Shuetsu Haseyama

Characteristics of lift and restoring force in HTS bulk-Application to two-dimensional maglev transporter

One of the advantages of magnetic levitation using a high-temperature superconducting (HTS) bulk is that stable levitation can be achieved without any control systems. The authors have been investigating the electromagnetic behaviors of an HTS bulk to realize a two-dimensional magnetic levitating transporter without any fixed guides. The characteristics of lift and stability are key parameters to design and optimize such a device. They measured the lift and the restoring force of a YBCO bulk, displaced by a distance in lateral direction, for various field-cooling conditions and permanent-magnet arrangements. Both lift and restoring force are closely related to the air gap in the field-cooling process, distance between the permanent magnets, number of permanent magnets, and permanent magnet arrangement, that is, external magnetic field distribution. The most suitable arrangement of permanent magnets depends on the required levitation height and the weight of the levitating part. It can be considered that the size of the levitating part and geometry are also very important to determine the optimal arrangement in the maglev device.

Bi-2223 large sized magnetic shield prepared by jointing sintered bulks

Abstract In order to fabricate large sized superconductor plate shielding magnetic field above several mT, small pieces of sintered bulk were jointed with superconductor paste prepared with mixture of calcined powder and organic vehicle. Thirteen Bi-2223 four-cornered bulks were jointed superconductively to 40 mm 2 and 4 mm thick plate. The magnetic shielding property was measured at 77 K. Uniform magnetic field was applied perpendicular to the plate surface. Two-dimensional distribution of the magnetic flux density over the sample surface was measured by a Hall prove parallel to the sample surface. When magnetic field of 15 mT was applied to the sample, the magnetic flux penetrated the sample along the jointed line. Magnetic shielding effect of the sample was observed uniformly with the external magnetic field of 10 mT.

Microwave Surface Resistance of Bi 2Sr 2CaCu 2Ox Thick Films on Large-Area Metallic Substrates

As a feasibility study for application of a high-T c material to an accelerator cavity, Bi2Sr2CaCu2Ox thick films were formed on large-area metallic substrates. The microwave surface resistance of the films was measured over a temperature range from 4.2 K to 300 K using a demountable cylindrical copper cavity operated at 3 GHz in the TE011 mode. The area of the end plate was 177 cm2 and the thickness of the films was around 50 µm. The films were formed either on silver foils (on copper) or on a silver plate, coated by either a screen-printing or a spray-coating method, sintered either in air or in a Bi2O3 atmosphere, both at 885–890°C, and either annealed in nitrogen gas at 600°C or not annealed. The ratio of the microwave surface resistance of the best film to that of the copper was 0.18 at 10 K and 0.65 at 77.3 K. A comparison of the microwave surface resistance is made between Bi2Sr2CaCu2Ox and YBa2Cu3O7-x films.

Temperature and Magnetic Field Dependences ofFlux Pinning Force in High-Tc Superconductor Tl2Ba2Ca2Cu3Ox

The magnetic flux pinning force in Tl 2 Ba 2 Ca 2 Cu 3 O x high- T c superconductor ( T c =120 K) were measured as functions of temperature and magnetic field by using a torque magnetometry. The magnetic torque curves exhibit a large rotational hysteresis accompanied with a delayed angle for the rotation of applied magnetic fields. The number density of fluxoids and the pinning force acting on the fluxoids were estimated using a combined model with the Bean model and the Silcox-Rollins model for low and high magnetic field regions, respectively. The pinning force depends on the temperature as (1- t 2 ) 15/2 , where t is a normalized temperature by 80 K. Above 80 K, the pinning force is too small to be observed, and it indicates that the fluxoids may become into a flux flow state.

Microstructure of Bi-2223 Phase in oxide/Ag Multi-Layered Bulk

Bi-2223 is suitable to be applied under low field and near liquid nitrogen temperature. Jc value of the bulk materials is much smaller than that of the wire and tape materials. This should limit application field of the bulk. Then, we tried to improve Jc properties of Bi-2223 bulk by inserting Ag sheets into oxide. It was found that Jc values of the multi-layered bulk were improved in proportional to the number of Ag sheets. We investigated the microstructure of the Bi-2223/Ag multi-layered bulk. As a result, good alignment and dense structure of the oxide phase was observed near the interface between Bi-2223 layer and Ag sheet.

