Quench Characteristic and Minimum Quench Energy of 2G YBCO Tapes

Abstract

Due to a much extended current sharing regime and to the power law like E-J characteristics instead of the critical state, the quench characteristics of high temperature superconductors (HTSs) potentially differs from LTS. The understanding of thermal stability is therefore of crucial importance to meet the performance requirements set up by applications. In this work the quench characteristic and MQE measurements were carried out on 2G YBCO tape in self-field and field (0.1 T) scenario, in a wide range of temperature (40-80 K), where the conductors have a modest power exponent n ~ 20-30. The study focuses in particular on high current in the vicinity of Ic (j = I/Ic ~ 1), where power law current sharing dominates. Instead of vanishing with (1 - j), as expected for the critical state, the measured MQE is much higher near Ic. The high MQE and the heat generation of a non-(1 - j) scaling were constantly found in the temperature range 40 K-80 K of measurements. Such an enhanced MQE in the high current regime could be significant for HTS applications and suggests the possibility of sufficient stability very close to Ic. We show that the results can be explained by approximating the non-linear current sharing power-law heat generation with temperature by an equivalent critical state at a higher current sharing temperature. While the power-law and critical state converge at low j regions, the non-linear temperature dependence of thermal properties needs to be considered due to elevated quench/current sharing temperatures.