Speaker
Description
In magnetically confining plasma experiments, measurement of ion dynamics is of great
importance to study the impurity transport in the scrape-off-layer (SOL) and divertor.
Impurities from the divertor areas may degrade the core energy confinement, if transported too
far upstream in the SOL. The Doppler coherence imaging spectroscopy (CIS) is a relatively
new technique [1] for the observation of ion and neutral flows. It is a passive optical diagnostic
which produces 2D images of line-integrated measurements of the ion flow or ion temperature.
Doppler CIS measurements conducted in the poloidal field divertor of the medium-sized
tokamak experiment ASDEX-Upgrade and the optimized stellarator Wendelstein 7-X reveal
near-sonic (Mach ~ 1) impurity ion flows in the divertor. The SOL and divertor impurity ion
flows in tokamaks and stellarator SOL are subject to many forces [2]: they can either be
transported downstream by e.g. friction with the main plasma flow, but also upstream due to
thermal gradient forces, for example. In AUG, the impurity flows measured with the Doppler
CIS were observed to be parallel to the magnetic field lines, pointing away from the divertor
target plates. In W7-X, perpendicular transport is expected to play a larger role [3] and first
measurements have been conducted.
Both Doppler CIS measurements in AUG and W7-X are aimed at a fundamental understanding
of the impurity SOL transport in different divertor regimes and to determine operation scenarios
that prevent impurity transport into the core, which is also relevant for e.g. ITER. A new method
was used to gain absolutely calibrated flow measurements in AUG and W7-X and will be
presented, along with first measurement results and interpretation.
