TRANSIENT FLUX DYNAMICS IN OPTICALLY IRRADIATED YBCO THIN-FILM SWITCHES

A high-current-density, superconducting thin film will exclude a perpe ndicular magnetic field, produced either by a coil or a magnet. When t he film is driven into the normal state by a fast optical pulse, the s creening currents decay, allowing flux to enter. The process of flux e ntry can be observed by measuring the induced voltage across a coil cl osely coupled to the film. This is equivalent to the operation of an o pening switch and can be used to generate fast current pulses. This co ncept has been experimentally demonstrated in low high magnetic fields , corresponding to the reversible and irreversible regimes, using 500- nm-thick YBCO films and a 1.064-mu m, 150-ps pulsed laser. Theoretical analyses of current redistribution in the film associated with the tr ansient flux motion are compared with experimental results. Prospects for applications of this concept are discussed.