Various superconducting detector solenoids for particle physics have been developed in the world. The key technology is the aluminum-stabilized superconducting conductor for almost all the detector magnets in particle physics experiments. With the progress of the conductor, the coil fabrication technology has progressed as well, such as the inner coil winding technique, indirect cooling, transparent vacuum vessel, quench protection scheme using pure aluminum strips and so on. The detector solenoids design study is in progress for future big projects in Japan and Europe, that is, ILC, FCC and CLIC, based on the technologies established over many years. The combination of good mechanical properties and keeping a high RRR is a key point for the development of Al-stabilized conductor. The present concern for the detector solenoid development is to have been gradually losing the key technologies and experiences, because large-scale detector magnets with Al-stabilized conductor has not been fabricated after the success of CMS and ATLAS-CS in LHC. Complementary efforts are needed to resume an equivalent level of expertise, to extend the effort on research and to develop these technologies and apply them to future detector magnet projects. Especially, further effort is necessary for the industrial technology of Al-stabilized superconductor production. The worldwide collaboration with relevant institutes and industries will be critically important to re-realize and validate the required performances. Some detector solenoids for mid-scale experiment wound with conventional copper-stabilized Nb-Ti conductor require precise control of magnetic field distribution. The development efforts are on-going in terms of the magnetic field design technology with high precision simulation, coil fabrication technology and control method of magnetic field distribution.

A model of superconducting magnet energy storage device has been fabricated to demonstrate its cooling scheme by using liquid hydrogen flow through thermosiphon loops. A stack of three double pancake coils wound with MgB2 Rutherford cables are in thermal contact with thermosiphon pipes through pure copper plates which cover the each pancake coil surface. To prevent eddy current from being induced in the copper plates, the latter are slit into strips. After completion of the model device, performance test was carried out by actually supplying liquid hydrogen. The coil has been kept at a temperature lower than 21 K and has been charged up to a nominal current of 600 A. On the other hand, a large amount of evaporation of liquid hydrogen due to oscillation of some sort and gradual temperature rise at the coil terminals resulting in quench were observed, and these issues should be resolved in the future.

Superconducting Magnetic Energy Storage (SMES) has been a promising option amongst potential other storage devices to support world-wide demands for introducing more renewables into the utility grid. If MgB2 strands are used for SMES, liquid hydrogen, one of the renewables, could be used not only as a clean energy source but also as a coolant for the superconducting device. For large-scale coil design, mechanically fragile multi-filament strands should be used for their low AC loss feature considering that the transport current inside the coil would be always changing. To realize such a design, we designed and fabricated the large current capacity for AC-use Rutherford cable, together with experimental tests for its feasibility assessment. Based on the latest test results and development of commercial MgB2 strands with high mechanical strength, and this research and development of kA-class cable at liquid helium temperature for extrapolating the critical current (Ic) at hydrogen temperature, we believe this approach has the potential to make a practical SMES device with MJ capacity. In this paper, the world's largest-capacity AC cable design and test results including critical current evaluation under several background field strengths are shown, and the stability and current re-distribution are also discussed.

Double pancakes (DPs) for a Superconducting Magnetic Energy Storage (SMES) coil have been developed using MgB 2 Rutherford type superconductors. The DPs with 400 mm ID and about 600 mm OD were wound with Rutherford type conductors cabled by twisting multi-filamentary MgB 2 strands. For use in an indirect cooling system, the DPs and thin pure copper sheets as thermal conductors were alternately stacked, and the SMES coil was assembled. In the experiment, while continuous triangular current waveforms up to 600 A and DC current were supplied to two configurations of the SEMS coil, the AC loss at 4.2 K was measured by calorimetric method. By comparing the losses under each excitation and configuration, the AC loss in the SMES coil and an eddy current loss in the copper sheets were obtained, separately. The resultant AC loss in the SMES coil was in agreement with the theoretical values.

