The characteristics of ion acoustic solitons in non-Maxwellian plasmas

Ion acoustic solitons may be associated with the electrostatic solitary structures observed in the space plasma environment. Earlier models describing these solutions assume Maxwellian distribution for electrons imbedded in the fluid ions and predict enhanced density that have difficulty in explaining some of the observed features of depleted density associated with electrostatic solitons. Improved models incorporating nonthermal electrons are shown to be able to produce solitary structures with depleted density [R. A. Cairns , Geophys. Res. Lett. 22, 2709 (1995)]. In this paper general solutions of ion acoustic solitons are derived for which the electrons are modeled by the kappa distribution characterized by the kappa parameter that has been found to well represent the particle distribution observed in space plasmas. It is shown that solitary structures with depleted density are unlikely to exist in non-Maxwellian plasmas with general kappa distribution. Detailed comparisons are made of the solutions based on Cairns et al. and kappa velocity distributions.