WB1-3-INV

Recent progress in 2G wires and superconducting joints

Dec.1 10:15-10:35 (Tokyo Time)

*Tatsuoki Nagaishi1, Kotaro Ohki1, Tatsuhiko Yoshihara1, Takeharu Kato2, Daisaku Yokoe2, Ryuji Yoshida2, Tsukasa Hirayama2, Yuichi Ikuhara2,3

Sumitomo Electric1

Japan Fine Ceramics Center2

University of Tokyo3

A superconducting joint technology of high-temperature superconductors (HTSs) is the key technology to realize persistent current operation of prominent HTS magnets such as NMR and MRI magnets. We have developed an intermediate grown superconducting (iGS®) joint of 2G wires or REBa2Cu3Ox (RE: rare earth elements, REBCO) coated conductors (CCs) [1]. Previously, we demonstrated the characteristics of iGS® joints, such as a high critical current above 100 A and a joint resistance with less than 10-12 Ω. To evaluate the performance of the iGS® joints in a real NMR magnet system, we made a coil connected with the iGS® joints and it was operated in a persistent-mode (PM) generating 0.1 T in a 9.3 T background magnetic field of a PM low temperature superconductor (LTS) outer coil. We succeeded in acquiring a commercial level NMR spectrum and magnetic field stability of 0.07ppb/h over one year [2].

In this research we have investigated a fabrication mechanism of iGS® joints by changing heat treatment time [3]. We used YBa2Cu3Ox for a precursor layer and GdBa2Cu3Ox for CCs to make the joint boundaries clear. C-axis and a-axis grains emerged at the boundaries while most of the precursor layer was still microcrystalline with zero minute heat treatment. With 1 minute heat treatment 10 nm to 100 nm thick c-axis grains were found at the boundaries with disoriented grains between them. After 20 minute heat treatment, the precursor layer became totally c-axis oriented.

In the JST-Mirai program [4], a 9.39 T LTS/REBCO NMR magnet is under development as a prototype with a final goal of a 30.5 T NMR magnet. For this use we developed a REBCO CC with higher tensile strength than our previous one by replacing the base substrate of the clad tape [5] from stainless steel to Hastelloy®. The tensile strength measured more than 470MPa.

This work was supported by the JST Mirai-Program Grant Number JPMJMI17A2.

[1] K. Ohki, et al., Supercond. Sci. Technol. 30 (2017) 115017.
[2] Y. Yanagisawa et al., 26th International Conference on Magnet Technology, Mon-Af-Po.1.13-011[20&21] (2019).
[3] T. Kato et al., Supercond. Sci. Technol. 33 (2020) 105008.
[4] H. Maeda et al., IEEE Trans. Appl. Supercond. 29 (2019) 4602409.
[5] T. Nagaishi et al., Physica C 469 (2009) 1311-1315.

Keywords: 2G wire, REBCO, superconducting joint, NMR