The COMET experiment, which is being prepared at the Japan Proton Accelerator Research Complex (J-PARC), aims to explore the rare decay phenomenon of muons. This phenomenon is not allowed in the Standard Model of elementary particles but is expected to occur due to new physics beyond the Standard Model. In the COMET experiment, superconducting magnets are used throughout the muon beamline. The Pion Capture Solenoid concentrates the pions generated by the injection of proton beams into the target. Since this magnet surrounds the target, it is designed to operate in a high radiation environment. The Muon Transport Solenoid guides the muons generated by the decay of pions. This magnet maximizes the muon yield and reduces the other background particles. The Detector Solenoid acts as a spectrometer of the electrons generated by the decay of muons. These low-temperature superconducting magnets are now being developed and constructed. The current lead box is also constructed to supply high currents to the magnets. It provides a thermal gradient from the room-temperature part of the power supply to the low-temperature part of the coil. It is designed to provide a large thermal gradient over a short distance using high-temperature superconductors. Using the current lead box, all magnets, including the high-temperature superconducting leads, are cooled by conduction cooling. In this paper, the construction status of the COMET superconducting magnet system is reported.

Cryogenic system of the superconducting magnet for COMET (COherent Muon to Electron Transition) experiments has been constructed in the J-PARC since FY2013. The cryogenic system can be roughly divided into superconducting magnet, refrigerator system and inter-connect system. The refrigeration system is composed of cold box and warm screw compressor system which are located on the surface. On the contrary, magnet system will be installed in the underground. Therefore the inter-connect system is mainly composed of current lead box and transfer line, which are regarded as a system for connecting between ground facility and the underground superconducting system. Since the superconducting magnet is cooled by two-phase flow helium at around 4.5 K, the transfer line has an adiabatic structure with shield line of around 50 K. In addition, conduction cooled superconducting cables are laid in parallel with the two-phase flow cooling line. In this study, simulation on the pressure drop of gas-liquid two-phase flow of helium is introduced to determine the cooling pipe diameters in the transfer line. Then the detail structures of the transfer line and cooling scheme of the superconducting cables optimized by several experiments will be presented.

To realize the practical application of Superconducting Magnetic Energy Storage (SMES) systems cooled by liquid hydrogen, MgB2 is promising as a material for SMES coils in terms of reducing cost in the future and enabling high critical temperature above the temperature of liquid hydrogen. Major technological development issues to realize the application of SMES coils are fabrication of the Rutherford superconducting cable with a kA-class current capacity and fabricating the coils using both Wind and React (W&R) and React and Wind (R&W) methods. Since there is little data regarding the allowable bending strain of the MgB2 strand before heat treatment, an experiment was conducted and it was determined to be approximately 4 % before the fabrication of the cable. The Rutherford cable was designed and developed based on analysis of the space curve theory because the complex bending strain is exposed to the MgB2 filaments during the cable and coil fabrication processes. However, the critical currents measured using cables developed according to the design were degraded approximately 30%. This degradation can be explained as being due to local deformation of the strands caused by compression at the cross-over point between the strands of the conductor. The broken sections of the Nb barrier, which were observed by reviewing SEM images of the strand cross-section, can cause degradation of the critical current. Two double pancake coils, which were primarily wound using the Rutherford cables and manufactured applying both the R&W and W&R methods for the purpose of comparing fabrication processes, were connected in series to excite the coils. As a result, an operating current of 600 A was successfully achieved.

MgB2 wires have been provided by several manufacturers, showing enough critical current (Ic) for practical applications in relatively low-field. Because the MgB2 has critical temperature above boiling temperature of hydrogen, dc power distribution system with low carbon emission using MgB2 superconducting magnetic energy storage (SMES), named advanced superconducting power conditioning system has been proposed. For the system, the MgB2 coil production technology obtaining 30 kJ stored energy the investigation about the SMES coil consists of 600 A, 1.7-T Rutherford-type conductors made of commerciallyavailable MgB2 wires. Due to strain sensitivity before/after heat treatment for MgB2 production, the proper designs of the large-scale twisted conductors both in wind and react, react and wind methods are needed, choosing optimized twist pitches and cable compaction factors. To demonstrate the SMES coil performance, we have been carried out the test campaign of conductors and small prototype coils in various temperature and background field conditions. These results are used for a computer simulation for estimating full size double pancake coil performance of the system, based on the non-steady state heat conduction analysis. The calculated result seems to be a good tool for predicting coil performance for the large capacity energy storage operation.

