Hybrid superconducting screens combining disk-shaped bulks and closed-loop coated conductors: modelling and experimental validation

In this communication, we demonstrate numerically and experimentally the remarkable DC magnetic screening ability of hybrid superconducting screens combining a 30 mm-diameter disk-shaped superconducting bulk with different closed superconducting loops made from coated conductors. The loops are placed coaxially with the bulk. The DC and inhomogeneous field to be screened is produced by a coil. This configuration is studied using a 2D axisymmetric finite element model solved by the H-phi formulation. The measurements are then performed at 77 K using a bespoke, cryogenic 3-axis Hall probe. The results show that such a hybrid superconducting screen allows the maximum screening factor SF above the bulk to be roughly doubled. In addition, the area of the spatial region for which SF > 2 is multiplied by a factor ~ 4 when compared to a situation involving only a disk-shaped bulk. The finite element model is used to investigate the influence of the inhomogeneity of the applied field on the screening effect. Then, we use the model to show that it is possible to optimize the loop size to maximize both the maximum SF and the screened surface.