Setup and initial results from the magnetic flux surface diagnostics at Wendelstein 7-X

Wendelstein 7-X is an optimized stellarator with superconducting magnetic field coils that just started plasma operation at the Max-Planck-Institut fur Plasmaphysik (IPP) Greifswald. Utilizing the electron beam technique the first vacuum flux surface measurements were performed during the commissioning of the magnet system. For the magnetic configurations investigated so far the existence of closed and nested flux surfaces has been validated. All features of the configuration designed for the initial plasma operation phase, including a predicted island chain, were confirmed. No evidence on significant magnetic field errors was found. Furthermore, the effect of the elastic deformation of the non-planar coils was confirmed by the measurements.