Particle transport in density gradient driven TE mode turbulence

TL;DR

This study investigates how steep electron density gradients influence particle transport in TE mode turbulence within tokamaks, comparing gyrokinetic and fluid models to understand impurity behavior.

Contribution

It provides new insights into impurity peaking factors and their dependence on density gradients and impurity charge, bridging gyrokinetic and fluid modeling approaches.

Findings

Impurity peaking factor is weakly dependent on impurity charge.

Impurity peaking factor is significantly smaller than the electron density gradient.

Results show transition from TE to temperature gradient driven turbulence.

Abstract

The turbulent transport of main ion and trace impurities in a tokamak device in the presence of steep electron density gradients has been studied. The parameters are chosen for trapped electron (TE) mode turbulence, driven primarily by steep electron density gradients relevant to H-mode physics, but with a transition to temperature gradient driven turbulence as the density gradient flattens. Results obtained through non-linear (NL) and quasilinear (QL) gyrokinetic simulations using the GENE code are compared with results obtained from a fluid model. Main ion and impurity transport is studied by examining the balance of convective and diffusive transport, as quantified by the density gradient corresponding to zero particle flux (peaking factor). Scalings are obtained for the impurity peaking with the background electron density gradient and the impurity charge number. It is shown that the impurity peaking factor is weakly dependent on impurity charge and significantly smaller than the driving electron density gradient.