Comparing the thermal stability of NbTi and Nb3Sn wires

The investigation of quenching in low temperature superconducting wires is of great relevance for a proper design of superconductive cables and magnets. This paper reports the experimental results of a vast measurement campaign of quench induced by laser pulses on NbTi and Nb3Sn wires in pool boiling helium I. A comparison of the quench behavior of two typical NbTi and Nb3Sn wires is shown from different standpoints. Different qualitative behaviors of the voltage traces recorded during quenches and recoveries on NbTi and Nb3Sn wires are reported and analyzed. It is shown that the Nb3Sn wire exhibits a quench or no-quench behavior, whereas quenches and recoveries are exhibited by the NbTi wire. The two wires are also compared by considering the behaviors of the two main parameters describing quench, i.e. quench energies and quench velocities, with respect to operating current, pulse duration, and magnetic field. It is shown that the Nb3Sn wire exhibits a ‘kink’ of the quench energy versus current curve that makes the quench energy of Nb3Sn lower than that of NbTi at some intermediate current levels. Both the qualitative differences of the voltage traces and the different behaviors of quench energies and velocities are interpreted through a coupled electromagnetic–thermal model, with special emphasis on the detailed description of heat exchange with liquid helium.