Neutral Excitation, Ionization and SOL Power Loss of Lower Hybrid Waves in the Alcator C-Mod Tokamak

The efficiency of Lower Hybrid Current Drive (LHCD) in Alcator C-Mod discharges diminishes precipitously in high density (line-averaged $\bar{n}_e > 10^{20} [m^{-3}]$), diverted plasmas as seen by the lack of indicative hard X-ray (HXR) bremsstrahlung and reduction in loop voltage. VUV, Visible and infrared light, as well as measurements of ne,Te in the SOL show significant change in the high density regime with the application of Lower Hybrid power. Poloidal dependence of LHCD-induced hydrogen Lyman-alpha emission in high density plasmas was investigated using a filtered poloidally-viewing pinhole camera. Due to limitations in the camera radial resolution, \emph{a priori} assumptions of the emission region were used to extract global emission values. Estimations are made of the electron cooling rate utilizing the Lyman-alpha emission and S/XB coefficients and are correlated to various experimental parameters for the dependency of power loss. The measurements indicate that Lyman-alpha power is enhanced globally by LHCD. Work supported by USDOE awards DE-FC02-99ER54512 and DE-AC02-76CH03073.