Charge-exchange spectroscopy at the W7-AS stellarator employing a high-energy Li beam

Combined measurements of ion density, temperature and poloidal rotation of impurity ions have been carried out in the gradient region of the Wendelstein 7-AS plasma, employing charge-exchange spectroscopy with the high-energy neutral Li beam and C 6+ /C 5+ ions. The present state of the experimental technique is described. Results are obtained in discharges with high central ion temperatures of 1.3 keV, central electron densities of 7 × 10 19 m −3 . Under these conditions the diagnostic covers a region of about 7 cm radial extent, corresponding to ion temperatures between 50 and 800 eV. Poloidal rotation velocities up to (35±2.5) km s −1 were measured in a narrow shear layer at the plasma edge. The contribution of ion diamagnetic and E × B drift is discussed. The radial electric field is derived from a simplified radial force balance equation.