Investigation of pellet-triggered MHD events in the ASDEX upgrade

In order to gain deeper insight into the process of MHD activity triggered by pellets we extended our previous analysis (standard type-I edge localized modes (ELMs)) to type-I ELMs in radiative edge scenarios, type-III ELMs, the quiescent H-mode regime, and core mode activity such as neoclassical tearing modes or snakes. Pellet triggering of mode activity has turned out to be a quite general feature, but only in case of the ELMs can it be unambiguously attributed to prompt local impact by the pellet. For edge plasma conditions characterized by higher resistivity, the growth time of spontaneous ELMs increases while the plasma changes from the type-I into the type-III regime. However, pellet-triggered ELMs retain fast rise times. In the quiescent Hmode, pellets still trigger ELM-like mode activity, but no longer accompanied by a significant release of energy from the plasma. Published in Russian in Fizika Plazmy, 2008, Vol. 34, No. 9, pp. 771–775. The text was submitted by the authors in English.