Optimization of the active MHD spectroscopy system on JET for the excitation of individual intermediate and high-n Alfvén eigenmodes

The stability of Alfv´en eigenmodes (AEs) is studied experimentally in the JET tokamak, by observing the plasma response to antenna-driven frequency-sweeping perturbations at the plasma edge. During the 2008/9 experimental campaigns, the complete set of the new AE antennas was operated and damping measurements for intermediate toroidal mode numbers (n) were collected under various plasma conditions. The quantity and the quality of the measurements reflect a significant effort put in the technical aspects of the diagnostic. We describe the results of the work on the optimization of the antenna currents and on the upgrade of the real-time resonance tracking system that allows one to target in real-time modes with specific n. As an example of the optimized performance of the diagnostic, the paper concludes with a report on the first results regarding the dependence of the measured damping rates of n = 3 and n = ±5 TAEs on background plasma parameters.