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Magnetic refrigeration technology is expected to be a highly efficient process at a temperature of around 20 K, which is the hydrogen liquefaction temperature. In magnetic refrigeration, a magnetic field change is applied to a magnetocaloric material (MCM) to obtain a magnetocaloric effect. In addition, since the greater the magnetic field change, the better the cooling characteristics, the magnetic field strength of permanent magnets is insufficient, and the use of superconducting coils that can generate strong magnetic fields with low power consumption is essential. We are researching and developing a static magnetic refrigeration system (SMRS) that does not have moving parts to obtain magnetic field changes, and generates them by altering the energizing current to the coil. The key to devising this system is an AC loss of the superconducting coil. In this study, we measured the AC loss under energization conditions of multiple palm-sized REBCO coils at liquid nitrogen temperature, and calculated the efficiency of the SMRS by improving the accuracy of the analysis method for evaluating the AC loss, based on the results. We report the results and discuss the technical feasibility of SMRS., source:N. Hirano, Y. Onodera, T. Mito, Y. Motoki and A. Kawagoe, "Basic Research on a Magnetic Refrigeration System for Cooling to Liquid Hydrogen Temperature," in IEEE Transactions on Applied Superconductivity, vol. 33, no. 5, pp. 1-5, Aug. 2023, Art no. 4702605, doi: 10.1109/TASC.2023.3263786., source:http://doi.org/10.1109/TASC.2023.3263786, identifier:0000-0002-1565-8353

To evaluate the hysteresis loss in stacked HTS tapes for large current-carrying conductors, a single REBCO tape and 50 stacked REBCO tapes were modeled with the finite element method, including T-A formulation. Using the model, hysteresis losses in the single and stacked tapes were calculated under a condition that the direction of an external varying magnetic field was perpendicular to the tape plane. The calculation results were in good agreement with the measurement results. Consequently, the developed models are valid for a hysteresis loss calculation. In addition, we investigated magnetic field penetration into the stacked tapes using the model. The investigation shows that the external varying magnetic field used in the measurements cannot penetrate the center of the stacked tapes., source:https://doi.org/10.1585/pfr.18.2405013, identifier:0000-0002-1989-867X

In this work, stacked model conductors consisting of dozens of YBCO tapes were fabricated and experimentally investigated to determine whether the hysteresis and coupling losses affect each other. When an oblique magnetic field is applied to the tape, hysteresis and coupling losses are expected to be generated simultaneously. A uniform AC transverse magnetic field was applied to the sample in liquid nitrogen, and the AC losses were measured via the pickup coil method. The measurements were carried with the magnetic field applied at various angles with respect to the tape wide surface. The measured AC losses were separated into hysteresis and coupling losses. The measured hysteresis losses well agreed with the theoretical values for a square cross-section superconductor. This indicates that hysteresis losses can be considered in terms of the magnetic field component perpendicular to the flat face of the YBCO tape. The coupling time constant was found to be independent of the applied magnetic field angle. This shows that coupling losses can be considered in terms of the magnetic field component parallel to the tape's wide surface, and the permeability in the conductor can be assumed to be the vacuum permeability., source:https://doi.org/10.1585/pfr.16.2405071, identifier:0000-0003-3100-6328

It is expected to build a sustainable social system that uses “hydrogen” as a fuel to generate electricity without emitting CO2. To realize this, technology for storing a large amount of hydrogen is indispensable, and storage as liquid hydrogen is ideal. However, the efficiency of the cooling device in the temperature range around 20 K required for long-term storage with liquid hydrogen is low, and the equipment is huge and expensive, so it has not been established as a widely used technology. Magnetic refrigeration is expected to be a highly efficient refrigerator in the temperature range of around 20 K because it can realize an ideal refrigeration cycle. However, in magnetic refrigeration, it is necessary to give a magnetic field change to the magneto caloric material (MCM). Further, in order to perform cooling with a large capacity and extremely low temperature by magnetic refrigeration, the magnetic field strength of a permanent magnet is insufficient, and it is indispensable to use a superconducting coil capable of generating a strong magnetic field with low power consumption. This study aims to develop a static magnetic refrigeration system using multiple high-temperature superconducting coils. By utilizing the energy storage characteristics of the superconducting coil, we are considering a magnetic refrigeration system that can repeatedly generate magnetic field changes to save energy without the need for large amounts of energy to be taken in and out of the outside. We report on the technical feasibility of a static magnetic refrigeration system using HTS coils. The power consumption including the AC loss of two superconducting coils, which is the basic configuration of the static magnetic refrigeration system, is calculated, and the efficiency is estimated as a ratio to the assumed refrigeration capacity of the MCM., source:N. Hirano, Y. Onodera, T. Mito, Y. Ueno and A. Kawagoe, "Development of Static Magnetic Refrigeration System Using Multiple High-Temperature Superconducting Coils," in IEEE Transactions on Applied Superconductivity, vol. 32, no. 6, pp. 1-5, Sept. 2022, Art no. 0500105, doi: 10.1109/TASC.2022.3152456., source:https://doi.org/10.1109/TASC.2022.3152456

