Design Changes and Impact on the Production of the Non-Planar Coils for the W-7X Experiment

The Max-Planck-Institut fur Plasmaphysik is building the stellarator fusion experiment WENDELSTEIN 7-X (W7-X) at the branch institute in Greifswald, Germany. The 50 non-planar superconducting coils are currently manufactured by industry and use a specially developed NbTi cable-in-conduit conductor. The manufacture of the coils includes the conductor, winding of the conductor, vacuum pressure impregnation as well the embedding of the winding pack into a cast steel casing, the final machining and the installation of the helium cooling system on the casing. Design changes became necessary during production in the connection areas of the casings due to more detailed design and structural analysis. In addition, the insulation and the welds in the termination area need to be improved. New quench detection cables were qualified. LINAC inspections allowed to check the presence of casting defects in the thick casings. Additionally high voltage tests in vacuum under Paschen-minimum conditions turned out to be a very sensitive inspection method to check the integrity of the electrical insulation