High performance one-step grown half-moon shaped YBCO bulk superconductors

High-temperature superconducting (HTS) undulator exploiting the high trapped field of HTS bulk superconductors enables the design of extremely short-period insertion devices for synchrotron light sources and free electron lasers. In such a promising application the trapped field performance and the uniformity of the HTS bulk superconductors are essential. In this study, the half-moon shaped YBa2Cu3O7−δ (YBCO) single-grain superconductors have been directly grown by the top-seeded melted-growth (TSMG) method. Half-moon shaped samples directly grown from preforms with four different type of seed crystal arrangements were compared with that cut from larger cylindrical bulk superconductors in regarding to the trapped magnetic fields and correspondingly the distribution. We found that the arrangement of seed crystals greatly affects the melt-growth process and hence the homogeneity of the samples. The one-step grown half-moon shaped samples show higher trapped field (Btrap), 0.542 T for a 24 mm and 0.785 T for a 32 mm diameter sample, and better uniformity of trapped field distribution compared to that obtained from machining with Btrap of 0.427 T and 0.528 T. It was found that the growth sectors would be restricted when the seed crystal was placed at the edge of a preform, and the angle of the seed crystal, parallel or 45° to the long edge would influence the melt growth as well.