Improvement of Critical Current In Bi-2223/Ag HTS Tapes by the Bubbling Control

In general, the bubbling, generated during the fabrication of the tapes, breaks the superconducting filament, and critical current of the tapes will be decreased. Heat-treatment schemes of Bi-2223/Ag HTS tapes were modified, such as pre-annealing of multi-stacked billet, 2-step main sintering and ramp rate etc. The generation of bubbling was drastically decreased from 20 bubbles/m to 0 ~ 1 bubble/m by the modified heat-treatment. Therefore, the value of critical current of the tapes without bubbling was increased almost twice higher than that of already existing tapes. Critical current up to 42 A in 40 m length Bi-22231Ag tapes have been measured at 77K, self-field, 1$mutextrm{V}$/cm criterion. It could be confirmed that elimination of bubbling is effective to maintain the superconducting property along the tape length.