HPSF Conference 2025

The development of fusion energy in magnetic confinement devices relies heavily on simulations of plasma behavior. Gyselalib++ is a new open-source C++ library under active development by a European distributed and multidisciplinary team of physicists, mathematicians, and computer scientists at EPFL, CEA/IRFM, Maison de la Simulation, IPP Garching, and CINES. Gyselalib++ is itself built on top of PDI, DDC and Kokkos and provides mathematical tools for gyrokinetic semi-Lagrangian codes for tokamak plasma simulations. This presentation will introduce the library, its design and the rationale behind its development, and will highlight its key features. It will showcase how the choice of Kokkos made it possible to achieve high performance on modern hardware with performance portability over a wide range of hardware, and will explain the need to introduce DDC to improve development safety. We will discuss feedback from this experience, analyze our successes and the limitations of the approach, especially when it comes to performance, performance portability, and programmability of the code by a highly diverse team in terms of background.