The impact of resonant magnetic perturbations (RMPs) on the edge of MAST L-mode plasmas is studied using a mid-plane reciprocating probe equipped with a Gundestrup probe head. A strong impact on the characteristics of the ion saturation current fluctuations is observed just inside the separatrix, with a broadening of the power spectrum and an asymmetrization of the probability distribution functions towards non-Gaussian shapes. No major effect is found in the scrape-off layer (SOL). Floating potential measurements are used to evaluate the modification of the plasma potential profiles. The radial electric field profile flattens when RMPs are applied, leading to a theoretically expected increase in Er inside the separatrix and a decrease in the SOL. A consistent change is observed on the perpendicular and parallel flows which tend to increase inside the separatrix. In contrast, in the SOL, a braking of the rotation is observed with the application of RMPs. All these effects occur only above a threshold in the amplitude of the current applied in the RMP coils and are not toroidally localized.
L–H transition trigger physics in ITER-similar plasmas with applied n = 3 magnetic perturbations