prediction that an electron beam propagates in a state close to marginal stability, i.e. one where the fluctuation-dependent growth rate is compensated for by the damping rate ([@Robinson92]; [@Robinson93]). In this view, the growth rate of beam-plasma instability is perturbed by the ambient density fluctuations ([@Robinson92]). The third, more traditional group of theories, considers the beam propagation in the limit of weak turbulence theory ([@Ryutov70]; [@Takakura76]; [@Magelssen77]; [@Takakura82]; [@Grognard85]). The basic idea is that the electron beam generates Langmuir waves at the front of the electron stream and the waves are absorbed at the back of the stream, ensuring electron propagation over large distances. However, this idea was not proved for a long time ([@Melrose90]). Recently Mel’nik has demonstrated analytically ([@Melnik95]) that a mono-energetic beam can propagate as a beam-plasma structure (BPS). This result has been confirmed numerically ([@Kontar98]) and applied to the theory of type III bursts ([@Melnik99]). The solution obtained ([@Melnik00a]) directly resolves Sturrock’s dilemma ([@Sturrock64]) and may explain the almost constant speed of type III sources. However, the influence of plasma inhomogeneity on the dynamics of a BPS has never been studied although the correlation between Langmuir wave clumps and density fluctuations demonstrates the importance of such 