Craig J. Christopherson

Development of twisted high‐temperature superconductor composite conductors

Multifilamentary high‐temperature superconductor (HTS) composite conductors have been developed for alternating current (ac) applications. A twisted HTS conductor containing the Bi‐2223 phase fabricated using a modified powder‐in‐tube technique is reported. Transport critical current densities of 13 800 and 10 900 A/cm 2 (77 K, self‐field, 1 μV/cm) have been achieved for twisted tape and wire conductors with twist pitches of 3.7 and 3.6 mm, respectively. These conductors are strongly linked and are thus suitable for use in ac applications.

Advances in the fabrication and characterization of HTSC composite conductors

Abstract Recent advances in the performance of high-temperature superconductor (HTSC) multifilamentary composite conductors have been dramatic. Using powder-in-tube techniques that are based on scalable processes, conductor (J e ) and filament (J c ) critical current densities in excess of 6,700 and 26,500 A/cm 2 (77 K, self field) have been achieved, respectively. Pilot production scale conductors have achieved J e and J c values of 2,100 and 8,900 A/cm 2 (77 K, self field) across 1.16 km using a 1×10 -11 Ω cm criterion. Magneto-optic results have been correlated with microstructural features within these high-performance samples.

AC loss measurements on model Bi-2223 conductors

Measurements of the AC loss in applied magnetic fields at 77 K have been made on model composite Bi-2223 conductors. A vibrating sample magnetometer (VSM) and a dual Hall sensor magnetometer (HSM) were used to cover the frequency range from below 0.01 Hz to over 250 Hz at AC fields up to 0.05 T rms. The VSM was limited to the frequency range below 0.2 Hz. A comparison of the two measurement techniques was possible at intermediate frequencies. The samples consisted of vertical stacks of well separated flat filaments of superconductor in Ag and Ag-alloy matrix, allowing a range of filament coupling conditions to be explored.

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.

Advances in the development of HTS composite conductors

Abstract The performance of high-temperature superconductor (HTS) composite conductors is rapidly advancing. Filament current densities of greater than 32,000 A/cm 2 (77 K, self field, 1 μV/cm) have been achieved in multifilamentary composite conductors prepared with scaleable powder in tube techniques. This has allowed the fabrication of composite conductors with overall conductor current densities of 9100 A/cm 2 . These advances are being applied to the manufacture of composite conductors with lengths in excess of 1 km and filament currents densities of 8900 A/cm 2 (77 K, self field, 1 × 10 −11 Ω-cm). Recent advances in the development of high J c composite conductors will be reviewed. The performance and characterization of long length conductors will be described and the integration of these conductors into practical applications will be reported.

Non-destructive magneto-optical imaging analysis of superconducting (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} composites

The superconducting filaments in (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x}/Ag composite tapes have been imaged directly through the outer silver sheath of an unpolished tape by means of a magneto-optical imaging technique. The images reveal the morphology and alignment of the uppermost layer of filaments located as much as 112 {mu}m below the unpolished tape surface, the depths of these filaments, and the homogeneity of the magnetic flux distribution within these filaments. These results demonstrate that the magneto-optical technique is a valuable nondestructive tool for analyzing (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} composite tapes. {copyright} {ital 1996 Materials Research Society.}

Supercurrent dissipation and strain-induced damage in (Bi, Pb)2Sr2Ca2Cu3O10/Ag tape

Supercurrent dissipation and strain-induced damage in (Bi, Pb)2Sr2Ca2Cu3O10/Ag high-temperature superconductor composite tape, at 77 K in self-field, are studied by I–V curve analysis. Five dissipation models are considered, and differently processed tapes are compared. After making self-field corrections, which are normally ignored but we find essential to do, collective flux creep stands out as the only dissipation mechanism which explains the data. Confidence in the analysis comes not only from the goodness of fit, but also from experimental confirmation of two fitted parameters. The identification of the main dissipation mechanism has great practical value, because it enables definitive tape characterization, based on intrinsic physical properties.

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.