Development of "Cavitons" and Trapping of rf Field

A new kind of parametric instability is observed in a nonuniform plasma in which a resonant rf electric field and a density cavity grow simultaneously through mutual enhancements. The threshold is observed to be virtually zero and the growth rate is linearly dependent on pump intensity, {E₀}^2. Ponderomotive force and wave trapping are observed to be the mechanisms which drive the instability.