Fluid models of impurity transport via drift wave turbulence

Abstract

Turbulent transport due to drift waves is a critical issue for fusion physics across all magnetic confinement geometries. Three-component fluid equations are used to find the eigenmodes and eigenfrequencies of a nonuniform, magnetized plasma with a four dimensional fluctuation vector composed of fluctuations of the electron density, the working gas ion density, the impurity density, and the electrostatic plasma potential. This structure of the eigenmodes and eigenvectors is shown for two collisionality regimes: (i) the collisional drift waves appropriate for the scrape-off-layer and the edge plasma in limiter discharges and (ii) the trapped electron mode taken in the limit of a Terry-Horton fluid description for the core plasma. From the eigenmodes and eigenvectors the part of the density and potential fluctuations that are out-of-phase is computed. The quasilinear particle fluxes are analyzed as a function of the power spectrum of the plasma potential fluctuations and the gradient parameters characterizing the Ohmic, H, and internal transport barrier confinement modes. A reversal in a direction of impurity flux is observed by changing the sign of the impurity density gradient length. After reversal, the impurity flux is directed outward and it is a favorable for fusion plasmas.