Recovery Characteristics of Coated Conductors

We investigated recovery characteristics of commercially-available coated conductors (CCs) after quenches. The CC had a hastelloy substrate and an Ag protection layer without stabilizer. The CC samples were subjected to simulated AC over-current to induce quenches. Both resistance measurement and bubble imaging were taken during the recovery. The samples were immersed in liquid nitrogen during the experiment. During the recovery, resistance of CC samples decreased monotonously to zero in some cases. In other cases, it decreased in two steps, first slowly and then faster. Resistance behavior depended on voltages applied during over-current period as well as sample dimension. It was related to cooling by liquid nitrogen and recovery propagation behavior, which could be observed directly by bubble imaging. The bubble imaging and the resistance measurement results matched with each other. The recovery generally propagated faster in thinner and wider samples as well as when higher voltages were applied during the over-current period. This recovery behavior was understood quantitatively with the concept of heat transfer to the surrounding liquid nitrogen. Heat balance equation was solved, and the calculated data were compared with experimental results.