FLUX-PINNING AND SUPERCONDUCTIVITY IN IN-SITU PREPARED AL-DOPED AND ZN-DOPED CU-NB COMPOSITE WIRES

The effects of Al and Zn on the critical current density, upper critic al field and pinning force of in situ prepared Cu-Nb wires have been s tudied. Doping this system by 1 wt% of these impurities results in a c hange in critical current density and pinning force. The critical curr ent density increases at lower fields for both additives but decreases at high fields. The upper critical field H-C2 shows a decrease for bo th additives. We have modified the Kramer flux pinning law for these t wo additives. It is found that the value of n, which is a constant in the scaling law of Fietz and Webb with a value of 2.5, varies in the c ase of these additives and does not remain constant.