A new mechanism for filament disconnection at the X-point: poloidal shear in radial E × B velocity

Abstract

Plasma filaments generated by turbulence in the scrape-off layer are sometimes observed in experiments and simulations to disconnect from the target plate in the vicinity of the X-point, resulting in a ‘quiescent zone’ with reduced fluctuations, possibly affecting the fluctuating part of the divertor heat loads. This phenomena is usually explained by the flux tubes squeezing, induced by flux expansion, down to scales where collisions dominate. In this work, we consider an additional mechanism spontaneously arising at the X-point: the poloidal shear in radial velocity. Through a simple model, tested against 3D global turbulence simulations, we quantify the effectiveness of this disconnection mechanism and identify ways to control it.