When two superconducting materials are separated by an insulator of very few thickness and are connected by a wire, a dc current flows in the external circuit (dc.Josephson effect). However, if the two superconducting materials are connected to a dc power, an ac microwaves are produced at the junction (ac josephson effect).
In this case, the current persists only for a short time unlike the first case where this current was persisted longer. Is it the alone difference between the two kinds of Josephson effects ?