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)(2)Sr2Ca2Cu3Ox and YBa2Cu3Oy tapes are discussed.