Ac-losses of superconducting Bi-2223 tapes with two different time constants

Ac-loss and time constant measurements were performed with Bi-2223 tape conductors in Ag matrix at 4.2 K and at 77 K. The frequency dependence of the loss curve shows the expected maximum at ωτ=1. In some cases the loss curve goes through a minimum in the higher frequency range and then increases again, with a possible second maximum. It is shown that this second increase is explained by eddy currents in the silver matrix, which are described by a second time constant ϑ≪ τ. Both time constants, τ and ϑ can be seen in time constant measurements. The full theoretical description of time constant and loss measurements is given using a slab model. The agreement with the measurements is very good in parallel field orientation where the slab model is a good approach, and it is still a valuable approach in perpendicular field.