A hybrid MHD-gyrokinetic model CASTOR-K developed for the study of AE stability in the presence of energetic ions has been applied to the interpretation of recent measurements of Alfvén waves in JET. These include the detailed AE damping measurements performed using the AE antenna excitation system and also the observations of Alfvén cascades in strongly reversed shear scenarios at JET. The mode conversion between the AEs and kinetic Alfvén waves and the relation to the Alfvén continuum is studied and the calculated damping is compared with the experimental data. The contribution of ICRH driven minority ions to the growth rate of the novel-type mode localised around the point of zero magnetic shear is calculated. This mode is shown to be clearly linked to the ideal MHD "Alfvén continuum", computed with the CSCAS code and consistent with the observation of a quasi-periodic pattern of upward frequency sweeping Alfvén Cascades in JET.