Description
Negative triangularity (NT) is a promising ELM-free alternative to conventional H-mode operation. However, experimental studies have shown that achieving divertor detachment in NT is more challenging than in positive triangularity (PT) configurations at comparable upstream conditions and divertor geometry [O. Février et al., Plasma Phys. Control. Fusion 66 (2024)]. In this work, we investigate the role of scrape-off layer (SOL) turbulence and plasma–neutral interactions in determining exhaust properties in PT and NT using first-principles numerical simulations. We perform multi-species turbulence simulations of the tokamak SOL with the GBS code [P. Ricci et al., Plasma Phys. Control. Fusion 54 (2012)], self-consistently coupled to the kinetic neutral solver KINDNES. The plasma model includes electrons, atomic and molecular ions, while atomic and molecular neutrals are treated kinetically, enabling a self-consistent description of three-dimensional turbulence, ionization, dissociation, and neutral transport. Magnetic configurations are selected to have identical divertor geometry and comparable upstream conditions, while varying the upper triangularity, in order to decouple the effects of plasma shaping from those of particle and power exhaust. The simulations reproduce a reduced SOL width in NT compared to PT, associated with reduced turbulence levels, in qualitative agreement with experimental observations and previous theoretical work. The full three-dimensional dynamics are analyzed, allowing a detailed characterization of turbulence properties and transport mechanisms in the two configurations. By comparing parallel and perpendicular transport channels, we explore mechanisms that may contribute to more localized power loads and reduced divertor cooling in NT, providing insight into factors that could make detachment more difficult to achieve than in PT. Thanks to the self- consistent treatment of neutrals with KINDNES, we assess differences in plasma–neutral coupling between PT and NT under the same upstream conditions, thus enabling an analysis of the effect of neutral penetration and ionization patterns on divertor performance.