H. Ogiwara

High-density recording capability of granular media composed of Co-Pt grains and SiO/sub 2/ matrix

Co-Pt and SiO/sub 2/ granular films were prepared on a Cr seed layer. Co-Pt grains dispersed in the SiO/sub 2/ matrix discretely. Conical grains grew in contact with the Cr layer and spherical grains grew between the conical ones. Coercivity exceeded 2 kOe and coercive squareness reached about 0.7 at a remanent magnetic moment of 0.4 memu/cm/sup 2/. Activating magnetic moment was 10/sup -15/ emu and the index of the thermal stability was about 100. Bit error rate was held below 10/sup -5/ up to a linear density of 280 kfci. The recording pattern at the track width of 1 /spl mu/m was clearly visible. The Co-Pt and SiO/sub 2/ granular media have potential for 5 Gb/in/sup 2/ recording.

The Helium Magnetic Refrigerator I: Development and Experimental Results

Development of a small helium refrigerator with high reliability and high efficiency is needed for progress in superconductive device applications.

Flow pattern, void fraction and pressure drop of refrigerant two-phase flow in a horizontal pipe—II: Analysis of frictional pressure drop

Two-phase flow in horizontal pipe was analyzed with simplified models for annular and stratified flow. The velocity profiles for the liquid and gas phase were described with the Prandtl mixing length. From this analysis, the frictional pressure drop was calculated with the modified Baker map for flow pattern transition. The intermediate region, i.e. wavy flow, was interpolated between annular and stratified flow. Comparison of this analysis with existing experimental data of refrigerants showed good agreement.

Reciprocating Magnetic Refrigerator for Helium Liquefaction

We have developed a reciprocating magnetic refrigerator for liquefying helium from a temperature in the 15 K region. The working material [gadolinium-gallium-garnet (GGG) single crystal, 30 mm in diameter and 40 mm in length] is placed at the end of the piston. When GGG is placed in a high-intensity magnetic field (4.5 T), its temperature rises to 15 K. The inner surface of the cylinder is cooled by an auxiliary refrigerator; the generated heat is removed through the narrow gap between GGG and cylinder (less than 50 um in the 15 K region) filled with gaseous helium. When the magnetic field in the GGG is eliminated by moving the piston, the GGG temperature falls below 4.2 K and the refrigeration occurs by condensing the helium on the GGG surface.

A novel use of superconducting oxides in a non-contact carrier for VLSI plants

Abstract A high-Tc superconductor has outstanding intergrain superconductivity and troublesome intergrain electrical conductivity at the same time. But once we consider to utilize the intergrain characteristic only, neglecting the intergrain conductivity, a new world of applied superconductivity is open before us. An yttrium-family class superconductor by the processing technique by which proper sizes and delicate distribution of precipitates are introduced in the material1). The fishing effect showing the stable floating of superconducting oxide materials has its origin in this strong pinning force. Now in a advanced Japanese VLSI plant a magnetically supported non-contact wafer-carrier is used in order to avoid the production of even traces of fine dust made by the friction of the wheels2–3). In this system the controlled attractive force between conventional electro-magnets and an iron guideway is used. The outstanding fishing effect of a strong pinned yttrium-family superconducting oxide processed by the QMG method can be expected to replace electro-magnets. We testfabricated a magnetically suspended non-contact carrier in the same dimension as a VLSI wafer-carrier currently used, with four QMG processed yttrium-family bulk pellets4). The carrier runs at any controlled speed with a load of under 3 kg, with very high stability in the vertical and lateral positions. It was driven by a linear induction motor. The outline of this system and its carrier will be reported as well as the superconducting levitation performance of the carrier.

A parasitic magnetic refrigerator for cooling superconducting magnet

Experimental results are presented for a practical magnetic refrigerator equipped with a large-field racetrack superconducting magnet, an auxiliary GM (Gifford-McMahon) refrigerator, and a liquid-helium vessel for magnetic refrigeration cooling. In this design the magnetic refrigerator is equipped with 14 pieces of GGG (gadolinium-gallium-garnet) single-crystal material on a rotating disk that operates along the gradient of the magnetic field produced by the racetrack superconducting magnet. The heat generated by the magnetic refrigerator is removed by an auxiliary GM refrigerator through the heat absorber made of a high-thermal-conductivity metal. The cold station of the magnetic refrigerator can be connected to the liquid-helium vessel by a high-thermal-conductivity rod to recondense the gaseous helium in the vessel. Refrigeration power measurements are presented and discussed. >

Critical current density and best transport current of an Ag-sheathed Bi-2223 tape conductor

Abstract A critical current density of as high as 66,000 A/cm 2 has been achieved in an Ag-sheathed Bi-2223 superconductor. Also a coil wound with the same kind of wires has generated a magnetic field of 1.5 T. The conductors of this coil consisted of six elemental conductors connected in parallel. The reason why the parallel conductors were used was that it was difficult to fabricate a single conductor which had the capability of passing a large amount of current at a high critical current density. In an Ag-sheathed Bi-2223 superconductor, one limiting factor prevents a single conductor from having a large current-passing capability and the highest critical current density, at the same time. A larger amount of current passes through a conductor with a larger cross-section. However, we can only realize a higher critical current density with a conductor of a smaller cross-section. This core size limitation (CSL) gives rise to many problems that need to be solved when considering large scale applications in the electrical engineering field with Ag-sheathed Bi-2223 superconductors.

WHAT HAPPENED TO CRYOGENIC AND SUPERCONDUCTING EQUIPMENT IN THE GREAT HANSHIN EARTHQUAKE

At 5:46 a.m. on 17 January 1995, a big earthquake with a magnitude of 7.2 on the Richter scale struck the Kansai area in western Japan. It was a shallow dislocation earthquake and resulted in huge damages in this area. Kobe, with a population of one million, was greatly affected by this disastrous earthquake. There are many hospitals, laboratories and universities in this area, and various kinds of cryogenic and superconducting equipment were about to go into operation. The Cryogenic Association of Japan immediately organized a special committee for damage investigation on this equipment purely from the technical point of view. This paper is presented as a quick report on what happened to MRI magnets, cold evaporators and other cryogenic and superconducting equipment in the universities affected by this earthquake.

Superconducting Current Lead Development of BiPbSrCaCuO

Cylindrical superconducting rods composed of Pb doped Bi-Sr-Ca-Cu-O, 10∼ 15 cm long and 10∼ 20 mm in diameter, were fabricated by a cold isostatic pressing (CIP) method. To evaluate their electric properties as current leads, critical current (Ic) and contact resistance to the ceramic superconductor were investigated. As a result of improvements, transport Ic value of 480 A at 77 K, that of more than 1000 A at 4.2 K, and contact resistance of less than 1.7×10−9 Ω (contact resistivity of less than 1.3×10−8 Ωcm2) were achieved.

ADIABATIC DEMAGNETIZATION COOLING SYSTEM FOR FAR INFRARED DETECTOR

An adiabatic demagnetization cooler for an astronomical far infrared detector has been built. The operating temperature was designed to be below 0.3 K. Paramagnetic salt, manganese ammonium sulphate, was prepared as a magnetic working substance. The cooler, including a superconducting magnet, was designed for use in space. The superconducting magnet was indirectly cooled and operated by small current up to 13.3 A, the maximum field being 3.5 T. As a preliminary step, adiabatic demagnetization to zero field was implemented. The lowest temperature obtained was 0.50 K, for 5.0 K initial temperature. The reason for not reaching below 0.3 K is discussed.