High-performance Ba_1−x K _x Fe₂As₂ superconducting joints for persistent current operation

Abstract

High-performance superconducting joint is the key to achieving persistent-mode magnet. Herein, the superconducting joint between Ba1-xKxFe2As2 (Ba-122) superconducting tapes was prepared by a simple cold-pressing method, and the joint resistance of the iron-based superconducting joint was estimated by field-decay method for the first time. Via the SEM, EBSD, EPMA and XCT measurement, it is found that the joint sample CP80 shows fine performance. At 4.2 K and 10 T, a transport critical current Ic of 105 A for the joint sample CP80 was measured, and the critical current ratio (CCR = Ijoint c/Itape c) of the joint was 94.6%. On the other hand, the joint exhibit pretty low joint resistance of 2.7×10-13 Ω in self-field at 4.2 K. Among iron-based superconductors (IBS), this experiment is the first to successfully fabricate a superconducting joint with such high CCR and low joint resistance. All those show the great prospective to apply Ba-122 in a series of practical applications that require superconducting joints as key components.

Fabrication of multi-filament(Ba,A)Fe2As2 (A: Na, K) HIP round wires and a small superconducting coil

“…For further enhancement of the J c in round wires, which are more suitable for winding coils, an improvement in texturing, an increase in the density of the superconducting core, and a reduction in impurities are demanded. On the other hand, other aspects of tape and/or wire developments besides enhancement of the J c have been studied, such as multi-filament wire fabrication [32][33][34], fabrication of coils using long wires or tapes [29,31,[35][36][37][38][39], making joints between tapes [40][41][42], evaluation of the strain effect on the J c [7,43], and low cost fabrication using a Cu or Cu/Ag composite metal sheath [44][45][46]. In particular, fabrication of multi-filament wires and tapes is an indispensable process toward applications, to provide protection against magnetic flux jumps and thermal quenching [47], and to reduce the alternating current (AC) loss induced by the eddy currents in the metallic matrix and the inter-filament coupling currents [2].…”

High-performance joints between iron-based superconductors: a key step towards applications

“…The recent work of Zhu et al [22], reports an effective method for the joining of IBS superconducting tapes based on the cold pressing technique. The authors have shown that a high-performance, ultra-low-resistance joint can be formed by cold pressing, and that higher pressures generally improve the quality of the joint.…”