STUDIES OF THE CRITICAL STATE AND DEMAGNETIZATION EFFECTS IN CERAMIC DISK OF Y-BA-CU-O SUPERCONDUCTOR

This paper reports on studies of the critical state and demagnetization effects in Y-Ba-Cu-0 (YBCO) ceramic disc-shaped superconductors. The profiles of shielding and trapped magnetic flux were measured across superconducting ceramic and pressed-powder disc-shaped samples. These experiments allowed the authors to distinguish between intergranular and intragranular components of shielding, and to determine that the shielding close to the sample edges is strongly reduced due to the intergrain flux flow. Computer calculations of the shielding field profiles were performed, taking into account intergrain and intragrain components of shielding and demagnetization effects at the disc edges. The reproduction of intergrain shielding was carried out with a model disc that consists of an array of coaxial current loops lying in the disc plane and carrying current at the level of the intergrain critical current density. In order to account for demagnetization effects, current loops at the disc edges were removed. Intragrain shielding was calculated using a model disc filled with small current loops (magnetic dipoles) which simulated shielding of individual superconducting grains.