Non-ambipolarity of perpendicular plasma transport and asymmetry of particle flow onto the tokamak rail limiter

Abstract

Non-ambipolarity in plasma fluxes onto the surface of the graphite rail limiter in T-10 is manifested in the regimes with high values of the parameter I p d n e , where d is the SOL-width. A rise in I p d n e is accompanied by an electron temperature rise in the SOL. The maximal difference of floating potentials at the probes located on ion an electron sides of the limiter reached 54 V. The current density through the limiter in the toroidal direction near the limiter tip was equal to a half of the Spitzer current density. Experimental data from T-10 on asymmetry of floating potentials are qualitatively represented by a simple model fo longitudinal electron equilibrium along the magnetic field tube connecting ion and electron sides of the limiter. A model of radial peripheral plasma transport for the tokamak is proposed. The model is based on the splitting of a radial ion/electron flux into two terms Γ i = Γ i A + Γ i neo , Γ e = Γ e A + Γ e st , where Γ i,e A is the ambipolar flux, Γ e st is the electron flux due to magnetic field line stochastization, Γ i neo is the neoclassical ion flux. The model allows a qualitatively explanation of the variety of experimental facts related to a non-ambipolarity in plasma fluxes to the rail limiter, toroidal rotation and ballooning asymmetry of transverse transport at plasma peryphery.