Abstract
The superconducting properties of Nb and Nb3Sn are greatly improved by the introduction of nanometre-scale Cu filaments as artificial pinning centres (APCs). The maximum pinning force for an APC Nb sample can be 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 samples increases as the sample diameter becomes smaller. The temperature scaling of the APC Nb sample is very similar to that of an optimized NbTi superconductor. The proximity effect is observed in the APC Nb samples 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 equiaxed grain structure, which results from the fine distribution of Cu APCs. A sample reacted at 650°C has the highest pinning force. The pinning peak shifts from 0.2 reduced magnetic field to about 0.3.