Atsushi Kume

A.C. transport properties of the high-Tc superconducting cable consist of the transposed segment conductor

The interlayer current distribution in the cylindrical multi-layered conductors was one of the problems on using high-Tc superconducting materials for A.C. current loading cable. We developed cable conductors consist of transposed segments made of Ag-sheathed Bi-2223 tape. One transposed segment consist of 5 Ag-sheathed tapes. The segments were wound spirally on former in order to construct the cable conductor. A.C. current loading tests was performed. We measured current wave form of the each tape which composed a transposed segment. No phase difference existed in each tapes.

Influence of the Surface Conditions to the A.C. Losses of Layered Ag-Sheathed Bi-2223 Conductor

We investigated effect of the surface conditions to the a. c. losses of layered conductor consisted of Ag-sheathed Bi-2223 tapes. The tapes were produced by the powder-in-tube method. These tapes were treated to be different layer conditions, the a. c. losses under self-field were measured by the a. c. transport measurement method. First, we investigated the influence of surface resistance by using non treatment tapes, resistive metal coated tapes, hastelloy sheet between tapes, and insulator between tapes. In the case of resistive metal coated tapes, the resistance between the tapes were 5.4 X lO-1 Ωcm2 (77K) and then a. c. loss was same as the value of insulator between tapes. Second, we investigated the difference of parallel segment and transposed segment. In the case of transposed segment, the a. c. loss was reduced to about 75% of parallel segments.

The Development of the High-Tc Superconducting Cable Consist of the Transposed Segment Conductor

We developed cable conductors consist of transposed segments made of Ag-Mg-Sb alloy sheathed Bi-2223 tapes developed by Showa electric wire & cable co., LTD.. One transposed segment consists of 5 Ag-Mg-Sb alloy sheathed tapes. The segments were wound spirally on former in order to construct the cable conductor. At a.c. loading, a comparison of the current phase between the five tapes in a segment shows good agreement and the phase was in good agreement with the phase of the conductor. And, the amplitude between these tapes showed good agreement. From these results, the current was sharing equally to each tape in the transposed segment conductor. The a.c. loss exhibited about the cubic dependence of the current and about the proportional of the frequency.

Surface Condition and Superconducting Properties of Ag-Sheathed Tape

We investigated surface condition of Bi-2223 Ag-sheathed tapes, and also researched relationship between microstructures and mechanical properties. It was recognized that the size of Ag crystal grains grown by annealing varied with heat treatment temperature. Samples, which coarse Bi-2223 platelike grains were also recognized to be grown near to the surface partially after annealing at relatively high temperature, sometimes showed degradation in superconductivity after heat cycle between room temperature and Liq.N2 temperature. We verified a possibility of degradation with behavior of Liq.N2 in the sample by investigating properties for heat cycle of the samples covered with epoxy resin.

Design of the High-Tc Superconducting Model Cable

We designed high-Tc superconducting model cable considering current distribution, being based on the concept of cooling. For conductor and shield conductor, we designed transposed segments from the point of view to enhance equivalent current distribution in the superconducting tapes of the core. Mechanical properties of Bi-2223 Ag sheathed tapes were investigated for the purpose of finding condions to fabricate transposed segment. We measured coolant pressure loss of corrugated tube actually and calculated viscosity loss and coefficient of friction. Applying formula obtained from the results of experiment, relationship between cooling distance and coolant pressure loss was evaluated.

Fabrication of the Model Cable using Bi-2223 Ag Sheathed Tapes

A superconducting model cable was designed and fabricated. The cable consisted of conductor, electric insulation, thermal insulation, LN2 paths for cooling, and corrugated aluminum sheath with PVC layer. The conductor was divided into ten segments in order to improve flexibility. Laminated Bi-2223 Ag sheathed tapes were put in grooves of the segments. The thermal insulation layer using super-insulation was evacuated during the evaluation of the cable. Critical current of the cable was 1.2 kA at 77K, and did not change before and after the cable fabrication and by the heat cycles.

Synthesis of the Carrier Doped Infinite-Layer Films by rf Thermal Plasma Evaporation

We tried to deposit (Sr1−xCax)0.9CuO2#x2212;δ films, so-called “infinite-layer” structure, on (100) SrTiO3 substrates by using radio-frequency thermal plasma evaporation. The crystal structure of films was confirmed to be of the (00l) oriented infinite-layer structure by X-ray diffraction. But the temperature dependence of electrical resistivity showed no superconductivity in spite of varying ratios of Sr/Ca. Probably carrier was needed for infinite-layer structure to show superconductivity, so we doped Na to raw materials as hole doping and deposited films.

Superconducting Wire of High Tc Oxide by Diffusion Process

The diffusion process between Y2BaCuO5 and Ba-Cu oxide has been investigated for fabricating a YBa2Cu3O7-y wire. At above 926°C, the solid-liquid reaction at the boundary between Y2BaCuO5 and Ba-Cu oxide has been observed because of decomposion of Ba-Cu oxide. By X-ray diffraction analysis, it was revealed that Ba-Cu oxide was consisted of BaCuO2 and CuO2 at the room temperature. The obtained maximum critical current density of a wire was 730A/cm2 which was not so high comparing with the value of the basic bulk specimen of 1,900A/cm . The heat--treating conditions and the microscopic diffused texture will be investigated in detail to improve the critical current density.

Characterization and Superconducting Properties of High Tc Oxide Wire

Y-Ba-Cu oxide wires have been fabricated by a powder metallurgical technique. A metal tube and a compacted powder of precursors of Y-Ba-Cu oxides were cold-worked. The components was well-mixed Y2BaCu05, BaCu02 and Cu0 powders. Cold-worked wire was heat-treated after removing the metal sheath. Crystal structure of the oxides turned to orthorhombic Y1Ba2Cu307-y after short heat-treatment at 950°C. Critical temperature and critical current density are reported and discussed.