Optimization of ion temperature and rotation measurements by CXRS

Ion temperature (Ti) and toroidal rotation (vtor) profiles are routinely measured at ASDEX Upgrade (AUG) by means of charge exchange recombination spectroscopy (CXRS). Generally the diagnostic utilizes charge exchange emission from C impurities, which are naturally found in the plasma, in the presence of neutral beam injection (NBI). Following the coverage of the plasma facing components of AUG with tungsten the C concentration has strongly decreased and the signal to noise ratio of the measured profiles has degraded. Different techniques aimed at improving the Ti and vtor measurements are being explored. Modulation of the neutral beams is used to separate passive and active (charge exchange) emission. In addition, CXRS measurements using other impurities than C are tested. One method uses injection of Ne gas in the discharge without perturbing the plasma. Another method exploits the operation with N2 seeding as a tool for divertor cooling. A quantitative analysis of the signal to noise ratio for each method is presented and the relative merit of each technique is assessed with respect to representative discharge conditions in ASDEX Upgrade.