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Recently, we developed a superconducting joint between two multi-filamentary Bi2223 tapes with the joint by incongruent melting (JIM) method [1]. 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 [1]. The measurement results for Bi2223 persistent current coil with the joint will be presented in MT26 at Vancouver.
Acknowledgements:
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.
[1] 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.
