MHD phenomena in advanced scenarios on ASDEX Upgrade and the influence of localized electron heating and current drive

On the one hand. MHD instabilities in advanced tokamak scenarios are favour able as they can contribute to thc stationarity of the current profiles and act as a trigger for the formation of internal transport barriers (ITBs). lit particular, fishbone oscillations driven by fast, particles arising fro nt NBI are shown to trigger ITBs in low and reversed magnetic shear dischar ges. During the whistling down period of the fishbone oscillation the trans port is reduced around the corresponding rational surface, leading to all i ncreased pressure gradient. This behaviour could be explained by the redist ribution or the resonant fast particles resulting lit a sheared plasma rota tion due to the return current in limit, bulk plasma, which is equivalent t o a radial electric field. Oil the other hand, MHD instabilities, limit the accessible operating regime. Ideal and resistive MED modes such as double tearing modes, infernal modes and external kinks degrade the confinement or even lead to disruptions in ASDEX Upgrade reversed shear discharges. Local ized electron cyclotron heating and current drive are shown to significantl y affect the MHD stability of this type of discharge.