Improved trapped field performance of single grain Y-Ba-Cu-O bulk superconductors containing artificial holes

The intrinsic mechanical properties of single-grain RE-Ba-Cu-O bulk high temperature superconductors can be improved by employing a thin-wall geometry. This is where the samples are melt-processed with a pre-defined network of artificial holes to decrease the effective wall thickness. In this study, the tensile strengths of thin-wall YBCO discs were determined using the Brazilian test at room temperature. Compared with conventional single grain YBCO discs, the thin-wall YBCO discs displayed an average tensile strength that is 93 % higher when the holes were filled with Stycast epoxy resin. This implies a thin-wall sample should, in theory, be able to sustain a trapped field that is 39 % higher without exceeding the mechanical limit of the sample. High-field magnetisation experiments were performed by applying magnetisation fields of up to 11.5 T, specifically to break the samples in order to verify the effect of increased mechanical strength (and improved cooling) on the ability of bulk (RE)BCO to trap field successfully. The standard YBCO sample failed when it was magnetised with a field of 10 T at 35 K, suffering permanent damage. As a result, the standard sample could only trap a maximum surface field of 7.6 T without failure. On the other hand, the thin-wall YBCO sample survived all magnetisation cycles, including a maximum magnetisation field of 11.5 T at 35 K, demonstrating a greater intrinsic ability to withstand significantly higher electromagnetic stresses. By subsequently field-cooling the thin-wall sample with 11 T at 30 K, a surface field of 8.8 T was trapped successfully without requiring any external ring reinforcement