Plasma configurations with shear reversal are prone to the excitation of unusual Alfven eigenmodes by energetic particles. These modes exhibit a quasiperiodic pattern of predominantly upward frequency sweeping ( Alfven cascades ) as the safety factor q changes in time. This work presents a theory that employs two complementary mechanisms for establishing Alfven cascades: ( 1 ) a nonstandard adiabatic response of energetic particles with large orbits and ( 2 ) toroidal magnetohydrodynamic effects that are second-order in inverse aspect ratio. The developed theory explains the transition from Alfven cascades to the toroidicity induced Alfven eigenmodes ( TAEs ) , including modifications of the TAEs themselves near the shear reversal point.
