Impurity flows and plateau-regime poloidal density variation in a tokamak pedestal

TL;DR

This paper analyzes impurity density and flow variations in a tokamak pedestal, revealing regime-dependent poloidal impurity distribution and flow modifications, especially in the plateau regime of main ions.

Contribution

It provides the first calculation of impurity density and flow modifications in the plateau regime, highlighting differences from previous regimes and extending understanding of impurity behavior.

Findings

Impurity density can be higher on either inboard or outboard side in the plateau regime.

Impurity density is always higher on the inboard side in banana or Pfirsch-Schl"uter regimes without rotation.

Impurity flow modifications are characterized for various main-ion collisionality regimes.

Abstract

In the pedestal of a tokamak, the sharp radial gradients of density and temperature can give rise to poloidal variation in the density of impurities. At the same time, the flow of the impurity species is modified relative to the conventional neoclassical result. In this paper, these changes to the density and flow of a collisional impurity species are calculated for the case when the main ions are in the plateau regime. In this regime it is found that the impurity density can be higher at either the inboard or outboard side. This finding differs from earlier results for banana- or Pfirsch-Schl\"uter-regime main ions, in which case the impurity density is always higher at the inboard side in the absence of rotation. Finally, the modifications to the impurity flow are also given for the other regimes of main-ion collisionality.