Ion-acoustic waves in an inhomogeneous plasma with negative ions

The propagation of the ion-acoustic waves (IAWs) in a collisionless, unmagnetized inhomogeneous plasma composed of warm positive and negative ions with different masses and isothermal electrons is investigated. The reductive-perturbation method is employed to reduce the basic set of fluid equations to the variable coefficients Korteweg–de Varies (KdV) equation. It is found that both compressive and rarefactive solitons can propagate in the system. Below (above) certain values of positive ions densities the system supports rarefactive (compressive) solitons. The dependence of solitons amplitude and width on the system parameters is investigated.