Neoclassical transport of tungsten ion bundles in total-f neoclassical gyrokinetic simulations of a whole-volume JET-like plasma

TL;DR

This paper demonstrates a gyrokinetic bundling technique for modeling tungsten impurity charge states in whole-volume JET-like plasmas, revealing impurity flux behaviors and asymmetries affecting neoclassical transport.

Contribution

It introduces a novel bundling method for tungsten ions in gyrokinetic simulations, improving efficiency and capturing complex impurity flux dynamics in the plasma.

Findings

Tungsten accumulates at the pedestal top due to charge-dependent fluxes.

Large poloidal asymmetries influence neoclassical tungsten fluxes.

Temperature screening correlates with impurity asymmetries.

Abstract

The application of a bundling technique to model the diverse charge states of tungsten impurity species in total-f gyrokinetic simulations is demonstrated. The gyrokinetic bundling method strategically groups tungsten ions of similar charge, optimizing computational efficiency. The initial radial configuration of these bundles and their respective charges are derived from a coronal approximation and the quasi-neutrality of the plasma. A low-density JET H-mode like plasma is simulated using the neoclassical version of XGC across the entire plasma volume, spanning from the magnetic axis to the divertor. An accumulation of tungsten is observed at the pedestal top, as a result of low-Z tungsten ions moving inward from the scrape-off-layer (SOL) into the core region and high-Z tungsten ions moving outward from the core into the pedestal. This organization of the fluxes cannot be captured by a single tungsten-ion simulation. Large up-down poloidal asymmetries of tungsten form in the pedestal and strongly influence the direction of neoclassical fluxes. The temperature screening effect and its correlation with asymmetries is analyzed.