Enhanced toroidal flow stabilization of edge localized modes with increased plasma density

TL;DR

This study reveals that increasing plasma density significantly enhances the stabilizing effect of toroidal flow on edge localized modes in tokamaks, providing new insights into ELM control strategies.

Contribution

First demonstration that higher plasma density amplifies toroidal flow stabilization of ELMs through two-fluid MHD calculations.

Findings

Toroidal flow stabilization of ELMs is significantly enhanced by increased plasma density.

Higher collisionality regimes favor ELM mitigation via toroidal rotation.

The results explain experimental observations of improved ELM control at higher plasma densities.

Abstract

Toroidal flow alone is generally thought to have important influence on tokamak edge pedestal stability, even though theory analysis often predicts merely a weak stabilizing effect of toroidal flow on the edge localized modes (ELMs) in experimental parameter regimes. For the first time, we find from two-fluid MHD calculations that such a stabilization, however, can be significantly enhanced by increasing the edge plasma density. Our finding resolves a long-standing mystery whether or how toroidal rotation can indeed have effective influence on ELMs, and explains why the ELM mitigation and suppression by toroidal rotation are more favorably achieved in higher collisionality regime in recent experiments. The finding suggests a new control scheme on modulating toroidal flow stabilization of ELMs with plasma density, along with a new additional constraint on the optimal level of plasma density for the desired edge plasma conditions.