Conceptual design of light impurity monitor for Wendelstein 7-X

As plasma impurity ions can significantly influence the properties of a fusion plasma by dilution and enhancement of the radiation losses, the process of monitoring of their concentrations is one of the most important tasks. A Light Impurity Monitor is needed for monitoring the contamination of the stellarator plasma by carbon, nitrogen, boron, and oxygen impurities, which are indicators for the overload of the plasma facing components, leakage of the vacuum vessel, or wall condition, respectively. Their concentration will be estimated on the basis of emission intensities of their hydrogen-like ions. In this paper a conceptual design of such a spectrometer is presented, including the description of the geometry, the acquisition system and safety systems. (authors)