K. DeMoranville

Examination of current limiting mechanisms in monocore Bi/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub x/ tape with high critical current density

Magneto-optical imaging, electromagnetic measurements and SEM have been used for the characterization of a monocore BSCCO tape made by oxide powder-in-tube process which had a transport J/sub c/ (77 K, 0 T) of 37 kA/cm/sup 2/. Our study evaluates the connectivity between superconducting grains and reconstructs the local current distribution at <10 /spl mu/m scale. Some local regions are found to carry up to 180 kA/cm/sup 2/ at 77 K, a new record for BSCCO wires.

Overpressure processing of Ag-sheathed (Bi, Pb)2Sr2Ca2Cu3Ox tapes

Abstract Heat treatments of monocore and multifilament Ag-sheathed 2223 tape were carried out using overpressure (OP) processing in a static and a flow OP system between 125 and 180 bar. Mass density measurements and microstructural observations of the oxide core show that OP processing densified the core, achieving up to 95±1% of the theoretical density. Our first runs in the flow OP system yielded J c as high as 41 kA/cm 2 (0 T, 77 K), which is 89% of J c in a fully processed tape with an optimized conventional heat treatment.

Overpressure processing Bi2223/Ag tapes

We report on the effect of overpressure processing on the electromagnetic properties and microstructure of monocore and multifilamentary Bi2223/Ag tapes. Samples at various stages of the usual thermo-mechanical processing for Bi2223/Ag tapes (from as-rolled to fully processed) were subjected to annealing at 815-820/spl deg/C for 18-108 h in a static Ar+O/sub 2/ atmosphere at the overall pressure 17.5/spl plusmn/0.5 MPa (pO/sub 2/= 0.003-0.02 MPa). Density measurements, microhardness tests, and SEM examination of polished sections reveal a notable densification of overpressure-processed samples. For partly reacted (so called HT1) samples, we found that overpressure processing for 36 h is sufficient to densify the Bi2223 core from 70/spl plusmn/5 to 87/spl plusmn/4% theoretical density and increase self-field J/sub c/(77 K) from 8/spl plusmn/1 to 30/spl plusmn/5 kA/cm/sup 2/ The results show that one-step processing of Bi2223/Ag tapes is possible.

Magnet cable technology development for high-temperature superconductor composite wire

Abstract Magnet cabling technology has been developed for Bi-based HTS composite wire. Concentric round cabling as well as Rutherford cabling has been proven in > 100 m lengths. For Bi-2223 precursor composite wire, post-cabling deformation is required to achieve high transport engineering current density (Je), and early results have reached 5500 A/cm2 at 77 K and self-field. Cable-and-deform conductor has similar magnetic field retention and anisotropy as conventional, nontransposed multifilament Bi-2223 composites with comparable Je. HTS magnet cabled composites have great potential for providing high Ic, Je, and reducing fabrication cost.

Magnet Conductor Development Using Bi-2223 High Temperature Superconducting Wire

Cabling and filament stacking technology has been developed for Bi-based HTS composite wire. Concentric round cabling as well as Rutherford cabling has been proven in >100m lengths. For Bi-2223 precursor composite wire, post-cabling deformation is required to achieve high transport engineering current density (Je), and results have reached 5500 A/cm2 at 77K and self-field. Stacked conductors are roll deformed prior to multifilament consolidation and multifilament stacks have reached 5600 A/cm2 at 77K and self field. These HTS composites have great potential for providing high Ic, Je, and reducing fabrication cost. An overview of this new processing route will be presented.

Continuous multistrand assembly techniques for Ag clad superconducting wire

A method to continuously combine and deform silver clad superconducting strands has been developed. This technique has been used to fabricate multifilament superconducting tapes consisting of Bi-2223, high temperature superconducting precursors. Results show that silver has the unique ability to be bonded together in a continuous strand process without requiring a protective atmosphere. The approach uses a continuous process to combine relatively fine wires that are aligned in the desired configuration, held in intimate contact and heat-treated to promote metallurgical bonding. Silver grain growth across strand interfaces has been documented in processed tapes and lengths approaching 100 meters have been fabricated. Engineering critical current densities (J/sub c/) as high as 19000 amps/cm/sup 2/ (77 K, self-field, 1 /spl mu/V/cm) have been recorded in short samples.