Quenching of superconductivity and propagation of the resulting normal phase in YBCO films

For the development of resistive fault current limiters understanding of the transition into the normal state is a crucial point. Thereby, there is a ongoing discussion of whether this quench formation is due to a thermal or a non-thermal process. Fast propagation velocity of the quench and a transition clearly below the critical temperature are hints at a non-thermal effect. We have investigated quench formation optically. Thereby, we found that the quench formation velocity is above 10 m s-1 along a YBCO stripe. After a certain quench length, which depends on the applied voltage, the propagation mechanism changes and the propagation velocity is reduced to 0.5 m s-1. We proved the optical results by measuring the quench propagation velocity via the voltage drop at taps separated by a defined distance. To explain quench formation we build up a thermal model within a numerical simulation. Thereby, flux flow motion leads to a thermally induced transition. Dissipated energy is transferred into the substrate, where it diffuses further on. This leads to a fast enlargement of the normal zone. The calculated propagation values are in good agreement with the experimental results