The freeway model: New concepts in understanding supercurrent transport in Bi-2223 tapes

A variety of mechanisms for supercurrent transport in (Bi, Pb)₂ Sr₂ Ca₂ Cu₃ O_x (Bi-2223) tapes have been proposed, including the brick-wall and railway-switch models and the more recent freeway model. In this article, these models are compared to a growing library of data, including structural and transport studies on specific grain boundary types as well as the systematics of microstructure and transport in the polycrystalline tapes, including new transmission electron microscopy data on some of the highest-performing samples yet fabricated. Additionally, the freeway model is developed, with the concepts of rotary junction bottlenecks corresponding to edge colony boundaries, of lane changes corresponding to c-axis redistribution within colonies, and on-ramps corresponding to tilted and bent grains.     

Laws of approach to magnetic saturation for interacting and isolated spherical and cylindrical defects in isotropic magnetostrictive media

Laws of approach to magnetic saturation are derived for interacting spherical and cylindrical defects in isotropic magnetostrictive media like amorphous materials. The normalized longitudinal magnetic deviation ΔM/M goes as 1/H²for both cases, provided all defects have the same sign. For randomly signed defects, 1/H^5/4and 1/H^3/2laws for spheres and cylinders, respectively. Isolated cylindrical defects obey a 1/H or 1/H²law depending on whether the defect is small or large compared to an exchange length.     

Progress in Nanoengineered Microstructures for Tunable High‐Current,High‐Temperature Superconducting Wires

High critical current densities (J_c) in thick films of the Y₁Ba₂Cu₃O_7–δ (YBCO, T_c ≈ 92 K) superconductor directly depend upon the types of nanoscale defects and their densities within the films. A major challenge for developing a viable wire technology is to introduce nanoscale defect structures into the YBCO grains of the thick film suitable for flux pinning and the tailoring of the superconducting properties to specific, application‐dependent, temperature and magnetic field conditions. Concurrently, the YBCO film needs to be integrated into a macroscopically defect‐free conductor in which the grain‐to‐grain connectivity maintains levels of inter‐grain J_c that are comparable to the intra‐grain J_c. That is, high critical current (I_c) YBCO coated conductors must contain engineered inhomogeneities on the nanoscale, while being homogeneous on the macroscale. An analysis is presented of the advances in high‐performance YBCO coated‐conductors using chemical solution deposition (CSD) based on metal trifluoroacetates and the subsequent processing to nano‐engineer the microstructure for tuneable superconducting wires. Multi‐scale structural, chemical, and electrical investigations of the CSD film processes, thick film development, key microstructural features, and wire properties are presented. Prospects for further development of much higher I_c wires for large‐scale, commercial application are discussed within the context of these recent advances.     

Superconducting materials for large scale applications

Since the 1960s, Nb-Ti (superconducting transition temperature T/sub c/=9 K) and Nb/sub 3/Sn (T/sub c/=18 K) have been the materials of choice for virtually all superconducting magnets. However, the prospects for the future changed dramatically in 1987 with the discovery of layered cuprate superconductors with T/sub c/ values that now extend up to about 135 K. Fabrication of useful conductors out of the cuprates has been difficult, but a first generation of silver-sheathed composite conductors based on (Bi,Pb)/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub 10/ (T/sub c//spl sim/110 K) has already been commercialized. Recent progress on a second generation of biaxially aligned coated conductors using the less anisotropic YBa/sub 2/Cu/sub 3/O/sub 7/ structure has been rapid, suggesting that it too might enter service in the near future. The discovery of superconductivity in MgB/sub 2/ below 39 K in 2001 has brought yet another candidate material to the large-scale applications mix. Two distinct markets for superconductor wires exist-the more classical low-temperature magnet applications such as particle accelerators, nuclear magnetic resonance and magnetic resonance imaging magnets, and plasma-containment magnets for fusion power, and the newer and potentially much larger market for electric power equipment, such as motors, generators, synchronous condensers, power transmission cables, transformers, and fault-current limiters for the electric utility grid. We review key properties and recent progress in these materials and assess their prospects for further development and application.     

Advanced technology/electromagnetism-superconducting wire getshotter

The significance of superconducting wires made of high-critical-temperature copper-oxide-based ceramics is discussed. The fabrication of wires made from the powdered ceramic material is described, and the characteristics of the resulting wires, particularly the critical current density, are examined. The progress to long wire lengths is discussed, and some applications are considered