Phase-resolved X–point energy modulation enables adaptive detachment against large ELMs

Abstract Monitoring divertor detachment is indispensable for sustained tokamak operation under reactor-relevant conditions, yet remains challenging with conventional diagnostics. A physics-informed framework termed the X–point Ionization and Radiation Interface Structure (X–IRIS) is proposed for robust detachment assessment. By leveraging the relative phase shift between two sightlines adjacent to the X–point, X–IRIS furnishes a calibration-free metric of detachment states, independent of direct electron-temperature measurements near the divertor targets. This approach quantifies the direction and magnitude of turbulent filament transport between the X–point and divertor, uncovering the link between cross-separatrix flow asymmetry and detachment states. X–IRIS thus provides a promising solution for non-invasive detachment monitoring in next-generation tokamak reactors.