Pedestal and Eᵣ profile evolution during an edge localized mode cycle at ASDEX Upgrade

Abstract

The upgrade of the edge charge exchange recombination spectroscopy diagnostic at ASDEX Upgrade has enabled highly spatially resolved measurements of the impurity ion dynamics during an edge-localized mode cycle (ELM) with unprecedented temporal resolution, i.e. 65 μs. The increase of transport during an ELM induces a relaxation of the ion, electron edge gradients in impurity density and flows. Detailed characterization of the recovery of the edge temperature gradients reveals a difference in the ion and electron channel: the maximum ion temperature gradient Ti is re-established on similar timescales as ne, which is faster than the recovery of Te. After the clamping of the maximum gradient, Ti and Te at the pedestal top continue to rise up to the next ELM while ne stays constant which means that the temperature pedestal and the resulting pedestal pressure widen until the next ELM. The edge radial electric field Er at the ELM crash is found to reduce to typical L-mode values and its maximum recovers to its pre-ELM conditions on a similar time scale as for ne and Ti. Within the uncertainties, the measurements of Er align with their neoclassical predictions Er,neo for most of the ELM cycle, thus indicating that Er is dominated by collisional processes. However, between 2 and 4ms after the ELM crash, other contributions to E ' B flow, e.g. zonal flows or ion orbit effects, could not be excluded within the uncertainties.