The radial extent and spatial structure of type-I edge localized modes (ELMs)
in ASDEX Upgrade are investigated using data from a mid-plane manipulator
equipped with Langmuir probes and a fast visible imaging camera and are
compared to data from MAST. Plasmas with a range of toroidal magnetic
fields have been studied. The radial extent of the ELM efflux is found to
be largest at the smaller toroidal magnetic field. A study of a series of shots on
ASDEX Upgrade with different plasma edge to wall separation suggests that
the closeness of the wall does not have a stabilizing effect on the radial extent of
the ELM. The data from the mid-plane manipulator and from visible imaging
are consistent with non-linear ballooning mode theory, which predicts that the
ELM has a filament like structure. |