Recently, we developed a superconducting joint between two multi-filamentary Bi2223 tapes with the joint by incongruent melting (JIM) method . During the incongruent melting process, Bi2223 phase is separated to Bi2212, Bi2201, and liquid phases. Since the Bi2212 is also high-temperature superconductor, the superconducting joint can be obtained without recrystallization of Bi2223 from the Bi2212 and liquid, during a short heating treatment as 1 min at 890 °C. To obtain a high critical current, it is better to keep the crystal orientation of Bi2223/Bi2212 filaments with crystal growth at interface of joint along vertical direction of tape (c-axis). In this study, we suggested a lap-type multi-junction method to increase the effective interface area of superconducting current path, toward improvement of the critical current. In experiment, three junctions for a joint sample was prepared and obtained critical current above 16 A at 77 K. We have been obtained the critical current of 177 K at 4.2 K for joint fabricated by JIM method, which is about 15 times that measured at 77 K (12 A). Considering this increasing rate, the multi-junction sample may have a large critical current above 200 A at 4.2 K. The resistances at 77 and 4.2 K in a persistent current coil show the same ultra-low value about 1 pΩ, after half a day or less from the start of persistent current operation . The measurement results for Bi2223 persistent current coil with the joint will be presented in MT26 at Vancouver.
This work was supported by JST-Mirai Program Grant Number JPMJMI17A2, MEXT project of Leading Initiative for Excellent Young Researchers (LEADER) Project ID 16810210, and JSPS KAKENHI Grant Number JP18K04719, Japan.
 X. Jin, Y. Suetomi, R. Piao, Y. Matsutake, T. Yagai, H. Mochida, Y. Yanagisawa, H. Maeda, “Superconducting joint between multi-filamentary Bi2Sr2Ca2Cu3O10+δ tapes based on incongruent melting,” Supercond. Sci. Technol., vol. 32, 2019, Art. no. 035011.