Development of a Quasi-Isotropic Strand Stacked by 2G Wires

This paper presents a concept of quasi-isotropic high-temperature superconducting (HTS) strands with round and square cross sections made from REBa
₂
Cu
₃
O
_7-x
(RE=rare earth, REBCO) coated conductor, the so-called second-generation (2G) HTS wires under development at North China Electric Power University. Considering several key issues for fabricating the quasi-isotropic strands, for instance, in-plane bending performance of 2G wire, isotropic-strand bending performance, strand termination method, and critical current in liquid nitrogen (LN
₂
) temperature and self-field, a feasible manufacturing method by using mature laser welding is suggested and investigated experimentally. After fabricating several short-length strand samples consisting of 72 REBCO wires with an outer diameter of 7.5 mm, critical currents in straight and bending and under direct current (DC) magnetic fields with different orientations were tested in LN
₂
temperature. The critical current in straight strand is in agreement with the simulated one; the anisotropy of the critical current is less than 8% in the orientation range of 0°-90° with a DC magnetic field of 0.5 T. After successfully finishing a 10-m-length strand, it was demonstrated that the laser welding technique is an attractive and feasible method for manufacturing practical long strands which have potential applications in large-scale high-field magnet and energy transmission.