Quenching in a High-Tc Superconducting Ring

The peculiarities in quenching of a superconducting region in a bulk BSCCO 2212 high-temperature superconducting ring are experimentally investigated. The quenching process is initiated by a fast increase of induced ac current exceeding a critical value. It was found that the transition proceeded in two stages with markedly different resistance and with a sharp jump between stages. The normal state transition in the ring begins with the occurrence of a relatively weak resistivity leading to a gradual heating. This is the first stage of the transition, which can be delayed for several ac periods until the energy dissipated is sufficient to produce a normal zone. It is shown that the transition to the normal state can be accomplished by the occurrence of a resistive domain being heated up to a high temperature. Effects of inhomogeneities in the critical current along the superconductor on the nature of the transition are discussed.