Properties of ion- and electron-acoustic solitons are investigated in an unmagnetized multi-component plasma system consisting of cold and hot electrons and hot ions using the Sagdeev pseudo-potential technique. The analysis is based on fluid equations and the Poisson equation. Solitary wave solutions are found when the Mach numbers exceed some critical values. The critical Mach numbers for the ion-acoustic solitons are found to be smaller than those for electron-acoustic solitons for a given set of plasma parameters. The critical Mach numbers of ion-acoustic solitons increase with the increase of hot electron temperature and the decrease of cold electron density. On the other hand, the critical Mach numbers of electron-acoustic solitons increase with the increase of the cold electron density as well as the hot electron temperature. The ion-acoustic solitons have positive potentials for the parameters considered. However, the electron-acoustic solitons have positive or negative potentials depending whether the fractional cold electron density with respect to the ion density is greater or less than a certain critical value. Further, the amplitudes of both the ion- and electron-acoustic solitons increase with the increase of the hot electron temperature. Possible application of this model to electrostatic solitary waves (ESWs) observed on the auroral field lines by Viking spacecraft is discussed

[1] Electrostatic solitary waves (ESWs) have been observed in the Earth's magnetosheath region by Cluster. A mechanism for the generation of these structures in terms of electronacoustic solitons and double layers is discussed. The model simulates the magnetosheath plasma by a four-component plasma system consisting of core electrons, two counterstreaming electron beams, and one type of ions. The analysis is based on the fluid equations and the Poisson equation, and employs the Sagdeev pseudopotential techniques to investigate the solitary waves. The electric field amplitudes, the time durations, and the propagation speeds of the solitary structures predicted by the model are in good agreement with the observed electric fields, pulse widths, and speeds of the electrostatic bipolar pulses.

Abstract. Large amplitude ion-acoustic and electronacoustic waves in an unmagnetized multi-component plasma system consisting of cold background electrons and ions, a hot electron beam and a hot ion beam are studied using Sagdeev pseudo-potential technique. Three types of solitary waves, namely, slow ion-acoustic, ion-acoustic and electron-acoustic solitons are found provided the Mach numbers exceed the critical values. The slow ion-acoustic solitons have the smallest critical Mach numbers, whereas the electron-acoustic solitons have the largest critical Mach numbers. For the plasma parameters considered here, both type of ion-acoustic solitons have positive potential whereas the electron-acoustic solitons can have either positive or negative potential depending on the fractional number density of the cold electrons relative to that of the ions (or total electrons) number density. For a fixed Mach number, increases in the beam speeds of either hot electrons or hot ions can lead to reduction in the amplitudes of the ion-and electron-acoustic solitons. However, the presence of hot electron and hot ion beams have no effect on the amplitudes of slow ion-acoustic modes. Possible application of this model to the electrostatic solitary waves (ESWs) observed in the plasma sheet boundary layer is discussed.

Spacecraft observations revealed the presence of electrostatic solitary waves (ESWs) in various regions of the Earth's magnetosphere. Over the years, many researchers have attempted to model these observations in terms of electron/ion acoustic solitary waves by using nonlinear fluid theory/simulations. The ESW structures predicted by fluid models can be inadequate due to its inability in handling kinetic effects. To provide clear view on the application of the fluid and kinetic treatments in modeling the ESWs, we perform both fluid and particle‐in‐cell (PIC) simulations of ion acoustic solitary waves (IASWs) and estimate the quantitative differences in their characteristics like speed, amplitude, and width. We find that the number of trapped electrons in the wave potential is higher for the IASW, which are generated by large‐amplitude initial density perturbation (IDP). The present fluid and PIC simulation results are in close agreement for small amplitude IDPs, whereas for large IDPs they show discrepancy in the amplitude, width, and speed of the IASW, which is attributed to negligence of kinetic effects in the former approach. The speed of IASW in the fluid simulations increases with the increase of IASW amplitude, while the reverse tendency is seen in the PIC simulation. The present study suggests that the fluid treatment is appropriate when the magnitude of phase velocity of IASW is less than the ion acoustic (IA) speed obtained from their linear dispersion relation, whereas when it exceeds IA speed, it is necessary to include the kinetic effects in the model.