Time dependent electric field and E-I curves in Bi-2223 tapes carrying DC currents and exposed to perpendicular AC magnetic fields

A study of the time-dependent electric field, E(t), and E-I curves of BSCCO/Ag tapes at 77 K is presented. Measurements were performed on tapes carrying DC transport current and exposed to external AC (0-500 G, 4-400 Hz) magnetic fields perpendicular to the broad side of the tape. E-I curves measured at frequencies exceeding 50 Hz and at amplitudes of the AC field below 400 G are well described by power law in the range between 0.1 and 10 µV/cm of the electric field. The results within this domain of parameters are discussed, assuming a narrowing down of the DC current path under the application of a perpendicular AC field. Nearly linear dependency of electric field on transport current was observed at the frequency-amplitude domain below 10 Hz and above 500 G. Using magneto-optical techniques we are able to determine that in this domain the AC magnetic field fully penetrates the tape. Behaviour of E-I curves under these conditions can be elucidated using the dynamic resistance model in conjunction with the assumption that the magnetic field fully penetrates the superconductor.