Modelling of Alfven waves in JET plasmas with the CASTOR-K code

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