Secondary instability of electromagnetic ion-temperature-gradient modes for zonal flow generation

TL;DR

This paper develops an analytical fluid model to study how finite plasma beta influences zonal flow generation by electromagnetic ITG modes, revealing enhanced zonal flow growth near marginal stability and implications for turbulence suppression.

Contribution

It introduces a new analytical model incorporating finite beta electromagnetic effects into ITG-driven zonal flow generation analysis.

Findings

Zonal flow growth rate increases with plasma beta near marginal stability.

ITG turbulence and transport decrease faster with beta than linear predictions.

Finite beta effects are crucial for understanding turbulence regulation in tokamaks.

Abstract

An analytical model for zonal flow generation by toroidal ion-temperature-gradient (ITG) modes, including finite $\beta$ electromagnetic effects, is derived. The derivation is based on a fluid model for ions and electrons and takes into account both linear and nonlinear $\beta$ effects. The influence of finite plasma $\beta$ on the zonal flow growth rate ($\gamma_{ZF}$) scaling is investigated for typical tokamak plasma parameters. The results show the importance of the zonal flows close to marginal stability where $\gamma_{ZF}/\gamma_{ITG}>>1$ is obtained. In this region the parameter $\gamma_{ZF}/\gamma_{ITG}$ increases with $\beta$, indicating that the ITG turbulence and associated transport would decrease with $\beta$ at a faster rate than expected from a purely linear or quasi-linear analysis.