In this Letter an exact solution for nonlinear cold-electron plasma oscillations against a periodic ion background is found. The main difference with respect to the known solution corresponding to a uniform ion background is that, after a while, electron density peaks will appear. This phenomenon, which was forseen in general terms by Dawson, has possible practical implications which are indicated briefly. A thermal limitation on the peaks is given.

• Received 2 December 1988

DOI:https://doi.org/10.1103/PhysRevLett.62.2269