Electrostatic Korteweg–de Vries solitons in pure pair-ion and pair-ion–electron plasmas

Linear and nonlinear electrostatic waves are studied in unmagnetized pure pair-ion (PI) and pair-ion–electron (PIE) plasmas. The nonlinear electrostatic potential structures are obtained using the reductive perturbation technique. It is found that potential hump and dip structures are obtained in pure PI plasmas, when there is a slight difference of temperature between positive and negative ions. The electrostatic potential humps are formed when the temperature of the negative ions is greater than that of the positive ions, while the potential dips are obtained in the reverse temperature condition of the plasma species. The electrostatic solitons are also obtained in the presence of electrons in PI plasmas. It is found that only potential dip structures are obtained in the PIE plasma case. The numerical results are also presented for illustration.