Transition from particle trapping to a quasi-linear-like beam-plasma system

Experimental observations show that the beam-plasma instability generates a modified beam distribution function which can destabilize new modes. These sideband modes nonlinearly saturate, modify the beam further, and a cascade proceeds. For strong beams the cascade and attendent phase mixing lead to a quasilinear-like spectrum of waves and a nearly plateau-like beam. For absolute instability, the approach to a quasilinear system is slower than for the convective instability because the spectrum is fundamentally discrete.