Kinetic corrections to the 2-point-model and applications to predictions in SPARC and C-Mod

Next generation high-field tokamaks will move exhaust regimes into new territory; high exhaust powers combined with narrow heat flux widths will push Scrape-Off Layer (SOL) conditions to ever lower collisionalities. In such regimes kinetic effects on parallel energy transport become important. The well-known “2-point-model” (2PM) is commonly applied to experimental interpretation of separatrix conditions, and as a reduced-model for scoping future devices. These applications however rarely account for kinetic effects, leading to systematic errors in low collisionality conditions.

SPARC SOL modelling is underway using both high-fidelity codes (SOLPS-ITER) and with extended-2PM scoping tools. In this work, kinetic correction scalings for both heat flux suppression and sheath enhancement effects, derived in previous work [1], are integrated into the 2PM solver within cfsPOPCON. In SPARC H-modes, the tool predicts SOL collisionalities ν_SOL<1, with flux reduction and sheath enhancement factors of ~0.1 and ~2.7 respectively. Upstream temperatures rise in high-performance scenarios from 300 to 600eV. Implications for SPARC exhaust power handling are discussed across a range of turbulence parameter α_t. The kinetic-corrected 2PM is also applied to C-Mod data, assessing its influence on upstream separatrix identification.

[1] D. Power et al 2023 Nucl. Fusion 63 086013