The a.c. Losses in (Bi,Pb)₂Sr₂Ca₂Cu₃O_x silver-sheathed superconducting wires

In this study, a.c. losses in BSCCO silver-sheathed wires, both single- and multi-filamentary, were investigated by means of a.c.-magnetization and a.c.-transport techniques. It was shown that the longitudinal magnetization a.c. loss in a single-filamentary wire could be quantitatively explained by the simple sum of the magnetic hysteresis loss of the superconducting core and the eddy current loss in the silver sheath, while those in multi-filamentary wires behaved quite differently, possibly being affected by electromagnetic coupling between filaments. On the other hand, the self-field a.c. loss of all the wires employed was found to be well described by a simple expression derived for a uniform superconducting cylinder based on Bean's model. Namely, the self-field a.c. loss was determined solely by the critical current /_c and /_p//_c (where /_p is the peak value of the transport current), regardless of their cross-sectional structure and the distribution of the current flow is considered to have an elliptical symmetry even for multi-filamentary wires, where the critical state is established from the outermost filaments toward those in the interior. It is suggested that the self-field loss of multi-filamentary wires could be reduced if the distribution of the current flow can be made equivalent for all filaments.