nan Hideki

Fabrication of Assembled Conductor of Bi-Based Multilayered Wires

Setting a goal to apply oxide superconductor to electric power equipment, we have been carrying on with the development of multilayered wires, which are each constituted of oxide layers and silver layers. The multilayered wire is characterized in that low silver ratios and high Jc values are made producible, by thinning and uniforming its superconducting layers, subject to optional wire shapes. For instance, a tape wire with a silver ratio of 1.3 gave birth to a Jc of 21300A/cm2 and an overall Jc (Je) of 9270A/cm2. In the purist of a conductor of a large DC capacity, a layered conductor of 1000A class, which contains 210 tape wires, was developed. This conductor was demonstrated in terms of no quench breaking out with pulses of 2600A-peak. In addition, a stranded conductor of a 100A class containing 6 alumina-fiber insulated round wires was developed and found to have the loss contents consisting mainly of hysteresis loss.

Fabrication of Conductor Using Bi-Based Multilayered Wires

Fabrication and current-carrying characteristics of multilayer type superconducting wire are reported. It is tape-shaped, and has metallic outer sheath of Ag. The inner part of the wire has nearly stratified structure composed of alternatively stacked several Ag and Bi-“2223” superconducting oxide layers. The “overall Jc” (Je) and its magnetic field dependence of this type of wire have been remarkably improved in comparison with those of widely reported multifilamentary Ag-sheathed wires. Bundling 92 of the multilayered wires (typically 0.16 mm wide and 3.8 mm thick; Ic=41.3 A which corresponds to 20.4 kA/cm2 of Jc at LN2 temperature and in a self-field), a large-current carrying conductor is assembled, which has 3.05 kA of Ic. This value corresponds to Je of 3.95 kA/cm2 (Ag/Bi-“2223” ratio of ∼2.0). We have also fabricated a nearly square-shaped wire (0.81 × 0.87 mm2 in a transverse cross section) using Ag and/or Ag-0.2 wt% Mg alloy as an outer sheath and/or internal core materials. Jc increases when the Ag/Mg alloy is used for the outer sheath and/or internal core compared to the case when only pure Ag is used. For mechanical properties, it is shown that usage of the Ag/Mg alloy for the outer sheath highly increases mechanical strength of the wire while that for the internal core is not so effective.

Fabrication of Bi-Based Superconductor

Aiming for electric power application of oxide superconductors around liquid nitrogen temperature, a wire with multilayer structure comprising Bi-2223 layers and silver layers was developed. The wire features thin, uniform superconductive layers, assorted optional shapes (e.g., round, square and tape form) and easiness of reducing a silver-ratio that is expected to improve overall λJc. The model wire of this study has the silver-ratio reduced up to 1.3, resulting in 4100 (A/cm2) of λJc. As a result of rating the average pinning force Fp based on the I-V analysis, it was predicted that effective pinning centers had arisen from cold working and heat treatment. The strength of the Bi-2223 layer was some 100 (MPa) in view of mechanical properties of the multilayer wire. In search for a conductor of large current capacity, a layered conductor with tape wires was fabricated on trial. The work process slightly degraded the Ic, but the AC loss was found to be hysterisis loss overall.

Fabrication and Properties of Bi-Based Multilayered Wires

In an attempt to moderate magnetic anisotropy of critical current density (Jc) and improve overall Jc, a jelly-roll method and a multi-pipe method were applied to fabricate multilayered wires, which underwent performance tests for Jc temperature dependence, mechanical property and AC loss. A double pancake coil was made on trial, considering the mechanical property of a multilayered tape.

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.

Development of Bi-2223 Multifilamentary Tapes for Power Cable

Bi-2223 multifilamentary tapes show the most progress among high temperature superconducting wires under development for power transmission cables. While it is fairly easy to make a long Bi-2223 multifilamentary tape, a 50m long tape was made to undergo an electrical test, producing Jc of 21.6kA/cm2 on its entire length. It has been brought out that long and short tapes have similar statistic Jc distributions as teh result of a d2E/dJ2 analysis. A twisted tape with pitch of 9mm produced merely 50% of the AC loss arising from an untwisted one, with almost no sacrifice of Jc. Ag-Mg alloy sheathed tapes displayed double the tensile strength of a pure silver sheathed tape and showed some improvement in resistance to tensile and bending strains.