Edge profiles in high power L-mode plasmas and extrapolation to SPARC

Core modeling of fusion plasmas shows that overall temperature profiles are highly sensitive to conditions at the plasma edge, in the outer 5-10% of the plasma. Predictive modeling of the edge region is not yet routine, particularly for regimes such as L-mode which are limited by transport vs MHD. In its initial campaign, SPARC plans to plans to avoid H-mode operation, to avoid associated transients, and operate in L or I-mode, with a range of predictions for fusion Q [1]. We report here on further studies of L-mode edges in C-Mod plasmas, with relatively high B_T of 5-8 T, to inform expectations and plans for this campaign. Profiles of electron temperature and density from Edge Thomson Scattering are fit with smooth functions and gradients and scale lengths analysed. In many discharges, T_e profiles are near linear from edge to core but in some cases a steeper edge T gradient is observed. We will report on trends with plasma and heating parameters, focusing on relatively high RF power L-mode discharges such as those with high B and/or unfavorable drift direction. Profiles will be compared with some discharges in the I-mode regime, which features a strong T pedestal. Approaches for extrapolating C-Mod profiles to SPARC and other future fusion devices will be compared. [1] P. Rodriguez-Fernandez et al, Phys. Plasmas 31, 062501 (2024).