Alexis P. Malozemoff

Progress in high temperature superconductor coated conductors and their applications

Second generation (2G) high temperature superconductor (HTS) wires are based on a coated conductor technology. They follow on from a first generation (1G) HTS wire consisting of a composite multifilamentary wire architecture. During the last couple of years, rapid progress has been made in the development of 2G HTS wire, which is now displacing 1G HTS wire for most if not all applications. The engineering critical current density of these wires matches or exceeds that of 1G wire, and the mechanical properties are also superior. Scale-up of manufacturing is proceeding rapidly, with several companies already supplying the order of 10 km annually for test and demonstration. Coils of increasing sophistication are being demonstrated. One especially attractive application, that relies on the specific properties of 2G HTS wire, is fault current limitation. By incorporating a high resistivity stabilizer in the coated conductor, one can achieve high resistance in a quenched state during a fault event and at the same time provide significant heat capacity to limit the temperature rise. A test of a 2.25 MVA single phase system at 7.5 kV employing such wire by the Siemens/AMSC team has demonstrated all the key features required for a cost-effective commercial system. A novel approach to providing fault current limiting functionality in HTS cables has also been introduced.

Low-cost YBCO coated conductor technology

Deformation-textured, non-silver substrates, and solution-based deposition of buffer and superconductor layers offer routes to a low-cost YBCO coated-conductor technology for high-temperature superconducting wire. Several significant steps towards such a technology are reported here: a solution-based Gd2O3 seed buffer layer was deposited by a web-coating technique over a metre-length tape of deformation-textured nickel with excellent texture and uniformity. Also, short full-stack samples with YBCO performance up to 0.8 MA cm-2 at 77 K were prepared at Oak Ridge National Laboratory (ORNL) and American Superconductor (ASC) using a CeO2/YSZ/CeO2 buffer sequence on textured nickel and a trifluoroacetate (TFA) precursor YBCO process; in this case the buffers are deposited by e-beam and magnetron sputtering.

Flux creep in high temperature superconductors

Abstract Magnetic studies of flux creep in high temperature superconductors show many features unexpected in the conventional Anderson-Kim theory, which assumes a thermal activation mechanism and uncorrelated motion of vortex bundles. An alternative phenomenology is provided by the more recent collective pinning theories. Experiments probing this new phenomenology are reviewed, including long-time relaxation, flux-creep annealing and studies near T c .

HTS wire at commercial performance levels

Short rolled multifilamentary BSCCO-2223 oxide-powder-in-tube (OPIT) wire has reached a core critical current density J/sub c/ over 73,000 A/cm/sup 2/ (77 K, self-field, 1 /spl mu/V/cm) in multiple samples, with engineering (full-cross-section) current density J/sub c/ of 22,800 A/cm/sup 2/ (77 K, self-field, 1 /spl mu/V/cm). Regular production wires several hundred meters long show average engineering current density over 10,000 A/cm/sup 2/ (77 K, self-field, 1 /spl mu/V/cm), a benchmark for commercial electric power applications such as cables and motors. Cost studies indicate that cost-performance below

Uniform performance of continuously processed MOD-YBCO-coated conductors using a textured Ni?W substrate

10/kA-m is attainable for full-scale production levels, Next-generation YBCO-123 coated conductor technology offers further potential cost-performance improvements.

YBCO coated conductors by an MOD/RABiTS/spl trade/ process

Second-generation coated conductor composite HTS wires have been fabricated using a continuous reel-to-reel process with deformation-textured Ni–W substrates and a metal-organic deposition process for YBa2Cu3O7−x. Earlier results on 1 m long and 1 cm wide wires with 77 K critical current performance greater than 100 A cm−1 width have now been extended to 7.5 m in length and even higher performance, with one wire at 132 and another at 127 A cm−1 width. Performance as a function of wire length is remarkably uniform, with only 2–4% standard deviation when measured on a 50 cm length scale. The length-scale dependence of the deviation is compared with a statistical calculation.

Multifilamentary Bi-2223 composite tapes made by a metallic precursor route

Commercialization of YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) superconducting coated conductor composite (CCC) technology requires a cost-effective continuous manufacturing process. High critical current YBCO CCC wires with excellent uniformity over length have been fabricated using an all-continuous process. The conductor architecture consists of a metal organic derived YBCO layer, coated on a deformation-textured NiW alloy substrate buffered with Y/sub 2/O/sub 3//YSZ/CeO/sub 2/. Critical current at 77 K, self-field, of up to 118 A was achieved in 1 cm-wide tapes over 1.25 meter lengths, with a standard deviation of 3% measured on a 5 cm scale. The high uniformity and performance supports the feasibility of commercial long-length CCC wire based on deformation textured metal substrates and solution-based deposition of YBCO.

HTS Wire: status and prospects

A process based on metallic precursors has been developed for manufacturing high filament count oxide superconductor-silver composite tapes with critical current densities of up to 7.5 kA/cm/sup 2/ at 77 K in zero field. A 30-cm prototype multistrand conductor made of these tapes has a critical current of 240 A at 77 K over a 9 cm gauge length, with an average critical current density of 6 kA/cm/sup 2/. The mechanical properties of tapes made from metallic precursors containing up to 10000 Bi-2223 superconducting oxide filaments were investigated. Critical tensile strains average 0.6%, and bend tests show negligible dropoff in current density up to a 0.70% surface strain. The critical current decrease beyond the 0.70% surface bend strain follows a simple model based on extensive filament damage beyond the critical tensile strain. Increased flow stresses of the composite tapes, compared to similarly processed silver, indicate considerable strengthening of the composite by the oxide filaments.<<ETX>>

YBCO coated conductors by an MOD/RABiTS™ process

Abstract Practical, robust high temperature superconducting (HTS) wire is a composite of high temperature superconductor and metal. The composite provides many advantages, including improved mechanical properties and stability. Multi-filamentary composite fabricated with the BSCCO HTS material has achieved performance for commercial applications, and commercial price/performance is on the near horizon. This wire enables HTS applications such as power cables, marine propulsion motors, utility generators and magnets for materials processing. Coated conductor is also a composite, combining the YBCO HTS material with a metal or metal-alloy substrate; this technology is in the stage of research and development. The status and commercial prospects of these wire technologies are reviewed.

Investigation of YBCO Coated Conductors for Fault Current Limiter Applications

Commercialization of YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) superconducting coated conductor composite (CCC) technology requires a cost-effective continuous manufacturing process. High critical current YBCO CCC wires with excellent uniformity over length have been fabricated using an all-continuous process. The conductor architecture consists of a metal organic derived YBCO layer, coated on a deformation-textured NiW alloy substrate buffered with Y/sub 2/O/sub 3//YSZ/CeO/sub 2/. Critical current at 77 K, self-field, of up to 118 A was achieved in 1 cm-wide tapes over 1.25 meter lengths, with a standard deviation of 3% measured on a 5 cm scale. The high uniformity and performance supports the feasibility of commercial long-length CCC wire based on deformation textured metal substrates and solution-based deposition of YBCO.