Condition for Steep Density Gradient at Separatrix

TL;DR

This paper investigates the factors affecting the steepness of the plasma density gradient at the separatrix, focusing on the roles of profile curvature, neutral gas, electron heating, and electric fields in plasma confinement.

Contribution

It establishes the conditions linking density gradient steepness to SOL parameters like curvature, neutral gas density, and electric fields, providing insights into plasma edge behavior.

Findings

Density gradient slope depends on SOL profile curvature.

Neutral gas density and electron heating influence profile curvature.

Radial electric field relates to ion pressure gradient near the separatrix.

Abstract

The slope of the plasma density gradient at the separatrix is influenced by the curvature of the density profile in the scrape-off layer (SOL). This curvature is determined by the parallel flow loss rate and the ionization rate in the SOL, which are influenced by the neutral gas density and electron heating in that region. The radial electric field is also influenced by the ion pressure gradient just inside the separatrix.