This paper reports the first quantitative analysis of the measurements of the damping rate (γ/ω) for stable Alfvén eigenmodes (AEs) with toroidal mode number (n) in the range |n| = 3–15 as a function of the edge plasma elongation (κ95). We find that the damping rate γ/ω versus κ95 for medium-n toroidal AEs (TAEs), with n = 3 and n = 7, increases for increasing elongation, i.e. its scaling versus κ95 follows the same trend previously measured and explained theoretically for the n = 1 and n = 2 TAEs. Theoretical analysis of the measurements for the n = 3 TAEs has been performed using the LEMan code. The results are in good agreement (within a factor of two) for all the magnetic configurations where there is only a very minor up/down asymmetry in the poloidal cross-section of the plasma. These experimental results further confirm the possibility of using the edge shape parameters as a real-time actuator for control of the stability of alpha-particle driven AEs in burning plasma experiments, such as ITER.
Optimization of the active MHD spectroscopy system on JET for the excitation of individual intermediate and high-n Alfvén eigenmodes