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In this paper, we report the novel experimental observation of both unstableand stable Toroidicity-induced Alfv\'en Eigenmodes (TAEs) measuredsimultaneously in a JET tokamak plasma. The three-ion-heating scheme(D-DNBI-3He) is employed to accelerate deuterons to MeV energies, therebydestabilizing TAEs with toroidal mode numbers n = 3-5, each decreasing in modeamplitude. At the same time, the Alfv\'en Eigenmode Active Diagnosticresonantly excites a stable n = 6 TAE with total normalized damping rate$-\gamma/\omega_0 \approx$ 1%-4%. Hybrid kinetic-MHD modeling with codes NOVA-Kand MEGA both find eigenmodes with similar frequencies, mode structures, andradial locations as in experiment. NOVA-K demonstrates good agreement with then = 3, 4, and 6 TAEs, matching the damping rate of the n = 6 mode withinuncertainties and identifying radiative damping as the dominant contribution.Improved agreement is found with MEGA for all modes: the unstable n = 3-5 andstable n = 2, 6 modes, with the latter two stabilized by higher intrinsicdamping and lower fast ion drive, respectively. While some discrepancies remainto be resolved, this unique validation effort gives us confidence in TAEstability predictions for future fusion devices.

Simultaneous measurements of unstable and stable Alfv\'en Eigenmodes in JET