Envelope nonlinear drift structures in a non-equilibrium plasma near the boundary of marginal stability

An explosive instability of the ion-temperature-gradient (ITG)-driven modes (ηi modes) near the boundary of marginal stability is considered as a driving mechanism for subcritical turbulence. It is shown that boundedness of the wave interaction region leads to saturation of the instability. The possibility of coherent soliton-like structure formation in both slab and toroidal geometries is demonstrated by numerical simulation. An analytical soliton solution is found in some special cases.