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We have investigated Nb-47Ti multifilament wire with 12 volume percent artificial pinning centers (APC). The superconducting properties of APC wires containing either ferromagnetic nickel pins with a copper barrier or non-magnetic copper pins are compared. The optimum diameter for these pins is found to be ∼10 nm. Designs with Ni pins show a clear performance advantage over those with pure Cu only, being almost 70% higher for otherwise identical filament diameter and pin diameter and arrangement. Designs with ∼1 μm filaments were found to suffer from proximity coupling to the external copper matrix, and a further 19% improvement was found for a second Ni design with ∼17 μm filament diameter. This design also exhibited the highest upper critical field of any APC design made so far. Annealing the wires for a few minutes at 100 to 200 °C produced even better performance, reaching > 5000 A/mm2 at 5 T and 4.2 K in the best design. Field emission scanning electron microscopy (FESEM) revealed a new feature in the pin nanostructure due to the short annealing for both designs. Voids are formed on the outside of each pin as a result of inter-diffusion between Ni, Cu, and/or Ti, which may improve pinning by reducing the proximity coupling of the pins to the Nb47Ti matrix. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

Supercon has investigated an innovative process for the fabrication of Nb3Al conductor. Monofilament Nb-Al jelly-roll composite wire was fabricated. This wire was then converted to ultra-fine alloy powder by an electro-exploded wire technique, and the powder was used to make conductor by a powder-in-tube process. The development effort demonstrated that alloy powder particle sizes as small as 0.30 micrometers (median by volume) having a composition very near that of the input wire could be achieved using the electro-explosion process. Monofilament powder-in-tube wire was successfully fabricated without wire breakage. The results of the investigation will be discussed, with emphasis on powder characteristics. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

Nb[sub 3]Al superconductors have shown promising performance compared to Nb[sub 3]Sn conductors when processed by the Melt-Quench/Ordering Heat Treatment (MQ-OHT) process. In this process, a precursor wire containing a fine structure of Nb and Al is ohmically heated to temperatures in the range of 2000°C to melt the Nb-Al, and is then rapidly quenched to form a supersaturated bcc phase. An ordering heat treatment is then applied to convert the bcc phase to superconducting A15 phase material. Typically, the fine Nb-Al structure in the precursor wire is obtained by the jelly-roll (JR) process. In order to achieve good critical properties by MQ-OHT, the input precursor wire must have a suitable Nb:Al thickness ratio, an Al layer thickness thin enough to allow uniform bcc phase formation, and an outer Nb sheath thickness large enough to prevent bursting during MQOHT processing. At present, the primary challenge for industry is to meet these demands in precursor wires of practical piece-length (>100 m). The results of Supercon's efforts in this area will be presented. Results of MQ-OHT trials on Supercon JR precursor wire will also be presented. These results suggest a more complicated relationship between Nb:Al thickness ratio and absolute Al layer thickness than has previously been realized. [ABSTRACT FROM AUTHOR]