Progress in scale-up of REBCO STAR™ wire for canted cosine theta coils and future strategies with enhanced flexibility

We report recent developments in the scale-up of symmetricRE-Ba-Cu-O (REBCO) tapes with 15-22 mu m thick substrates. Using these symmetricREBCO tapes, we fabricated up to 10 m long, symmetric tape round (STAR (TM))REBCO wires, less than 2 mm diameter, using 1.02 mm and 0.81 mm diameter copper formers. The critical current of the long STAR (TM) wires made in lengths of 2-10 m ranges from 465 A to 564 A at 77 K, self-field. This wire was then used to construct a single-layer, full-depth groove, three-turn canted cosine theta (CCT) coil with a minimum bend radius of 15 mm. This three-turn CCT coil retains 95% of itsI(c)even when wound at a such a small bend radius. This result confirms the capability of fabricating CCT coils with STAR (TM) wire at a tilt angle of 30o which would yield a dipole transfer function of 0.48 T kA(-1)at a 15 mm bend radius. Further, the architecture of STAR (TM) wire was modified for anI(c)retention of >90% at an even smaller bend radius of 10 mm with the aim of increasing the dipole transfer function. The higher dipole transfer function enabled by STAR (TM) wire is an important step toward the eventual goal of a 5 T maximum dipole field in aREBCO-based CCT coil. At a bend radius of 10 mm, a six-layer STAR((TM))wire exhibits a critical current of 288 A at 77 K, self-field, i.e. 94%I(c)retention and 617 A at 4.2 K in a 15 T background field, which equals aJ(e)of 412.7 A mm(-2)at a Lorentz force of 9.3 kN m(-1). This level of flexibility and the high performance of STAR((TM))wire in high fields at 4.2 K and with a small bend radius underscores its potential use in compact and low-cost high-field magnet and related applications.