A study of the perpendicular particle transport properties in the scrape-off layer of ASDEX

Abstract

The flux of energetic (E ≥ 100 eV) atoms emanating from the outer target plate in the divertor chamber of ASDEX is measured by classical corpuscular diagnostic techniques. The atom flux is caused by ions from the main plasma which are neutralized and backscattered at the target plate. The spatial profile of backscattering atoms is analysed in terms of parallel ballistic flight of ions onto the target plate and perpendicular diffusion. The diffusion coefficient D in the scrape-off layer is found to be anomalous and to agree with D-values as deduced from impurity transport analysis for the main plasma, both for Ohmically heated hydrogen and deuterium discharges and beam-heated L- and H-plasmas. The transient phases of density decay experiments, the plasma build-up phase, and MHD effects are also investigated.