Development of Large-Scale Racetrack Coil Wound With REBCO-Coated Conductors

A newly designed racetrack coil wound with REBCO-coated conductor was developed and demonstrated. The coil shape was improved to achieve consistent dimensional accuracy, and the winding structure was improved to prevent degradation in the epoxy-impregnated windings. The wire length of the fabricated large-scale coils was 574 m, and the overall size was 434 mm × 796 mm. This wire length was longer than that of any of the coils the authors fabricated previously. The outer radiuses in both the semicircular sections and the pseudo-straight sections, which had a slight curvature, were approximately the same in the two coils, to within 1 mm, indicating that good dimensional accuracy was obtained consistently. Furthermore, the n-value was sufficiently high at 24 in an electric field range from 10^{- 9} to 10^{- 7} V/cm at 77 K, which indicates that the coils had no damaged area in the windings.