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Bulk High-Temperature Superconductors for High Field Apps

At the fourth annual conference of the Innovative Electronics Manufacturing Research Centre, at Loughborough, UK September 2, 2009, David Cardwell, Professor of Superconductor Engineering at the University of Cambridge, gave a presentation entitled Bulk High Temperature Superconductors for High Field Applications, illustrated with live demonstrations of magnetic levitation accompanied by dramatic stage-smoke effects from the liquid nitrogen he used to cool his superconductor samples. In his context, "high-temperature" referred to the boiling point of liquid nitrogen, 77°K, (-196°C), as opposed to that of liquid helium, 4°K. The only class of superconductor material suitable for 77°K operation was large-grain, boundary-free Rare-Earth Barium Copper Oxide, the rare-earth options being Yttrium, Samarium or Neodymium. The Yttrium-based material YBa2Cu3O7 (YBCO), processed in the form of large single grains by melt processing and peritectic solidification, offered the best short-term opportunity. Professor Cardwell discussed the bulk microstructure of YBCO, and explained the effect of second-phase inclusions on the flux-pinning capability of the material. Methods had now been developed to incorporate nano-scale inclusions into the bulk structure, and a 10-200nm nano-phase based on RE2Ba4CuMOy had been shown to form effective artificial flux-pinning sites. Although these materials required further refinement in microstructural homogeneity, they appeared extremely promising for improved critical-current-density bulk superconductors. There were potential applications in magnetic bearings, flywheel energy storage, motors, generators and NMR imagers.To see Professor Cardwell's full presentation, click here.