Density-Step-Excited Ion Acoustic Solitons

Highly nonlinear ion acoustic solitons are produced by the superposition of a $15{\lambda }_{\mathrm{D}}$-wide photoionized plasma slab on a dc background. The Mach number increases with the initial step ratio $R$ up to $M\approx 1.95$ for $R\approx 10$. Above $M\approx 1.8$, $R\approx 6$, however, the profiles diffuse rapidly as they propagate. For Mach numbers $M\lesssim 1.8$, a linear interaction is observed in the collision of two solitons traveling in opposite directions, whereas two solitions moving in the same direction exhibit a nonlinear interaction.