On a semiclassical model for ion-acoustic solitons in ultrarelativistic pair plasmas and its classical counterpart

Abstract

Large ion-acoustic solitary waves are investigated in a multispecies plasma model consisting of warm positive ions in the presence of ultrarelativistic electrons and positrons, in a Sagdeev pseudopotential formalism. A parametric investigation determines existence regions in terms of fractional densities, temperature ratios, and soliton speeds. Various examples of pseudopotential functional forms, as well as those of the resulting soliton and electric field profiles, can then be generated numerically, and some typical illustrations have been included. Rather than adiabatic pressuredensity relations for the hot species, the classical nonrelativistic counterpart involves Boltzmann distributions, which differ qualitatively from the literature. Surprisingly, the soliton and electric field profiles show scant differences at the same compositional parameters between the two extremes even though the physical description of the hot species is radically different. A brief comparison has also been included between the fully nonlinear Sagdeev pseudopotential descriptions and their respective associated weak-amplitude limits (treated via a reductive perturbation technique) in which nonlinearities have been truncated to low powers of the electrostatic potential. Again, the soliton profiles are not radically different at comparable amplitudes, leaving the underlying physical reasons for such a similarity an open problem.

Short-wavelength soliton in ultrarelativistic electron-positron-ion plasmas

“…Recently, ion-acoustic solitons in a plasma with ultrarelativistic electrons and positrons were studied in detail in Ref. [14] using the fluid model and the Sagdeev potential formalism and a comparison between this ap- * Electronic address: vlashkin62@gmail.com proach (corresponding to strong nonlinearity), and the the reductive perturbation approach (weak nonlinearity and weak dispesion k 3 ≪ 1) leading to the KdV equation was made. The theory of nonlinear waves in an nondegenerate ultrarelativistic plasma in the short-wavelength limit k ≫ 1, where the linear dispersion has an exponential character ω ∼ k exp(−k 2 ) (known in physics as the so-called dispersion of "zero sound" [15]), is fully absent.…”