Parallel shear flow instability in the tokamak edge

Frédéric Schwander (1) , Guillaume Chiavassa (1) , Guido Ciraolo (1) , Philippe Ghendrih (2) , Livia Isoardi (1) , A. Paredes (1) , Yanick Sarazin (2) , Eric Serre (1) , Patrick Tamain (2)

1 M2P2 - Laboratoire de Mécanique, Modélisation et Procédés Propres
2 IRFM - Institut de Recherche sur la Fusion par confinement Magnétique

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).

Domaines: Mécanique des fluides [physics.class-ph]; Mécanique des fluides [physics.class-ph]

Frédéric Schwander, Guillaume Chiavassa, Guido Ciraolo, Philippe Ghendrih, Livia Isoardi, et al.. Parallel shear flow instability in the tokamak edge. Journal of Nuclear Materials, 2011, 415 (1), pp.S601-S604. ⟨10.1016/j.jnucmat.2010.10.073⟩. ⟨hal-00848536⟩