Compressive and Rarefactive Solitons for Fast and Slow Ion Acoustic Waves in Multi-Ion Plasmas

The Kadomtsev-Petviashvili (KP) equation is derived for an electrostatic wave in unmagnetized multi-ion plasmas using the reductive perturbation method. It is found that two ion sound waves with fast and slow speeds can propagate in such a multi-ion plasma provided both ions are considered to be inertial and one of the ion component in two ion species plasma is taken to be warm as well. The potential hump (compressive) and dip (rarefactive) structures of the slow and fast ion acoustic waves are obtained for different combinations of multi-ion plasmas i.e., H+(warm)-O+(cold)-e, H+(warm)-H+(cold)-e, O+(cold)-H-(warm)-e, and H+(cold)-H-(warm)-e. It is found that, in the case of multi-ion H+(warm)-O+(cold)-e and H+(warm)-H+(cold)-e plasmas, the slow ion acoustic wave solitons form both potential hump (compressive) and dip (rarefactive) profiles depending on the temperature and concentration of the warm ion species, while the fast ion acoustic wave solitons only form the potential hump structures. However, in the case of O+-H--e and H+-H--e plasmas, the slow ion acoustic wave solitons form potential hump (compressive) structures, while the fast ion acoustic wave solitons form potential dip (rarefactive) structures. No flip in the nonlinear structure of the slow ion acoustic wave soliton is found in the negatively charged, warm hydrogen ions of O+-H--e and H+-H--e plasmas. The effects of the density and temperature of the warm ion species on the formation of nonlinear potential hump and dip structures in multi-ion plasmas are investigated in detail. The numerical results are also presented for illustration, which are applicable to space and laboratory multi-ion plasma situations.