Quench propagation in large area YBCO films

We studied quench propagation in double-sided samples of YBCO thin films covered by a gold top layer and deposited on sapphire wafers. The length of the YBCO structures was up to 0.5 m. A critical current density /spl sim/2-3 MA per centimeter square at 77.8 K was found over the entire YBCO film. Quench development in large-area YBCO thin film appears to be a complicated process. Depending on test conditions and external circuit parameters, normal spots may appear and disappear during the quench process. In double-sided samples quench development is strongly affected by thermal interaction between the two films through the substrate's heat conductivity. This thermal conduction should be considered during the design of fault current limiters made from such films. Mutual thermal interaction of a film through a substrate may also be used for acceleration of normal zone propagation using active or passive heaters on opposite sides of the substrate.