UEDGE simulation of edge plasmas in DIII-D double null configurations

Abstract

Analysis of plasma flow in the edge of double null hybrid mode DIII-D plasmas is reported. The two dimension fluid plasma code UEDGE [T. Rognlien et al., J. Nucl. Mater. 196–198, 347 (1992)] is used for the analysis. The effect of impurity radiation from intrinsic carbon sputtered from plasma facing surfaces is included as is the effect of plasma drifts. Two discharges in which the flux surfaces through the poloidal field nulls (X-points) are separated by 1 cm at the outer midplane are analyzed. The discharges differ only in the direction of the ion ∇B drift. It is shown that the flow of both primary ions and intrinsic impurities is dominated by the effect of plasma drifts. Variations in the recycling of deuterium ions, as seen in Dα emission profiles, are qualitatively consistent with experiment and are driven by the effect of E×B drifts associated with radial gradients of the electron temperature at the secondary separatrix. Trace argon impurity is introduced to simulate the transport of argon used in the experiment to enhance divertor radiation power. Penetration of the trace argon to the closed field lines depends on the direction of the ion ∇B drift, consistent with experiment. The analysis described here includes the effect of a deuterium gas puff to establish the “puff and pump” configuration. The poloidal flow of impurities is a balance between the projection of the parallel flow and poloidal drifts, primarily from E×B. It is shown that the effect of the gas puff is primarily to alter the electron temperature profile and thus affects impurity flow via alteration of E×B drifts, not via entrainment in deuterium ion parallel flow.