Impact of rotating magnetic islands on density profile flattening and turbulent transport

International audience; The impact of rotating magnetic islands on background radial profiles in ă the presence of strong turbulent transport is analysed, with particular ă emphasis on island widths of the order of 6-10 ion Larmor radii. Only ă the case of ion temperature gradient (ITG) turbulence is considered. A ă significant reduction of fluctuations is found when island and ă turbulence co-rotate and the island width is of the order of the radial ă correlation length of turbulence. This reduction is not due to a ă flattening of ion temperature, suggesting an additional mechanism. A ă nonlinear transfer of energy from small to large scale structures might ă be responsible for the stabilization at a scale close to the radial ă correlation length of turbulence. It is shown that in the presence of ă intermediate magnetic islands rotating in the ion diamagnetic direction ă the density flattening survives the radial turbulent transport, ă representing a destabilizing effect for a magnetic island in terms of ă bootstrap current. However, this flattening is not necessarily due to an ă adiabatic response of trapped ions. Owing to the fast parallel motion of ă electrons, their temperature is always flattened. Finally, when the ă island width is large enough (island width greater than 18 ion Larmor ă radii), the standard profile flattening leading to a linear ă stabilization of turbulence dominates over the other mechanisms.