No abstract

The hysteresis loss in a Sm1Ba2Cu3O7−δ coated conductor was estimated from magnetic field profiles measured by the scanning Hall probe method. Current, Ia, and magnetic field, Ba, were applied simultaneously; Ba was applied in the normal direction with respect to the tape surface. Ba and Ia were varied from Bpeak to −Bpeak and from Ipeak to −Ipeak, respectively, with the ratio α = Ia/Ba fixed during the variation. Three values of α were taken for the three load lines. The values of Bpeak/Ipeak were varied from 0 mT/0 A to 10.7 mT/116 A, 99.1 mT/50 A, and 298.2 mT/46.1 A, respectively, for the three load lines. From the measured values of magnetic field profiles, the current profiles were calculated by the iterative inversion method. From the current profiles, the flux density profiles and the hysteresis loss, Q, were then calculated for various values of Ipeak(= αBpeak) in each load line. The results were compared with theoretical calculations based on Brandt’s model. When Bpeak was about 300 mT, the estimated values of Q were several times smaller than the theoretical values of Q with the self-field Ic0. The low value of Q in this case is due to the field dependent Ic and the saturation effect of the current profiles, which results in significant reduction of the induced magnetic moment, M.

A simple model for estimating the hysteresis energy loss of coated conductors under a general load line was studied. We took advantage of the characteristic line I b (H a ) to determine the major parameters used in this model. The value of I b (H a ) was based on the scanning Hall probe measurements (SHP) on a Sm 1 Ba 2 Cu 3 O 7−δ coated conductor. During SHP measurement, a magnetic field (H a ) and current (I a ) were applied simultaneously and were varied along 11 different load lines. From the values of SHP measurements, the current density profiles, J (x, H a , I a ), were calculated using a numerical inversion method. We define the quantity I b = w −w |J (x, H a , I a )| dx and we calculated I b at many points (H a , I a ) in every load line. We found that when I a is less than I b and the flux trap regions are absent, the values of I b for all points (H a , I a ) constitute a single line I b (H a ), which can be easily extrapolated to a high field. This line provided a major parameter for our model.