Trapped Field and Flux Creep in Stacked (Gd,Y) Superconductor Tape Arrays

The effect of in-field critical current and number of tapes in crisscross-arranged stacks of zirconium-doped (Gd,Y)Ba₂Cu₃O_x superconductor tape arrays on the magnitude and decay of trapped magnetic field at 77 K has been investigated over an area of 36 × 36 mm. The trapped field was found to vary with zirconium content, increasing from 0% to 7.5% Zr addition and decreasing from 7.5% to 15% Zr addition, consistent with the magnitude of critical current of the tapes at 1 T and 77 K. The trapped field in the stacked superconductor tape arrays was observed to increase linearly with the number of layers of tapes in the stack, even up to 236 layers. A logarithmic time-dependent decay of trapped magnetic field was observed in all stacks, consistent with the phenomenon of thermally-activated flux creep. The rate of decay of trapped field was found to decrease with increasing number of tapes in the stacked superconductor tape arrays.