Breakdown of quasilinear theory for incoherent 1-D Langmuir waves

Abstract

Quasilinear theory for the usual weak warm beam instability is reconsidered. It is found that mode-coupling terms yield non-negligible corrections to the quasilinear diffusion coefficient and mode growth rates. These mode coupling effects give rise to non-Gaussian statistics that invalidate both the usual Fokker–Planck equations and the resonance broadening theories.