Textured-Powder Jelly-Roll Process for High-Performance Bi-2212/Ag Wire

Superconducting wire is used in electromagnets that are used in energy research particle accelerators, fusion tokomaks and in biomedical research - NMR imaging and spectroscopy. New frontiers in those areas of research require ever higher magnetic field strength, and that requires ever-more robust superconductors. Bi-2212 is the only one of the high-temperature superconductors that can be made in round wire. Improving its performance is of considerable importance for research in those fields. Performance is limited by two properties of the superconducting cores within the wire: too much porosity and the too little connectivity. ATC is developing a new way of making high-performance superconducting wire using the high-temperature superconductor Bi-2212. The method uses a roll-processing technique to orient the grains of the material so that they all lie in the direction in which current will flow in the wire. This favorable orientation is preserved in the final wire-drawing by making a jellyroll composite of the superconducting layers in silver foil. This jelly-roll method improves the porosity and connectivity in the wire, and has reasonable prospects to yield significant improvement in wire performance. The jelly-roll wire is made using a machine that is used in the pharmaceutical industry to roll compact powders of drugs to do the same thing for the superconducting powder. As the powder is roll-compacted its flake-like particles naturally orient so that their flat faces are parallel. The collaboration of Accelerator Technology Corp. and Texas A & amp;M University will use this approach to make continuous ribbons of the superconducting powder. The ribbons will be jacketed in a silver sheath and further compacted to form the jelly-roll round wire. In the proposed Phase 1 effort the team will commission the processing machinery and use it to make test coupons of the superconducting tape. The tape will be heat-treated to link all of the superconducting grains within the wire. The team will do a process development in which the parameters of that heat treatment are optimized to give the best possible performance. The jelly-roll superconducting wire is being developed to give higher current density for the magnets needed for high-energy accelerators and for spectrometers for biomedicine. The same process should work for the higher-temperature superconductor Bi-2223, which has important applications for high-efficiency electric motors and generators for electric power transmission, wind turbines, energy storage, and all-electric cars. Indeed Toyota is today developing a superconducting motor for its model of all-electric car. That motor utilizes Bi-2223. The textured jelly-roll method has the potential to provide major benefit for those applications