How Zonal Flow Affects Trapped Electron Driven Turbulence in Tokamaks

TL;DR

This paper investigates how self-generated zonal flows influence trapped-electron mode turbulence in tokamaks, revealing their weak excitation at short wavelengths and implications for controlling plasma instability.

Contribution

It demonstrates that zonal flow excitation in CTEM turbulence is mathematically similar to ion temperature gradient turbulence and identifies parameters affecting this process.

Findings

Zonal flow excitation in CTEM is weak at short wavelengths.

Trapped electrons influence zonal flows only through linear dynamics.

The study offers parameters for controlling CTEM instability.

Abstract

The role of self-generated zonal flows in the collisionless trapped-electron mode (CTEM) turbulence is a long-standing open issue in tokamak plasmas. Here we show, for the first time, that the zonal flow excitation in the CTEM turbulence is formally isomorphic to that in the ion temperature gradient turbulence. Trapped electrons contribute implicitly only via linear dynamics. Theoretical analyses further suggest that, for short wavelength CTEMs, the zonal flow excitation is weak and, more importantly, not an effective saturation mechanism. Corresponding controlling parameters are also identified theoretically. These findings not only offer a plausible explanation for previous seemingly contradictory simulation results, but can also facilitate controlling the CTEM instability and transport with experimentally accessible parameters.