The effect of the plasma potential on characteristics of beams formed by electrostatic ion optics

In glow-discharge based plasma emission structures the potential difference Δφ, between plasma and the screen electrode of the ion optics may equal 0-1 kV depending on the electrode system. This paper presents results of computer simulation and experimental study of the formation of argon ion beams having the energy of 0.5-50 keV and the current density of 1-10 mA/cm² at various Δφ values. It is shown that large Δφ, which are typical of hollow-cathode discharges, have an effect upon the efficiency of the ion extraction from plasma, require a higher accelerating electric field strength and/or cause a drop in the maximum density of the beam current. Extraction of ions and formation of high-perveance low-divergent beams are impaired due to a presence of thick layer of space charge, which affects the shape of the plasma boundary in apertures of the ion optics