S. Fuchino

Running Performance of a Pinning-Type Superconducting Magnetic Levitation Guide

A pinning-type superconducting magnetic levitation guide with bulk high-Tc superconductors was studied for use as a goods transportation system, an energy storage system, etc. A superconducting magnetic levitation running test apparatus with a circular track of ca. 38 m length, 12 m diameter, which comprises the magnetic rail constituted by Nd-B-Fe rare-earth permanent magnets and steel plates, was manufactured to examine loss and high-speed performance of the magnetic levitation guide. Running tests were conducted in air. These tests clarify that a vehicle supported by a superconducting magnetic levitation guide runs stably at speeds greater than 42 km/h above the circular track.

Feasibility of a goods transportation system with a superconducting magnetic levitation guide – load characteristics of a magnetic levitation guide using a bulk high-Tc superconductor

Abstract This paper proposes a goods transportation system with a pinning-type superconducting magnetic levitation guide setting in a vacuum passage and describes the system outline. Load characteristics of the superconducting levitation guide used this system are analyzed by a newly developed electromagnetic field analysis program; then, it is evaluated for whether it has sufficient load characteristics as a non-contact guide for this system. Calculation results show that the superconducting levitation guide has sufficient levitation force in the large gap, which become an effective space for thermal insulation between the magnetic rail at room temperature and superconductors cooled to cryogenic temperatures. Comparison between calculated and measured values was done to examine program validity in a small model; it showed good agreement both quantitatively and qualitatively.

Hydraulic characteristics in superconducting power transmission cables

The hydraulic characteristics of sub-cooled nitrogen in superconducting power transmission line have been investigated to design the transmission line. To estimate the friction factor in corrugated pipes, the pressure drop was measured across a 10-m length corrugated pipe for various mass flow rates and compared with that in smooth pipes (Proc. 17th Cryo. Eng. Conf. (1998) 475). Another concern is the cooling method of the transmission line. A usual counter-flow cooling method has been found to be very difficult at liquid nitrogen temperature, because the thermal conductivity of the dielectric materials between the counter-flows at liquid nitrogen temperature are 10 times larger than that at liquid helium temperature. Instead, an externally cooling method was proposed (Proc. 17th Cryo. Eng. Conf. (1998) 475). As the results, the friction factor of outer corrugated jacket within three cables has become an important parameter to design the transmission lines. This friction factor is measured and compared with various formulas in this paper.

Characteristics of high-stiffness superconducting bearing

Magnetic bearings using a high-Tc superconductor have been studied. Generally the bearing makes use of the pinning effects to get the levitation force. The stiffness of the bearing, however, is extremely low as compared with industrial-scale conventional one. To improve the bearing stiffness we propose a disc-type repulsive superconducting thrust bearing with a slit for the restraint of the flux. Both theoretical and experimental evaluation on the load performance was carried out, and it is clarified that the proposed superconducting bearing has higher stiffness.

Numerical analysis of a superconducting bearing

High-Tc superconducting bearings are expected as a key technology for flywheel energy storage systems (FWES). However, low bearing stiffness behavior becomes a serious obstacle to realize FWES. We have so far suggested various kinds of bearing construction to improve the bearing stiffness, but the various improvements of superconducting bearings bring complicated magnetic circuit structure, which makes the analysis of the bearings and realization difficult. For this reason, we have been constructing the numerical analysis program using three-dimensional sealer potential method based on the critical state model to proceed with the stiffness improvement study. In this paper, we show the validity of the developed program for the disc-type superconducting bearing, which consists of a superconductor and a permanent magnet. This means that we can estimate the behavior of real size superconducting bearings for FWES.

