The influence of tape arrangements on the critical current of Bi-2223 superconducting current leads

The current lead is an important application of high temperature superconductors. In this work, superconducting current leads are assembled by using Bi-2223 tapes with J_c = 32000 A/cm² at 77 K under self-field. The influence of self field on the critical current (I_c) is studied by changing the distance (d) between neighboring tapes. With our in-situ d changing device, I_c values of current leads with 2 and 3 tapes are measured as a function of d (0.5-15 mm). It is found that the total I_c decreases greatly if d < 1.0 mm due to the influence of self-field. An analysis method concerning the field dependent property and self-field distribution of the current lead is suggested and compared with the experimental data. Finally 6-tape current leads are prepared. Copper layers are added as protection circuits, which are put between neighboring tapes. The total I_c is about 0.681 of the sum of I_c of each individual tape when d = 0.26 mm. This ratio increases to 0.835 if 1 mm thick copper layers are put between two adjacent tapes (d = 1.26 mm). It agrees with our calculation quite well. This knowledge helps us to design tape arrangements in current leads and other HTS devices using large current.