Lithium beam charge exchange diagnostic for edge ion temperature measurements at the ASDEX Upgrade tokamak

Charge exchange recombination spectroscopy, utilizing a fast lithium beam as the recombination source, has been successfully applied to measuring edge ion temperature profiles of fully stripped carbon and helium ions in Ohmic, L-mode and H-mode plasmas with a radial resolution of about 6 mm. The temperatures of the carbon and helium ions agree within their respective experimental error bars in discharges where both could be measured. Depending on the plasma scenario, impurity content, beam penetration, etc, either helium or carbon can be the better choice for accurate edge measurements. The impact of edge localized modes (ELMs) on this diagnostic method has been noted. Temperature profiles in between ELMs can be determined as long as the ELM frequency is less than half the frame rate of the detector, i.e. less than about 60 Hz. In a first application, accurate measurements in L-mode plasmas with dominant electron heating and low density show much higher ion temperatures than electron temperatures across the separatrix.