Parametric decay of Alfvén waves in multicomponent plasmas

Abstract

The parametric couplings of a finite amplitude Alfv\'en wave in a multicomponent plasma are investigated including the effect of damping. The important case of a fusion plasma with deuterium, tritium, and \ensuremath{\alpha} particle ions, heated by neutral beam injection, is analyzed in detail. Because of the modification in the linear dispersion relation caused by the drifting ions, there appear many couplings to sound waves and an electromagnetic modulational instability. The threshold on the pump amplitude is determined as a function of the damping rates. The relevance of our results to the stability of toroidal Alfv\'en eigenmodes in tokamaks is discussed. \textcopyright{} 1996 The American Physical Society.