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Description
Large-scale racetrack coils wound with two kinds of REBCO-coated conductors were developed and tested. The two conductors had different critical currents, thicknesses and also allowable delamination stresses respectively for comparison. The total wire length of the fabricated two coils was 978 m and 945 m, and the overall size was 0.57 m x 1.14 m and 0.51 m x 1.08 m. The coils were impregnated with epoxy resin as bonding material to maintain the coil shape. Nevertheless, a racetrack-shaped coil is easily deformed at the straight parts, since the retention force due to the winding tension in the straight parts is not as high as in the semicircular parts so that it is difficult to achieve consistent dimensional accuracy. And a non-uniform resin between turns will cause the unexpected thermal stresses. Therefore the coil windings were being compressed continuously using a compression roller during the winding processes. The winding thickness in both of the semicircular parts and the straight parts showed approximately the same values within 0.5 mm, indicating that good dimensional accuracy was obtained consistently. Furthermore, the n-values of the two coils were sufficiently high as 24 and 23, respectively, in a voltage range from 10^-9 to 10^-8 V/cm at 77 K, which indicates that the coils had no damaged area in the windings.
| Submitters Country | Japan |
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