Trapped field in individual and stacked rings of bulk melt processed Y-Ba-Cu-O

Single grain rare earth barium cuprate [(RE)BCO] high temperature superconductors can trap large magnetic fields. In principle, samples can be stacked to form a quasipermanent magnet with a high length to width aspect ratio for engineering applications. The flux trapping properties of a stack of ring-shaped samples of Y-Ba-Cu-O (YBCO) were measured both on the surface and through the bore. Significant discrepancies between the experimental results and the predictions of a simple theory based on the Biot-Savart model were observed. These differences can be accounted for by the presence of a high density of small cracks parallel to the ab planes, which inhibit the circulation of current around the sample.