Bubbling in the fabrication of Bi-2223/Ag wires using PIT process

One of the most important factors to get better properties of Bi-2223/Ag tapes in the PIT process is the elimination of the bubbling that causes the swelling of the tapes during the heat-treatment and restricts the current path. Therefore, the critical current of the tapes could be decreased. We have modified heat-treatment schemes of Bi-2223/Ag tapes, such as the preannealing of multi-stacked billet, two-step main sintering, and ramp rate of heating, etc. The generation of the bubbling was drastically decreased from 20 to 0-1 bubble/m by the modified heat-treatment. Furthermore, the critical current of the tapes with removed bubbles was obtained up to almost twice higher than that of the tapes with the bubbles. We confirm that the elimination of the bubbling becomes effective factor to keep the superconducting properties along the tape length.