[en] Superconducting Y-Ba-Cu-O bulks with J_c as high as 30 kA/cm² (at 77 K and 1 T) containing both Y-123 and Y-211 phases were utilized in the present work. With different post-annealings, the authors obtained samples with different degrees of peak effect in the J_c -vs- H characteristics. Using specimens with TEM observable areas as wide as 20 x 20 (microm)², large-area high-resolution transmission-electron-microscopic (LA-HRTEM) observations were made for the samples with different degrees of peak effect. Statistical analyses were made for the size of Y-211 particles and the distance between adjacent twin boundaries. It is revealed that (1) Y-211 particles including those of very small diameters have nothing to do with the peak effect, while (2) the inter-twin-boundary distance is undoubtedly correlated with the degree of peak effect. Further investigation on the twin boundary structure indicates that lower Tc regions may be formed in the vicinity of twin boundaries to provide fluxions with mesoscopically distributed weak pinning centers

[en] The YBa₂Cu₃O₇ films were prepared on polycrystalline {1 1 0}<1 1 0> textured Ag substrates without any buffer layers using a MOD (metal organic deposition) method in various heat treatment condition. The Y:Ba:Cu cation ratio of the precursor solution was 1:2.6:4.5 molar ratio. The deficient of a Cu element was observed in the films prepared under a low oxygen partial pressure (p(O₂)=0.0002 atm). The amount of Cu element was decreased with increasing the annealing temperature. From X-ray pole figure measurements, we confirmed a weak biaxial crystal orientation in the YBCO films prepared on a {1 1 0}<1 1 0> textured polycrystalline Ag substrates at 900 deg. C for 2.5 h in air. On the polycrystalline {1 1 0}<1 1 0> textured Ag substrates, the observed epitaxial relationship with YBCO lattice is <1 1 0> YBCO parallel <1 1 0> Ag

[en] Superconducting magnetic bearing for flywheel requires the characteristics such as higher stiffness, lower loss and higher stability. There are two types of superconducting magnetic bearings, one is axial gap type and another is radial gap type and the characteristics of these types are quite different. We think that the supporting system of superconducting flywheel should support the rotor at one position near the center of gravity to minimize the cooling energy loss. We propose that the bearing composed of axial gap type and radial gap type is necessary from the result of this investigation, because the characteristics about both types of bearings should be compensated each other

[en] Superconducting flywheel usually adopts carbon fiber resin mold plastic (CFRP) material that has the basic characteristics such as higher strength and lighter weight. Stabilized rotation of flywheel requires lower unbalance individually about flywheel and supporting disc. And supporting disc is needed to steadily follow the expansion of the inside diameter on the flywheel by centrifugal force and keep the concentricity of the flywheel and its own rotating axis. We developed the flywheel rotor, which was composed of CFRP flywheel, and partially spherical supporting disc made of high strength aluminum. They were combined with expanse fitting each other and most precisely machined to realize the extremely precise axial symmetric shape and enable to be supported and driven at the point near the center of gravity. We manufactured and confirmed that the flywheel rotor rotated up to peripheral speed of 628 m/s quietly without permanent set

[en] Flywheel with superconducting magnetic bearings requires the characteristics for the motor/generator such as lower loss, higher efficiency, lower bearing load and more displacement tolerance of the radial directions. We developed an extremely flat shape axial gap type motor/generator which consists of a rotor with permanent magnets and slotless windings to satisfy these characteristics. We introduced the system for adjusting intensity of the excitation to decrease the eddy current loss during the storage and to get the controllability of electromotive force for variable speed operation during charging and discharging. We manufactured the motor/generator of output power 17 kW at 10,000 rpm. It was tested to perform the fundamental functions of motor and generator at partial speeds up to 4000 rpm

[en] A present Japanese national project for SMES development focuses on the development of cost reduction technologies for a small-scale SMES for power system control. Optimal SMES system concepts were developed for power system stabilization and for load fluctuation compensation or frequency regulation. Performance of the designed superconductors was analyzed through fabrication and tests of short sample superconductors. Then, two kinds of model coil systems were manufactured and tested for evaluation of the design concepts and cost reduction technology developments. A multi-pole solenoid coil set as a model coil system for load fluctuation compensation SMES was successfully tested, for example, in 10 000-pulse iterative charge-discharge operations. In addition, application of high-T_C superconductors to SMES has been studied for further cost reduction, more reliable operation, etc

[en] Textured Ag tape is one of the most ideal substrates for the next generation high-T_c wires operable in liquid nitrogen. {1 1 0}<1 1 0> textured Ag tapes were obtained by cold rolling and subsequent heat treatments. The texture of the tape after cold rolling (before annealing) was typical 'brass type'. For obtaining the {1 1 0}<1 1 0> texture, oxygen should exist in the Ag tape during the heat treatment. We find a two-step annealing is very effective to achieve the better {1 1 0}<1 1 0> textured Ag tape, compared with the samples annealed in one-step; the better grain alignment and the smoother surface could be obtained. Moreover, 300 deg. C annealing in O₂ atmosphere allow us to obtain the {1 1 0}<1 1 0> texture by only 3 min final heat treatment at around 800 deg. C. This is beneficial to achieve the higher production speed of YBa₂Cu₃O₇ coated conductors

[en] The segmental structure of bulk superconductor will be needed designing ultra-large scale high temperature superconducting magnetic bearing for MWh class superconducting flywheel. The N-S poles of permanent magnetic ring assembly were arranged alternately to radial direction and the influences to magnetic levitation and rotating characteristics of the separate position of bulk superconductor to radial direction were tested. It was found when the separate position of bulk superconductor was coincided with the joint of the N-S poles of permanent magnets, both the magnetic levitation and the rotating characteristics were the same as the case of non-separate superconductor. When its position was the center of one side pole of permanent magnets, the levitation was the same as the case of non-separate superconductor, but the behavior of rotating characteristics changed and the loss increased as compared with the case of non-separate type

[en] NdBa₂Cu₃O₇ (Nd-123) and YBa₂Cu₃O₇ (Y-123) films were fabricated on {1 0 0}<0 0 1> or {1 1 0}<1 1 0> textured Ag tapes by a pulsed laser deposition technique and a metal organic decomposition method using metal naphthenates solution. Good biaxial crystal orientations were achieved in the Nd-123 films prepared on the {1 0 0}<0 0 1> textured Ag tapes by the laser deposition technique. Biaxially oriented Y-123 films were also obtained on the {1 1 0}<1 1 0> textured Ag tapes by the pulsed laser deposition technique and a metal organic decomposition method. We obtained the prospect that the high deposition rate and the thickening the film will solve both the groove problem and the Cu diffusion problem when the textured Ag tapes were used as substrates for coated conductors

[en] We developed rectangular-shaped Bi-2212 conductors. At 4.2 K and 30 T, the 37- and 349-filament conductors exhibited J_C values of 151 and 125 kA/cm², respectively. Moreover, we measured the distribution of I_C for a 25 m-class 349-filament conductor. The end-to-end I_C value was 66 A at 63 K, self-field, and the variation in I_C was about ±10%. We also fabricated a test coil with 50 m-class, 349-filament conductor. The test coil carried 510 A (using a criterion of 10^-13 Ω m) and generated B₀=0.95 T at 4.2 K without backup field, resulting in a current density in the test coil of 150 A/mm². The coil performance was almost 80% that of a short sample with a magnetic field applied perpendicular to the tape surface