Targeting realistic geometry in Tokamak code Gysela

TL;DR

This paper introduces a new interpolation method and mesh strategy in the Gysela gyrokinetic code to improve the realism and efficiency of tokamak plasma simulations, addressing key geometric and computational challenges.

Contribution

A novel interpolation technique and non-uniform mesh approach are developed for the Gysela code to better handle realistic plasma geometries in gyrokinetic simulations.

Findings

Improved handling of mesh singularity at r=0

Reduced memory and computational costs

Validated convergence and robustness

Abstract

In magnetically confined plasmas used in Tokamak, turbulence is responsible for specific transport that limits the performance of this kind of reactors. Gyrokinetic simulations are able to capture ion and electron turbulence that give rise to heat losses, but require also state-of-the-art HPC techniques to handle computation costs. Such simulations are a major tool to establish good operating regime in Tokamak such as ITER, which is currently being built. Some of the key issues to address more realistic gyrokinetic simulations are: efficient and robust numerical schemes, accurate geometric description, good parallelization algorithms. The framework of this work is the Semi-Lagrangian setting for solving the gyrokinetic Vlasov equation and the Gyseka code. In this paper, a new variant for the interpolation method is proposed that can handle the mesh singularity in the poloidal plane at r=0 (polar system is used for the moment in Gysela). A non-uniform meshing of the poloidal plane is proposed instead of uniform one in order to save memory and computations. The interpolation method, the gyroaverage operator, and the Poisson solver are revised in order to cope with non-uniform meshes. A mapping that establish a bijection from polar coordinates to more realistic plasma shape is used to improve realism. Convergence studies are provided to establish the validity and robustness of our new approach.