Karl Wohlleben

Development of A15 Multifilamentary Superconductors

The superconducting properties of bronze processed Nb3Sn multifilamentary conductors are dependent on the structure and the diffusion treatment of the conductor. The tin concentration of the bronze, the volume ratio bronze to niobium, the filament diameter and the filament distribution are significant. The current carrying capacity can be increased considerably by the suitable addition of third elements. On the other hand conductor properties are sensitively influenced by diffusion temperature and diffusion time. High diffusion temperatures favor a high critical temperature Tc and a high critical flux density Bc2, low diffusion temperatures promote a better flux pinning by the increasing number of grain boundaries. As a consequence optimal diffusion conditions for high critical currents at high fields, and high critical currents at low fields, are different. Finally the influence of mechanical stress on the superconducting properties has to be regarded. Depending on the composition of the conductors different compressive stresses are acting on the Nb3Sn layers.1–10