Gardner Solitons and Double Layers in a Multi-Ion Plasma With Degenerate Electrons

A precise theoretical investigation is made on ion-acoustic (IA) solitary waves (SWs) and double layers (DLs) in a degenerate multi-ion plasma (composed of inertial positive and negative ions and degenerate electrons). The standard reductive perturbation method is employed to derive the Korteweg-de Vries (K-dV), the mixed K-dV (mK-dV), and the Gardner (GE) equations. The GE admits SW and DL solutions for mu around its critical value mu(c) (where mu(c) is the value of mu corresponding to the vanishing of the nonlinear coefficient of the K-dV equation). The basic features of IA SWs and DLs are analyzed. It is found that the characteristics of IA SWs found from GE are different from those of the K-dV solitons and mK-dV solitons. The implications of our results to different space and laboratory plasma situations, where opposite polarity ions are observed, are briefly discussed.