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.