Effects of Plasma Parameters on Dust-Ion Acoustic Solitary Structures in Collisionless Unmagnetized Plasmas with Nonthermal Electrons and Positrons

Abstract

The Sagdeev pseudo-potential approach is utilized to study the propagation of arbitrary-amplitude dust-ion acoustic (DIA) nonlinear structures in a collisionless four-component unmagnetized plasma. The plasma model consists of warm adiabatic ions, nonthermal positrons, nonthermal electrons, and immobile negatively charged dust grains. The Sagdeev potential analysis confirms the existence of positive-potential solitary waves (PPSWs), positive-potential supersolitons (PPSSs), and positive-potential double layers (PPDLs). In contrast, negative-potential supersolitons (NPSSs) are not supported by the system, whereas negative-potential solitary waves (NPSWs) and negative-potential double layers (NPDLs) are found to exist. The coexistence of PPSWs and NPSWs is also demonstrated. To provide physical insight into the formation of these nonlinear structures, phase-space portraits of the associated dynamical system are constructed. The phase portraits provide a good illustration of how PPSWs are modified both before and after a PPDL is formed. The influence of key plasma parameters on the amplitudes of PPSWs, NPSWs, PPSSs, and on the coexistence region of PPSWs and NPSWs is systematically examined. A critical positron to electron number density \(n_{pc}^c\) is identified, such that the amplitude of PPSWs decreases for \({n_{pc}} \leqslant n_{pc}^c\) and increases for \({n_{pc}} \geqslant n_{pc}^c\), with all other plasma parameters held fixed within the PPSW existence domain.