Analysis of the Interlayer Joint Resistance of the Superconducting Coils of W7-X

The superconducting coils of the Wendelstein 7-„X (W7-X) stellarator use a cable-in-conduit conductor that is wound as double layers. These double layers are connected by low-ohmic joints to limit ohmic heating. All joints were equipped with voltage taps to allow identification of the double layer causing a quench. During the current tests of the superconducting coils, the differences between adjacent voltage taps were measured, and the joint resistances between the double layers were estimated. The cryogenic tests of the 50 nonplanar and 20 planar coils provided a unique opportunity to analyze the variation of the resistance of 250 joints of the nonplanar coils and of 40 joints of the planar coils. The statistical analysis shows that the resistance of most of the joints was well below the specified value of 1 nΩ.