IMPROVED PINNING IN NB AND NB3SN SUPERCONDUCTORS

The superconducting properties of Nb and Nb3Sn are greatly improved by the introduction of nanometre-scale Cu filaments as artificial pinnin g centres (APCs). The maximum pinning force for an APC Nb sample can b e four times that of bulk Nb. The pinning peak also shifts to a higher reduced magnetic field. The upper critical field of the APC Nb sample s increases as the sample diameter becomes smaller. The temperature sc aling of the APC Nb sample is very similar to that of an optimized NbT i superconductor. The proximity effect is observed in the APC Nb sampl es when the size of the APCs is about twice the coherence length of Nb . In APC Nb3Sn samples, the pinning force of Nb3Sn is increased owing to a fine equixed grain structure, which results from the fine distrib ution of Cu APCs. A sample reacted at 650-degrees-C has the highest pi nning force. The pinning peak shifts from 0.2 reduced magnetic field t o about 0.3.