Kinetic investigation of a collisionless scrape-off layer with a source of poloidal momentum

Abstract

The influence of a source of poloidal momentum on the collisionless tokamak scrape-off layer (SOL) is investigated. The solutions of the kinetic equation for ion flow and the corresponding system of fluid equations assuming zero ion heat flux are compared. The two models agree quite well for small poloidal Mach numbers of the momentum source, and for larger Mach numbers near the target towards which the drift is directed. At the other target the agreement is poor because the kinetic heat flux dominates energy transport near the stagnation point. The kinetic model yields smooth solutions for any value of poloidal drift. The fluid model breaks down at a particular supersonic poloidal Mach number due to the appearance of a singularity on the domain. The failure of the fluid model does not represent a real detachment, but is simply a mathematical artefact caused by the truncation of the series of fluid moment equations.