Abstract
Reductive perturbation method has been employed to obtain a modified KdV equation and to show the excitation of ion acoustic solitons in an ion beam-plasma system consisting of bulk of cold ions, beam ions and non-isothermal and resonant electrons (both trapped and free electrons). The effect of ion beam velocity, beam ion density and plasma ion to beam ion mass ration on the amplitude and width of ion acoustic solitons has been investigated. The beam amplification rate of solitons amplitude is found to depend upon the ion beam velocity. There exists a critical ion beam velocity below which the ion beam is unable to generate solitons and this threshold ion beam velocity is an increasing function of the ion beam concentration and the mass ratio of background plasma ions and beam ions.