Description
Separatrix conditions, as the interface between open and closed field lines, influence SOL/divertor power and particle exhaust and are also correlated with core confinement and density peaking [1,2]. Multi-machine database studies consistently report strong sensitivities of global performance to edge parameters [3], motivating full-radius investigations of the underlying transport causality.
The full-radius integrated modelling framework HFPS, which is an IMAS-coupled version of the JINTRAC workflow, has been successfully used to predict a WEST L-mode plasma evolution heated by LHCD [4]. Based on this reference work [4], parameter scans of separatrix density and temperature are performed, while keeping heating, fueling, radiation and current fixed to isolate separatrix effects. Physics-based separatrix conditions obtained from SOLEDGE and SOLPS-ITER database scalings are also applied. The investigation reveals a strong sensitivity of core density and temperature to separatrix conditions, with changes in turbulent particle flux propagating inward up to ρ=0.6. A fivefold increase in separatrix density leads to a 35% increase in the energy content. Standalone TGLF-sat2 calculations, verified against linear gyrokinetic simulations, show that higher separatrix density or lower separatrix temperature, and associated rise in collisionality, enhance inward particle flux leading to more peaked core density profiles. The impact of dominant ion heating is compared to dominant electron heating. Furthermore the impact of separatrix is explored using more experimentally realistic settings such as feedback of the gas source on the line averaged density and/or self-consistent LHCD heating source absorption.
[1] D. Silvagni et al., Nucl. Mater. Energy 42, 101867 (2025).
[2] T. Eich et al., Nucl. Mater. Energy 42, 101896 (2025).
[3] C. Bourdelle, J. Morales, J.-F. Artaud, et al., Nucl. Fusion 63, 056021 (2023).
[4] T. Fonghetti et al., Nucl. Fusion 65, 056018 (2025).