Anomalous edge plasma transport, neutrals, and divertor plasma detachment

TL;DR

This paper investigates how neutrals influence anomalous edge plasma transport by affecting zonal flow generation, showing that neutrals can enhance transport even without suppressing the underlying turbulence, especially relevant in detached divertor regimes.

Contribution

It reveals that neutrals impact zonal flow generation rather than turbulence growth, leading to increased plasma transport, a novel insight into neutral effects in edge plasma physics.

Findings

Neutrals have minimal effect on linear RDW growth rates.

Neutrals significantly reduce zonal flow generation in nonlinear stages.

Enhanced plasma transport correlates with increased neutral density in detached divertor regimes.

Abstract

An impact of neutrals on anomalous edge plasma transport and zonal flow (ZF) is considered. As an example, it is assumed that edge plasma turbulence is driven by the resistive drift wave (RDW) instability. It is found that the actual effect of neutrals is not related to a suppression of the instability \textit{per se}, but due to an impact on the ZF. Particularly, it is shown that, whereas the neutrals make very little impact on the linear growth rate of the RDW instability, they can largely reduce the zonal flow generation in the nonlinear stage, which results in an enhancement of the overall anomalous plasma transport. Even though only RDW instability is considered, it seems that such an impact of neutrals on anomalous edge plasma transport has a very generic feature. It is conceivable that such neutral induced enhancement of anomalous plasma transport is observed experimentally in a detached divertor regime, which is accompanied by a strong increase of neutral density.