Effect of divertor conditions on ionization and neutral density profiles in the edge and SOL in DIII-D

We compare the ionization and neutral density profiles in the edge and scrape-off layer (SOL) in DIII-D plasmas with measurements obtained from the Lyman-Alpha Measurement Apparatus (LLAMA) diagnostic for different divertor conditions. The impact of divertor closure (USN with a closed divertor and LSN with an open divertor) and state of divertor conditions (attached/detached) are investigated in H-mode plasmas on both the low and high field side of the plasma below the midplane. For the LSN vs USN configurations, measurements are taken at different poloidal locations relative to the X-point, allowing to study the influence of the detachment on the ionization and neutral density profiles at different positions. Divertor closure plays an important role in trapping neutrals, impacting the pedestal and SOL density and temperature profiles and the density at the onset of detachment. Results will be compared with modelling SOLPS predictions from [1]. Understanding how ionization profiles relates to pedestal structure, divertor closure and detachment onset is crucial for closing the Integrated Tokamak and Exhaust Performance (ITEP) knowledge gap. This research is beneficial for our understanding of possible fueling scenarios for future machine operation like ITER and future fusion reactor.

[1] A.C. Sontag et al 2017 Nucl. Fusion 57 076025