ORIGINAL PAPER Ion acoustic solitary waves in high relativistic plasmas with superthermal electrons and thermal positrons K Javidan 1 and H R Pakzad 2 * 1 Department of Physics, Ferdowsi University of Mashhad, 91775 1436 Mashhad, Iran 2 Department of Physics, Bojnourd Branch, Islamic Azad University, Bojnourd, Iran Received: 15 September 2011 / Accepted: 27 June 2012 Abstract: Propagation of ion acoustic waves in plasmas containing superthermal electrons, thermal positrons and high relativistic ions is investigated. It is shown that the Korteweg-de Vries (KdV) equation describes the nonlinear waves in such plasmas. The effects of relativistic ions and superthermal electrons on the soliton identifications are discussed. Keywords: Relativistic plasma; Nonlinear; Ion acoustic soliton PACS Nos.: 52.27.Ny; 52.35.Fp; 52.35.Sb 1. Introduction The dynamics of ion-acoustic waves has been studied for several decades both theoretically and experimentally [1–3]. The first experimental observation of ion-acoustic solitons has been made by Ikezi et al. [4]. In the limit of small amplitude approximation in the equations, one can derive some forms of nonlinear differential equations for one spatial dimension situations like Korteweg-de Vries (KdV), modi- fied Korteweg-de Vries (m-KdV) or nonlinear Schrodinger equation, etc. Such equations have well known extended solutions, like solitary waves or solitons. A great number of authors have studied ion-acoustic solitary solutions using the reductive perturbation technique in different plasmas [5, 6]. In contrast to the usual plasmas that consist of electrons and positive ions, it has been observed that the nonlinear waves in plasmas containing additional components such as positrons have different characters [7]. The behaviour of the electron– positron–ion plasmas help us to find better knowledge about the early universe which assumes to be a kind of plasma [8, 9], describing the active galactic nuclei [10], pulsar magnetospheres [11] and also the solar atmosphere [12]. Positrons can be used to probe particle transport in tokomaks since they have sufficient lifetime. In this case, two-com- ponent (e–i) plasmas become a three-component (e–i–p) medium [13]. During the last decade, e–p–i plasmas have attracted the attention of several authors [14–17]. It is well known that the behaviour of ion acoustic solitary waves is modified when the ion velocity approaches the speed of light. In such situation, relativistic effect becomes dominant and the wave amplitude, width and its energy change. A great deal of attention has been devoted to the study of different types of collective processes in electron–positron (e–p) and electron–positron–ion (e–p–i) plasmas with relativistic ions [18–26]. Relativistic plasmas occur in a variety of situations, such as, space-plasmas [27], laser-plasma interaction [28], plasma sheet boundary layer of the earth’s magnetosphere [29], in the Van Allen radiation belts [30]. The relativistic effects may be induced by the fluid velocity of the relativistic particles which has speed near the light velocity. Also it is possible that the relativistic effects are induced by thermal effects of the particles under concern. In this case, the ratio T/ mc 2 cannot be neglected. Moreover, one can consider a pair (electrons and positrons) production by relativistic ions as studied by Becker et al. [31]. It has been found that the electron and ion distributions play the crucial role in characterizing the physics of the nonlinear wave structures [32–37]. Numerous investiga- tions of space plasmas [35–43] clearly indicate the pres- ence of superthermal electron and ion structures as ubiquitous in a variety of astrophysical plasma environ- ments. The latter may arise due to the effect of external forces acting on the natural space environment plasmas or *Corresponding author, E-mail: pakzad@bojnourdiau.ac.ir Indian J Phys DOI 10.1007/s12648-012-0159-2 Ó 2012 IACS