Temperature dependence of critical currents and ac transport losses in (Bi, Pb)2Sr2Ca2Cu3Ox and YBa2Cu3Oy tapes

The critical currents and self-field ac losses of YBa2Cu3Oy coated conductors and (Bi,Pb)2Sr2Ca2Cu3Ox tapes were measured at several temperatures between 45 K and the respective critical temperature. The temperature dependence of ac losses was measured at 50 Hz using the lock-in method for a transport current. The frequency dependence of ac loss was measured at 55 K for transport current frequencies from 25 to 400 Hz. The results show that variation of ac transport loss as a function of normalized critical current is nearly the same at all temperatures in the measured temperature range for both YBa2Cu3Oy and (Bi,Pb)2Sr2Ca2Cu3Ox tapes. The temperature dependence of the loss factor, however, is different for (Bi,Pb)2Sr2Ca2Cu3Ox and YBa2Cu3Oy tapes because of the ferromagnetic loss in the NiW-based coated conductor substrate. Similarities and differences in the temperature and frequency dependence of ac transport losses between (Bi,Pb)2Sr2Ca2Cu3Ox and YBa2Cu3Oy tapes are discussed.