Influence of deviations in the coil geometry on Wendelstein 7-X plasma equilibrium properties

Wendelstein 7-X (W7-X) is a modular advanced stellarator with a magnetic field optimized for good plasma confinement and stability, which went into operation in December 2015 at the Max-Planck-Institut für Plasmaphysik in Greifswald, Germany. The magnet system of W7-X consists of 70 superconducting coils with as-built-shapes and positions which deviate from the designed ones due to manufacturing and positioning tolerances as well as due to deformations under different kinds of loads. Step-by-step evaluation of the magnet system geometry during the machine construction included measurements of the winding pack geometry characterizing deviations of each coil filament caused by the fabrication process and the tracking of coil positions during main assembly steps. In addition finite element calculations were performed with help of the 360° ANSYS Global Model (a finite element model, representing the whole W7-X magnet system, including all superconducting coils and their support structure) in order to define possible coil deformations under the dead-weight, cool-down and electromagnetic loads in different operation regimes. This paper shows the comparative analysis of different types of deviations in the coil geometry and discusses their influence on plasma equilibrium properties.