CHARACTERIZATION OF HIGH-CURRENT Nb_3Sn CABLE-IN-CONDUIT CONDUCTORS VS APPLIED SHEATH STRAIN

摘要

The three superconducting subcoils for the 45-T Hybrid Magnet System now being assembled at the National High Magnetic Field Laboratory (NHMFL) all use Cable-In-Conduit Conductors (CICC); two of these contain strain-sensitive, multifilamentary Nb_3Sn wires. With the extremely high peak fields in which the conductors for these coils must operate - nearly 17 T for one Nb_3Sn coil and approximately 13 T for the other - it is essential to account for the total intrinsic filament strain resulting from the combination of differential contractions during cooldown from the reaction temperature and the hoop loading of conductors during energization of the magnet. We have examined this problem through tests of specially constructed model conductors, wherein the NHMFL split-solenoid was used to measure critical currents of over 10 kA, at fields up to 14 T, and with applied longitudinal loads up to 250 kN. We describe the results of these tests, the correlation of the full-scale CICC results with critical-current vs applied-strain measurements on single wires, and our projections of the operating margins expected for the Nb_3Sn coils in the 45-T Hybrid.