Superior critical current of Symmetric Tape Round (STAR) REBCO wires in ultra-high background fields up to 31.2 T

Abstract

Symmetric Tape Round (STAR) wire fabricated with an ultra-thin RE–Ba–Cu–O (REBCO, RE = rare earth) coated conductor has a high engineering current density (Je) and remarkable flexibility. It is a competitive candidate for future canted cosine theta magnets with smaller winding radii that operate at fields above 20 T at 4.2 K. STAR wires consisting of six or eight REBCO coated conductor layers have been fabricated with an outer diameter smaller than 2 mm. We performed in-field tests of the critical current of STAR wires at 4.2 K in background fields up to 31.2 T. At a 15 mm bending radius, Je values of 438 A mm−2 at 20 T and 299 A mm−2 at 31.2 T were obtained. These are the highest Je values measured in any reported round-geometry REBCO wires at such ultra-high background magnetic fields. This exhibits the potential of STAR wires in future compact accelerator magnets.