Spectroscopic investigation of the dynamics of ions and neutrals in the ASDEX Upgrade Divertor II

Abstract Detachment at the separatrix is a promising possibility to reduce the peak power load onto the divertor target plates. We investigated this topic spectroscopically at ASDEX Upgrade by measuring particle velocities using Doppler spectroscopy. The experimental data show a reduction of the chord averaged hydrogen velocity along the separatrix by about a factor of 3. Another important subject is flow reversal: after a brief discussion of 2D-code predictions and the conditions for detection we present spectroscopic evidence for flow reversal of C 2+ -ions in the ASDEX Upgrade divertor II. The comparison of these spectroscopic data with B2-EIRENE modeling shows good qualitative and quantitative agreement.