Ion acoustic solitons, double layers and supersolitons in a collisionless unmagnetized plasma consisting of nonthermal electrons and isothermal positrons

Abstract

Employing the Sagdeev pseudo-potential technique the ion acoustic solitary structures have been investigated in a collisionless unmagnetized plasma consisting of adiabatic warm ions, nonthermal electrons and isothermal positrons. The qualitatively different compositional parameter spaces clearly indicate the existence domains of solitons and double layers with respect to any parameter of the system. The present system supports negative potential double layers which always restrict the occurrence of negative potential solitons. The system also supports positive potential double layers when the ratio of the average thermal velocity of positrons to that of electrons is less than a critical value. However, there exists a parameter regime for which positive potential double layers cannot restrict the occurrence of positive potential solitary waves and in this region of the parameter space, there exist positive potential solitary waves after the formation of positive potential double layers. Consequently, positive potential supersolitons have been observed. The nonthermality of electrons plays an important role in the formation of positive potential double layers as well as positive potential supersolitons. The formation of positive potential supersoliton is analysed with the help of phase portraits of the dynamical system corresponding to the ion acoustic solitary structures.