Shuichi Kohayashi

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.

Size effect and pinning potential for YBCO systems prepared by modified melt texture growth

Abstract High-T c superconductors of YBa 2 Cu 3 O 7 system including Y 2 BaCuO x grains, which play a role of the flux pinning center, were prepared by modified melt-texture-growth method. The pinning potential of the YBa 2 Cu 3 O 7 pulverized into different particles size is investigated as functions of magnetic fields, the size of the Y 2 BaCuO x segregation and the particle size.

Flux Pinning Mechanism of High-T c Y–Ba–Cu–O Superconductor Containing Artificial Pinning Centers Y2BaCuO5

Magnetic field and temperature dependences of magnetic torque and magnetic relaxation were investigated on Y–Ba–Cu–O superconducting systems containing Y 2 BaCuO 5 artificial particulate precipitates. Two different types of pinning forces were found to act on fluxoids. One is the intrinsic pinning force due to a layered structure of Cu–O planes and the other is the extrinsic pinning force due to Y 2 BaCuO 5 precipitates. The intrinsic pinning force is effective when the applied magnetic field is lying within an angle Δθ out of the Cu–O planes. The pinning potential obtained from the magnetic relaxation measurements is expressed by the form of log ( J c / j ) where j is the shielding current density. The pinning mechanism is discussed in terms of the planar pinning at the precipitates and the transformation of fluxoid lines from stepwise to linear.

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.

Microstructure and critical current density of the YBaCuO superconductor prepared by melt process

Abstract The critical current density (Jc) value increases along the growth direction from the top to the bottom of the YBaCuO samples prepared by a melt process with a unidirectional growth technique. The volume fraction of Y2BaCuO5 (211) particle is constant all over the sample, while the average size decreases along the growth direction from the top to the bottom. The dependence of Jc on the volume fraction and the particle size agrees with the theoretical result. It seems that an increase of Jc along the growth direction from the top to the bottom can be attributed to the decrease of the 211 average size. The cause of the inhomogeneity for the 211 particle size is discussed.

Nd-422 content dependence of superconductivity in a large-sized single-domain Nd-system superconductor

We investigated the effect of the molar ratio of the Nd4Ba2Cu2O10 (Nd-422) phase in a NdBa2Cu3Ox (Nd-123) superconductor on the superconducting properties of a large-sized single-domain Nd-system melt-textured bulk fabricated using a seeding and temperature gradient method in 0.1% oxygen atmosphere. The single domain of Nd-system superconductors, about 18 mm in diameter and 5 mm in thickness, was fabricated reproducibly. The maximum Jc value was about 4.5 × 104 A cm−2 at 77.3 K and self-field, and the maximum trapped field was about 0.34 T when the molar ratio of Nd-123/Nd-422 was 1/0.25.

Superconductivity deterioration of single-domain Nd-system melt-textured bulk doped with Pt

Abstract We fabricated single-domain Nd-system superconductors by a seeding and temperature gradient method in 0.1% oxygen atmosphere. Pt doping effect on the superconductivity was investigated. In the sample doping with 1.0 wt.% of Pt, the T c (on-set) and the T c (off-set) were 93 and 87 K, respectively, and the T c (off-set) was several degrees lower than that of undoped sample, and the J c value in the magnetic field up to 1.3 T decreased to one-third of the undoped sample. It was suggested that the J c lowering came from a broad superconducting transition with the lowering T c (off-set).

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.