Generation of high-current electron beam in a wide-aperture open discharge

Abstract

In the present study, it was examined generation of nanosecond-duration electron-beam (EB) pulses by a wide-aperture open discharge burning in helium or in a mixture of helium with nitrogen and water vapor. In the experiments, a discharge cell with coaxial electrode geometry, permitting radial injection of the electron beam into operating lasing medium, was used, with the cathode having radius 2.5 cm and length 12 cm. It was shown possible to achieve an efficient generation of a high-intensity electron beam (EB pulse power ∼250 MW and EB pulse energy up to 4 J) in the kiloampere range of discharge currents (up to 26 kA at ∼12 kV discharge voltage). The current-voltage characteristics of the discharge proved to be independent of the working-gas pressure. The existence of an unstable dynamic state of EB, conditioned by the presence of an uncompensated space charge accumulated in the discharge cell due to the exponential growth of the current in time during discharge initiation and the hyperbolic growth of current density in the direction towards the tube axis, was revealed. The obtained pulsed electron beam was used to excite the self-terminated laser on He 21P10-21S0 transition. The oscillations developing in the discharge cell at high discharge currents put limit to the pumping energy and emissive power of the laser excited with the radially converging electron beam.

Peculiarities of breakdown and current development in a pulsed open" discharge

“…The weak dependence of I(U) on the gas pressure or its absence fundamentally distinguishes this type of discharge from an anomalous glow discharge [8] and is a feature of discharges with a predominance of the photoemission mechanism of electron generation both in the OD and in the discharge with hollow cathode [9,10]. This behavior of I(U) can be explained by the fact that fast electrons, oscillating at a distance discharge gap−drift space−discharge gap up to their complete deceleration produce the same number of resonant VUV photons, regardless of the stopping power of the working medium.…”

Switching high-voltage pulses with subnanosecond fronts by an open-discharge pulse shaper

“…In these devices, the OD is initiated in a narrow (0.2 to 10 mm wide) accelerating gap between continuous cathode and grid anode, from which electrons enter an extended drift space. A principal feature that distinguishes OD from discharges of other types is that the former operates under conditions where the main kind of electron emission from the cathode is the photoemission under the action of resonant VUV radiation of a working gas [6,11]. This regime of emission automatically ensures a long working life of the cathode and high efficiency of electron beam generation.…”

“…Recent achievements in this field have made possible the creation of com pact devices capable of generating pulsed electron beams with nanosecond durations [6] at energies up tõ 10 keV and current up to ~25 kA, which are promis ing sources for the excitation of various lasers [4,7] and some other applications [8][9][10]. In these devices, the OD is initiated in a narrow (0.2 to 10 mm wide) accelerating gap between continuous cathode and grid anode, from which electrons enter an extended drift space.…”

“…The small interelectrode gap ensures rapid de ionization of discharge plasma, which allows electron beam pulses to be generated at a repetition frequency of up to 10 6 Hz [13]. Therefore, the OD can serve a basis for the creation of current and voltage pulse shapers capable of operating at high repetition fre quencies.The experiments were performed in a discharge cell with coaxial electrode geometry analogous to that recently employed in [6]. The internal diameter of a SiC cathode was 50 mm, the interelectrode gap width was 3 mm, and a grid anode has a diameter of 44 mm, a length of 20 mm, and a geometric transparency of μ = 0.9.…”

“…The experiments were performed in a discharge cell with coaxial electrode geometry analogous to that recently employed in [6]. The internal diameter of a SiC cathode was 50 mm, the interelectrode gap width was 3 mm, and a grid anode has a diameter of 44 mm, a length of 20 mm, and a geometric transparency of μ = 0.9.…”