Numerical analysis of current density distributions in bi-2223 tapes under self and external fields

Bi-2223 was a kind of significant superconductor material with high current carrying capability, it was commonly applied in fields such as high temperature superconducting magnet, nuclear magnetic resonance spectrometer (NMR), magnetic resonance imaging (MRI), and other equipments. The design of superconducting magnet and the AC loss calculation were relevant to the distributions of current density and magnetic field in the conductor. The current and magnetic field distributions in Bi-2223 conductors based on Brandt's method through the Matlab was calculated, including the effects of self and external field. For the convenience of calculation, the perpendicular and parallel field dependence of critical current obtained by experiment substituted for Kim-type or Bean model J_c(B) dependence. Three conditions were applied: (1) external magnetic field only, (2) transport current only, (3) transport current together with external magnetic field. The results showed that when the amplitude of transport current I_m<20 A or applied magnetic field B_m<100 mT, J_z (x) increased with the increase of transport current and applied magnetic field. When I_m>20 A or B_m>100 mT, the max value of J_z(x) declined with the increase of amplitude of transport current and applied magnetic field. The screening current density decreased with the increase of frequency, but the distribution of J_z(x) was not so much relevant to the I_a frequency. If the transport current was ramped into a Bi-2223 tape with the background magnetic field, the current density would not be symmetric to the conductor center and the saturated current density would decrease with the increase of B_m.