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.

Prototype Bi-2223 based composite conductors have been fabricated to provide inherent passive fault current limiting functionality in devices. An HTS insert strand possessing a high resistivity sheath (HRS) was laminated to two metallic strips to provide additional capacity to absorb the heat generated during a fault. Sheath resistivities up to 45 times that of pure Ag were achieved. We summarize the electrical response of 10 to 100 cm straight sections of conductor to pulsed dc and ac currents several times the critical current. DC pulsed I-V characteristics have been obtained over 7 to 8 orders of magnitude of voltage. For electric field levels around 10 V/m, the I-V curves demonstrate the advantage of the HRS conductor in facilitating fault current limiting over the conventional Ag-sheathed Bi-2223 approach. The recovery time for ac faults of 10 Vim was mapped out for various fault hold times. Instantaneous operational recovery was observed for fault hold times up to 3 seconds

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.

Cabling and filament stacking technology has been developed for Pi-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 (J(e)), and results have reached 5500 A/cm(2) at 77K and self-field. Stacked conductors are roll deformed prior to multifilament consolidation and multifilament stacks have reached 5600 A/cm(2) 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.

Multifilamentary (Bi, Pb)2Sr2Ca2Cu3Ox/Ag composites have been studied by a nondestructive magneto-optical imaging technique in order to determine the effect of filament architecture on the local magnetic flux distribution. The images reveal the homogeneity of the flux distribution in the upper layer filaments under magnetizing and demagnetizing conditions, and the alignment and morphology of these filaments in tapes with nine different composite structures. Certain types of filament arrangements led to homogeneous flux distributions, while other types caused localized inhomogeneities in the flux distribution. Nonuniform filament thickness also resulted in a highly inhomogeneous flux distribution. These results are useful in selecting optimal composite structures for power applications.

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.

The superconducting filaments in (Bi, Pb)2Sr2Ca2Cu3Ox/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 μm 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)2Sr2Ca2Cu3Ox composite tapes.

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.

The performance of high-temperature superconductor (HTS) composite conductors is rapidly advancing. Filament current densities of greater than 32,000 A/cm2 (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/cm2. 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/cm2 (77 K, self field, 1 × 10−11 Ω-cm). Recent advances in the development of high Jc 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.