Suppression of nonlinear interchange mode by zonal counterstreaming flow generation

Nonlinear evolution of interchange mode produces both vortex flow and shear flow in a scrape-off layer (SOL) plasma with unfavorable magnetic curvature. When the Rayleigh number becomes the order of 10(5), the shear flow exceeds the vortex flow and the zonal counterstreaming flow appears in the perpendicular direction to the ambient magnetic field. Simultaneously, the fluctuation level decreases and the associated cross-field transport becomes almost classical. However, since reduction of the saturation level weakens the shear flow generation, an intermittent oscillatory behavior appears and continues. Transport due to the vortex flow measured with a Nusselt number may depend on the Prandtl number for a given Rayleigh number. (C) 1996 American Institute of Physics.