Argon, neon, and nitrogen impurity transport in the edge and SOL regions of a Tokamak

TL;DR

This study uses numerical simulations to analyze impurity transport mechanisms in a tokamak's edge and SOL regions, revealing how different impurities move inward or outward due to turbulence and plasma structures.

Contribution

It introduces an analytical relation for impurity ion density and demonstrates impurity transport behaviors specific to argon, neon, and nitrogen in turbulent plasma conditions.

Findings

Argon ions move more inward than neon and nitrogen.

Most impurity species predominantly move outward, but some inward transport occurs.

Inward impurity flux is linked to density holes and plasma turbulence phenomena.

Abstract

Numerical simulations of the interchange plasma turbulence in the presence of medium-Z impurities (N2 , Ne, Ar) seeding have been performed using BOUT++. These simulation results are used to study the impurity transport mechanism in the edge and scrape-off layer (SOL) regions. An analytical relation for the impurity ion density with the vorticity, sources and sinks, and mass to charge ratio has also been derived. Simulation shows that Ar+ moves more strongly inward compared to N+ and Ne+ that has been verified from the analytical relation. The most abundant species move both in the inward and outward directions, but on average they mainly move outward. These behaviors have been confirmed using cross-correlation techniques. The inward transport or negative flux of the impurity ions is found directly associated with the monopolar density holes in the presence of the electron temperature gradient whereas the outward transport is associated with the plasma blobs. The inward impurity transport has been analyzed using hole fraction analysis. ~44% of Ar+, ~28% of Ne+, and ~25% of N+ ions of their total impurity densities are transported inward mainly through the avalanche events of the turbulent plasma.