Towards a microstructural description of the superconducting properties

A discussion is provided of the state of our microstructural knowledge about filamentary Nb-Ti and Nb3Sn conductors. The situation is believed to be much clearer for Nb-Ti than for Nb3Sn, due to recent successes in elucidating the microstructures of Nb-Ti composites by TEM. Considerable changes in some earlier ideas of flux pinning are proposed and some semi-quantitative measures of precipitate flux pinning in Nb-Ti alloys are described. The situation is less advanced for Nb3Sn. The Jcis controlled by a greater number of variables and it is in general not clear that individual microstructural measurements can be taken to be typical of the whole composite.