Normal Transition Behaviors in Nb₃Sn Superconducting wires at High Temperatures

Abstract

Normal transition behaviors such as minimum quench energy and normal-zone propagation velocity along longitudinal direction for two types of copper-stabilized Nb₃Sn conductors have been investigated at temperatures over 4.2K in He gas atmosphere compared with NbTi/CuNi composite conductor. Both of bronze-processed and powder-processed Nb₃Sn conductors show minimum quench energy several times as large as that of the NbTi conductor. Quench current for AC operation of the NbTi conductor is crucially degraded from critical current for DC operation. On the other hand, quench currents for the two types of Nb₃Sn conductors reach their respective critical currents. Normal-zone propagation velocities for both Nb₃Sn conductors are one order of magnitude lower than that of the NbTi conductor at the same temperature load factor. The experimental propagation velocity is well estimated by taking account of heat transfer from the conductor to its surroundings.