Transient response of 50 KiloAmp Y-Ba-Cu-O rings and ring pairs to pulsed magnetic fields

Shielding current limits and magnetic diffusion characteristics have been measured at 77 K in large-grain YBCO rings with oriented microstructures. The samples are surrounded by a drive coil that can achieve magnetic fields in excess of 1 Tesla and induce currents in excess of 50 kA when driven by a current pulse of a few msec duration. Simultaneous magnetic measurements with a Rogowski coil and a Hall probe allow determination of the induced current in the sample and the field in the center of the sample. These measurements show that field penetration occurs in a complex way that includes delays and transient effects caused by magnetic diffusion and sample heating. Dramatic threshold effects are observed that are probably related to a creep-flow transition coupled with local heating effects. Geometric effects are investigated using a single drive coil and a pair of YBCO rings with various spacings. A test geometry equivalent to a simple penetration-type inductive fault current limiter is used; the experimental results are therefore of interest for design and characterization of these devices