Study of Intense Electron Beams Produced by High-Voltage Pulsed Glow Discharges

Abstract

Abstract-We report the generation of high-current-density (20 A/cm 2 ) pulsed electron beams from high-voltage (48-100 kV) glow discharges using cathodes 7.5 em in diameter. The pulse duration was determined by the energy of the pulse generator and varied between 0.2 ps and several microseconds, depending on the discharge current; The largest electron beam current (900 A) was obtained with an oxidized aluminum cathode in a helium-oxygen atmosphere. An oxidized magnesium cathode produced similar results, and a molybdenum cathode operated at considerably lower currents. A small-diameter ( < 1 mm) well-collimated beam of energetic electrons of very high current density ( > 1 kA/cm 2 ) was also observed to develop in the center of the discharge. Electrostatic probe measurements show that the negative glow plasma density and the electron beam current have a similar spatial distribution. Electron temperatures of 1-1.5 eV were measured at 7 em from the cathode. The plasma density (8.5 • 10ncm-3 at 450 A) was found to depend linearly on the discharge current. In discharges at high currents a denser and higher temperature plasma region was observed to develop at approximately 20 em from the cathode. We have modeled the process of electron beam generation and predicted the energy distribution of the electron beam. More than 95 percent of the electron beam energy is calculated to be within 10 percent of that corresponding to the discharge voltage.

A simple model of a glow discharge electron beam for materials processing

“…The cold cathode electron gun we are considering is similar to that developed by Ranea-Sandoval et al [3] and used by Mingolo et al [14] for the production of amorphous surfaces. This electron gun can produce high currents up to about 900 A at accelerating voltages of about 65 kV, in pulses of 0.2-30 s.…”

“…With the sparkgap open, the high voltage source charges the capacitor . When the spark-gap is triggered, the capacitor discharge produces a pulsed high-voltage glow discharge, with wellknown characteristics [3], [14].…”

“…In order to obtain high current density pulses, it is necessary for the cathode to have a high secondary electron emission yield. Oxidized aluminum or magnesium cathodes are usually employed [3], [14]. A small fraction (5-10%) of O 2 is usually incorporated to the inert gas (He) to maintain cathode oxidation.…”

“…Recently, Mingolo et al [14] applied a cold cathode electron gun to the amorphization of Mg-Zn alloys. For the latter application we have utilized a particularly simple type of large cathode area pulsed discharge electron gun, that can produce high-power density focused electron beams following the secondary emission of electrons by ion bombardment of the cathode surface [3], [14].…”

Study of the soft X-ray emission from carbon ions in a capillary discharge

“…High voltage discharges in vacuum or at low pressure are known to generate intense beams of high energy electrons [25]- [27]. Repeated shots from a conically tapered capillary discharge have been previously observed to produce a small diameter hole in the anode [ 131.…”