Critical current, electro-mechanical properties and specific heat of bronze Nb3Sn conductors

The fabrication process leading to a Nb3Sn wire by using the bronze route with 15.4 wt per cent of Sn is described. The critical current density, Jc, is studied as a function of the applied magnetic field, B, up to 25 T; the uniaxial strain, ε, was measured up to 17. In the second part our device for measuring Ic(ε) is presented. The device is based on the concept of the Walters spring (WASP), which allows to measure long length wires (voltage taps distance up to 50 cm), up to 1000 A and to obtain an absolute measurement of the strain value. It is thus possible to measure the voltage-current relation of technical superconducting wires and tapes down to 0.01 μV/cm, an important requirement for the characterisation in view of applications like NMR high field magnets which require persistent mode operation with high current densities. Finally specific heat measurements on Nb3Sn wires prepared at GAP have allowed to determine for the first time the overall distribution of Tc in the filaments. The onset of Tc was observed at 17.2 K, the Tc distribution being centred at 15.9 K. This analysis confirms the reduction of Tc due to the Ti addition and the presence of a distribution of Sn in Nb3Sn bronze wires. (authors)