Study on critical current distribution in CT-OP Bi-2223 tape based on the scanning Hall probe magnetic microscopy

Critical current (I_c) of a Bi-2223 tape fabricated by controlled-overpressure (CT-OP) sintering method has been attained up to 200 A-class in recent years. However, current limiting factors have not been fully clarified yet. In this study, we have investigated local current distributions in a CT-OP Bi-2223 tape by using the scanning Hall probe magnetic microscopy. As a result, it has been found that large sheet current flows in the center of the sample. Even though the influence of self-field is taken into account, there is a clear difference of local I_c across the width. The maximum sheet current value in the center of the tape is 400-450 A/cm when we applied the bias current of 100 A, which is equal to the I_c at around 87 K. This value is equivalent to 800-900 A/cm at 77 K taking into account the value of I_c. Furthermore, such current distribution continues uniformly in length direction. From these results, we have concluded that improvement of current uniformity across the tape width is the effective way to enhance critical current for the present CT-OP Bi-2223 tape. Our results show the feasibility for 300 A-class I_c at 77 K.