Superconducting-magnetic heterostructures as a new method of decreasing transport AC losses in multifilamentary and coated superconductors

Numerical modelling was used to investigate the effect of decoupling the filaments in superconducting tapes by magnetic screening on transport AC losses. Both multifilamentary Bi-2223 tapes and multifilamentary YBCO coated conductors were modelled. Different configurations of multifilament geometry with filaments covered with layers of a soft iron with non-linear B(H) characteristic were considered. Calculations of contribution of the individual filaments to AC loss were conducted for selected configurations. A comparison of the calculated AC loss results in the multifilamentary conductors with a perfect inter-filamentary decoupling was provided. The obtained AC loss level of modelled 55 "coupled" filaments agrees at the critical current value with the experimental results achieved for 55-filamentary Bi-2223 tape. Since the multifilamentary YBCO coated conductors appear to be a favourable solution for low AC losses applications, the factors which affect the percolative nature of current flow in superconducting coated conductors, such as grain size and sample dimensions, have also been studied in order to predict critical current density variations. (C) 2001 Elsevier Science Ltd. All rights reserved.