Stability of relativistic solitons in a three-species plasma

An extended 1D kinetic model of relativistic solitons in three-species plasmas is suggested, and the stability condition of the solitons is derived. The range of parameters for stable solitons are specified in the frequency-temperature plane. The regions for solitons in electron-positron-ion plasmas and negative ion plasmas are calculated and specified. With the insertion of another species of charged particles into the plasmas, relativistic solitons appear stable over a wider range of frequencies and temperatures. In electron-positron-ion plasmas, the regions are expanded toward higher values in the frequency-temperature plane. In negative ion plasmas, the regions are broadened only at higher temperatures, which results from the heavy mass of the negative ions. The stability conditions are affected by both the mixing ratio αm and the net charge of the third species.