In theASDEXUpgrade tokamak, the power deposition structures on the divertor
target plates during type-I edge localized modes (ELMs) have been investigated
by infrared thermography. In addition to the axisymmetric strike line, several
poloidally displaced stripes are resolved, identifying an ELM as a composite
of several subevents. This pattern is interpreted as being a signature of the
helical perturbations in the low field side edge during the non-linear ELM
evolution. Based on this observation, the ELM related magnetic perturbation
in the midplane can be derived from the target load pattern. In the start phase
of an ELM collapse, average toroidal mode numbers around n ≈ 3–5 are foundevolving to values of n ≈ 12–14 during the ELM power deposition maximum.
Further information about the non-linear evolution of theELMmode structure is
obtained from statistical analyses of the spatial distribution, heat flux amplitudes
and number of single stripes. |