the Bi2223 HTC leads. Furthermore, we confirmed that two GM/JT cryocoolers could maintain the steady state; however, for safety reasons, we decided to use three GM/JT cryocoolers in the case of continuous excitation at more than 350 A.

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A variable operation, pressure-type quench relief valve (VQRV) has been developed by the High Energy Accelerator Research Organization (KEK) for superconducting magnet systems. It is based on the Kautzky valve, featuring a long extension structure, a high radiation-proof gas seal with Poly-Ether-Ether-Ketone (PEEK) and an actuator driven by differential pressure between a process value and a set value. The VQRV was tested under a high radiation environment up to 2.5 MGy. The gas leak rate and heat load were measured at 4.2 K. A measured heat loss of less than 1.5 W and a seat leakage rate of 4.5 × 10^-7 kg/sec are low enough for cryogenic system operation in the J-PARC neutrino beam line.The design and test results of the VQRV are described in this technical report.

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