Gyrokinetic simulation of ITG turbulence with toroidal geometry including the magnetic axis by using field-aligned coordinates

TL;DR

This paper extends gyrokinetic simulations of ITG turbulence to include the magnetic axis using field-aligned coordinates, improving accuracy and revealing differences in electrostatic potential distribution.

Contribution

The study develops a new simulation domain including the magnetic axis and introduces a novel Poisson solver, enhancing the accuracy of gyrokinetic turbulence modeling.

Findings

Improved gyrocenter conservation with magnetic axis inclusion

Different zonal field and potential distribution compared to previous models

Enhanced simulation accuracy near the magnetic axis

Abstract

Abstract Simulation domain in field-aligned coordinates of the electrostatic gyrokinetic nonlinear turbulence global code, NLT, is extended to include the magnetic axis. The artificial boundary near the magnetic axis is replaced by the natural boundary. The singularity at the magnetic axis in Vlasov solver is treated by considering the spatial relation of fixed grid points in field-aligned coordinates. A new Poisson's equation solver is developed, the coefficient matrix of algebraic equations is derived by using Gauss's theorem. Nonlinear relaxation test of the ITG turbulence with adiabatic electrons is performed. The gyrocenter conservation is much improved by including the magnetic axis in the simulation domain. The zonal field and the radial distribution of the perturbed electrostatic potential are different from previous results without the magnetic axis.