Gyrokinetic prediction of core tungsten peaking in a WEST plasma with nitrogen impurities

TL;DR

This paper uses gyrokinetic simulations to predict tungsten behavior in a WEST plasma, showing how nitrogen impurities influence tungsten peaking and implications for ITER operations.

Contribution

It provides the first comprehensive gyrokinetic prediction of tungsten peaking in WEST including impurity effects and validates these predictions with synthetic diagnostics.

Findings

Nitrogen impurities reduce neoclassical tungsten peaking on-axis.

Overall tungsten peaking increases with nitrogen impurities due to reduced turbulence screening.

Validation of simulations with synthetic bolometry diagnostics.

Abstract

Tungsten peaking is predicted in the core of a WEST plasma with total-f gyrokinetic simulations, including both collisional and turbulent transport. This prediction is validated with a synthetic diagnostic of the bolometry. Although nitrogen impurities are shown to reduce the neoclassical peaking of tungsten on-axis, the overall tungsten peaking increases when nitrogen impurities are present, as they reduce the turbulence screening off-axis. This finding is important for the plasma current ramp-up phase of ITER, where light impurities seeding will be desirable to achieve low temperatures at the plasma-facing components and reduce tungsten sputtering. It provides further argument for applying early ECRH heating to maintain margins on the core power balance. The neoclassical peaking factor is cross-verified between XGC and FACIT. The heat flux at separatrix and the heat load width are modeled by XGC and compared to WEST data.