Nonlinear Decay and Plasma Heating by a Toroidal Alfvén Eigenmode.

We demonstrate theoretically that a toroidal Alfvén eigenmode (TAE) can parametrically decay into a geodesic acoustic mode and kinetic TAE in a toroidal plasma. The corresponding threshold condition for the TAE amplitude is estimated to be |δB_{⊥}/B_{0}|∼O(10^{-4}). Here, δB_{⊥} and B_{0} are, respectively, the perturbed magnetic field of the pump TAE and the equilibrium magnetic field. This novel decay process, in addition to contributing to the nonlinear saturation of energetic-particle or α-particle driven TAE instability, could also contribute to the heating as well as regulating the transports of thermal plasmas.