MODE-COUPLING EFFECTS ON ALPHA-PARTICLE-DRIVEN LONG-WAVELENGTH ALFVEN-WAVE INSTABILITY

It is demonstrated both analytically and numerically that mode couplin gs play an important role in the nonlinear evolution of alpha-particle -driven long wavelength Alfven wave instabilities. The mode coupling p rocess is characterized by a beat between two linearly unstable Alfven waves having opposite frequencies, which generates a linearly stable, static (zero frequency) mode. The backreaction of the static mode ten ds to stabilize the Alfven instabilities by eliminating the phase shif t between the alpha pressure and the Alfven fluctuations.