Nonlinear dust-acoustic structures in space plasmas with superthermal electrons, positrons, and ions
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USTY PLASMA
Nonlinear Dust-Acoustic Structures in Space Plasmas with Superthermal Electrons, Positrons, and Ions1 E. Saberiana, *, A. Esfandyari-Kalejahib, and M. Afsari-Ghazib a Department b Department
of Physics, Faculty of Basic Sciences, University of Neyshabur, Neyshabur, Iran of Physics, Faculty of Sciences, Azarbaijan Shahid Madani University, Tabriz, Iran *e-mail: [email protected] Received November 29, 2015; in final form, March 9, 2016
Abstract—Some features of nonlinear dust-acoustic (DA) structures are investigated in a space plasma consisting of superthermal electrons, positrons, and positive ions in the presence of negatively charged dust grains with finite-temperature by employing a pseudo-potential technique in a hydrodynamic model. For this purpose, it is assumed that the electrons, positrons, and ions obey a kappa-like ( κ ) distribution in the background of adiabatic dust population. In the linear analysis, it is found that the dispersion relation yield two positive DA branches, i.e., the slow and fast DA waves. The upper branch (fast DA waves) corresponds to the case in which both (negatively charged) dust particles and (positively charged) ion species oscillate in phase with electrons and positrons. On the other hand, the lower branch (slow DA waves) corresponds to the case in which only dust particles oscillate in phase with electrons and positrons, while ion species are in antiphase with them. On the other hand, the fully nonlinear analysis shows that the existence domain of solitons and their characteristics depend strongly on the dust charge, ion charge, dust temperature, and the spectral index κ . It is found that the minimum/maximum Mach number increases as the spectral index κ increases. Also, it is found that only solitons with negative polarity can propagate and that their amplitudes increase as the parameter κ increases. Furthermore, the domain of Mach number shifts to the lower values, when the value of the dust charge Z d increases. Moreover, it is found that the Mach number increases with an increase in the dust temperature. Our analysis confirms that, in space plasmas with highly charged dusts, the presence of superthermal particles (electrons, positrons, and ions) may facilitate the formation of DA solitary waves. Particularly, in two cases of hydrogen ions H+ ( Z i = 1) and doubly ionized Helium atoms He2+ ( Z i = 2 ), the mentioned results are the same. Additionally, the mentioned dusty plasma does not support DA solitons with positive polarity (compressive solitons). Furthermore, our analysis confirms that DA double layers cannot exist in such a system. Moreover, the positron density has not a considerable effect on the behavior of DA solitons in our model. DOI: 10.1134/S1063780X17010111
Most of the astrophysical plasmas usually contain highly charged (negative/positive) impurities or dust particulates in addition to the electrons, positrons and ions. Hence, the formation of a four-component electron–positron–ion–dust (e–p–i–d) plasma is common in space plasmas. It
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