This study is aimed at the development of high-temperature superconducting (HTS) magnets for application in a fusion experimental device next to the Large Helical Device (LHD). By applying the features of an HTS, high current density and high stability can be balanced. As a candidate conductor, REBCO tapes and pure aluminum sheets are laminated and placed in the groove of an aluminum alloy jacket with a circular cross-section, after joining a lid to the jacket using friction stir welding, and twisting the conductor to homogenize its electrical and mechanical properties. The FAIR conductor derives its name from the processes and materials used in its development: Friction stir welding, an Aluminum alloy jacket, Indirect cooling, and REBCO tapes. Initially, the degradation of the critical current of the FAIR conductor is observed, which was eventually resolved. The development status of the FAIR conductor has been reported., source:Toshiyuki Mito et al 2020 J. Phys. Commun. 4 035009, source:https://doi.org/10.1088/2399-6528/ab7954, identifier:0000-0002-1705-9039

As a high-temperature superconducting (HTS) conductor with a large current capacity applicable to a nuclear fusion experimental device, REBCO (REBa 2 CuO y ) tapes and high-purity aluminum sheets are alternately laminated, placed in a groove of an aluminum alloy jacket having a circular cross section, and the lid is friction-stir welded. To make the current distribution and mechanical characteristics uniform, the conductor is twisted at the end of the manufacturing process. In the early prototype conductor, when the I c was measured in liquid nitrogen under self-magnetic field conditions, I c degradations were observed from the beginning, and the characteristic difference between the two prototype samples under the same manufacturing conditions were large. Furthermore, I c degradation was progressed by repeating the thermal cycle from room temperature to liquid nitrogen temperature. This I c degradation did not occur uniformly in the longitudinal direction of the conductor but was caused by local I c degradation occurring at multiple locations. If the conductor was not manufactured uniformly in the longitudinal direction, the difference in thermal shrinkage between the REBCO tape and the aluminum alloy jacket caused local stress concentration in the REBCO tape and buckling occurred. Element experiments to explain this mechanism were conducted to clarify the conditions under which I c degradation due to buckling occurs. Then prototype conductors were tested with improved manufacturing methods, and as a result, I c degradation could be suppressed to 20% or less. We have achieved the prospect of producing a conductor with uniform characteristics in the longitudinal direction., source:T. Mito et al., "Improvement of Ic degradation of HTS Conductor (FAIR Conductor) and FAIR Coil Structure for Fusion Device," in IEEE Transactions on Applied Superconductivity, vol. 31, no. 5, pp. 1-5, Aug. 2021, Art no. 4202505, doi: 10.1109/TASC.2021.3069923., source:https://doi.org/10.1109/TASC.2021.3069923, identifier:0000-0002-1705-9039

Highly efficient liquid hydrogen storage system is studied with magnetic levitation using high-temperature superconducting (HTS) coils. The system also has high safety in case of emergency, such as an earthquake, with a seismic isolation to absorb vibrations provided by HTS levitation coils setup on the ground side. In such an emergency case, it is considered that a large amount of ac losses are generated in HTS coils, and the winding temperature may rise to lead to a coil quench. In this study, the self-oscillation-type heat pipe (OHP), whose thermal transport property is much greater than that of solid thermal conduction, is used to cool the coil windings. As a result, an HTS coil equipped with an OHP cooling system can be realized, supporting both low heat loads in the usual operation and high heat loads in an emergency., source:T. Mito et al., "Highly Efficient Liquid Hydrogen Storage System by Magnetic Levitation Using HTS Coils," in IEEE Transactions on Applied Superconductivity, vol. 27, no. 4, pp. 1-5, June 2017, Art no. 3600705, doi: 10.1109/TASC.2017.2653228., source:https://doi.org/10.1109/TASC.2017.2653228, identifier:0000-0002-1705-9039

We have proposed a new method for detecting unusual local conditions in a high-temperature superconducting coil. In this method, two kinds of pick up coils for measuring electric fields and magnetic fields are used to obtain Poynting's vectors around the coil. This is a noncontact method using pick-up coils around the vessel for cooling the coil. The method has the following benefits: safe detection, easy handling, high sensitivity, and high usability. The purpose of this paper is to clarify the relation of measured signals to the conditions of the windings. When a temperature rise has been produced locally in the Bi-2223 solenoidal coil, Poynting's vectors around the coil and the temperature of windings were measured. It was found that the measured signals rapidly decrease as the temperature of the winding achieved a critical level, making this a reliable method to estimate the conditions in the windings.