Osamu Kasuu

Characterization of Bi2Sr2CaCu2Ox Superconducting Rods and Tapes

Highly oriented superconducting rods or tapes of Bi2Sr2CaCu20x have been developed. The rods were grown by laser pedestal growth method. The Ag composite tapes were prepared by partial melt method.

2.3kA BSCCO Rod Grown by Laser Pedestal Growth Method

Bi2Sr2CaCu2Ox superconducting rods were grown by the laser pedestal growth method.The samples were 4mm in diameter and 150mm in length. The critical current for DC and AC at 4.2K have been attained to be 2.3kA and 4.6kAp, respectively. The AC losses at 50Hz and 77.3K were also examined by using transport technique. The AC loss of 4.4W/m at 400Ap-50Hz operation is enough low for a current lead application in comparison of the copper joule loss.

Recent Progress in HTS Wire Technology at the Super-GM Project

Super-GM has been conducting a 12-year project since FY 1988 for research and development of HTS wires to apply electric power components in parallel with generator research. Recent results in the development of HTS wires at Super-GM project are reviewed. Bi2223 by multi-pipe method and Bi2212 by partial melting method are tried to scale up the process up to 1000m and are currently being made into demonstrated coils or a large current conductor. Y123 by IBAD method yields 1.1x106A/cm2 in short length and 2.1x105A/cm2 in 0.7m length. Y123 by PLD method and Tl1223 by spray pyrolysis method have been combined with cube texturing technique textures the Ag tape. We have focused its efforts on speeding up the process and enhancing quality control. Components technology, highlighted in this project, is to develop HTS based components of 200V-100A or 400V-10A class fault current limiting elements (CLE’S) by PLD and CVD methods and AClkA or DC3kA class current leads using the Bi2212 rods demonstrating clearly the advantage of HTS.

R&D on HTS Wires in the Super-GM Project

The HTS wires have been developed for the application to electric power apparatuses in the Super- GM project. We made steady progresses in the fundamental wire characteristics and fabricated some trial products toward applications. The current capacities and the critical current densities of the Bi-2223, Bi-2212, Tl-1223 and Y-123 wires have been improved. A IkArms class AC lead and two types of Y-123 current limiting elements were trially fabricated and their properties were examined. As for the evaluation technique, Abrikosov decorated pattern of magnetic flux lines was observed for a Bi2212 single crystal using Bitter decoration technique.

In Situ Observation of Phase Changes in Bi2212 Superconducting Tapes by High Temperature X-ray Diffraction

High-temperature X-ray diffraction has been used to investigate an aspect from partial melting state to crystallization for Bi2Sr2Ca1Cu2Oz tapes. When a sample having a nominal composition of Bi2Sr2Ca1Cu2Oz was heated in air, the simple XRD pattern that is, (Sr,Ca)1Cu1O2 and liquid, in partial melting state was observed and the XRD pattern nearest to single phase of 2212 was obtained. When the same sample was heated in oxygen, Bi-(Sr,Ca)-O and Bi-2201 phases additional to (Sr,Ca)1Cu1O2 largely remained in partial melting state. Such phases were hard to react and precipitated after transformation to the 2212 phase. The Ag addition was effective to reduce impurity phases in oxygen cooling.

Experimental Study on kA-class HTC Superconducting Current Lead

Highly oriented superconducting rods of Bi2Sr2CaCu2Ox have been grown by Laser pedestal method. The rods were 4.0mm in diameter and 200mm in length. The rod and the copper terminal electrodes were soldered together and GFRP substrate fixed them. The leads have operated in liquid helium on condition that upper ends of current leads were cooled by liquid nitrogen. Temperature of current lead and evaporation of liquid helium have been measured and heat leak have been calculated.

Preparation and Characterization of Superconducting Fibers Grown by Laser Pedestal Growth Method

Bi2Sr2CaCu2Ox superconducting fibers were prepared by laser pedestal growth method. Laser pedestal growth method is one of the directional solidification method. Important parameters for alingment in the crystal growth are temperature gradient at solid-liquid interface and the growing rate. The effect of the two parameters to the critical current density was investigated. As it is important to keep the uniformity of the diameter to prepare a long fiber, the auto-diameter-control system with fuzzy function was investigated. With the system, 370μm fiber was prepared and measured the superconducting characters.