OpenMP Target Offloading for Hybrid Fluid-Kinetic Plasma Simulations in JOREK: Accelerating Fusion Research on GPU Enabled Clusters

The study of plasma instabilities in magnetic confinement fusion devices is crucial for the design and operation of future fusion power plants. Numerical simulations play a key role in understanding these complex physical phenomena. The finite element code JOREK implements magnetohydrodynamic (MHD) and hybrid fluid-kinetic models to simulate these instabilities and explore potential mitigation strategies. With the increasing prevalence of GPU-accelerated architectures in high-performance computing, adapting JOREK to efficiently exploit these systems has become essential. The complexity of the code presents significant challenges due to its use of high-order finite elements, various physics models, including a kinetic description of runaway electrons (REs) and the fully implicit time stepping required by extreme scale separations in fusion plasmas. We have ported the matrix construction, the iterative solver, and the particle loop for the runaway-electron kinetic model to GPUs using OpenMP target offloading and optimized GPU libraries, achieving good performance and scaling across multiple nodes. These developments mark an important step, enabling large-scale, high-fidelity hybrid fluid-kinetic simulations of tokamak plasmas on GPU-accelerated clusters, accelerating progress toward predictive, numerical, physics-based fusion reactor design.