Optimization of the heat treatment of Nb3Sn-superconductors

The physical properties of (NbX)3Sn-superconductors strongly depend on the heat treatment (HT) during which the superconducting phase is formed by solid state diffusion. This is due to the fact that the thickness of the A15-layer and the grain structure are functions of the HT-parameters. Therefore an optimization of the HT-parameters, i.e., annealing temperature and time, is necessary for future applications of this material in NMR-spectroscopy. We present results of E(I)-measurements of differently heat treated samples and show the influence of the HT on Ic, Bc2 and the pinning force. Interpolation of the data allows us to create complete Ic(B,T,t)-surfaces, which will be presented, too