Edge tokamak transport in regimes with high collisionality

Abstract

AbstractIn the strongly detached regimes, especially in future tokamak reactors, plasma in the divertor and in some special regions like vicinity of highly radiating X‐point is strongly collisional. Ion gyrofrequency becomes less than Coulomb collision frequency and might be of the order of ion‐neutral collision frequency. For such parameters, parallel and perpendicular ion diffusion and mobility caused by ion‐neutral collision becomes important and can to large extent determine density profiles and currents distribution in the divertor. In the present article, plasma profiles in the vicinity of divertor plates were analysed. It is demonstrated that density profiles are determined by combination of parallel and perpendicular ambipolar diffusion. Results of analytic calculations are compared with Particle‐In‐Cell Monte‐Carlo Collisions (PIC MCC) simulations of magnetized plasma and collisional transport of magnetized ions from quasi‐neutral region to the material surface. Analytic expressions are compared with the results of particle in cell simulations done for different angles between magnetic field and material surface and different plasma parameters. Impact of velocity of neutral particles on ion fluxes and currents is also investigated. Consequences for divertor plasma typical for ITER and other future tokamak‐reactors are discussed.