Transport AC Loss Properties of a Bi-2223 Superconducting Coil From 0.1 Hz to 10 Hz
We propose a method to evaluate transport AC losses in Bi-2223 superconducting coils by integrating the local external-field losses of the stacked taped wires over the coil's windings. We measured the transport AC losses of a 16 double-pancake coil of twisted Bi-2223 Ag-sheathed tapes, in the frequency range from 0.1 to 10 Hz at liquid nitrogen temperature. We also measured the external-field losses of short specimens of 6-stack Bi-2223 wires both in perpendicular and parallel field configurations through a saddle-shaped pickup coil method. The external losses are mainly due to hysteresis losses in the superconducting filaments and coupling losses among the filaments. The local external-field loss in the test coil is approximately calculated as the sum of perpendicular- and parallel-field losses of the short specimen. In the calculation, geometrical effects because of the neighboring turns in the coil are also considered, in addition to the magnitude and direction distributions of the local magnetic field. We compared the numerically evaluated external-field losses to the measured transport AC losses, and discussed the applicability of the proposed method.