Emission current formation in plasma electron emitters
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Emission Current Formation in Plasma Electron Emitters V. A. Gruzdev and V. G. Zalesski Polotsk State University, ul. Blokhina 29, Novopolotsk, Vitebsk oblast, 211440 Belarus Received January 20, 2009
Abstract—A model of the plasma electron emitter is considered, in which the current redistribution over electrodes of the emitter gasdischarge structure and weak electric field formation in plasma are taken into account as functions of the emission current. The calculated and experimental dependences of the switching parameters, extraction efficiency, and strength of the electric field in plasma on the accelerating voltage and geometrical sizes of the emission channel are presented. DOI: 10.1134/S1063780X10130179
1. INTRODUCTION In the mid20th century, the development of elec tron beam technologies stimulated the study of devices alternative to thermalemission guns in which gas dis charges were used to generate highenergy electron beams [1]. The largest practical advances were achieved in the study of three main methods for gen erating highenergy electron beams, i.e., (i) electron beams produced in a highvoltage dis charge (HVD), (ii) ion–electron emission in a highvoltage glow discharge (HVGD), and (iii) electron emission from lowvoltage discharge (LVD) plasma followed by electron acceleration [1]. The relation of the beam current to other parame ters (voltage, pressure) in devices with HVD is pre sented by the theory of highvoltage discharge with a hollow cathode and a main potential drop in the anode region of the discharge gap [1]. Similar dependences in devices with HVGD are presented by the theory of highvoltage discharge with a main potential drop in the nearcathode region [1]. To describe the processes of electron current switching from LVD to the accelerating gap, the plasma probe theory was adapted by Zharinov and Kovalenko [2] for the first time. In this paper, the two electrode model of a plasma generator with electron emission from plasma to the accelerating gap through an anode hole was considered. It is assumed that charged particle motion in plasma is collisionless. The ratio of the density of the thermal electron current jT to the current density ja to the anode was assumed to be much greater than unity in order of magnitude, which corresponds to the horizontal shape of the current– voltage (I–V) characteristic id(Ud) of the discharge generating the emitting plasma. Based on an analysis of this model, the authors of [2] showed that the elec tron extraction efficiency α (the ratio of the electron emission current ie to the discharge current id) can
reach unity at the plasma emission surface area Se much smaller than the anode area Sa. Moreover, the condition was formulated, under which acceleration of electrons emitted from plasma can be implemented, Se j G ≤ 1, where G ≈ T . Se + Sa ja
(1)
An important methodological significance of this study by Zharinov [2] is that it was first noted the need to consider the state of nearwall layers in the e
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