Spectrally Accelerated Edge and Scrape-Off Layer Gyrokinetic Turbulence Simulations

TL;DR

This paper introduces a spectral velocity-space approach in gyrokinetic simulations of edge and scrape-off layer turbulence, significantly reducing computational costs while maintaining accuracy, thus enabling more efficient high-fidelity plasma turbulence modeling.

Contribution

The paper develops and implements a novel spectral formulation in the GENE-X code, achieving at least a tenfold reduction in computational cost for edge turbulence simulations.

Findings

Spectral approach reproduces key turbulence profiles with high accuracy.

Achieves approximately 50x speed-up compared to grid-based methods.

Enables high-fidelity simulations within days on modern supercomputers.

Abstract

This paper presents the first gyrokinetic (GK) simulations of edge and scrape-off layer (SOL) turbulence accelerated by a velocity-space spectral approach in the full-f GK code GENE-X. Building upon the original grid velocity-space discretization, we derive and implement a new spectral formulation and verify the numerical implementation using the method of manufactured solution. We conduct a series of spectral turbulence simulations focusing on the TCV-X21 reference case [Oliveira D. S. et al., Nucl. Fusion 62, 096001 (2022)] and compare these results with previously validated grid simulations [Ulbl P. et al., Phys. Plasmas 30, 107986 (2023)]. The spectral approach reproduces the outboard midplane (OMP) profiles (density, temperature, and radial electric field), dominated by trapped electron mode (TEM) turbulence, with excellent agreement and significantly lower velocity-space resolution. Thus, the spectral approach reduces the computational cost by at least an order of magnitude, achieving a speed-up of approximately 50 for the TCV-X21 case. This enables high-fidelity GK simulations to be performed within a few days on modern CPU-based supercomputers for medium-sized devices and establishes GENE-X as a powerful tool for studying edge and SOL turbulence, moving towards reactor-relevant devices like ITER.