Comprehensive full-f drift-kinetic and delta-f gyrokinetic simulations of a linear plasma device based on the gyro-moment approach

TL;DR

This paper presents the first comprehensive full-f drift-kinetic and delta-f gyrokinetic simulations of a linear plasma device, revealing detailed turbulence dynamics and the interplay between DK and GK fields under various collisionalities.

Contribution

It introduces a self-consistent electrostatic model coupling DK and GK fields using a spectral expansion, and demonstrates their interaction and turbulence characteristics in a linear device setting.

Findings

DK ion distribution is approximately bi-Maxwellian.

GK fields do not influence DK fields at typical collisionality.

Reduced collisionality amplifies small-scale turbulence and reveals GK Kelvin-Helmholz-like modes.

Abstract

First of a kind comprehensive full-f drift-kinetic (DK) and $\delta$-f gyrokinetic (GK) turbulent simulations are carried out in a linear plasma device. We self-consistently derive an electrostatic model including large-scale slowly-varying DK-ordered fields coupled to small-scale rapidly-fluctuating GK-ordered fields. By relying on the critical balance ordering, we show that the electrons are described by a drift-reduced Braginskii model while we rely on a Hermite-Laguerre spectral expansion for describing both the DK and GK parts of the ion distribution function. Global simulations are carried out using the parameters of the linear device LAPD, showing that the DK part of the ion distribution function is approximately a bi-Maxwellian. Fast spectral convergence both for the DK and GK Hermite-Laguerre expansion coefficients is observed, and that the GK fields do not affect the DK fields at the physical LAPD collisionality. Only when the collisionality is reduced and the source term is amplified for the GK fluctuations, an amplification of small-scale turbulent structures is observed. The findings are supported by linear results that show that the simulations are dominated by turbulent fluctuations that are Kelvin-Helmholz driven. Additionally, a GK Kelvin-Helmholz-like mode is observed in the low-GK-collisionality regime which can non-linearly drive small-scale structures.