Electron Plasma Wavebreaking and Caviton Formation

The properties of large-amplitude electron plasma waves are experimentally investigated. An intense plasma wave is resonantly excited by a longitudinal VHF electric field oscillating at the plasma frequency. The size of the wave, and its impact on the plasma, is maximal when the resonant layer is placed at the top of a broad, flat density profile. Electric field energy densities W= ~ E^2/4pi n_{c}T _{e}>10^3 are produced, along with copious electrons and ions of kinetic energy K>10^3T_{e}. A deep density cavity (delta n/n~0.5) forms in the resonant region. Reconstruction of the wave, from detailed measurements of electric field amplitude and phase, demonstrates wavebreaking and accounts for the observed energetic particles. Calculation of the ponderomotive force of the localized plasma wave yields an ion flow comparable to that observed in the experiment. Processes are studied with a variety of indirect and in situ diagnostics. Results are compared with those of a one-dimensional particle-in -cell computer simulation. This study helps illuminate strong Langmuir turbulence phenomena and is relevant to laser-plasma and ionospheric-heating experiments.