Pellet injection with improved confinement in ASDEX

An intensive campaign to study the consequences of repetitive pellet injection was carried out on ASDEX. It was possible to improve by pellet injection considerably the plasma confinement compared to earlier investigations. In addition we could advance considerably the understanding of the relevant mechanisms. The dominant difference between the earlier and the recent experiments was different recycling in the plasma boundary and the divertor. While the earlier campaign aimed at low-recycling pellet injection (LRP) to study the genuine pellet fuelling, the second campaign aimed at an improvement of the density limit. (orig.)