Full-F Turbulent Simulation in a Linear Device using a Gyro-Moment Approach

TL;DR

This paper presents a gyro-moment based simulation approach for plasma turbulence in a linear device, demonstrating convergence and comparing results with fluid models, advancing the understanding of full-F plasma dynamics.

Contribution

It introduces a full-F gyro-moment hierarchy model for turbulence simulation in linear devices, incorporating nonlinear collisions and boundary conditions, and compares it with traditional fluid models.

Findings

Higher-order gyro-moments are damped in high-collisional regimes.

Qualitative agreement between gyro-moment and fluid simulations.

Convergence properties of the gyro-moment expansion are demonstrated.

Abstract

Simulations of plasma turbulence in a linear plasma device configuration are presented. These simulations are based on a simplified version of the gyrokinetic (GK) model proposed by B. J. Frei et al. [J. Plasma Phys. 86, 905860205 (2020)] where the full-F distribution function is expanded on a velocity-space polynomial basis allowing us to reduce its evolution to the solution of an arbitrary number of fluid-like equations for the expansion coefficients, denoted as the gyro-moments (GM). By focusing on the electrostatic and neglecting finite Larmor radius effects, a full-F GM hierarchy equation is derived to evolve the ion dynamics, which includes a nonlinear Dougherty collision operator, localized sources, and Bohm sheath boundary conditions. An electron fluid Braginskii model is used to evolve the electron dynamics, coupled to the full-F ion GM hierarchy equation via a vorticity equation where the Boussinesq approximation is used. A set of full-F turbulent simulations are then performed using the parameters of the LArge Plasma Device (LAPD) experiments with different numbers of ion GMs and different values of collisionality. The ion distribution function is analyzed illustrating the convergence properties of the GM approach. In particular, we show that higher-order GMs are damped by collisions in the high-collisional regime relevant to LAPD experiments. The GM results are then compared with those from two-fluid Braginskii simulations, finding qualitative agreement in the time-averaged profiles and statistical turbulent properties.