Magnetic shielding of short thick GdBCO tube fabricated by the buffer aided TSIG method

Melt-textured (RE)Ba2Cu3O7 superconductors (where RE is a rare earth element like Y, Gd or Dy) have a significant potential for passive magnetic shielding. Their critical current density Jc, however, is not uniform throughout the sample and this fact needs to be taken account to design a large magnetic shield made of these materials. In this work, magnetic shielding properties have been investigated at 77 K in an axial magnetic field for short GdBCO tubes fabricated by the top-seeded infiltration and growth (TSIG). The tubes, having ~ 10 mm thick walls, were studied with or without caps made of the same material. First, the shielding factor measured at several positions along the axis of the open tube was used to assess the non-uniformity of the shielding performance along the z axis. Second, four different configurations were brought when closing a tube with a disk, and their shielding performances were measured and compared. Third, we investigated the magnetic shielding efficiency for the tube closed with caps of different geometrical characteristics. The thickness of the cap used to close one side of the tube was shown to be an important parameter; experimental results showed that the same efficiency of a given cap could be obtained by stacking up two thinner caps with the same total height. Finally, the shielding behaviour of the open tube was modelled in order to investigate the flux penetration and to analyse the possible distribution of the critical current density Jc in the non-uniform GdBCO tube. The field dependence of the shielding factors measured at five elevations along the axis of the tube could be reproduced qualitatively by considering the GdBCO tube made of 3 layers, each of them with a constant Jc. This gives evidence that a simple model ignoring the field dependence of the critical current density can be used to reproduce the experimental magnetic shielding data. The model was also used to show the field penetration into the tube walls. These results are useful for getting better understanding of the properties of bulk superconductors synthesized by the TSIG process and to identify, in a non-destructive manner, which parts of the samples could be improved to obtain a good shielding performance.