Spectroscopic camera system at Wendelstein 7-X

Abstract A network of spectroscopic cameras was installed and successfully operated during the entire operation phase 1 of the optimized stellarator, Wendelstein 7-X. This diagnostic system enabled spatially resolved measurements of photon fluxes at specific wavelengths. Narrow band pass filters in the optical path allowed for targeted photon flux measurements of various spectral lines, specifically for the main ion species, hydrogen, and the primary impurity, carbon. The cameras were arranged in a stellarator-symmetric configuration, with one camera assembly per half-module. Each camera was equipped with a 135 ° ultra-wide field-of-view lens centered on the divertor, enabling comprehensive observation of the entire divertor unit, including the baffle and most of the surrounding heat shield. This configuration achieved coverage of 56 % of all plasma-facing surfaces at W7-X, providing a spatial resolution up to 1.4 pixel/cm at a frame rate of 25 Hz. This diagnostic system supports a wide range of applications, from studies of ionizing particle fluxes and wall recycling to investigations of plasma radiation and detachment, edge impurity sources, and their distribution. This paper details the diagnostic system's observation geometry, measurement principles, calibration processes, inter-diagnostic comparisons, synthetic diagnostic modeling, and plans for further development.