First results of the Coherence Imaging Spectroscopy Systems on Wendelstein 7-X

Coherence Imaging Spectroscopy (CIS) is a camera-based interferometry diagnostic capable of measuring 2D impurity flow velocities for a selected visible emission line from the plasma. A spatial interference pattern encoding the spectral line properties is overlaid on the plasma image by the use of α-BBO birefringent crystals. The CIS 2D measurement capability and high optical throughput are attractive for the complex magnetic island topology of Wendelstein 7-X (W7-X). Two CIS systems have been designed and set up to face the challenging experimental conditions of W7-X. The field of view of each system images the same island divertor portion from nearly perpendicular directions for improved emission and flow interpretation in the W7-X geometry. The diagnostic has been used during the OP1.2 experimental campaign, observing the plasma at different magnetic configurations, densities, and heating powers. Measured velocities on the order of km/s were observed and the behavior of multiple impurities, mainly carbon and helium, will be presented. The diagnostic output is also compared with dedicated EMC3-EIRENE simulations.