Heat transfer characteristics of liquid nitrogen for cyclic heating

Bubble formation and the critical heat flux to transit to boiling state for cyclic heat inputs have been investigated using a platinum - 0.5at% cobalt (Pt-Co) wire and a silver sheathed Bi-2223 tape, in order to evaluate the cooling stability for superconducting AC power apparatus. Sinusoidal cyclic heat inputs ranging from 2 to 150 Hz were applied to a horizontal thin wire immersed in a pool of saturated liquid nitrogen under normal atmospheric pressure. A high-speed video camera with a frame speed of 1000 frames/s has been used to observe bubble formation around the wire. The bubble frequency and the critical heat flux to transit to boiling state have been measured for each frequency. As a result, it has been found that the bubble frequency and the critical heat flux have depended on the heating frequency. The same experiment has been performed on a silver sheathed Bi-2223 tape, however, the mechanism of bubble formation is different. The dependence of the critical heat flux on the heating frequency has been also observed.

Transient Heat Transfer Characteristics of Liquid Helium in Centrifugal Acceleration Field

Transient heat transfer of liquid state helium in centrifugal acceleration fields up to 1300G have been investigated for studying the stability characteristics of the rotor field windings of a superconducting generator. In the experiment, temperature resistive platinum-0.5% cobalt (Pt-Co) thin wire was used as the temperature sensor and heater to measure the heat transfer characteristics. The thermal mass of the Pt-Co wire was small enough to observe the temperature fluctuation due to bubbling in the boiling heat transfer. In this paper, influence of the centrifugal acceleration on the transient heat transfer and its mechanism are discussed based on the experimental results. It was observed that, for step heating with heat flux higher than maximumheat flux at steady state nucleate boiling, quasi-nucleate boiling appeared also in centrifugal acceleration field at the beginning of the heating, and that duration of the quasi-nucleate boiling was not much dependent on the acceleration field for relative high heat flux. This phenomenon was explained by bubble formation process in the boiling heat transfer. In this study, a high speed video camera was used to observe the relation of the bubble formation process and the temperature fluctuation of the Pt-Co wire in the normal gravity.

Medical protein separation system using high gradient magnetic separation by superconducting magnet

A high gradient magnetic separation system for medical protein using affinity magnetic nano-beads has been developed. Medical protein such as monoclonal antibody or immunoglobulin is an important substance as a medicine for cancer etc. However; the separation system of these medical protein has very low separation rate and the cost of product is extremely high. The developed system shows very high separation efficiency and can achieve low cost by large production rate compared to the system now using in this field. The system consists of a 3T superconducting magnet cooled by a cryo-cooler, a filter made of fine magnetic metal wires of about 30μm diameter and a demagnetization circuit and a liquid circulation pump for solvent containing medical protein. Affinity magnetic nano-beads is covered with the medical protein after agitation of solvent containing the protein and nano-beads, then the solvent flows through the system and the beads are trapped in the filters by high gradient magnetic field. The beads are released and flow out of the system by the AC demagnetization of the filters using LC resonance circuits after discharge of the magnet. The test results shows 97.8% of the magnetic nano-beads in pure water were captured and 94.1% of total beads were collected.

Measurement of Losses of Current Leads With Bi2223/Ag Tape Conductors Above Liquid Nitrogen Temperature

We measured the heat flow of current leads used for high-Tc superconducting apparatuses operating at liquid nitrogen temperature by the nitrogen boil-off method. To reduce the heat flow at the cold end of the current leads, the use of commercial Bi2223 silver-sheathed (Bi2223/Ag) tape conductors for current leads above liquid nitrogen temperature was also studied. We derived average Lorenz numbers between room temperature and liquid nitrogen temperature from the measurement results to assess the performance of the current leads. We tested Bi2223/Ag-soldered oxygen-free copper leads and obtained slightly lower heat flows and average Lorenz numbers than those of solid copper leads. The average Lorenz numbers of copper alloys were measured as well.

Cooling Characteristics in Long Channels with Sub‐cooled Nitrogen

When designing a superconducting power cable, it is very important to investigate its cooling characteristics. Therefore a proportionally reduced cooling model was constructed at about 1/10 of the real‐scale cable in length and diameter, and basic data about the initial cooling characteristics, pressure drop characteristics, and cooling instability were acquired. Then, the cooling characteristics for a real‐scale cable were estimated from these basic ones.