Critical currents in Bi-2223 tapes near T-c under magnetic field and gamma-irradiation

The critical temperature and critical current of Bi-2223 tapes have been st udied near T-c under a magnetic field and gamma -irradiation. T-c decreases from 109 to 96 K with an increase in B up to 100 mT. In the 100-110 K rang e I-c decreases by about 75-85% at steady rates in low fields up to 20-50 m T, then decreases to zero at slower rates with further increase of field. T he I-c versus B plots are non-exponential in small fields (up to 30 mT at 1 00 K and up to 10 mT at 108 K) and change to exponential form at higher fie lds and temperatures due to the increased role of flux flow for the current dissipation. The T-c of the tapes decreases from 109 to 106 K with an incr ease in the gamma -dose up to 50 MR, most of the change taking place in low doses up to 10 MR. The critical currents of the tapes decrease by about 50 -60% with gamma -irradiation under low doses up to 10 MR, then changes very little at higher doses up to 50 MR. We propose that gamma -irradiation red uces the anisotropy of the oxygen and carrier distributions in the tapes ca using the decrease in T-c and I-c; but the links between the grains, being predominantly SIS-type, have not been effectively changed by gamma -irradia tion.