Measurement and calculation of Alfvén eigenmode damping and excitation over a full toroidal spectrum

A broadband experimental study of Alfvén eigenmode (AE) damping and excitation examines both low-n and high-n AEs (0<|n|<9) with a single diagnostic. Direct measurements of the damping rate of stable AEs with the active MHD system, in conjunction with analytic and numerical calculation, indicate that AE stabilization in Alcator C-Mod is largely due to radiative damping. AEs are also regularly observed to become unstable during ICRF heating above 3MW. The most unstable modes have moderate-n around n=4, in agreement with the common scaling of k _θρ _fast1 at maximum excitation.