Electric potential of a macroparticle in beam-plasma systems
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Y PLASMA
Electric Potential of a Macroparticle in Beam−Plasma Systems A. A. Bizyukova, E. V. Romashchenkob, K. N. Seredaa, and A. D. Chibisova a
Karazin Kharkiv National University, pl. Svobody 4, Kharkiv, 61007 Ukraine b V. Dahl East Ukrainian National University, Luhansk, 91034 Ukraine Received March 20, 2008; in final form, November 27, 2008
Abstract—Dusty plasma research is one of the most extensively developed areas of modern plasma physics. In spite of the large number of papers devoted to determining the electric potential of dust grains in gas dis charge plasmas, this problem is still far from being resolved completely. In this paper, the behavior of the float ing electric potential of a macroparticle in an electron beam−plasma system is studied in the framework of the orbit motion limited model taking into account secondary electron emission. PACS numbers: 52.27.Lw, 52.40.Mj DOI: 10.1134/S1063780X09060063
1. INTRODUCTION Studies of dusty plasmas are of great practical importance, because such plasmas play a decisive role in many technological vacuum−plasma processes, such as vacuum arc methods for depositing decorative and hardening coatings [1]. These methods are based on the generation of a metal plasma flow containing macroparticles (metal drops with sizes from several microns to a few hundred microns) by a lowpressure arc discharge. The presence of liquid drops in the plasma flow worsens the coating parameters. The removal of macroparticles from the plasma flow by applying magnetic separators decreases the deposition rate, because a major fraction of the working material is lost in the separator [2]. Alternative methods of plasma purification may be evaporation [3] and Ray leigh decay [4] of macroparticles. To raise the effi ciency of these processes, it is necessary to increase the electric potential difference between the macroparti cle and the plasma. One of the methods for substan tially increasing the macroparticle potential is to inject an electron beam into the dusty plasma. In this paper, the floating electric potential of a dust grain in an electron beam−plasma system is studied in the framework of the orbit motion limited (OML) model with account of secondary electron emission [5, 6]. 2. STEADYSTATE ELECTRIC POTENTIAL OF A DUST GRAIN Let us consider a beam−plasma discharge in which the number density of dust grains is low and the dis tance l between neighboring dust grains is much larger than the charge screening length λ d in plasma. This allows us to consider the problem in the model of a sol itary dust grain in plasma. To determine the dust grain
potential, we will use the model of orbital motion of charged plasma particles in the central field of a charged dust grain. This model, which was developed by Langmuir for a spherical electric probe in plasma [6], adequately describes ion trajectories only if the potential decreases with distance from the grain more slowly than 12 . In the framework of our model, the r potential inside the Debye sphere is assumed to decrease as 1 , i
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