Quench Protection Study of a 14 T Conduction-Cooled Magnet Built With Nb3Sn and NbTi Superconducting Coils for PPMS

A 14 T conduction-cooled superconducting magnet with a clear cold bore of 50 mm in diameter is designed and fabricated for a physical property measurement system. The magnet is built with six Nb3Sn coils and five NbTi coils arranged coaxially. To reliably protect the 14 T magnet, a passive quench protection scheme is developed, including a novel coil subdivision method and heater network design. The novel coil subdivision method mixes a NbTi coil and an Nb3Sn coil into the same subdivision to reduce the hot-spot temperature of the Nb3Sn coil. Different heaters parameters are compared and analyzed to obtain a lower hot-spot temperature. In addition, an efficient way of raising the ratio of copper to superconductor in the superconducting wires is used to reduce the hot-spot temperature of the Nb3Sn coils in the low magnetic field region. An in-house quench simulation code in MATLAB, including a finite difference method for the Nb3Sn coils in the low magnetic field region and a quench ellipsoid propagation model for the other coils, has been developed. This article describes the details of the passive quench protection scheme and presents the quench simulation results.