Continuing experimental studies of beam‐plasma interactions in a magnetic field have shown an assortment of nonlinear effects to be present during a well‐developed instability. Observations have been made of: the vanishing of the spatial growth rate; electron cross‐field diffusion in synchronism with the unstable electric field; generation of harmomics of the fundamental interaction frequency up to the seventh; similarities in the spatial behavior of all seven harmonics; and the existence of a wavenumber power spectrum whose average behavior over the domain of the harmonic peaks is proportional tok−5±0.5, in agreement with certain theories of plasma turbulence. The data suggest that the large‐amplitude fundamental electric field is the driving force for the nonlinearity that generates the harmonics, and that the fundamental, and the harmonics as well, represent waves traveling with a phase velocity equal to that of the slow space‐charge wave on the electron beam. An interpretation is offered in terms of an approach to stationary plasma turbulence through a linear beam‐plasma interaction, followed by harmonic generation, wave‐wave coupling, and ultimate broadening of the emission peaks into a continuous spectrum.