  This paper presents a dedicated study of plasma-antenna (PA) coupling with
the Alfven Eigenmode Active Diagnostic (AEAD) in JET. Stable AEs and their
resonant frequencies f, damping rates $\gamma$ < 0, and toroidal mode numbers n
are measured for various PA separations and limiter versus X-point magnetic
configurations. Two stable AEs are observed to be resonantly excited at
distinct low and high frequencies in limiter plasmas. The values of f and n do
not vary with PA separation. However, $\vert\gamma\vert$ increases with PA
separation for the low-f, but not high-f, mode, yet this may be due to slightly
different edge conditions. The high-f AE is detected throughout the transition
from limiter to X-point configuration, though its damping rate increases; the
low-f mode, on the other hand, becomes unidentifiable. The linear resistive MHD
code CASTOR is used to simulate the frequency scan of an AEAD-like external
antenna. For the limiter pulses, the high-f mode is determined to be an n = 0
GAE, while the low-f mode is likely an n = 2 TAE. During the transition from
limiter to X-point configuration, CASTOR indicates that n = 1 and 2 EAEs are
excited in the edge gap. These results extend previous experimental studies in
JET and Alcator C-Mod; validate the computational work performed by Dvornova et
al 2020 Phys. Plasmas 27 012507; and provide guidance for the optimization of
PA coupling in upcoming JET energetic particle experiments, for which the AEAD
will aim to identify the contribution of alpha particles to AE drive during the
DT campaign.
