Gyrokinetic simulations of the impact of fast ions on turbulence in ARC

Burning plasmas in future fusion devices will be characterized by a large population of fast alpha particles, which is a regime far outside the capability of present day experiments. It is therefore crucial to use high-fidelity modeling capabilities to predict how alpha particles will interact with core turbulence and influence confinement. It has been observed both numerically and experimentally that high-energy particles can potentially lead to a significant increase in fusion performance by stabilizing turbulence [1]. This occurs through a variety of linear and nonlinear feedback mechanisms including wave-particle resonance, finite-beta stabilization, and excitation of fast-ion (FI) instabilities which indirectly affect the transport [2]. In this work, local CGYRO [3] simulations are used to study the effects of fast ions on core turbulence in the ARC fusion power plant [4]. Flux-matched gyrokinetic profile predictions produced using PORTALS-CGYRO [5], combined with fast ion profiles calculated via interpretive TRANSP [6] are used to investigate the linear stability of the local turbulence and compare to predictions of FI-destabilized toroidal Alfvén eigenmode (TAE) instabilities. Nonlinear CGYRO simulations are performed which demonstrate the effects of fast particles and unstable fast-ion modes on the background turbulence. Limitations of the local gyrokinetic approach and future directions for this research are discussed.

References:

[1] J. Citrin and P. Mantica. PPCF. 65 033001 (2023)

[2] Y.S. Na et al. Nat. Rev. Phys. 7, 190–202 (2025)

[3] J. Candy et al. J. Comp. Phys. 324 73-93 (2016)

[4] A. Creely et al. Symposium on Fusion Engineering (2025)

[5] P. Rodriguez-Fernandez et al. Nucl. Fus. 64 076034 (2024)

[6] A.Y. Pankin et al. Comp. Phys. Comm. 312 109611 (2025)