Frequency dependence of self-field AC losses in Bi-2223/Ag tapes

We have studied the frequency dependence of self-field ac losses in multifilamentary Bi-2223/Ag tapes at 77 K. The losses were measured at the frequencies of 1-400 Hz. The electromagnetic loss measurements were completed by the measurement of the magnetic flux distribution inside the tape due to the ac transport current at different stages of the ac cycle. According to the results the ac losses per cycle at fixed current amplitude are the higher the lower the frequency. The experimental results were compared to numerical ones computed using the finite-element method. The comparison between the experimental and computational results states that the frequency dependence of the losses per cycle is mainly caused by finite values of index n (of the E(J)-characteristics) due to thermally activated flux creep. As a result, the self-field penetrates the deeper into the conductor the lower the frequency, which means higher hysteresis losses per cycle.