REVERSAL OF PHASE-VELOCITY OF A NEGATIVE-ENERGY MODE AND BISTABILITY IN A DRIVEN-DAMPED DRIFT WAVE SYSTEM

The eigenvalues of the steady states in a nonlinear drift wave system driven by a sinusoidal wave are investigated. A relevance is found between the appearance of bistability and the fact that the negative linear phase velocity of one resonance mode reverses nonlinearity in the frame following the driving wave. The system energy can be enhanced when this negative-energy mode is changed into a positive one. The wavenumber for the occurrence of the resonance varies with the driving frequency of the external wave. This fact leads to the repeated appearances of groups of bistable states in the parameter space.