Multifilamentary Nb3Sn superconducting strands fabricated with high niobium fractions have exceptionally high critical-current densities but are sometimes marginally stable during testing. We report a technique for determining the pre-strain in such conductors, in which additional stabilizing copper is electroplated onto the conductor and the pre-strain is determined by extrapolation to the as-fabricated niobium fraction. This technique is used to measure the pre-strain in conductors with high niobium fractions of 20% to 30%. Values of the pre-strain, εmax in these conductors are reduced to the range 0.1% to 0.2%, which is significantly less than the εmax values of 0.2% to 0.4% in traditional bronze-process Nb3Sn conductors (where niobium fractions are typically about 10% to 15%). However, including about 20% dispersion-strengthened copper into the conductor matrix restores εmax to the range 0.25% to 0.35%, thus providing practical levels of εmax for magnet design in high-niobium-fraction strands.
Citation: IEEE Transactions on Applied Superconductivity
Pub Type: Journals
axial strain, copper-alloy, critical current, niobium-tin, thermal contraction