Gyrokinetic and gyrofluid investigation of magnetic islands in tokamaks

The evolution of a tearing mode is a multi-scale problem, involving lengths from below the ion gyroradius up to the dimensions of the system. The effects due to finite ion Larmor radius on the island dynamics are investigated by means of numerical gyrokinetic and gyrofluid simulations in tokamak geometry. In gyrokinetic runs, the magnetic island is prescribed. The coupling induced by a static island between small and large scale fluctuations in the case of electrostatic turbulence is discussed and the role of the perturbed magnetic geometry on the electron response is highlighted. Simulations in the presence of a rotating island, excluding background turbulence, allow a clear, self-consistent determination of the electrostatic potential associated with the island rotation and of the relevant plasma profiles for arbitrary island widths. Finally, the first gyrofluid simulations showing the growth of an island in the presence of electromagnetic turbulence for parameters typical of a mid-size tokamak are presented