Observations and empirical scalings of the high-confinement mode pedestal on Alcator C-Mod

On the Alcator C-Mod tokamak [Phys. Plasmas 1, 1511 (1994)], radial profiles of electron temperature (Te) and density (ne) are measured at the plasma edge with millimeter resolution Thomson scattering [Rev. Sci. Instrum. 72, 1107 (2001)]. Edge transport barriers in the high confinement regime (H mode) exhibit Te, ne pedestals with typical widths of 2–6 mm, with the Te pedestal on average slightly wider than and inside the ne pedestal. Measurements at both the top and the base of the pedestal are consistent with profiles obtained using other diagnostics. The two primary H-mode regimes on C-Mod, enhanced Dα (EDA) and edge-localized mode free, have been examined for differences in pedestals. EDA operation is favored by high edge collisionality ν*, in addition to high edge safety factor q95. Scaling studies at fixed shape yield little systematic variation of pedestal widths with plasma parameters, though higher triangularity is seen to increase the ne pedestal width dramatically. Pedestal heights and gradient...