The Effect of Intermediate Pressure in the OPIT Fabrication on the Current Paths and the Current Carrying Capability of Bi-2223 Tapes

Intermediate pressing techniques in the OPIT fabrication of high temperature superconducting Bi-2223 tapes have evolved from plane strain pressing into more continuous methods such as rolling, continuous pressing and eccentric rolling. In this study one of the most promising methods have been investigated, and novel techniques to characterize the tape quality have been taken into use: magneto optical imaging was used to detect the current paths inside the superconducting tape and to reveal differences between tapes that were intermediately pressed differently. The filaments in the tapes were extracted and shattered by ultrasonic vibration in order to check the size distribution. Bending tests were performed to show differences in current carrying capability as a function of an applied external load. It is shown how the pressing load greatly influences the current carrying capability of the finished high temperature superconducting tapes. By selecting the right pressing method it is possible to optimise the I_cand J_evalues.