Effect of sonic poloidal flows in determining flow and density asymmetries for trace impurities in the tokamak edge pedestal

TL;DR

This paper investigates how sonic poloidal flows influence impurity flow and density asymmetries in tokamak edge pedestals, combining analytical and numerical methods with experimental validation.

Contribution

It introduces a detailed analysis of poloidal flow effects, including shock formation, on impurity asymmetries, highlighting the importance of inertia terms in modeling.

Findings

Shock fronts can form at Mach numbers of order unity due to poloidal flows.

Inertia terms are crucial for accurately predicting impurity asymmetries.

Theoretical predictions agree well with ASDEX Upgrade experimental data.

Abstract

The structure of poloidal and toroidal flows of trace impurities in the edge pedestal of tokamak plasmas is studied analytically and numerically. Parallel momentum balance is analysed upon retaining the following terms: poloidal and toroidal centrifugal forces (inertia), pressure force, electric force, and the friction force. It is shown that, when the poloidal flow is such to produce a properly defined Mach number of order unity somewhere on the flux surface, shock fronts can form. The shock fronts can modify the predicted asymmetry structures in both the flow and the density profile along the poloidal arc. Predictions of the theory are shown against experimental observations in the ASDEX Upgrade tokamak, showing good qualitative and quantitative agreement if the inertia term associated with the poloidal flow is retained.