A strategy for core-edge integration leveraging low density and high temperature in the scrape-off layer

One of the most critical challenges in developing a fusion pilot plant (FPP) lies in simultaneously satisfying the requirements of plasma confinement and plasma exhaust. These are often in conflict, arising from the need to reconcile the extremely high fusion temperatures within the core plasma (>10 keV) with conditions that are sustainable for plasma-facing components. In this presentation, we propose a strategy for core-edge integration leveraging low scrape-off layer (SOL) density and high SOL temperature to significantly enhance confinement. We begin by presenting empirical evidence from the latest International Tokamak Physics Activity (ITPA) H-mode database, which reveals a naturally occurring high-confinement regime at low separatrix density. The data suggests that this favorable confinement results largely from transport dynamics in the pedestal, with a smaller (also favorable) effect attributable to magnetohydrodynamic (MHD) stability limits. Following this, we describe a theoretical gyrokinetic framework for understanding transport barriers, which is consistent with these empirical observations. The framework exploits two constraints, free energy and ambipolarity, to explain wide-ranging transport barrier phenomena. We then describe reduced models for pedestal transport, which are applied to pedestal profile evolution. This workflow exploits surrogate models to accelerate model development and profile prediction. Notably, the results qualitatively reproduce the major trends in the ITPA database relating to the dependence of confinement on separatrix parameters including the response of pedestal temperature profiles to the pedestal density. Tailoring of the density profiles can likely substantially improve confinement in burning plasma conditions. Lastly, we touch on a novel divertor concept, the super-XT divertor, which could facilitate the desired parameter regime in an FPP.