Papers by Author: Andre Sulpice

Abstract: Bi-2223 tapes are usually subjected to tensile strain, bending strain and compressive stress in the process of fabrication and applications. In this study, we have measured the critical current of Bi-2223 tapes as a function of transverse compressive stress. The effects of the cross section size and processing defects on the stress characteristics of AgMn-alloy sheathed Bi-2223 tapes are compared. The experimental results showed that the onset transverse compressive stress for degradation of Ic was lower in the thinner tape with a thin Ag sheath due to the stress concentration on the irregular interface. The bubbled tapes were more sensitive to the transverse stress compared to the nonbubbled tapes.

Abstract: In order to optimize the synthesis process of internal-Sn Nb3Sn wires, magnetization measurements have been performed on samples reacted at various temperatures between 650 and 725 °C and for time ranging from 8 to 200 h We compared samples of various origins, from NIN in Xi'an and Alstom in Belfort. These measurements give us access to critical and irreversibility temperatures. Although all Nb-Sn phases are superconductive, their critical temperatures are varying from 6 K (18at%Sn) to 18.3 K (25%atSn : stoichiometric Nb3Sn). Thus, Tc and T* measurements are related to the progress of tin diffusion and reaction in the wires. We correlate the results of magnetization with SEM (Scanning Electron Microscopy) and EDS (Energy Dispersive Spectroscopy) observations, which indicate directly the Sn content distribution across Nb filaments.

Abstract: The layer growth of the A15 (Nb3Sn) superconducting phase produced by the internal tin method on model monofilament wires was studied by neutron diffraction and electron microscopy techniques. Different ratios of the inner part of the wire (Sn/Cu) and the effect of the addition of 1% of zirconium to niobium were studied. The high temperature heat treatment plays a key role on the A15 formation and on the cost of the final wires produced. Different temperatures in the range 650-725°C and different annealing times in the range 8-200 hrs have led to the preparation of 72 different samples. The neutron diffraction study has evidenced the different phases formed during the heating treatment and the electron microscopy study has evidenced a power law for the growth rate of the A15 phase. In both studies the addition of zirconium in niobium is very effective on the growth rate of the A15 phase.