Makoto Okano

Characteristics of the magnetic gear using a bulk high-Tc superconductor

A magnetic gear which can transmit force without contact has operational benefits of requiring neither vibration, noise, nor lubrication. Still, its transmission force is considerably smaller than a mechanical gear. Strong magnets are needed to improve magnetic gear transmission force. For this purpose, a magnet formed by the pinning effect in a bulk superconductor might have magnetic flux density several times stronger than rare-earth permanent magnets. We propose a noncontact magnetic gear using a bulk high-Tc superconductor. In this paper, a three-dimensional electromagnetic field analysis program has been developed to analyze characteristics of the proposed gear. Two superconducting magnetic gears with different magnet configuration are manufactured, and their characteristics are measured. The analysis and the experiment explore the possibility of a magnetic gear using the pinning magnet formed in the superconductor.

Magnetic rail construction for a low loss superconducting magnetic levitation linear guide

A pinning-type superconducting magnetic levitation linear guide which consists of bulk high-T/sub c/superconductors and a magnetic linear rail with permanent magnets and steel plates was investigated for a goods transportation system, an energy storage system, and other uses. This paper describes the loss of this linear guide and a construction of the magnetic linear rail in which no inhomogeneous magnetic field is generated in a comparatively large gap in a long distance configuration. The loss is evaluated analytically by a newly developed electromagnetic analysis program. This proposed magnetic rail construction suppresses inhomogeneous magnetic fields generated by the existence of such spaces as temperature change countermeasures. We performed analyses and experiments on this construction. Results show that calculated and measured values concur well both quantitatively and qualitatively, proving that the proposed magnetic linear rail shows magnetic field distribution that is uniform in the running direction in the required gap.

Characteristics of a Superconducting Magnetic Bearing.

Both repulsive and attractive forces caused by the pinning state where a magnetic field is trapped in a superconductor are capable of noncontact steady support of an object in all directions. This paper describes the characteristics of the levitation forces, the force relaxation caused by the flux creep and the bearing loss under high rotational speed on a disc-type superconducting bearing at 77K, as well as the rotational characteristics of the pinning-type superconducting radial bearings. The bearing consists of Y1Ba2Cu3Ox(YBCO) oxide superconductors fabricated by the QMG (quench-melt-growth) process and rare-earth permanent magnets. The rotor with permanent magnets supported by the pinning force in the superconductor can be safely operated under high rotational speed.

Investigation of mixed convection caused by centrifugal acceleration

Abstract In this paper, the influence of a macro-flow, which is some kind of natural convection caused by heat-in leak in rotational cryostats, has been investigated. A cooling channel unit which has a main flow counter to the buoyancy direction has been made to simulate the macroflow influence. A high-speed camera have been used to observe the transient local convection. Also a thin film thermometer has been used to detect the transient temperature variation. As the result, some fluctuation caused by the macro-flow has been observed in the transient convection. The degradation of the transient temperature variation and steady heat transfer have been measured.

Study on Magnetically Levitated Conveying System Using Hybrid-Magnetized High

As an application of superconductors, we propose a magnetically levitated conveying system for clean rooms or vacuum chambers of semiconductor manufacturing industry. By using the pinning effect of superconductors, it is possible to make a stable levitation system without any mechanical contacts. This system consists of a levitated conveyer and a pair of magnetic rails. Considering a practical use of magnetically levitated conveying system, it is necessary to change levitation forces and stiffness. In this paper, we tried to apply pulsed-field magnetization (PFM) to improve the system. Moreover, dynamic characteristics of the levitated system are discussed to verify the effect of PFM for the system.

T{\rm c}

A superconducting fault current limiter (FCL) is one of the most useful devices to stabilize the electric power network system. And many types of superconducting FCLs have been proposed and developed. For the superconducting FCL, a normal phase transition phenomenon is the most important and fundamental function to increase FCL impedance, but it thermally shocks the device and brings excessive heat load to the refrigerator. The diode-bridge type of FCL is known as a superconducting FCL that does not require a direct normal phase transition in the function; the excessive current may actually trigger the current quench of the superconducting magnet. Therefore the elaborating technology against the normal phase transition must always be considered for any type of superconducting FCL. To solve the phase transition problem of the superconducting FCL, we propose a nonquench type of superconducting FCL in this paper. The proposed FCL belongs to the LC resonance-type FCL, and superconducting magnet current in the FCL can operate under a limited value by an arrester, which makes nonquench operation possible. This paper mainly describes numerical analysis and shows the validity of the proposed FCL by means of a small experiment.

Superconductors

Publisher Summary This chapter studies the influence of the surface roughness on nucleate boiling. The surface roughness in nucleate boiling is known to be an important parameter. It would trap foreign particles or gas which constitutes nucleation sites and liquid can be superheated inside the small cavities until the molecules attain the energy of vapor phase. This behavior is significant for room-temperature liquids because changes in the rms (root mean square) roughness values are known to affect the surface excess temperatures ΔT above the saturation temperature of the bulk liquid. Optimum surface conditions, however, are desirable for efficient cooling in some components of liquid-helium cryosystems. Therefore, it is very important to investigate the influence of the surface roughness in liquid helium nucleate boiling.

Possibility of A Nonquench Type Superconducting Fault Current Limiter

The effect of high gravitational field on superconducting properties was investigated on Bi(Pb)SrCaCuO thin films prepared by rf magnetron sputtering on MgO substrates. The gravity acceleration was applied to the samples during oxidation and annealing of the films in a rotating furnace in air. The high gravitational acceleration ranging from 1 G to 3500 G, where G is measured in a unit of 9.8 m/s2, resulting from centrifugal force was produced by rotating the furnace with high rotational speed. The experimental results have shown a tendency that the superconducting critical temperature increased by applying the high gravitational acceleration.

Influence of Surface Roughness on Transient Nucleate Boiling of Cryogens

Many projects starting in the 1960s, MHD and nuclear fusion projects, etc., demanded helium refrigerators with large capacity, high efficiency and excellent reliability. The rotating machine is essential to such systems. Since then, the rotating machines has been developed to realize large scale helium refrigerators. In this paper, the conception and the criterion design of rotating machines for the systems are described.