MgB 2 superconductors are promising candidates for application to devices such as Superconducting Magnetic Energy Storage, and generators. To apply MgB 2 conductors to such devices, the current capacity of a conductor must be in the kilo-ampere range. Meanwhile, because the current capacity of a MgB 2 conductor is typically approximately 100 A at 5 T and 4.2 K, multiple stranded cables are required. One candidate is the Rutherford-type cable. During the fabrication of Rutherford cables, strands are deformed by large bending strains at edge corners and indented at flat parts from the pressure of roller dies to maintain the cable shape. It is important to understand how critical current degrades during the fabrication of Rutherford-type cables. To optimize the strand transposition length, three types of Rutherford cables were fabricated and the critical current degradation depending on bending and indented strains was measured. Moreover, to investigate the degradation, inner structures of the strands were observed using micro-focused X-ray computed tomography and an electron probe micro analyzer.

Superconducting magnetic energy storage (SMES) devices of several tens of kJ class are generally suitable for voltage compensation for microgrids, which produce and distribute electric power to restricted areas. MgB2 material has been developed with superconducting properties by decreasing the production cost. Since hydrogen energy would be widely utilized to realize society with low carbon emission and stored in liquid state for reducing its volume, the power distribution system consisting of MgB2 SMES for compensation of voltage fluctuations cooled by the liquid hydrogen would be effective by synergy effect. However, the MgB2 introduction to large-scale devices is still not enough and under investigation. Our group carried out the investigations to develop MgB2 cable and pancake coil for the SMES device with specific capacity. The bending strain-sensitive characteristic of MgB2 material forces us to design the twisted conductors and pancake coils with various parameters properly within its tolerable bending strains of both before/after heat treatment. The conductor design for small pancake coils and large SMES coils is shown in this research, as well as the demonstration results of a small test coil fabricated as a prototype of SMES coil.

A superconducting transport solenoid for Decay Muon Line (D-line) at J-PARC Muon Science Facility was newly designed and manufactured. It was designed to generate a magnetic field in relatively large region (warm bore diameter 0.2 m), while keeping the same outer dimensions, connection interfaces to the existing refrigerator and the power supply of the previous machine [1-3]. Major changes of both solenoids are the reduction of the central magnetic field, the equipment of a warm bore and the adoption of the high T-c current leads. After the installation to the beam line, the initial cooling test, the excitation test and the emergency shutdown test at the rated current were conducted by KEK in order to confirm cryogenic and magnetic performance. These tests were successfully performed with no damege and indicated the solenoid was precisely manufactured and fulfilled the requirements. The solenoid has been under operation since July, 2015. This report describes the design, the manufacturing process, the magnetic field measurement at room temperature and the results of performance tests conducted by KEK.

A resistive type SFCL using REBCO tapes has high potential to limit fault currents quickly and to improve the reliability of a power system for its compactness and rapid increasing of resistance [1]. We have studied the thermal characteristics of a SFCL REBCO coil by numerical analysis using more precise analysis models. Influence of bubbles of boiling nitrogen is also considered in some cases. If bubbles are generated under fault conditions, a rapid local temperature rise may occur and even result in a permanent degradation of JC of REBCO layer. In this paper, we upgrade the previous FEM analysis model [2] for 3D thermal analysis of a REBCO coil in a resistive type SFCL (Fig.). Coupled problems of electromagnetic and thermal fields are solved for studying thermal characteristics of an SFCL REBCO coil immersed in liquid nitrogen. In computation of current distribution in the SFCL coil, a thin-plate approximation is applied to the REBCO tapes and FEM based on current vector potentials T is utilized. Current density J is defined by J=∇×T. The governing electromagnetic equation is given by ∇×(ρ∇×T)=∂B/dt (ρ: electric resistivity; B: magnetic flux density) [2]. In thermal analysis, the 3D structure of SFCL coil is modeled and the temperature rise is calculated under the condition of Joule heating, heat conduction, heat transfer, and cooling characteristics of liquid nitrogen.

