Soliton Reflection in Inhomogeneous e–p–i Plasma Having Negatively Charged Dust Grains

ABSTRACT

We examine the reflection of small‐but‐finite amplitude ion‐acoustic‐type solitons from equilibrium density gradients in an inhomogeneous electron–positron–ion (e–p–i) plasma containing negatively charged dust grains. Such gradients can act as effective reflecting interfaces and are relevant in laboratory dusty plasmas, sheath regions, and emerging pair‐plasma experiments. Using the reductive perturbation technique for slowly varying equilibria with finite electron and positron temperatures and initial drifts, we derive coupled modified Korteweg–de Vries (mKdV) equations for the evolution of incident and reflected solitary waves. The resulting phase‐velocity relation shows how key plasma parameters influence soliton propagation. An increase in the positron‐to‐electron temperature ratio raises the phase velocity and produces narrower, higher‐amplitude solitons, whereas increasing dust charge or dust concentration lowers the phase velocity and leads to broader, weaker structures due to enhanced space‐charge screening. Electron drift has a comparatively modest effect and mainly influences the soliton width. The plasma inhomogeneity leads to partial reflection of the incident soliton, and the reflection coefficient is evaluated. Dust charging suppresses reflection, while higher positron temperature enhances it. These results provide a clear physical picture of soliton reflection in dusty e–p–i plasmas and serve as useful benchmarks for laboratory and numerical studies.