The He/Ne beam diagnostic for line ratio spectroscopy in the island divertor of Wendelstein 7-X*

The line-ratio spectroscopy system on thermal He and Ne enables measurement of n_e and T_e in front of the horizontal divertor target, across the 5/5 island in the standard magnetic configuration. For the second divertor campaign of Wendelstein 7-X the observation system has been upgraded adding 27 new vertical lines-of-sight to the existing 27 horizontal ones. These lines are channeled to a 20cm and a 32cm focal length Czerny-Turner spectrometer allowing observation of the He and Ne lines as well as impurities and H lines with high spectral resolution. Gas injection is enabled by two boxes with 5 fast piezo valves each, mounted directly behind the divertor plates in one upper and one lower divertor module, which are magnetically connected in the 5/5 island configuration. He was used as routine gas while Ne was tested in order to extend the applicability of the diagnostic to the detached divertor regime at very low T_e (≪10eV). In this work T_e/n_e profiles across the divertor island are shown for different island widths. Results from Ne injection and the status of the development of a dedicated collisional-radiative model for Ne will be discussed.