High efficiency extreme ultraviolet overview spectrometer: Construction and laboratory testing

The new high efficiency extreme ultraviolet overview spectrometer system (HEXOS) has been developed to study impurity concentrations and impurity transport properties in the plasma of the stellarator W7-X. The HEXOS system consists of four different grating based spectrometers, which provide large etendue and good spectral resolution over a broad wavelength range (2.5–160nm, divided into four subsections with some overlapping). The mechanical arrangement as two double spectrometers allows for a compact installation geometry on W7-X. Laboratory testing and wavelength and intensity calibrations have been performed using a dc hollow cathode discharge (24–150nm) and a pinch discharge (2.5–30nm).