Fore-vacuum plasma-cathode electron sources

Abstract

This paper presents a review of physical principles, design, and performances of plasma-cathode direct current (dc) electron beam guns operated in so called fore-vacuum pressure (1-15 Pa). That operation pressure range was not reached before for any kind of electron sources. A number of unique parameters of the e-beam were obtained, such as electron energy (up to 25 kV), dc beam current (up 0.5 A), and total beam power (up to 7 kW). For electron beam generation at these relatively high pressures, the following special features are important: high probability of electrical breakdown within the accelerating gap, a strong influence of back-streaming ions on both the emission electrode and the emitting plasma, generation of secondary plasma in the beam propagation region, and intense beam-plasma interactions that lead in turn to broadening of the beam energy spectrum and beam defocusing. Yet other unique peculiarities can occur for the case of ribbon electron beams, having to do with local maxima in the lateral beam current density distribution. The construction details of several plasma-cathode electron sources and some specific applications are also presented.

Narrow-aperture electron beam in the forevacuum pressure range as a tool for dimensional processing of silica glass

“…Accelerated electron beam 4 was focused by magnetic lens 5 and was directed to the treated specimen 9 using magnetic beam deflection system 6. The electrode system and structural peculiarities of electron source, as well as its parameters and characteristics are described in more detail in the works [8][9][10]. Silica glass rods having 10 mm in diameter and 30 mm in length were used for investigation of hole form and milling depth.…”

“…Hence, due to presence of dense plasma in the beam transport area such electron sources are capable of performing treatment of both conductive materials and products and dielectrics without any means of surface charge compensation. Effectiveness of electron beam treatment of dielectrics using such sources is showed using the example of welding and vaporization of ultra-high temperature ceramics, sintering of ceramics, and polymer surface modification [9,10].…”

Electron beam deposition of ceramic coatings at fore-vacuum pressure

“…For efficient electron beam treatment of ceramics without undesirable surface charging, one needs to provide conditions for neutralization of the charge built-up on the ceramic target by the electron beam. These conditions can be provided by the use of the so-called "fore-vacuum pressure, plasma-cathode, electron beam source"; in such sources, the electron beam is extracted from a plasm at a pressure of about 5-20 Pa (as opposed to an electronemitting hot filament), and a secondary plasma (so-called 'beam-plasma') with density 10 10 −10 11 cm −3 is formed in the vicinity of the beam transport region [15]. Low-energy positive ions from the beam plasma provide charge neutralization of the e-beam irradiated surface of the ceramic target [14,16], or even within the volume of a dielectric cavity [17].…”

“…The fore-vacuum pressure plasmacathode electron beam source 1 utilized hollow-cathode glow discharge plasma. The source was mounted on the flange of vacuum chamber 2; the operating mode of the source was continuous [15]. FIGURE 1.…”

Generation of large cross-sectional area electron beams by a fore-vacuum-pressure plasma electron source based on the arc discharge

“…However processing of non-conducting (dielectric) materials in conventional vacuum range (< 10 -1 Pa) is problematical because non-conducting surfaces are charged by electron beam [3]. Fore-vacuum-pressure plasma electron sources allow to generate both continuous [4,5] and pulsed [6] electron beams at operating pressure ranging from several Pa to about a hundred Pa. In the fore-vacuum pressure range, negative surface charge is compensated by ion flow from the plasma, "beam plasma", generated by the ionization of the background gas by electron beam [7].…”