Compensation of 1/1 and 2/2 error field in Wendelstein 7-X via divertor heat load symmetrization

Abstract Recent experiments with the water-cooled, high-heat-flux divertor of the Wendelstein 7-X (W7-X) stellarator demonstrate substantial progress in error-field compensation. Numerical simulations reveal a pronounced sensitivity of divertor heat load distributions to error fields. Experimentally, wide-angle infrared cameras monitoring all ten divertor units show significant improvements in the symmetry of divertor thermal footprints when trim coils and control coils are employed to compensate intrinsic 1/1 and 2/2 error fields, respectively. The experimentally determined amplitude of the intrinsic 1/1 error field is consistent with results obtained seven years ago, despite different diagnostics, divertor components, and slight variation in magnetic configurations. For the first time, the intrinsic 2/2 error field has been compensated through a phase-scan experiment using control coil currents, supported and validated by simulations.