Doppler coherence imaging of divertor and SOL flows in ASDEX upgrade and Wendelstein 7-X

Abstract

Measurement of ion dynamics is of great importance to the study of plasma exhaust and impurity particle flows in the scrape-off-layer (SOL) and divertor in magnetic confinement experiments. Doppler coherence imaging spectroscopy (CIS) is a passive optical diagnostic that produces 2D images of line-integrated ion flow velocity. Doppler CIS flow measurements of neutral deuterium and impurities were conducted for the first time in the divertor of the medium-sized tokamak experiment ASDEX Upgrade. A detailed sightline, emission and magnetic field analysis was undertaken to identify location and direction of flows. Under the assumption of toroidal axisymmetry, they revealed mainly parallel impurity flows in the proximity of the X-point and target plates on the order of 20 km s-1. Two Doppler CIS systems are currently set up for the optimized stellarator Wendelstein 7-X (W7-X). The main task of this diagnostic will be the measurement of impurity ion flows in one of the island divertors of W7-X. EMC3-EIRENE simulations have been carried out to estimate the flow behaviour in the W7-X SOL.