Alcator C-Mod Mini-Proposal MP No . 757 Subject : MARFE Suppression and the Greenwald limit with High Density LHRF From :

The goal of this experiment is to characterize the Greenwald limit and related phenomena as affected by LHRF power. While the Greenwald limit is well described with respect to macroscopic tokamak parameters, the underlying cause of the Greenwald limit has yet to be fully proven. LHRF will be used as an actuator in this MP. LHRF in high density plasma is damped in the edge creating non-monotonic electron density profiles in the scrape-off-layer (SOL) [9]. By changing the ionization front (as seen through Lyα measurements), LHRF provides a way of changing SOL power and particle balances in a way not previously available on Alcator C-Mod. The SOL parameters have been shown to be important for the character of the Greenwald density limit, and will be changed through LHRF to test the Greenwald limit dependencies (outside of Ip, and a).