Status of Equilibrium Reconstructions for Wendelstein 7-X

The reconstruction of the plasma equilibrium is a vital tool for toroidal fusion experiments to understand plasma performance and interpret diagnostic signals. The procedure involves solving the MHD equilibrium, computing synthetic diagnostic signals, and comparing these signals to measured signals. The parameters that describe the equilibrium are adjusted to match the synthetic signals to the measured ones. Information gained from the reconstruction includes the shape and location of the plasma and profile information regarding the plasma pressure, current, and individual plasma species which are subsequently used to interpret diagnostic information and for further analyses.

Constraints for plasma reconstructions at Wendelstein 7-X (W7-X) include magnetic diagnostics, Thomson Scattering, interferometry, electron cyclotron emission, soft x-ray arrays and x-ray imaging crystal spectroscopy. Treatments of edge constraints related to the edge rotational transform and divertor location are also presented. The MHD equilibrium solution is provided by VMEC, which assumes solutions with nested, closed flux surface. The current status and future plans for equilibrium reconstructions for W7-X are shown and discussed.