Hidekazu Teshima

Processing and properties of QMG materials

Abstract Recent progress of Quench and Melt Growth (QMG) process is reviewed. QMG process is one of the melt processes for Y based superconductor. A pseudo single crystal (QMG crystal) which includes finely dispersed 211 phase in the matrix of 123 phase was produced by the original QMG process. The critical current density of the QMG crystal that has no high angle grain boundaries has been exceeding 104A/cm2 at 77K and 1T. The original QMG process was improved to make larger QMG crystals of which crystallographic orientation was controlled. Modified QMG process can be characterized by Pt addition in precursor preparation and seeding technique in growth process. Crystallinity of the QMG crystal made by this modified process was investigated. It appeared that there were two kinds of domain structures that depend on the growth direction. QMG crystals enlarged by this modified process are applicable to various fields. For instance, QMG crystal can operate as a bulk magnet. The maximum value of flux density was 4.5T at 40K on the surface. It was found that QMG crystal is thermally stable above 40K at least.

Effect of eddy current dampers on the vibrational properties in superconducting levitation using melt-processed YBaCuO bulk superconductors

Abstract The effect of eddy current dampers on the vibrational properties in superconducting levitation has been investigated using melt-processed YBaCuO bulk superconductors. In vertical vibration, the damping was about 100 times improved by inserting eddy current dampers into the gap between a superconductor and a magnet. On the other hand, in horizontal vibration, eddy current dampers did not greatly affect the vibrationaal properties of superconducting levitation up to a given thickness of eddy current dampers.

Comparison of the levitation forces of melt-processed YBaCuO superconductors for different magnets

Abstract It is difficult to compare the levitation force of superconductors for different magnets. A new parameter, α, is proposed in this paper, which is defined as the ratio of a superconducting levitation force to the limitation force for a given magnet. Using this parameter, the comparison between different superconducting levitation forces in melt-processed YBaCuO superconductors (QMG) has been done, such as a levitation force of 269 kN/m2 (=2.74 kgf/cm2) for a superconductor 77.3 mm in diameter and a magnet of NdFeB 50 mm in diameter, and a levitation force of 260 kN/m2 (= 2.65 kgf/cm2) for a superconductor 46.5 mm in diameter and a magnet of PrFeBCu 36 mm in diameter. The former is α = 0.67 and the latter is α = 0.81.

Design and Performance of Transmit Filters Using HTS Bulk Resonators for IMT-Advanced Applications

A transmit band pass filter using circular-disk high-temperature superconductor (HTS) bulk resonators was designed with a 5.0 GHz center frequency and a 100 MHz bandwidth for use in international mobile telecommunication (IMT) advanced applications. The frequency response and electromagnetic field were calculated using a three-dimensional simulator. The mode of the resonator was used because it had the smallest diameter. Using stripline (SL) resonators enhanced both the unloaded quality factor and the coupling between the input/output ports and resonators. The frequency response of the designed SL 3-pole Chebyshev filter meets the requirements of IMT-Advanced applications. Additionally, the maximum surface current of the HTS bulk filter was approximately 86% less than that of a conventional hairpin filter.

Mechanical properties of Gd123 bulk superconductors at room temperature

Abstract In order to investigate the mechanical properties of Gd123 single-grain bulk superconductors fabricated using a modified quench and melt growth method, tensile tests in the direction parallel and perpendicular to the c -axis have been carried out at 293 K by using the small specimens cut from bulk superconductors. As for the mechanical properties perpendicular to the c -axis, there was no significant difference between those in the crystal growth direction and those perpendicular to it. While the average value of the Young’s modulus of the bulk sample with 33.0 mol%-Gd211 secondary phase particles, 118 GPa, was higher than that of the bulk sample with 28.7 mol%-Gd211, 111 GPa, the average value of the tensile strength of the former, 36 MPa, was lower than that of the latter, 40 MPa. The tensile strength and the Young’s modulus in the c -axis, 10 MPa and 37 GPa, were quite low compared with those mentioned above. Poisson’s ratio based on the transverse strain in the c -axis, 0.15, was significantly smaller than that perpendicular to it, 0.30. In the specimens with higher length, however, the difference was decreased to some extent. With regard to the anisotropy of the Poisson’s ratio, the effect of a pre-existing micro-crack opening in the c -axis direction was discussed coupled with the constraints at the interfaces between the specimen and the sample holder.

