AC Loss in a Superconducting Bi-Sr-Ca-Cu-O Bulk Sample Carrying AC Transport Current

It is shown that the observed value of the AC loss of a cylindrical BSCCO bulk superconductor with the diameter of 9.6mm, carrying the AC transport current with the frequency of 60Hz, deviates noticeably from the theoretical values estimated from the critical state model. It is clarified that this deviation results from the fact that the internal distribution of flux density, B(r), is quite different from that predicted by the critical state model, when the AC transport current with the frequency, f, of 60Hz is applied to the sample with a large diameter, R, and with a low n-value. This conclusion is based on the numerically simulated results of B(r) obtained by solving the Maxwell equations using the observed Jc=Jc(B) and E(J)=E(0)(J/Jc)n characteristics for the DC electric field, E, the DC transport current density, J, and the DC critical current density, Jc, determined by the criterion of 0.1μV/cm. Finally, a general numerical chart of the AC loss against fR2Jc is presented for the various n-values, for the convenience of the design of the high-Tc current leads.