PROCESS DEVELOPMENT FOR PRODUCING NB3SN MULTIFILAMENT SUPERCONDUCTORS OF HIGH CURRENT DENSITY

THE CURRENT METHODS OF FABRICATING NB3SN MULTIFILAMENT SUPERCONDUCTORS PRESENT VARIOUS PROBLEMS. IN THE CONVENTIONAL BRONZE PROCESS, THE LOW TIN CONTENT OF THE 13.5-WT% SN BRONZE SERIOUSLY LIMITS THE CURRENT DENSITY AND LEAVES MUCH OF THE NB UNREACTED. THE RELATIVELY HIGH MELTING POINT, HIGHER SN BRONZES HAVE NOT BEEN USED BECAUSE THEY ARE REGARDED AS LARGELY UNWORKABLE. THUS, OTHER PROCESSES WERE DEVELOPED THAT USE EITHER PURE SN OR LOW MELTING POINT SN-RICH COMPOSITIONS (E.G., THE INTERNAL TIN AND THE DISTRIBUTED TIN METHODS) THAT FORCE EXTRUSION AND DRAWING TO BE DONE WARM OR COLD TO AVOID MELTING THE SN SOURCE. THE LOW TEMPERATURE WORKING SERIOUSLY AFFECTS FABRICATION COSTS AND LEADS TO BONDING PROBLEMS. THE PLANNED METHOD WILL USE THE HIGHER MELTING, EXTRA-HIGH SN BRONZES, BUT IN A MANNER THAT GREATLY OVERCOMES THE WORKABILITY PROBLEM. THE HIGHER SN CONTENT BRONZES WILL PROMOTE HIGHER CURRENT DENSITIES, SHORTER REACTION TIMES, MORE UNIFORM NB3SN LAYERS THROUGHOUT, LESS UNREACTED NB, ANDMORE EFFICIENT USE OF THE BRONZE VOLUME IN THE SUPERCONDUCTOR. ALSO, THE PROCESS WILL PERMIT USE OF SOLID RATHER THAN HOLLOW NB ELEMENTS, WHICH WILL BE LESS COSTLY AND ALLOW THE FABRICATION OF VERY FINE FILAMENTS. IN ADDITION, THE HIGHER MELTING POINT OF THE PROPOSED SN BRONZEOFFERS THE PROSPECT OF HIGHER EXTRUSION TEMPERATURES, HIGHER EXTRUSION RATIOS, AND FASTER DRAWING SPEEDS THAN ARE POSSIBLE WITH THE LOWER MELTING POINT SN SOURCES IN OTHER PROCESSES.