Validation of Wendelstein 7-X Fabrication and Assembly Stages by Magnetic Field Calculations

The Wendelstein 7-X stellarator, which is currently under construction in Greifswald, Germany, is a five-period machine, and many of the planned operational plasma scenarios are characterized by the rotational transform /2 = 1 at the plasma boundary. Such magnetic configurations are particularly sensitive to the symmetry-breaking perturbations caused by fabrication and assembly errors, which can occur at different stages of the device construction. Analysis of nonplanar and planar winding packs (WPs) fabricated up to the present time has confirmed the existence of a systematical portion in the manufacturing deviations. The level of the magnetic field perturbation due to the statistical part in manufacturing errors can be expected to be of order 1 × 10^-4 at the end of the WP production. Validation of different assembly steps and the resulting distortion of the current path will be done on the basis of the reference point measurements. The influence of the assembly errors and corresponding uncertainties on the magnetic field perturbation is estimated for some cases.