The impact of applied magnetic perturbations (MPs) on tokamak edge parameters has been investigated in ASDEX Upgrade low collisionallity L-mode discharges using a flexible set of in-vessel saddle coils (capable of generating n = 0, 1, 2 and 4 toroidal modes) and an extensive set of high resolution edge diagnostics. Doppler reflectometry is used principally to probe the MP field penetration and structure via the radial electric field Er and density fluctuation δne behaviour. Different MP response behaviour are observed for the near scrape-off-layer, SOL, (where Er flattens) and in the confinement region (where the negative Er well reverses). The radial structure of Er and δne are particularly sensitive to the degree of MP resonance with the edge rational field-lines. Specifically, the edge turbulence is enhanced for strongly resonant MPs and reduced when non-resonant. The toroidal structure of the MP response has also been probed for various MP configurations by rotating the MP field toroidally and is found to be different for the edge and near SOL regions.
High-accuracy characterization of the edge radial electric field at ASDEX Upgrade