Turbulence-based predictions of core plasma performance for the Infinity Two stellarator Fusion Pilot Plant

We use high fidelity transport simulations to predict transport characteristics and fusion performance of Type One Energy’s Infinity Two stellarator fusion pilot plant (FPP) concept [1]. Infinity Two is a high field quasi-isodynamic stellarator developed using modern optimization techniques to minimize neoclassical, turbulent, and energetic particle losses while remaining MHD stable [2]. A pellet fueled operating scenario is proposed that enables supporting an edge density gradient to substantially reduce ion temperature gradient (ITG) turbulence, while trapped electron mode (TEM) turbulence is minimized through optimizing for maximum-J (where J is the second adiabatic invariant). Nonlinear electromagnetic gyrokinetic simulations (GX [3]) illustrate the turbulence characteristics and dependencies, confirming the desired impact of the configuration and operational scenario on ITG and TEM dynamics while simultaneously avoiding onset of kinetic ballooning modes (KBM). Fusion performance is predicted using the recently developed Trinity3D (T3D) transport modeling framework, which leverages multi-scale gyrokinetic theory to efficiently predict macro-scale density and temperature profiles subject to micro-scale turbulent (nonlinear GX) and neoclassical (SFINCS [4]) losses. Energy sources include ECH and alpha heating, and radiation losses are included using representative impurity species (W, Ne, He). A baseline operating point is predicted with D-T fusion power of 800 MW at high fusion gain Q=40, respecting the Sudo density limit and MHD stability limits. We address fueling assumptions in the baseline scenario by making self-consistent predictions of the density profile with fueling from a pellet ablation model. We also examine sensitivity of the energy confinement to modifications of the assumed boundary temperature. Our analysis indicates there are credible solutions to self-consistently satisfy the transport, stability, heating, and fueling requirements for the Infinity Two stellarator FPP.

[1] W. Guttenfelder et al. J. Plasma Physics 91 (2025) E83

[2] C. Hegna et al. J Plasma Physics 91 (2025) E76

[3] N. R. Mandell et al. J. Plasma Physics 90 (2024) 905900402

[4] M. Landreman et al. Phys. Plasmas 21 (2014) 042503