Investigating particle flux-gradient relationships at the edge of high density plasmas through an empirical database and SOLPS-ITER modeling on Alcator C-Mod

Quantifying particle fluxes in the edge and pedestal region is crucial for understanding the formation of transport barriers. High fields (Bt > 5T) on C-Mod allow study of H-mode pedestals with high density, opaque edges. We present particle source and flux profiles spanning a region of ~6cm about the last closed flux surface (LCFS) inferred from line-integrated Ly-α brightness measurements at the outer midplane. This workflow is used to create a database of inferred particle fluxes and electron density gradients throughout the pedestal. Constraining edge neutral modeling with Ly-α presents a unique opportunity to study how deuterium neutrals affect the formation of the edge transport barrier. SOLPS-ITER is run interpretively on two upper single-null H-Mode shots. Changing pumping conditions affects the particle source, which is modeled with the EIRENE Monte Carlo neutral code in SOLPS-ITER. Experimentally, this has a small effect on the ne profile but does increase Te, possibly because of a reduction in heat sinks. A set of particle and heat diffusivities (D,e) is found iteratively to allow matches to experimental ne and Te profiles. Varying core flux boundary conditions constrained by experiment allows a study of the transport required to reproduce experimental profiles.