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

Plasma filaments generated by turbulence in the scrape-off layer are sometimes observed in experi- ments 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 diver- tor 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 mech- anism spontaneously arising at the X-point: the poloidal shear in radial E × B 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.