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Parallel shear flow instability in the tokamak edge

Abstract : The transition between the core and scrape-off layer of a tokamak corresponds to a marked momentum shear layer, owing to sheath acceleration on limiters which drives near-sonic flows along the plasma magnetic field in the scrape-off layer, and a parallel shear flow instability can possibly be triggered. The possibility of this instability driven by the velocity gradient is investigated numerically, using a minimum model of particle and parallel momentum transport in the edge of a tokamak, in a computational domain modelling a limiter plasma with background turbulence modelled as an effective diffusion. It is found that unstable regions can exist in the vicinity of a limiter, in agreement with experimental findings, when momentum radial transport - and therefore coupling between SOL and core flows - is sufficiently weak. Instability is reinforced by core rotation, and is found to be maximum downstream of the limiter (with respect to the core plasma flow).
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Submitted on : Friday, July 26, 2013 - 2:03:36 PM
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Frédéric Schwander, Guillaume Chiavassa, Guido Ciraolo, Philippe Ghendrih, Livia Isoardi, et al.. Parallel shear flow instability in the tokamak edge. Journal of Nuclear Materials, Elsevier, 2011, 415 (1), pp.S601-S604. ⟨10.1016/j.jnucmat.2010.10.073⟩. ⟨hal-00848536⟩



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