To promote renewable energy sources, we proposed a new system called the Advanced Superconducting Power Conditioning System (ASPCS), which consists of Superconducting Magnetic Energy Storage-system (SMES), Electrolyzer, and Fuel Cell, and is also combined with a liquid hydrogen station for vehicles. The SMES plays a role to compensate the fast fluctuations generated by the renewable energies. In case of the ASPCS with a capacity of 5 MW, we designed the 50 MJ-class SMES composed of 4 solenoid coils. The winding of the solenoid coils is double pancake and a basic coil is 2 m in diameter and 0.5 m in height. Each SMES coil is wound with MgB2 conductor and indirectly cooled at 20K by liquid hydrogen flowing through a thermo-siphon cooling system. Pure aluminum strips are inserted between the double-pancake coils and the pure aluminum plates gathering the strips lead to liquid hydrogen pipes. This scheme enables the strips and the plates to transfer the heat load in the coils to the cooling pipes and keep the coils at low temperature. On the other hand, we must consider that the strips generate eddy current loss which is strongly affected by a width of the strips. At the same time as the primary study of the SMES coils, we experimented on the thermo-siphon cooling system and investigated the relationship between the heat load and the heat extraction ability of the cooling system. The experiments showed that the cooling system could proficiently function. The estimation of eddy current loss from the particular cooling aluminum strips for the SMES in the ASPCS is reported with the results of the thermo-siphon driving experiment.

Power generation by renewable resources that are environment friendly has been attractive lately. However, it is a big problem that the output fluctuation from the renewable energy sources causes instability to the power network when they are directly connected to the utility grid. Although a power storage system is effective for compensating for the output fluctuation, this electric power storage system must have large capacity and quick response. We proposed an advanced superconducting power conditioning system (ASPCS) composed of two kinds of power storage systems. In this paper, we experimentally verified the validity of the compensating system for fluctuating output power using a superconducting magnetic energy storage and an electronic load instead of an electrolyzer. It was demonstrated that the ASPCS was effective for compensating for the output fluctuation of the renewable energy.

From the point of view of environment and energy problems, the renewable energies have been attracting attention. However, fluctuating power generation by the renewable energies affects the stability of the power network. Thus, we propose a new electric power storage and stabilization system, Advanced Superconducting Power Conditioning System (ASPCS), in which a Superconducting Magnetic Energy Storage (SMES) and a hydrogen-energy-storage converge on a liquid hydrogen station for fuel cell vehicles. The ASPCS proposes that the SMES coils wound with MgB2 conductor are indirectly cooled by thermo-siphon circulation of liquid hydrogen to use its cooling capability. The conceptual design of cooling scheme of the ASPCS is presented.

In order to use effectively renewable energy sources such as wind and photovoltaic power generations, we propose a new system, called Advanced Superconducting Power Conditioning System (ASPCS), that is composed of superconducting magnetic energy storage (SMES), fuel cell-electrolyzer (FC-EL), hydrogen storage, dc/dc and dc/ac converters, and controller. The new system compensates the fluctuating electric power generations with SMES having characteristics of quick response and large I/O power and with hydrogen energy having characteristics of large storage capacity. The ASPCS will be combined with a liquid hydrogen station for FC vehicles. The SMES is a key component of the ASPCS to compensate the fast fluctuations of the renewable energy generations that cannot be compensated by prediction using the Kalman filtering method. The design study of the 50 MJ SMES coil was performed with an MgB2 conductor to be operated at 5 T maximum and 20 K by using liquid hydrogen of the FCV stations. The stability and ac losses of the coil were estimated in this study.

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 10(7) 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/c(2) (FWHM) was achieved for the Sigma peaks of (pi(+/-), K+) reactions on a proton target in the first physics run of E19 in 2010.