Comparisons of neutral density profile predictions using SOLPS-ITER and KN1D with experimental neutral profiles in Alcator C-Mod*

Accurate modeling of neutral density profiles in future tokamaks has strong consequences for both fueling and profile shape predictions. We evaluate the ability of two codes, SOLPS-ITER and KN1D, to accurately simulate the neutral density profiles of L-mode, I-mode, and H-mode discharges in Alcator C-Mod for which experimental neutral densities have been measured. We first achieve well matched neutral profiles for the L-mode and H-mode discharges in SOLPS by optimizing perpendicular transport coefficient profiles, providing confidence in the fidelity of the SOLPS neutral model over a range of operating parameters. The I-mode neutral profile is less well matched, suggesting further physics effects may need to be considered in some cases. We then model these discharges using a one-dimensional kinetic neutral code,  KN1D [1], with wall neutral pressures from SOLPS used as inputs to KN1D. We compare the neutral density profile predictions of KN1D to those from SOLPS and experiment, to evaluate the ability of KN1D to accurately predict midplane neutral densities over a range of operating parameters when using SOLPS to make more intricate predictions is not an accessible or timely option. 

[1] LaBombard B. 2001 MIT Plasma Science and Fusion Center Research Report (RR-01-03)