Interaction of a dielectric macroparticle with a point charge in plasma
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TICAL, NONLINEAR, AND SOFT MATTER PHYSICS
Interaction of a Dielectric Macroparticle with a Point Charge in Plasma V. R. Munirov and A. V. Filippov* Russian State Research Center, Troitsk Institute for Innovation and Fusion Research, Troisk, Moscow, 142190 Russia *email: [email protected] Received January 30, 2012
Abstract—The electrostatic interaction of a charged spherical dielectric macroparticle with a point charge in a plasma in the presence of an external uniform electric field is considered. The electrostatic force and the torque acting on the macroparticle have been determined, and the form of the interaction potential has been established for a nonuniform distribution of free charge on the macroparticle surface. A simple (for calcula tions) expression for the interaction potential that describes well the exact potential at all interparticle dis tances is proposed. The angular velocity of the spinning of dust particles caused by a nonuniform distribution of free charge over their surface has been estimated. DOI: 10.1134/S1063776112080146
1. INTRODUCTION A dusty plasma is a convenient object for studying the properties of strongly coupled systems [1–3]. Many properties of such systems are determined by the interaction potential of charged macroparticles. In [4], we studied the interaction of a point charge with a charged conducting spherical body in a plasma by tak ing into account the Debye screening. We established that the interaction in the case where the spherical macroparticle charge remains constant during the approach differs greatly from the case where the sur face potential remains constant. Here, this problem is generalized to the case of a dielectric macroparticle. We consider the general case of a nonuniform distribu tion of free charge on the macroparticle surface. For a constant macroparticle surface potential, the dielec tric properties of the macroparticle play no role what soever, and this problem, basically, has already been solved in [4]. Therefore, in this paper, we consider only the case of a constant macroparticle charge. A non uniform charge distribution can be maintained, for example, during the photoemission charging of dust particles by an external source of ultraviolet radiation or on dust particles levitating in the nearelectrode layer of an RF discharge or in the cathode layer or strata in DC discharges, where electrostatic traps for dust particles are formed and there are strongly directed ion flows. The torque of the electrostatic forces acting on a macroparticle in a plasma was also determined.
2. THE FIELD OF A CHARGED MACROPARTICLE AND A POINT CHARGE IN PLASMA Consider the interaction between a spherical mac roparticle with radius a1 and dielectric permittivity ε1 and a point particle with charge q2. Since under labo ratory conditions dust particles usually levitate in regions with a sufficiently strong electric field that compensates the action of gravity, we will also include a constant electric field E0 in our analysis. Let us choose the origin of a Cartesian c
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