Oscillatory relaxation of zonal flows in a multi-species stellarator plasma

TL;DR

This paper investigates the oscillatory relaxation of zonal flows in a multi-species stellarator plasma using global gyrokinetic simulations, showing that single-species extrapolations can accurately predict multi-species behavior and aligning with experimental observations.

Contribution

It demonstrates that multi-species plasma oscillation frequencies and damping rates can be accurately predicted from single-species calculations using extrapolation formulas.

Findings

Oscillation frequency matches experimental data for TJ-II.

Single-species extrapolation formulas effectively predict multi-species behavior.

Realistic impurity concentrations explain observed damping rates.

Abstract

The low frequency oscillatory relaxation of zonal potential perturbations is studied numerically in the TJ-II stellarator (where it was experimentally detected for the first time). It is studied in full global gyrokinetic simulations of multi-species plasmas. The oscillation frequency obtained is compared with predictions based on single-species simulations using simplified analytical relations. It is shown that the frequency of this oscillation for a multi-species plasma can be accurately obtained from single-species calculations using extrapolation formulas. The damping of the oscillation and the influence of the different inter-species collisions is studied in detail. It is concluded that taking into account multiple kinetic ions and electrons with impurity concentrations realistic for TJ-II plasmas allows to account for the values of frequency and damping rate in zonal flows relaxations observed experimentally.