Edge toroidal momentum and its effect on the scrape-off layer

Abstract

Non-zero toroidal momentum in the direction of the main plasma current near the last closed flux surface (LCFS) is often observed in experiments. Such a momentum, if included as a boundary condition in the scrape-off layer (SOL) modelling, could have a profound effect on the poloidal dependence of the plasma parameters in the SOL. In a single-null divertor configuration, the toroidal momentum can generate asymmetries in the plasma parameters between the strike zones. The additional torque exerted onto the SOL due to the toroidal rotation causes compression of the plasma along the field lines, increasing the plasma pressure in the divertor branch that represents the ion drift side. The ion drift side is located at the inner strike zone when the ion Del B drift is directed towards the target, and at the outer strike zone for the reversed Del B drift. The expected influence of the toroidal momentum on the SOL asymmetries agrees qualitatively with experiment. It may help to explain the experimentally observed dependence of the asymmetries between the strike zones on the direction of the Del B drift