Non-linear localized ion-acoustic waves in electron–positron–ion plasmas with trapped and non-thermal electrons

Abstract

For an unmagnetized collisionless electron–positron–ion plasma, the effects of trapped and non-thermal electron distributions are incorporated in the study of arbitrary amplitude ion-acoustic solitary structures. Both highly and weakly analyses are examined by deriving an energy integral equation involving the Sagdeev potential for the large amplitude limit, and obtaining the non-linear partial-differential equations for the small but finite amplitude limit. It is shown that there exist ion-acoustic solitary waves with qualitatively different structures in a way that depend on the population of trapped and non-thermal electrons. In the presence of trapped electrons, fully non-linear analyses show that plasma can support only arbitrary amplitude compressive solitary waves. On the other hand, a consideration of the fast or non-thermal electron distribution provides the possibility of the coexistence of large amplitude compressive and rarefactive solitary waves, whereas both of them are decoupled in the small amplitude limit. It is found that the effects of such electron distributions and positron concentration change the maximum values of the Mach number and the amplitude for which solitary waves can exist. Furthermore, the non-thermally distributed electrons provide a KdV equation in the small amplitude limit, whereas the trapped electrons give rise to a modified KdV equation which exhibits a stronger non-linearity.