Institute of Geophysics, University of TehranJournal of the Earth and Space Physics2538-371X46220200722Dust-acoustic Solitary Waves in Space Dusty Plasmas with Nonequilibrium DistributionDust-acoustic Solitary Waves in Space Dusty Plasmas with Nonequilibrium Distribution3773947644010.22059/jesphys.2020.295062.1007183FAEhsan SaberianAssistant Professor, Department of Physics, Faculty of Basic Sciences, University of Neyshabur, Neyshabur, Iran0000-0002-5454-9942Rasoul Khoosheh ShahiM.Sc. Graduated, Department of Physics, Faculty of Basic Sciences, University of Neyshabur, Neyshabur, IranJournal Article20200101In this paper by using the most recent findings in the field of the Kappa distribution statistics for the non-equilibrium space plasmas, dust-acoustic waves have been studied in a dusty plasma comprising of the inertial dust particles with negative charges and suprahermal distributions of electrons and positrons. The velocity distribution function for stationay state of the plasma in this model is labeled by an invariant Kappa index () which is independent of the numbers of degrees of freedom, and the parameter which represents the the numbers of degrees of freedom. In linear analysis, the dispersion relation of dust-acoustic waves is studied, whrere the true sound speed of the problem is derived. The derived dust-sound speed is a generalized one which depends on the polytropic index of Kappa distributed paricles ( ), which itself depends on the spectral index and the potential degrees of freedom ( ). Generally, the dust-sound speed has its maximum in an equilibrium plamsa with Maxwellian distribution or isothermal electrons ( ), and it reduces by approaching to the anti-equilibrium regions with sub-isothermal electrons <br /> ( ). <br />On the other hand, in the non-linear analysis, the dust-acoustic solitary waves have been studied by deriving an energy-integral equation, where we have used the true dust-sound speed for defining the true Mach number (the fractional wave speed to the sound speed). The formation conditions of the potential well, the true Mach number domains, and the effects of the parameters of soliton speed, the spectral index <strong> </strong>and the potential degrees of freedom via the perturbation ( ) in the propagation of dust-acoustic solitary waves have been studied analytically and numerically. <br /> In such a plasma, only the negative polarity solitons are possible. The reason is the negative charge of dust paricles via the attracted electrons, which causes the formation of negative potential solitons. <br />The structure of dust-acoustic solitons are examined in the near-equilibrium states, where the spectral indices are distributed with the values of , and also in the far-from-thermal equilibrium states which are labeled by the spectral indices with the values of <strong> .</strong> <br />It is found that the threshold Mach nmber is proportional to the square root of the polytropic index of Kappa distributed paricles which vaies in the range . So, the threshold Mach number increases by approaching to the equilibrium state and it reduces in far-from-thermal equilibrium states. <br />It is shown that the subsonic solitons are possible in the far-from-thermal equilibrium plasmas. On the other hand, in an equilibrium plasma, corresponding to the asymptotic limit of , only the altrasonic solitons are possible which confirms the classical theory of solitons in equilibrium statistical mechanics. <br />It is found that the amplitude and steepening of the dust-acoustic solitons grows in far-from-thermal equilibrium states, which corresponds to the lower values of the spectral index . It is because of the impact the suprathermal particles on dust-acoustic solitons in that regions. Furthermore, an increase in Mach number results in the propagation of dust-acoustic solitons with more amplitude and steepening, in agreement with the standard theory of solitary waves. Moreover, decreasing the potential degrees of freedom causes an increase in the maximum amplitude and pulse steepening of dust-acoustic solitons.In this paper by using the most recent findings in the field of the Kappa distribution statistics for the non-equilibrium space plasmas, dust-acoustic waves have been studied in a dusty plasma comprising of the inertial dust particles with negative charges and suprahermal distributions of electrons and positrons. The velocity distribution function for stationay state of the plasma in this model is labeled by an invariant Kappa index () which is independent of the numbers of degrees of freedom, and the parameter which represents the the numbers of degrees of freedom. In linear analysis, the dispersion relation of dust-acoustic waves is studied, whrere the true sound speed of the problem is derived. The derived dust-sound speed is a generalized one which depends on the polytropic index of Kappa distributed paricles ( ), which itself depends on the spectral index and the potential degrees of freedom ( ). Generally, the dust-sound speed has its maximum in an equilibrium plamsa with Maxwellian distribution or isothermal electrons ( ), and it reduces by approaching to the anti-equilibrium regions with sub-isothermal electrons <br /> ( ). <br />On the other hand, in the non-linear analysis, the dust-acoustic solitary waves have been studied by deriving an energy-integral equation, where we have used the true dust-sound speed for defining the true Mach number (the fractional wave speed to the sound speed). The formation conditions of the potential well, the true Mach number domains, and the effects of the parameters of soliton speed, the spectral index <strong> </strong>and the potential degrees of freedom via the perturbation ( ) in the propagation of dust-acoustic solitary waves have been studied analytically and numerically. <br /> In such a plasma, only the negative polarity solitons are possible. The reason is the negative charge of dust paricles via the attracted electrons, which causes the formation of negative potential solitons. <br />The structure of dust-acoustic solitons are examined in the near-equilibrium states, where the spectral indices are distributed with the values of , and also in the far-from-thermal equilibrium states which are labeled by the spectral indices with the values of <strong> .</strong> <br />It is found that the threshold Mach nmber is proportional to the square root of the polytropic index of Kappa distributed paricles which vaies in the range . So, the threshold Mach number increases by approaching to the equilibrium state and it reduces in far-from-thermal equilibrium states. <br />It is shown that the subsonic solitons are possible in the far-from-thermal equilibrium plasmas. On the other hand, in an equilibrium plasma, corresponding to the asymptotic limit of , only the altrasonic solitons are possible which confirms the classical theory of solitons in equilibrium statistical mechanics. <br />It is found that the amplitude and steepening of the dust-acoustic solitons grows in far-from-thermal equilibrium states, which corresponds to the lower values of the spectral index . It is because of the impact the suprathermal particles on dust-acoustic solitons in that regions. Furthermore, an increase in Mach number results in the propagation of dust-acoustic solitons with more amplitude and steepening, in agreement with the standard theory of solitary waves. Moreover, decreasing the potential degrees of freedom causes an increase in the maximum amplitude and pulse steepening of dust-acoustic solitons.https://jesphys.ut.ac.ir/article_76440_eadc3057f3472c50502322bbd13c2480.pdf