Optimum Copper Stabilizer Thickness for Symmetric Tape Round (STAR) REBCO Wires with Superior Mechanical Properties for Accelerator Magnet Applications

Symmetric Tape Round (STAR) wires are only 1.6-1.9 mm in diameter and are made by winding 2.5-mm-wide REBCO tapes on an AWG 18 (1.02-mm diameter) copper wire former. Such ultra-small diameter wires are possible by the use of symmetric tapes where the REBCO film is positioned at the geometric center, close to the neutral axis. Such symmetric tape architecture is achieved by a strategic selection of the thickness of the copper stabilizer to match the thickness of the Hastelloy substrate. The substrate itself is made thin, to enable good tolerance to bend strain. The optimized STAR wire architecture is found to be mechanically robust and retain nearly 98% of its critical current of over 500 A at 77 K, self-field even when bent to a small radius of 15 mm. The superior bend strain tolerance of STAR REBCO wires make them suitable for use in canted cosine theta coils for future compact accelerator magnet applications.