The Role of Alpha Particles in Turbulence Suppression and Confinement Enhancement in SPARC and future reactors

Nonlinear, global gyrokinetic simulations indicate that explicitly including alpha particles leads to a large improvement in confinement in burning plasma devices. This enhancement is primarily due to alpha-driven turbulence suppression, which amplifies zonal flows and reduces micro-instability levels. Consequently, fusion alpha heating increases by over 20%, resulting in a notable boost in the overall fusion gain Q.



Accurately predicting plasma performance is critical for optimizing confinement and ensuring reliable operation in next-generation fusion reactors. In this work, we present the first high-fidelity plasma performance predictions for SPARC, based on nonlinear, global gyrokinetic simulations using the GENE-Tango framework. The analysis focuses on the impact of fusion-born alpha particles on plasma confinement. By capturing the full turbulent spectrum—including both Alfvén eigenmodes and micro-instabilities—our simulations reveal the essential role of interactions between alpha-particle-driven Alfvén modes, micro-turbulence, and zonal flows. These nonlinear couplings are shown to significantly influence turbulent transport in the presence of alpha particles.



We offer a detailed analysis of the nonlinear, multiscale dynamics that govern burning plasmas—accounting for turbulence, profile evolution, and heating. This study represents the most comprehensive and high-fidelity simulation of a burning plasma to date. Additionally, we outline strategies to further exploit the beneficial effects of alpha particles, suggesting promising directions for optimizing confinement in future burning plasma experiments.