Planned Active Spectroscopy in the Neutral Beam Injectors of W7-X

The new stellarator Wendelstein 7-X will employ a combination of beam-aided active spectroscopy systems. Active Charge Exchange Resonance Spectroscopy will be performed in the beam of a diagnostic neutral beam injector. This low power, low divergence neutral beam system allows for the spectroscopic measurement of impurity density profiles, ion temperature and radial electric field profiles with good spatial resolution. However, no toroidal rotation can be measured with it, because of the radial arrangement of the observation chords. This instead will be done by CXRS in the neutral NBI heating beams, in addition to Beam Emission Spectroscopy to monitor the beam absorption in the plasma. Finally, the Motional Stark Effect diagnostics in the NBI can measure the magnetic pitch angle to provide information on iota variations by the bootstrap current. This information is essential for reliable W7-X divertor performance, which depends strongly on the edge iota value. In this paper the beam injectors are described together with the beam properties and observation geometries. Details are given for the spectroscopic systems. The relevance of the observed plasma parameters is briefly discussed, with an emphasis on some stellarator optimization criteria.