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

Abstract : 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.
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Submitted on : Friday, February 10, 2017 - 5:24:23 PM
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D. Zarzoso, W. A. Hornsby, E. Poli, F. J. Casson, A. G. Ă Peeters, et al.. Impact of rotating magnetic islands on density profile flattening and ă turbulent transport. Nuclear Fusion, IOP Publishing, 2015, 55 (11), ⟨10.1088/0029-5515/55/11/113018⟩. ⟨hal-01465038⟩



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