Coherence imaging spectroscopy systems on Wendelstein 7-X for studies of island divertor plasma behavior

In Wendelstein 7-X (W7-X) the so called ''island divertor'' concept has been realized in order to exploit the intrinsic magnetic islands structure in the outer region of the plasma for impurity screening. EMC3/EIRENE simulations for W7-X and experiments for W7-AS show that particle friction can dominate over ion thermal force in a regime where divertor plasma detachment is expected, pushing the impurities towards the divertor target, thereby resulting in efficient impurity screening of the core plasma. 2D measurements of impurity flow patterns in the scrape-off layer with coherence imaging spectroscopy (CIS) systems are expected to significantly contribute to the physics understanding of this process. Since the CIS system allows 2D measurement of flow pattern and it has a high optical throughput, it is advantageous respect to a standard spectrometer in terms of amount of information about W7-X 3D geometry, signal to noise ratio and velocity and temperature resolution. The project is now in the design and set-up phase, in order to be able to use two CIS systems for investigating the island divertor plasma behavior at different magnetic configurations during the upcoming W7-X operation phase OP1.2.