Superconducting properties of i n s i t u–processed Nb3/Sn-Cu composites

Abstract

Performance characteristics for a family of Nb₃Sn‐Cu superconducting composites have been studied to determine the optimum value of various fabrication variables such as the Cu‐to‐Nb ratio, Sn content, reaction temperature, reaction time, and dendrite size in the original casting. Basic superconducting properties such as the critical current and effective upper critical field are found to change in a very regular way as these parameters change and there are clear design tradeoffs which can be made depending on the wire specifications needed. A typical high‐performance wire is made from a Cu₇₀Nb₃₀ casting with 2–8‐μm dendrite size reacted with a stoichiometric amount of Sn at 550 °C for 6 days. In this study there has been a special emphasis on materials made from casting of a Cu–20 wt% Nb dendritic alloy. Critical currents of this alloy are smaller than for the 30% Nb samples, but the wire can withstand about 3% bending strain at the outer surface of the wire with only modest degradation of the J_c values.