The impact of net power and edge particle source on the electron density pedestal of Alcator C-Mod

Understanding plasma transport and fueling at the edge of tokamak plasmas is critical to predicting the density and performance in next-generation reactors. Existing experimental data, combined with high-fidelity simulations of neutral kinetics, allows insight into important atomic/plasma processes that determine plasma profiles. To this end, SOLPS-ITER is run interpretively on Alcator C-Mod discharges with varied particle and energy content. We consider a scan of the net power (P_net), both with/without active cryopumping, and track changes in recycling particle fluxes and edge electron density (n_e) and temperature gradients. We use measurements from edge Thomson scattering and a Lyman-alpha camera to simultaneously constrain n_e and the neutral density. Experimentally, we observe degradation in the pedestal quality when P_net drops past ~2.4 MW. As this approaches the L-H power threshold, we see a dramatic rise in effective particle diffusivity at the location of maximum n_e gradient, by about an order of magnitude. Computationally, we attempt to model the change in transport by solving for particle and heat diffusivities that uniquely reproduce experimental plasma profiles as well as measured ionization source. We thus supplement experimental 1D findings with a 2D picture of transport and fueling in a high-density machine opaque to neutrals.