Modelling of the ASDEX scrape-off and divertor

Abstract For the divertor configurations of ASDEX a two-fluid model describing the plasma flow and energy transport in the scrape-off layer together with models for the neutral particle dynamics in the divertor chamber have been used to study the relation between the neutral molecule density and plasma density in the divertor and the scrape-off density at the midplane. Results of DEGAS Monte Carlo calculations prove the divertor entrance slits to be nearly impenetrable for neutrals in the presence of a plasma. A global recycling picture is suggested relying on edge density control by the divertor and a hydrogen ion inward drift in the main discharge region to maintain the bulk plasma density even in the absence of neutrals in the main chamber.