On the nonlinear coupling between micro turbulence and mesoscale magnetic islands in a plasma
Centre for Fusion, Space and Astrophysics, Department of Physics, University of Warwick - Coventry, UK, EU
2 Max-Planck-Institut für Plasmaphysik - Boltzmannstrasse 2, D-85748, Garching bei München, Germany, EU
Accepted: 2 August 2010
The interaction between small-scale turbulence (of the order of the ion Larmor radius) and mesoscale magnetic islands is investigated within the gyrokinetic framework. Turbulence, driven by background temperature and density gradients, over nonlinear mode coupling, pumps energy into long-wavelength modes, and can result in an electrostatic vortex mode that coincides with the magnetic island. The strength of the vortex is strongly enhanced by the modified plasma flow response connected with the change in topology, and the transport it generates can compete with the parallel motion along the perturbed magnetic field. Density and temperature gradients inside the island are below the threshold for turbulence generation, and the anomalous transport inside the island is determined by turbulence spreading. A finite radial temperature gradient inside the island is observed to persist despite the fast motion along the field, and is related to the trapped particles which do not move along the field around the island. Consequences for the stability of the neo-classical tearing mode are discussed.
PACS: 52.35.Ra – Plasma turbulence / 52.55.-s – Magnetic confinement and equilibrium
© EPLA, 2010