Hot Spot Stimulated Transition in YBCO Coated Conductors: Experiments and Simulations

Extensive applications of YBCO tapes claim for a comprehensive knowledge of their behavior in every possible operating condition. In particular, one of the main topics to explore is the tape stability against heat and current disturbances, in terms of minimum quench energy and normal zone propagation velocity (NZPV). In this work we present the results of NZPV measured in a 35 cm long YBCO coated conductors manufactured by SuperPower Inc. The tape is cooled by means of a cryocooler and kept under vacuum in order to achieve near-adiabatic conditions. Two independent heaters are positioned on the tape: one on the YBCO side and the other on the substrate side. The quench is monitored by recording the voltage and the temperature evolution along the tape. The NZPV, at 77 K, reaches a value larger than 2.5 cm/s for a bias current ${\rm I}=50\ {\rm A}$ which represents the 56% of the critical current value. The quench dynamics of the tape are discussed with the help of a simulation program based on the finite difference discretization of the tape with the Fourier's heat equation: the model is able to reproduce the experimental behavior.