ELMs as triggered and as triggering relaxation phenomena in ASDEX

In the ASDEX device, the relaxation phenomena known as ELMs are frequently isolated events in that no preceding and no following changes of plasma parameters occur. During the relaxation, a characteristic MHD mode is observed which is no precursor. ELMs may be triggered, however, by other MHD phenomena and they are able to trigger the onset of Mirnov oscillations, the transition from L-type confinement behaviour to the H mode and vice versa. This paper summarizes the measurements made in the ASDEX tokamak, in particular those with appropriate temporal resolution, i.e. at a data acquisition rate of typically 200 kHz. (orig.)