V. M. Orlovskii

On formation of subnanosecond electron beams in air under atmospheric pressure

This article reports on experimental studies of subnanosecond electron beams formed in air under atmospheric pressure. An electron beam with an amplitude of ∼170 A with a duration at FWHM of ∼0.3 ns has been obtained. Based on beam temporal characteristics and discharge spatial characteristics, the critical fields were supposed to be reached at plasma approach to anode. Simultaneously, the sharp high-energy pulse of e-beam current is generated. Of critical importance is the cathode type and occurrence on the cathode of plasma protrusions. It is shown that to get maximum amplitude of the electron beam in the gas diode, the discharge in the gas diode should be volumetric.

Electron beams formed in a diode filled with air or nitrogen at atmospheric pressure

We have studied the electron beam formation in a diode filled with a molecular gas at atmospheric pressure. A beam current amplitude of up to ∼20 A at an electron energy of ∼70 keV was obtained in an air-filled diode. It is suggested that the main fraction of runaway electrons at low initial values of the parameter E/p (∼0.1 kV/(cm Torr)) is formed in the space between cathode plasma and anode. As the plasma spreads from cathode to anode, the electric field strength between the plasma front and anode increases and the E/p value reaches a critical level.

Production of powerful electron beams in dense gases

Subnanosecond electron beams with the record current amplitude (∼70 A in air and ∼200 A in helium) were produced at atmospheric pressure. The optimal generator open-circuit voltage was found for which the electron-beam current amplitude produced in a gas diode was maximal behind a foil. It was established that the electron beam was produced at the stage when the cathode plasma closely approaches the anode. It was shown that a high-current beam can be produced at high pressures because of the presence of the upper branches in the curves characterizing the electron-escape (runaway) criterion and the discharge-ignition criterion (Paschen curve).

Luminescence of Crystals under the Action of a Subnanosecond Electron Beam

Subnanosecond avalanche electron beams formed in air at atmospheric pressure ensure intense luminescence of synthetic ruby and natural spodumene crystals.

Electron beam formation in helium at elevated pressures

The formation of a beam of runaway electrons in a diode filled with helium at a pressure from 0.1 to 760 Torr was studied under conditions of a pulsed ≈4 ns) high ≈200 kV) voltage applied to the discharge gap. Both theoretical results and experimental data indicate that the electron beam is generated both at a large strength of the electric field, when the fraction of runaway electrons is large, and in a field of low strength, where intensive electron multiplication takes place. In the latter case, a high current can be obtained despite a small fraction of runaway electrons relative to their total number. The electron beams obtained in the helium-filled diode had a current amplitude of up to 140 A (corresponding to a current density above 10 A/cm2) at an electron energy of ∼150 keV.

Electron beam formation in a gas diode at high pressures

Electron beam formation in krypton, neon, helium, and nitrogen at elevated pressures are experimentally investigated. It is shown that, when the krypton, neon, and helium pressures are varied, respectively, from 70 to 760 Torr, from 150 to 760 Torr, and from 300 to 4560 Torr, runaway electrons are beamed at the instant the plasma in the discharge gap approaches the anode and the nonlocal criterion for electron runaway is fulfilled. The fast-electron simulation of discharge gap preionization is performed. The simulation data demonstrate that preionization in the discharge gap is provided if the voltage pulse rise time is shorter than a nanosecond under atmospheric pressure.

Generation of X-ray radiation with a high pulse repetition rate by means of a volume discharge in an open gas diode

The subject of study is ultrashort avalanche-produced electron pulses generated in air under atmospheric pressure. The current amplitude of the pulses behind 45-μm-thick AlBe foil exceeds 100 A, and their FWHM is ≈0.2 ns. The conditions of generation of ultrashort pulses persist at repetition rates as high as 1.5 kHz. A volume discharge initiated in an open coaxial-electrode gas diode by high-voltage nanosecond pulses generates hard (> 60 keV) radiation.

Subnanosecond electron beams formed in a gas-filled diode at high pressures

Subnanosecond electron beams can be formed in gas-filled diodes at high pressures (up to 6 and 4 bar in helium and nitrogen, respectively). In a diode filled with air at atmospheric pressure, a beam current amplitude above 240 A was obtained at a pulse duration (FWHM) of ∼0.2 s and a beam current density of ∼40 A/cm2.

The formation of diffuse discharge by short-front nanosecond voltage pulses and the modification of dielectrics in this discharge

The dynamics of diffuse discharge formation under the action of nanosecond voltage pulses with short fronts (below 1 ns) in the absence of a source of additional preionization and the influence of a dielectric film on this process have been studied. It is established that the diffuse discharge is induced by the avalanche multiplication of charge initiated by high-energy electrons and then maintained due to secondary breakdowns propagating via ionized gas channels. If a dielectric film (polyethylene, Lavsan, etc.) is placed on the anode, then multiply repeated discharge will lead to surface and bulk modification of the film material. Discharge-treated polyethylene film exhibits a change in the optical absorption spectrum in the near-IR range.

Atmospheric pressure volume discharge without external preionization

The phenomenon of electric breakdown in air at atmospheric pressure without additional preionization was studied by experimental and theoretical methods. Using voltage pulses of different polarity with subnanosecond leading front and nanosecond width, volume discharge can be obtained under such conditions between electrodes of various configurations, in particular, between two point electrodes. The development of an ionization wave in nitrogen is described within the framework of a diffusion-drift approximation in a spherical geometry. The fact that the qualitative character of discharge is independent of the voltage pulse polarity is explained by the multiplication of background electrons in the high-density gas.