MEASUREMENTS OF AC LOSSES DUE TO TRANSPORT CURRENTS IN BISMUTH SUPERCONDUCTORS

Measurements of the losses of BSCCO-2223 and BSCCO-2212 tapes carrying AC transport currents are reported. Measurements were made at 77 K at frequencies in the range 20-60 Hz. The voltage waveforms generated by the AC transport are presented as well as the AC losses. For peak transport currents below 90% of the DC critical current the losses of BSCCO-2223 tapes are shown to be well described using an equation due to Norris [5] which assumes the presence of a critical state in the superconductor, and the power losses are proportional to the AC frequency (hysteresis losses). When the AC peak current approaches the DC critical current flux-creep effects dominate the losses, and the power losses cease to depend on frequency. In the BSCCO-2212 sample flux-creep effects dominate at all currents. The examination of the voltage waveform generated in the BSCCO-2223 sample shows the presence of both hysteretic and flux-creep generated voltages.