Effects of trapped particle dynamics on the structures of a low-frequency shear Alfven continuous spectrum

We analytically derive the structures of the low-frequency shear Alfven continuous spectrum due to resonant wave-particle interactions with magnetically trapped thermal particles in tokamaks. Our theoretical description asymptotically recovers known results in the relevant limits at both high and low frequencies; furthermore, it is relevant for assessing the accurate kinetic structures that are due to shear Alfven and acoustic wave spectra in toroidal geometry. Since there is a continuous transition between various shear Alfven wave and MHD fluctuation branches in many situations of experimental interest, the results reported in this work are of practical relevance for their interpretation when used in the theoretical framework of the general 'fishbone-like' dispersion relation.