  Two novel nonlinear mode coupling processes for reversed shear Alfven
eigenmode (RSAE) nonlinear saturation are proposed and investigated. In the
first process, RSAE nonlinearly couples to a co-propagating toroidal Alfven
eigenmode (TAE) with the same toroidal and poloidal mode numbers, and generates
a geodesic acoustic mode (GAM). In the second process, RSAE couples to a
counter-propagating TAE and generates an ion acoustic wave quasi-mode (IAW).
The condition for the two processes to occur is favored during current ramp.
Both processes contribute to effectively saturate the Alfvenic instabilities,
as well as nonlinearly transfer of energy from energetic fusion alpha particles
to fuel ions in burning plasmas.
