Gyrokinetic Study of Divertor Heat-Load Width in Turbulent Edge Plasma and Comparison with the Two-Point Model

Recent electromagnetic gyrokinetic simulations using XGC have successfully reproduced the divertor heat-flux width (λ_q) on present-day tokamaks and predicted significantly wider λ_q on full-current ITER [1] and in the turbulent QH-mode discharges on DIII-D [2] than Eich’s empirical scaling predictions. In this work, we extend the previous simulations with improved numerical accuracy and longer time simulation, enabled by a new quiet start scheme that reduces spurious transients and particle noise in the edge region [3]. With this more robust dataset, we examine heat-flux profiles in detail and compare them against the classical two-point model. Realistic divertor boundary conditions and neutral physics were essential to match experimental λ_q, underscoring their critical role in modeling SOL transport [2]. Additionally, preliminary analysis indicates that turbulence near the X-point [2] and along the divertor leg may contribute to the broadening of parallel heat flux. These results support the importance of incorporating comprehensive edge physics - including neutral, boundary, and turbulence effects - to adequately describe the heat-flux footprint in tokamak fusion reactors.



[1] C.S. Chang et al., Nucl. Fusion Nucl. Fusion 57, 116023 (2017); Phys. Plasmas 28, 022501 (2021)

[2] D. R. Ernst et al., Phys. Rev. Lett. 132, 235102 (2024)

[3] S. Ku et al., presented at APS-DPP 2025