Behavior of an inhomogeneous HTS film in the regime of a resistive current limiter

A high-temperature superconducting (HTS) YBCO thin film covered by a gold layer on sapphire substrate is a very attractive element for building resistive current limiters. The quench dynamics in an HTS thin film with a strong inhomogeneity of the critical current was studied in the circuits with AC and DC voltage sources. The temporal dependence of the normal zone length was found to be of a non-monotonic character. After the normal zone propagates at some distance, it reverses the direction of its motion. The successive returns of the film sections into the superconducting state are observed. Under AC condition, the normal zone can be divided into several parts separated by superconducting regions. This phenomenon is explained by the dependence of the thermal parameters of the sapphire substrate on temperature, in particular, the dramatic reduction of the heat conductivity of the sapphire with the increase of temperature.