Sagdeev pseudopotential analysis of nonlinear periodic ion-acoustic plasma waves

Abstract

A Sagdeev pseudopotential analysis is developed for the propagation of nonlinear periodic ion-acoustic waves in a plasma comprising cold fluid ions and Boltzmann electrons. To achieve a mathematically and physically consistent description, three essential requirements have to be obeyed: There is charge flux and mass conservation per cycle for both the species, the solutions reduce for very small amplitudes to linear waves, and the nonlinear periodic structures are generated by a perturbation of the undisturbed equilibrium. This is needed because many treatments in the literature of similar problems give inconsistent results, failing on one or more of the stated conditions, whether a reductive perturbation or a pseudopotential analysis is used. Once the Sagdeev pseudopotential is established, a detailed numerical analysis and a variety of graphical representations indicate that the periodic nonlinear structures are mostly subacoustic, in contrast to the better known supersonic solitons for the same or related plasma compositions. For a fixed propagation speed, it is shown that the wavelength of the solutions increases with amplitude.