Electromagnetic behavior on high-temperature superconducting bulk YBCO exposed to time-varying magnetic field

The authors present the results of a comprehensive study of the electromagnetic behavior of high-temperature superconducting bulk YBCO exposed to a time-varying magnetic field. The characteristic of the trapped magnetic flux is one of the key factors in the application of a high-temperature superconducting bulk, such as magnetic levitation systems, rotors of motors and bulk magnets. The time inconstancy of trapped flux, such as flux creep, is especially undesirable for its application system. The relationship between a time-varying external magnetic field and trapped flux is investigated experimentally using a field-cooled (FC) YBCO disk. The magnetic flux density just above the disk is measured by Hall probes lined up along the disk radius. The magnetic field decay, which may be independent of flux creep, is observed in the experiment and is influenced significantly by the frequency and amplitude of the AC external magnetic field. The effect of changing rate of applied magnetic field in field-cool process on trapped flux is also investigated experimentally.

Jointing of Bi-2223 sintered bulk using superconductor paste

Abstract In order to fabricate large sized superconductor bulk, small pieces of sintered bulks were jointed using superconductor paste prepared with mixture of calcined powder and organic vehicle. The superconductor paste was sprayed several times on the surface of the bulks. Four Bi-2223 bulks, 20×10×2 mm3, were stuck to 20 mm square plate and 4 mm thick. This sample was sintered at 840°C for 50 h and then, intermediately subjected to CIP and sintered again. After three times of CIP and sintering, the superconducting properties of Tc=104 K and Jc=7000 A/cm2 were obtained for the sample, which were almost the same as those of the sintered bulks. The magnetic property was measured at 77 K. When a uniform magnetic field was applied perpendicular to the plate surface, two-dimensional distribution of the magnetic flux density over the sample surface was measured with a Hall probe in the direction perpendicular to the sample surface. The flux leak of density 2 mT was observed at the center of the jointed sample where an external magnetic field of 15 mT was applied.

Development of Linear Actuator with YBCO Bulk Secondary

This paper presents the characteristic of linear actuator with high-temperature superconducting (HTS) bulk for secondary. We designed and constructed a single-sided and shortsecondary type linear actuator. The actuator is comprised of YBCO bulk secondary (rotor) and copper winding (primary) with iron core. Using this model, we measured the distributions of magnetic flux density in the air gap. We developed simulation code based on a finite element method (FEM) taking the voltage-current (E-J) characteristic into consideration to investigate electromagnetic behavior within the bulk exposed to time-varying magnetic field. The computed magnetic flux density distribution is compared with the experiment. Numerical investigation of the effect of pole pitch in the primary on thrust is also shown.

Preparation and Properties of Melt-Processed Large RE(Eu,Gd)-System Superconductor Bulk in Air

We have succeeded in preparing large c-axis oriented single-grained Y-system and Sm-system superconductors by the melt process in air. The grain growth was improved by adding Ag in the systems. In this study, the melt process was applied for preparing single-grained Eu-system and Gd-system. Calcined powder of compositions of RE1.8Ba2.4Cu3.408.5 (RE=Eu, Gd) with a Pt powder of 0.5 wt% was prepared. Ag was added into the calcined powder with content of 10 and 20 wt%, respectively. The crystallized temperature of them was determined by the liquidus temperature measured with TG-DTA. A single-grain of Ag-added Eu-system and Gd-system superconductors with a 45 mm diameter and a thickness of 20 mm were prepared by seeding and using the unidirectional growth technique by controlling the temperature gradient in the furnace. The relationship between the distribution of trapped magnetic flux density and Jc for the RE (RE=Sm, Eu and Gd)-system superconductors presented.

Analyses of the electromagnetic properties of oxide superconductors by the SRPM method

/spl Delta/Z (the difference in the impedance of a solenoid coil with and without a superconductive sample) of 0, 10, 20 and 30 wt% Ag-doped YBaCuO (c-axis oriented) and a Bi-based sintered sample were measured by the SRPM method between 200 Hz and 1 MHz at room temperature and liquid N/sub 2/ temperatures. At room temperature, frequency dependence of /spl Delta/Z was observed in both samples. These dependencies were analyzed using a serial circuit having the same resistance and inductance as the samples by which the existence of /spl Delta/Z was confirmed. Below T/sub c/, only /spl Delta/Z of a Bi-based sample was measured between 200 Hz and 1 MHz. /spl Delta/R (the real part of /spl Delta/Z) was evaluated as a function of frequency(f). /spl Delta/R from 0.25 to 1 kHz is assumed to be proportional to f/sup 2/ (normal skin effect). /spl Delta/R from 1 kHz to 50 kHz is proportional to f/sup 5/3/ (anomalous skin effect). /spl Delta/R from 50 kHz to 700 kHz is proportional to f/sup 2/3/ (anomalous skin effect). It was found that /spl Delta/R between 1 kHz and 700 kHz agrees with the property obtained by the equation confirming that it is in the region of anomalous skin effect.