$\texttt{stella}$: a mixed implicit-explicit, delta-f gyrokinetic code for general magnetic field configurations

TL;DR

The paper introduces $ exttt{stella}$, a new gyrokinetic simulation code employing a mixed implicit-explicit scheme to efficiently model electrostatic fluctuations with kinetic electrons in complex magnetic geometries.

Contribution

It presents a novel mixed implicit-explicit numerical scheme implemented in $ exttt{stella}$ for gyrokinetic simulations in general magnetic fields, improving over fully explicit methods.

Findings

Demonstrates advantages of the mixed scheme over explicit methods.

Provides benchmark comparisons for axisymmetric and non-axisymmetric equilibria.

Shows $ exttt{stella}$ can handle multiple ion species and full kinetic electrons.

Abstract

Here we present details of a mixed implicit-explicit numerical scheme for the solution of the gyrokinetic-Poisson system of equations in the local limit. This scheme has been implemented in a new code called $\texttt{stella}$, which is capable of evolving electrostatic fluctuations with full kinetic electron effects and an arbitrary number of ion species in general magnetic geometry. We demonstrate the advantages of this mixed approach over a fully explicit treatment and provide linear and nonlinear benchmark comparisons for both axisymmetric and non-axisymmetric magnetic equilibria.