Materials processing and machine applications of bulk HTS

We report a refrigeration system for rotating machines associated with the enhancement of the trapped magnetic flux of bulk high-temperature superconductor (HTS) field poles. A novel cryogenic system was designed and fabricated. It is composed of a low-loss rotary joint connecting the rotor and a closed-cycle thermosiphon under a GM cryocooler using a refrigerant. Condensed neon gas was adopted as a suitable cryogen for the operation of HTS rotating machines with field poles composed of RE–Ba–Cu–O family materials, where RE is a rare-earth metal. Regarding the materials processing of the bulks HTS, thanks to the addition of magnetic particles to GdBa2Cu3O7 − d (Gd123) bulk superconductors an increase of more than 20% in the trapped magnetic flux density was achieved at liquid nitrogen temperature. Field-pole Gd123 bulks up to 46 mm in diameter were synthesized with the addition of Fe–B alloy magnetic particles and assembled into the synchronous machine rotor to be tested. Successful cooling of the magnetized rotor field poles down to 35 K and low-output-power rotating operation was achieved up to 720 rpm in the test machine with eight field-pole bulks. The present results show a substantial basis for making a prototype system of rotating machinery of applied HTS bulks.

Low-Thermal-Conductive

The thermal conductivity kappa(T), thermal diffusivity alpha(T) and thermal dilatation dL(T)/L of the DyBaCuO bulk superconductor have been measured. The ab-plane kappa of the bulk at 50 K is about one third of that of the YBaCuO bulk, and moreover, the superconducting characteristics (critical current density Jc and superconducting transition temperature Tc) compare favorably with those of the YBaCuO bulk. The current-voltage (I-V) characteristics of the current lead fabricated from DyBaCuO bulk and the durability against the thermal quenching are as good as those of the YBaCuO lead. The DyBaCuO bulk is a promising material for the power current lead use to be replaced for the YBaCuO bulk

rm DyBaCuO

Damping properties in superconducting levitation have been investigated using melt-processed YBaCuO bulk superconductors. The damping of superconducting levitation is so small that additional noncontact dampers are required for practical use of superconducting levitation. Eddy current dampers and superconducting dampers of sintered YBaCuO materials have been proposed and studied as additional noncontact dampers. The damping coefficient has been improved about 20-fold by combining a copper damper with superconducting levitation, and further enhancement can be expected.

Bulk Superconductor for Current Lead Application

Abstract This paper describes the numerical and experimental superconducting levitation forces of a single-grained Y-Ba-Cu-O bulk superconductor of approximately 48 mm in diameter. The experimental levitation forces were measured by changing the magnet radius systematically. It was found experimentally that the levitation force shows a maximum when the magnet radius is slightly smaller than the superconductor radius. Comparison of the experimental and numerical levitation forces showed that even large bulk superconductors have a macroscopic value of J c as high as 2.0 × 10 4 A cm −2 , not much different from the microscopic value of J c .

Combination of Additional Noncontact Dampers and Superconducting Levitation Using Melt-processed YBaCuO Bulk Superconductors

The power-handling capability and frequency responses of superconducting bandpass filters (BPFs) at a center frequency around 5 GHz with a 100-MHz bandwidth were investigated for application to transmit filters. A 3-pole BPF was designed using a Chebyshev function with three pairs of the bulk ring resonators and the dielectric trimming rods with the same dimensions. Using this design, we simulated the frequency responses of the filter with low loss and passband ripple, and by adjusting positions of trimming rods a fine tuning of the filter responses was achieved. The BPF was fabricated using ring resonators made from a DyBa2Cu3Oy superconducting bulk and a pair of Al2O3 substrates in a Cu cavity with trimming mechanisms using dielectric rods. The filtering property with low insertion loss was clearly observed at 25 K. Power-handling capability of the 3-pole BPF of over 10 W (40 dBm) was observed.