Experimental study of quench in a short sample of Bi-2223/AgMg tape in a conduction-convection cooling regime

Superconducting magnets based upon high temperature superconductors (HTSs) are more stable than low temperature superconductors (LTSs). This means that the minimum quench energy (MQE) of a HTS is higher than that of a LTS. However, disturbances such as flux jump, wire movement and epoxy cracks can cause a thermal runaway. In this case, HTSs are vulnerable because of the low normal zone propagation velocity (NZPV) thus HTS magnets are not self-protecting. To design a safe operating point for such magnets, quench characterization and the cooling mode are important. In this article, the normal zone propagation evolution of a short sample of Bi-2223/AgMg high temperature superconducting tape has been investigated by applying localized heat pulses. Experiments were carried out based on cryogenic stabilization in N2 vapor. To enhance the thermal stability, the superconductor sample is mounted on a copper plate which is immersed in liquid nitrogen up to the given height. By increasing the current, we measured the rate of decrease of the MQE, the superconducting stability factor, the rate of increase NZPV, and the protection parameter against quench.