Field-cooled magnetization of Y-Ba-Cu-O superconducting bulk pair reinforced by full metal encapsulation under high magnetic fields up to 22 T

Abstract

We report on the field-cooled magnetization (FCM) process under magnetic fields of up to 22 T for the stacked Y-Ba-Cu-O (YBCO) bulk pair reinforced by a stainless steel (SUS316) container. On the basis of the numerically simulated mechanical stress in a bulk during FCM, the SUS316 container was designed by the numerical simulation to offer the sufficient hoop stress tolerance to the bulk trapping the magnetic field of 20 T. As a result, we obtained successfully the trapped field, BT, of 15.1 T by FCM from 18 T at 28 K at the center of the YBCO bulk pair. However, the extremely large-scale vortex jumps and large temperature rise occurred suddenly during FCM from a higher field of 22 T at a lower temperature of 23 K, and then a small crack was confirmed at the periphery of “both” YBCO bulks from the distorted contour maps of BT. The simultaneous break of both YBCO bulks probably in spite of sufficient mechanical reinforcement led us to conclude that the thermal instability triggered off the large-scale vortex jumps and large heat generation. The stress concentration induced thermally at the hot spot brought about the cracking.