Modulated Dust-Acoustic Wavepackets in a Kappa-Distributed Nonthermal Plasma Background

Abstract

Dust is a ubiquitous component of space and astrophysical environments occurring, for exam- pie, in planetary rings, comets, the Earth's ionosphere, interstellar molecular clouds etc. [1]. Dusty plasmas are known to support new electrostatic/electromagnetic modes, which were pre- dieted theoretically and confirmed experimentally [2, 3]. There are a number of observations which clearly indicate the presence of superthermal elec­ tron and ion structures as ubiquitous in a variety of astrophysical plasma environments. Both space and laboratory plasmas may contain a population of superthermal particles, due to which, a high-energy tail appears in the electron/ion distribution function that is conveniently modeled based by the Jc-distribution function. The general form of the Kdistribution and its relation to the Maxwellian distribution was frst discussed by Vasyhunas [4]. It is also observed that space plasmas can be modeled more effectively by the K ?distribution than by a superposition of Maxwellian distributions. Therefore, not surpris­ ingly, a large amount of research work has recently focused on the ef- feet of superther­ mal electrons obeying a Jc-type distribution; see e.g. in [5, 6]; also in [7] for technical details. In contrast to earlier models for nonthermal plasmas [8, 9, 10], the dynamics of nonlinear wavepackets against a Jc-distributed background have not yet been investi­ gated. In this paper, we study the dynamics of the modulated dust-acoustic wavepackets in a dusty plasma composed of Maxwellian electrons and ions with kappa distribution function. We employ a standard one-dimensional SSuid dust model, consisting of the continuity and momentum equations (for the scaled dust SSuid reduced density n and velocity u variables) and an adiabatic equation of state for the pressure p°^n^, for dustacoustic waves in a dusty plasma containing negative dust (charge qd = sZ^e, where s= qd/\qd = ±1 is the dust charge sign, either + or —), Maxwelhan electrons (tempera­ ture Tg) and nonthermal ions (charge qi = +Zie, temperature T , nonthermahty measured by Jc). The system is closed by Poisson' s equation -^ = —s{n— I) + ci(p + C2(p^ + C3(p^ (for the scaled electric potential (j>), where the right-hand side has been expanded near equilibrium. The coefficients ci, C2, cs, incorporating the essential physics of the problem, are Cm = —Tr[~\\zr ^T^im-^ — j^,~^ > where we have defined, using charge neutrahty at equilibrium, the parameters: