High-performance Magnetic Bearings using Field Shaping Function of Bulk Superconductors

本研究利用超导体的磁场整形功能，在小型实验装置上研究超导磁轴承的静态与动态特性。小型实验装置由用于产生磁场的Bi-2223超导线圈、用于场整形的YBCO超导体和作为转子的铁元件组成。超导线圈和超导块材由GM制冷机直接冷却。线圈中心处的最大磁通密度约为0.8T。使用该设备测量基本特性：冷却特性、超导线圈的激励、大块超导体的场成形特性、场成形材料的分割结构的影响、电磁力等，这些特性与数值分析的结果进行了比较，超导磁轴承的电磁力和旋转损耗特性及其与几个参数的关系例如磁通密度。由于旋转振动的共振，最大旋转速度低至9000 rpm，并且旋转损失大于预期。这是因为用于场整形的块体超导体的超导性质在更高的场中恶化，这几乎被数值分析所证实。因此，提高超导体的临界电流密度，提高超导体内部和超导体之间的超导特性，对于提高超导磁轴承的性能，使其成为更实用的低损耗轴承具有重要意义。

In this study, static and dynamics characteristics of superconducting magnetic bearings using field shaping function of bulk superconductors have been examined with a small-scale experimental equipment. Then its application as low-loss bearings for large high-speed rotating machines and further improvement of the characteristics have been discussed.The small-scale experimental equipment consists of Bi-2223 superconducting coil for magnetic field generation, YBCO bulk superconductors for field shaping, and an iron component as a rotor. The superconducting coil and the bulk superconductors were directly cooled down by a GM refrigerator. The maximum flux density at the center of the coil was about 0.8 T. Fundamental characteristics were measured using this equipment: Cooling characteristics, excitation of the superconducting coil, field shaping characteristics of the bulk superconductors, influence of division structure of the field shaping material, electromagnetic forces, etc. These characteristics were compared with the results of numerical analysis, which indicates fairy good agreement between them.Characteristics of electromagnetic force and rotational losses of the superconducting magnetic bearing and their dependence on several parameters such as the magnetic flux density were measured. The maximum rotational speed was as low as 9000 rpm due to the resonance of rotational vibration and the rotational losses were larger than expected. This is because superconducting properties of the bulk superconductors for field shaping were deteriorated in a higher field, which was almost confirmed by numerical analysis. Therefore, the increase of critical current density of the bulk superconductors and homogeneous and uniform superconducting properties in each superconductor sample and among superconductors are important to improve the performance of the superconducting magnetic bearings and to develop them as more practical low-losses bearings.