A dipole magnet generating 20 T and beyond will require high-temperature superconductors such as Bi2Sr2CaCu2O8-x and REBa2Cu3O7-x (RE = rare earth, REBCO). Symmetric tape round (STAR®) wires based on REBCO tapes are emerging as a potential conductor for such a magnet, demonstrating a whole-conductor current density of 580 A mm-2 at 20 T, 4.2 K, and at a bend radius of 15 mm. There are, however, few magnet developments using STAR® wires. Here we report a subscale canted cosθ dipole magnet as an initial experiment for two purposes: to evaluate the conductor performance in a magnet configuration and to start developing the magnet technology, leveraging the small bend radius afforded by STAR® wires. The magnet was wound with two STAR® wires, electrically in parallel and without transposition. We tested the magnet at 77 and 4.2 K. The magnet reached a peak current of 8.9 kA, 78% of the short-sample prediction at 4.2 K, and a whole-conductor current density of 1500 A mm-2. The experiment demonstrated a minimum viable concept for dipole magnet applications using STAR® wires. The results also allowed us to identify further development needs for STAR® conductors and associated magnet technology to enable high-field REBCO magnets.

RE-Ba-Cu-O (REBCO, RE=rare earth) Symmetric Tape Round (STAR®) wires of 1.5 – 2.5 mm in diameter have been fabricated with 4 – 12 strands of symmetric REBCO tapes made by Advanced Metal Organic Chemical Vapor Deposition (MOCVD). 1.5 mm diameter STAR® wires made with just four Advanced MOCVD tape strands are able to sustain nearly the same critical current (Ic ) as 2.5 mm diameter STAR® wires made with 12 commercial-grade tape strands. An Ic of 1070 A, corresponding to an engineering current density (Je ) of 597 A/mm2, has been demonstrated at 4.2 K, 30 T in 1.5 mm diameter, 4-strand STAR® wire at a bend radius of 15 mm. This Ic value exactly matches the Ic expected from the lift factor of the tape strands used in the wire. The 2.5 mm diameter STAR® wires made with 12 Advanced MOCVD tape strands exhibit an Ic of 1,075 A at 77 K, self-field and sustained currents of 2,500 to 2,750 A at 4.2 K, 30 T before burnout, corresponding to a Je greater than 500 A/mm2. These results show that the cost of STAR® wires can be substantially reduced using fewer tape strands of high-performance Advanced MOCVD tapes and that the superior bend performance of STAR® wires can be maintained even using 12 strands of Advanced MOCVD tapes with 4-µm-thick REBCO films.