Quick extraction of microwave pulses from a cavity by a superconducting polycrystalline BaPb1−xBixO3 thin film

Abstract

A superconducting polycrystalline BaPb1−xBixO3 thin film of 300 nm thickness is studied as a quick microwave switch. The film is installed in a cylindrical TE111-mode cavity made of copper with a resonant frequency of 2.84 GHz; the cavity is evacuated and immersed in liquid helium. Transition from the super- to normal conducting state of the film is made by a pulse current through the film with a current density of the order of 3×107 A/m2. The microwave pulse power, which is 1.2 times the cw input to the cavity, is extracted in a short time of less than 200 ns. The time response of the film switch is less than 30 ns, which is the limit of our measuring system. The observed output powers are compared with numerical analyses, and the possibilities for improving the pulse power gain are discussed.