Coexistence of parametric decay cascades and caviton collapse at subcritical densities

Results are reported on two-dimensional numerical solutions of Zakharov's model for strong Langmuir turbulence excited by powerful EM pump waves at subcritical densities, as in HF modification of the ionosphere and laser- plasma interactions. The results show that truncated parametric decay cascades can coexist with caviton collapse for moderate pump power. A high level of ion density fluctuations, driven primarily by caviton collapse, produces energy and power spectra which are not consistent with conventional weak turbulence theory. (Author)