Yoshiki Miyazaki

Temperature Dependency of Levitation Force and Its Relaxation in HTS

High-temperature superconductors (HTS) have high potential for various engineering applications such as a superconducting flywheel energy storage system. The attractive feature of the superconducting magnetic bearings in the energy storage system is a reduction in the rotational loss. In this study, we studied the feasibility of a superconducting magnet to support bulk superconductors in magnetic bearings with the aim of increasing the stored energy. The superconducting magnet has a room temperature bore of 100 mm with the maximum magnetic field of 3.5 T. In addition, we used a GM freezer (10 K in the lowest attainment temperature), which can control the temperature of the bulk superconductors. The used bulk samples were Y-Ba-Cu-O and Sm-Ba-Cu-O 46 mm in diameter and 15 mm in thickness fabricated with a top-seeded melt-growth process. We have studied the effects of the temperature and magnetic field on the levitation force and its time relaxation. The levitation forces were measured by applying the magnetic fields of 0-2 T at 10-77.3 K. It was found that the levitation force increased with lowering temperature in both samples. The time relaxation of the levitation force was also reduced with lowering temperature. Sm-Ba-Cu-O exhibited better performance in the levitation force and its time relaxation in a high temperature and high-field region.

Discussions About Measurement Results of Levitation Force and Its Time Relaxation Between GdBCO Bulk Superconductors and Superconducting Magnet With a High Magnetic Field Gradient

High temperature bulk superconductors have significant potential for various engineering applications such as a flywheel energy storage system. This system is expected to decrease the energy loss by using bulk superconductors for the bearing. Recently, the authors have developed a new superconducting magnet to realize the large levitation force. The magnet has two coils on the same axis and each coils current flows to the opposite direction. In this system, the axial component of magnetic field is canceled each other but the radial component of magnetic field is expected to be enhanced. In this paper, the authors measured the levitation force and its time relaxation at different bulk positions in both cases of one and two bulks by using this new magnet. From the results, it was made clear that the levitation force of two bulks was twice as large as that of one bulk and its time relaxation was decreased. In addition, Hall sensors were attached on the sample surface to measure the surface magnetic field distribution. The behavior of the magnetic field was discussed.

Detection of White Layer on Rail by Using SQUID

White layers, which often cause a break of a rail, are generated on its top surface when train wheels spin on it. Therefore its early detection of damaged conditions of the rail that may lead to a break is a critical activity in the rail maintenance. In this study, we have developed an effective method to detect the white layer on the top surface of the rail by using a Superconducting Quantum Interference Device (SQUID).

Study of Magnetocaloric Refrigerator on Room Temperature for Air Conditioners of Railway

This study aims at practical use of a cooling technology using a magnetocaloric effect for the purpose of energy saving of air conditioners of railway. A method to cascade magnetocaloric materials having the different temperatures is suggested to obtain an operating temperature required by air conditioner because a work point of the magnetocaloric material is limited to temperature around the Curie point of the material. La(Fe0.84Co0.06Si0.10)13 has an operating temperature that is lower than Gd. Accordingly, a magnetocaloric refrigerator system which has a magnetocaloric material of La(Fe0.84Co0.06Si0.10)13 is reported in this paper.

Preliminary study of HTS magnet using 2G wires for maglev train

There are several advantages by applying a high temperature superconducting wire to an on-board superconducting magnet for the maglev train. At first, an increase of thermal capacity of superconducting coils contributes a stability of the superconducting state of the coils. In addition, a reliability of superconducting magnet improves by simplification of the magnet structure. And the weight of the superconducting magnet and the energy consumption of the on-board cryocooler will decrease. Therefore, we examined the possibility on application of the 2G wire with a high critical current density in a high magnetic field. We performed numerical analysis regarding the weight of a superconducting magnet and the energy consumption of an on-board cryocooler in consideration of the characteristics of the 2G wire. Furthermore, we have carried out the Ic measurement for the commercial 2G wires under various experimental conditions such as temperature, magnetic field strength and angle. We also performed the trial manufacture and evaluation of Ic characteristics for the small race track-shaped superconducting coil.