Results from Real-time Open-loop Alfv\'{e}n Eigenmode excitation in Alcator C-Mod

The Active MHD diagnostic system excites Alfv\'{e}n eigenmodes in Alcator C-Mod and measures their damping rates, or margin to instability. Resonant modes are stimulated with two moderate-n antennas positioned above and below the outboard midplane. The antennas are fed by power amplifiers equipped with automatically tuned capacitive networks capable of matching in the range of 30 kHz to 1 MHz. The driving frequency follows in real-time the center of the Toroidal Alfv\'{e}n Eigenmode gap, $f_{TAE}=v_A/4\pi qR$, making small excursions away from the gap to observe the modes' damping characteristics. The effect of shear on mode damping rate was studied during an elongation scan of inner wall limited plasmas. The destabilizing effect of ICRF-heated fast ions with energies above 1/3 the Alfven speed, $v_A=B/ \sqrt{ \mu_0 \rho}$, was also studied. Finally the diagnostic regularly records mode damping rates in plasmas tailored to other experiments. Results are presented.