STUDY ON AC LOSSES OF HIGH Tc SUPERCONDUCTORS IN 50Hz APPLIED MAGNETIC FIELD

AC losses of Bi-2223/Ag tapes prepared by different processes and YBa2Cu3-xSnxOy bulk materials substituted partially by Sn for Cu have been investigated in a sinusoidal magnetic field H(t) with the frequency of 50 Hz at 77K. The experimental results showed that the appropriate decrease of temperature and time of the heat treatment can reduce AC losses in the monofilamentary tape.The reduction of thickness can also reduce AC losses.The subdivision of monofilamentary tape into multifilamentary tape will suppress the hysteresis loss.On the other hand, the coupling of interfilaments will increase the eddy current loss in Ag matrix.So the AC losses of the tape with 19 filaments are only about 20% less than the monofilamentary tape. The AC loss of Sn-added sample is lower than that of YBa2Cu3Oy.The content of Sn influences the dissipation characteristics of the YBa2Cu3-xSnxOy. The AC loss of YBa2Cu2.95Sn0.05Oy is lower than that of YBa2Cu2.94Sn0.06Oy.The addition of Sn has an important effect on the microstructure of the Y-system superconductor.The partial substitution of Sn for Cu can reduce the average size of Y2BaCuO5(211)particles and increase the boundaries between 211 and 123 phase. In addition,Sn can also lower the melting temperature of the Y-system superconductor.All of these lead to the increase of pinning-force and Jc hence the AC loss is decreased.