Critical aspects in the measure of the quench propagation velocities on HTS tapes

Abstract

This paper concerns the investigation of the quench propagation phenomena in High Temperature Superconducting HTS tapes. In particular the determination of the Normal Zone Propagation Velocity NZPV, is based on the measure of the time propagation of the normal zone by reading the rising voltages detected by voltage taps placed at known distances. Several experimental aspects related to the measured times and voltages with their dependencies on temperature have to be considered. In particular, the rise up of the temperature determines a time limit that has to be considered to avoid the damage of the tape. Based on our measures of NZPV and in agreement with the results of a numerical model developed for our experimental environment, it is shown that the time limit of the measures is set by the value of the bias current. The tape length traveled by the normal zone front wave is related to this measure time and depends on the value of the NZPV that have to be measured. Adopting a simplified approach, it is possible to forecast the values of the tape length that may be used for the NZPV measurements and how its value may change as a function of the bias current.