Magnetic Field Mapping Above the Superconducting Tape With Ni-Covered Edges

Covering the edges of a Bi-2223/Ag tape conductor by a layer of soft ferromagnetic material has positive impact on its two basic performance characteristics in low magnetic fields: the critical current is improved by $\sim$20%, and both the magnetization and transport AC loss are reduced. Reasonable theoretical prediction of the critical current in the tape is obtained by a numerical finite-element method: the whole superconducting portion is saturated by the critical current density assumed to be anisotropic and dependent on the magnetic field. However, for the prediction of AC loss the intermediate states with partial saturation of superconductor are also significant. We studied experimentally the development of magnetic field above a common multifilamentary Bi-2223/Ag tape with edges covered by nickel during stepwise change of the transport DC current. Indirect information about the distribution of electrical current and hence the process of magnetic flux penetration and dissipation at changing the value of current can be extracted from these experiments.