Long-length, high-temperature superconducting (HTS) wires capable of carrying high critical current, Ic, are required for a wide range of applications. Here, we report extremely high performance HTS wires based on 5 μm thick SmBa2Cu3O7 − δ (SmBCO) single layer films on textured metallic templates. SmBCO layer wires over 20 meters long were deposited by a cost-effective, scalable co-evaporation process using a batch-type drum in a dual chamber. All deposition parameters influencing the composition, phase, and texture of the films were optimized via a unique combinatorial method that is broadly applicable for co-evaporation of other promising complex materials containing several cations. Thick SmBCO layers deposited under optimized conditions exhibit excellent cube-on-cube epitaxy. Such excellent structural epitaxy over the entire thickness results in exceptionally high Ic performance, with average Ic over 1,000 A/cm-width for the entire 22 meter long wire and maximum Ic over 1,500 A/cm-width for a short 12 cm long tape. The Ic values reported in this work are the highest values ever reported from any lengths of cuprate-based HTS wire or conductor.

Ni tapes were textured by taking advantage of their secondary recrystallization. The 18 cm long tapes obtained had textures of single crystalline quality with their [001] axes tilted with respect to the surface and their [010] axes parallel to the rolling direction. YBCO/CeO 2 /YSZ/CeO 2 films grown on the Ni tape had the same crystalline orientations. Magnetic field dependent I -V relations were measured on a 5 cm section of the tape. J c defined by 1 mV criterion was 1.5 × 10 5 A cm −2 at 77 K under zero field and was reduced by ∼50% under the applied magnetic field of 5 T.

We measured the field profiles near the surface of a coated conductor (CC) under various applied fields by using the scanning Hall probe method. The field, applied in the normal direction, was increased from zero to 171.5 Oe and then decreased to −58.8 Oe. We could not analyse our data completely by the direct use of Brandt’s calculation but by a modification with unusual field dependences of the introduced parameters. Since Brandt’s original calculation was based on homogeneous films, it was not suitable for CCs with coarse granular structures. The modified calculations with appropriate parameters are related to the coarse granular structures. Those parameters, D, Jc, and R, represent the three characteristics of the flux penetration network: the average distance of flux penetrations, the density of critical sheet currents, and the range of meandering of the flux penetration front, respectively. The external field dependences of these parameters were different from those of the classical critical state model.

The hysteresis loss in a Sm1Ba2Cu3O7−δ coated conductor was estimated from magnetic field profiles measured by the scanning Hall probe method. Current, Ia, and magnetic field, Ba, were applied simultaneously; Ba was applied in the normal direction with respect to the tape surface. Ba and Ia were varied from Bpeak to −Bpeak and from Ipeak to −Ipeak, respectively, with the ratio α = Ia/Ba fixed during the variation. Three values of α were taken for the three load lines. The values of Bpeak/Ipeak were varied from 0 mT/0 A to 10.7 mT/116 A, 99.1 mT/50 A, and 298.2 mT/46.1 A, respectively, for the three load lines. From the measured values of magnetic field profiles, the current profiles were calculated by the iterative inversion method. From the current profiles, the flux density profiles and the hysteresis loss, Q, were then calculated for various values of Ipeak(= αBpeak) in each load line. The results were compared with theoretical calculations based on Brandt’s model. When Bpeak was about 300 mT, the estimated values of Q were several times smaller than the theoretical values of Q with the self-field Ic0. The low value of Q in this case is due to the field dependent Ic and the saturation effect of the current profiles, which results in significant reduction of the induced magnetic moment, M.

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