Coexistence of parametric decay cascades and caviton collapse at subcritical densities

We report results of two-dimensional numerical solutions of Zakharov's model for strong Langmuir turbulence excited by powerful electromagnetic pump waves at subcritical densities, as in hf modification of the ionisphere 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 primarly by caviton collapse, produces energy and power spectra which are not consistent with conventional weak turbulence theory.