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Register a new userDust ion acoustic solitary structures at the acoustic speed in presence of nonthermal electrons and isothermal positrons
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Added by
Anup Bandyopadhyay Dr.
Publication date
2018
fields
Physics
and research's language is
English
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The Sagdeev pseudo-potential technique and the analytic theory developed by Das et al. [J. Plasma Phys. 78, 565 (2012)] have been used to investigate the dust ion acoustic solitary structures at the acoustic speed in a collisionless unmagnetized dusty plasma consisting of negatively charged static dust grains, adiabatic warm ions, nonthermal electrons and isothermal positrons. The present system supports both positive and negative potential solitary waves at the acoustic speed, but the system does not support the coexistence of solitary structures of opposite polarity at the acoustic speed. The system also supports negative potential double layer at the acoustic speed, but does not support positive potential double layer. Although the system supports positive potential supersoliton at the supersonic speed, but there does not exist supersoliton of any polarity at the acoustic speed. Solitary structures have been investigated with the help of compositional parameter spaces and the phase portraits of the dynamical system describing the nonlinear behaviour of the dust ion acoustic waves at the acoustic speed. For the case, when there is no positron in the system, there exist negative potential double layer and negative potential supersoliton at the acoustic speed and for such case, the mechanism of transition of supersoliton to soliton after the formation of double layer at the acoustic speed has been discussed with the help of phase portraits. The differences between the solitary structures at the acoustic speed and the solitary structures at the supersonic speed have been analysed with the help of phase portraits.
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Arbitrary amplitude dust acoustic solitary structures have been investigated in a four component multi-species plasma consisting of negatively charged dust grains, nonthermal ions, isothermally distributed electrons and positrons including the effect of dust temperature. We have used the Sagdeev pseudo-potential method to discuss the arbitrary amplitude steady state dust acoustic solitary structures in the present plasma system. We have designed a computational scheme to draw the existence domains of different dust acoustic solitary structures. We have observed only negative potential solitary waves for isothermal ions. But for strong nonthermality of ions the system supports positive potential solitary waves, positive potential double layers and coexistence of solitary waves of both polarities. The positive potential solitary waves are restricted by the positive potential double layers but negative potential double layer has not been found for any parameter regime. The system does not support dust acoustic supersoliton of any polarity. The concentration of positrons plays an important role in the formation of positive potential double layers. Finally, the phase portraits of the dynamical system have been presented to confirm the existence of different dust acoustic solitary structures.
The purpose of this paper is to extend the recent work of Paul & Bandyopadhyay [Astrophys. Space Sci. 361, 172(2016)] on the existence of different dust ion acoustic solitary structures in an unmagnetized collisionless dusty plasma consisting of negatively charged static dust grains, adiabatic warm ions, nonthermal electrons and isothermal positrons in a more generalized form by considering nonthermal positrons instead of isothermal positrons. The present system supports both positive and negative potential double layers, coexistence of solitary waves of both polarities and positive potential supersolitons. The qualitative and the quantitative changes in existence domains of different solitary structures which occur for the presence of nonthermal positrons have been presented in comparison with the results of Paul & Bandyopadhyay [Astrophys. Space Sci. 361, 172(2016)]. The formation of supersoliton structures and their limitations have been analyzed with the help of phase portraits of the dynamical system corresponding to the dust ion acoustic solitary structures. Phase portrait analysis clearly indicates a smooth transition between soliton and supersoliton.
Employing the Sagdeev pseudo-potential technique the ion acoustic solitary structures have been investigated in an unmagnetized collisionless plasma consisting of adiabatic warm ions, nonthermal electrons and isothermal positrons. The qualitatively different compositional parameter spaces clearly indicate the existence domains of solitons and double layers with respect to any parameter of the present plasma system. The present system supports the negative potential double layer which always restricts the occurrence of negative potential solitons. The system also supports positive potential double layers when the ratio of the average thermal velocity of positrons to that of electrons is less than a critical value. However, there exists a parameter regime for which the positive potential double layer is unable to restrict the occurrence of positive potential solitary waves and in this region of the parameter space, there exist positive potential solitary waves after the formation of a positive potential double layer. Consequently, positive potential supersolitons have been observed. The nonthermality of electrons plays an important role in the formation of positive potential double layers as well as positive potential supersolitons. The formation of positive potential supersoliton is analysed with the help of phase portraits of the dynamical system corresponding to the ion acoustic solitary structures of the present plasma system.
We have used the Sagdeev pseudo-potential technique to investigate the arbitrary amplitude ion acoustic solitons, double layers and supersolitons in a collisionless magnetized plasma consisting of adiabatic warm ions, isothermal cold electrons and nonthermal hot electrons immersed in an external uniform static magnetic field. We have used the phase portraits of the dynamical system describing the nonlinear behaviour of ion acoustic waves to confirm the existence of different solitary structures. We have also investigated the transition of different solitary structures: soliton (before the formation of double layer) $rightarrow$ double layer $rightarrow$ supersoliton $rightarrow$ soliton (soliton after the formation of double layer) by considering the variation of $theta$ only, where $theta$ is the angle between the direction of the external uniform static magnetic field and the direction of propagation of the wave.
Sardar et al. [Phys. Plasmas 23, 073703 (2016)] have studied the stability of small amplitude dust ion acoustic solitary waves in a collisionless unmagnetized electron - positron - ion - dust plasma. They have derived a Kadomtsev Petviashvili (KP) equation to investigate the lowest - order stability of the solitary wave solution of the Korteweg-de Vries (KdV) equation for long-wavelength plane-wave transverse perturbation when the weak dependence of the spatial coordinates perpendicular to the direction of propagation of the wave is taken into account. In the present paper, we have extended the lowest - order stability analysis of KdV solitons given in the paper of Sardar et al. [Phys. Plasmas 23, 073703 (2016)] to higher order with the help of multiple-scale perturbation expansion method of Allen and Rowlands [J. Plasma Phys. 50, 413 (1993); 53, 63 (1995)]. It is found that solitary wave solution of the KdV equation is stable at the order k^2, where k is the wave number for long-wavelength plane-wave perturbation.
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