Ms. Michal Wasserman

Dendritic Flux Avalanches in Superconducting Hybrid Structures Exposed to Fast Ramping Magnetic Fields

Abstarct:

Type-II thin-film superconductors exposed to magnetic field often exhibit magnetic instabilities in the form of dendritic flux avalanches. These instabilities can have a catastrophic effect on the performance of superconducting applications (raising the local temperature well above T_c and even leaving permanent damages), even more so under high ramping fields. Recent experiments demonstrated suppression of the dendritic avalanches by coating the superconducting films with additional conducting layer (either normal-conducting or superconducting) but did not measure the suppression for high ramping rates. In this work, we exploited the unique fast MOI system in our lab, which allows the measurements of dendritic avalanches generated by ultra-fast ramping fields. The first part of the work investigates the flux avalanches' suppression in a partially Cu-coated NbN film, the partial metal coat layer suppressing nucleation along the coated edges completely and stopping advancing dendritic branches, due to the damping of vortex motion by induced eddy currents in the Cu coat layer. With increasing ramping rate, however, the suppression efficiency decreases. In the second set of experiments, we investigated the flux avalanches' suppression in partially Nb-coated NbN film, where the dendrites exhibit a much more complex behavior with the existence of two new and distinctive types of dendrites: Hybrid dendrites, that occupy both of the different superconducting layers of the hybrid structure, and are affected by both. And surface dendrites, that are created at the coat layer only, and not in the superconducting underlayer. Each of the new types of dendrites has its unique characterization and behavior, as is seen through their spatial dendritic shape and temperature dependency.