Dust ion acoustic solitons and double layers in a dusty plasma with adiabatic positive dust, adiabatic positive ion species, and Cairns-distributed electrons

The propagation of dust ion acoustic solitary waves and double layers is studied in a dusty plasma with heavy adiabatic positively charged dust grains and lighter adiabatic positive ions with Cairns-distributed electrons using the arbitrary amplitude Sagdeev pseudopotential approach. The analysis of the Sagdeev pseudopotential shows that this plasma model supports the propagation of positive solitons limited by the occurrence of the ion sonic point and negative solitons limited by the occurrence of double layers. Solitons of both polarities coexist for a range of some plasma parameters. We have shown that at a critical dust-to-ion density ratio, f, at which the third derivative of the Sagdeev pseudopotential vanishes, positive and negative solitons coexist without a soliton with finite amplitude at the acoustic speed, contrary to an earlier study. This suggests that the existence of a soliton with finite amplitude at the acoustic speed is not always a pre-requisite for the coexistence of nonlinear structures of both polarities. Positive and negative solitons coexist when the electrons are strongly nonthermal, with moderate ion thermal effects. Increasing ion thermal effect shifts the coexistence region to lower values of f, and when the ion thermal effects become important, negative solitons disappear and only positive solitons survive. The effects of different plasma parameters on the characteristics of the nonlinear structures have also been discussed in detail.