Comparative study of the dust particle population sampled during four consecutive campaigns in full-tungsten ASDEX Upgrade

Scanning electron microscopy images and energy-dispersive x-ray spectra were recorded for a total of about 4×10 ⁴ dust particles collected on the same position within the vacuum vessel via silicon wafers during four consecutive full-tungsten first wall campaigns of ASDEX Upgrade between 2007 and 2009. By careful analysis of the elemental composition and shape of the sampled particles, seven statistically relevant classes of dust were identified. The particle flux and area coverage of each class were normalized to the total plasma duration of each sampling period, revealing a high sensitivity of the dust composition to device conditioning. According to the present results, particles produced by arcing on divertor tiles with delaminated coatings were transported to the main chamber first wall.