V. Yu. Kozhevnikov

Spectrum of fast electrons in a subnanosecond breakdown of air-filled diodes at atmospheric pressure

In this work, the spectra of electron beams produced in air-filled diodes at atmospheric pressure were studied for different cathode designs. The feasibility of correct reconstruction of the electron beam spectrum from an experimental dependence of its attenuation factor in foils of different thicknesses was demonstrated. The electron energy distributions were calculated on minimum a priori assumptions by regularization of an ill-posed problem—a Fredholm integral equation. The spectra of a subnanosecond electron beam generated in the gas gap during the voltage pulse rise time were reconstructed and analysed. A time-of-flight spectrometer study and reconstruction of the spectrum from the data on e-beam attenuation confirmed the fact that groups of electrons with two-three characteristic energies can be generated in gas-filled diodes. In experiments, electrons of energy greater than that corresponding to the nominal voltage amplitude across the gap were detected.

Drift model of the cathode region of a glow discharge

A one-dimensional drift model of the cathode region of a glow discharge with allowance for both electron-impact ionization and charged particle loss is proposed. An exact solution to the model equations is obtained for the case of similar power-law dependences of the ion and electron drift velocities on the electric field strength. It is shown that, even in the drift approximation, a relatively wide transition layer in which the ion-to-electron current ratio approaches a constant value typical of the positive column of a glow discharge should occur between the thin space-charge sheath and the quasineutral plasma, the voltage drop across the space-charge sheath being comparable to that across the transition layer. The calculated parameters of the normal and anomalous glow discharges are in good agreement with available experimental data.

Runaway electrons and x-rays from a corona discharge in atmospheric pressure air

The characteristics of a corona discharge in atmospheric pressure air are studied using pulsed power generators that produce voltage pulses of different durations, polarities and shapes. The characteristics are measured in the single pulse, batch, and repetitively pulsed modes. It is shown that no matter what the voltage pulse polarity is, a corona discharge starts developing as a conical diffuse discharge near the electrode tip with a voltage rate of increase of 10 15 Vs 1 across an electrode of small curvature radius. With lower voltage rate of increase ( 10 13 Vs 1 or lower), one or several diffuse jets develop from this electrode. The diameter of the jets at their front is less than 1mm and depends on many factors (voltage pulse amplitude and increase, inter- electrode gap width, pulse repetition rate, etc). It is found that at long voltage pulse durations, the radiation spectrum of the corona discharge changes, and the bands and lines of the material of the electrode appear in the UV region at 200-300nm. It is demonstrated that a runaway electron beam in a corona discharge is generated and detected at a distance several times greater than the brightly glowing plasma region of the corona discharge. It is shown that x-rays are generated from a corona discharge at high pulse repetition rates of up to 1kHz.

Reconstruction of electron beam energy spectra for vacuum and gas diodes

In this paper, the spectra of electron beams produced in vacuum and gas diodes were analyzed to study the capabilities and limitations of their reconstruction from beam attenuation in foils of different thickness. The electron energy distributions were calculated using the Tikhonov regularization for Fredholm integral equations on minimum a priori assumptions. The spectra reconstructed in the study were those of electron beams, including a supershort avalanche electron beam, produced in experiments on a DUET plasma-cathode electron accelerator and SLEP-150M accelerator.

1D simulation of runaway electrons generation in pulsed high-pressure gas discharge

The results of theoretical modelling of runaway electron generation in the high-pressure nanosecond pulsed gas discharge are presented. A novel hybrid model of gas discharge has been successfully built. Hydrodynamic and kinetic approaches are used simultaneously to describe the dynamics of different components of low-temperature discharge plasma. To consider motion of ions and low-energy (plasma) electrons the corresponding equations of continuity with drift-diffusion approximation are used. To describe high-energy (runaway) electrons the Boltzmann kinetic equation is included. As a result of the simulation we obtained spatial and temporal distributions of charged particles and electric field in a pulsed discharge. Furthermore, the energy spectra calculated runaway electrons in different cross-sections, particularly, the discharge gap in the anode plane. It is shown that the average energy of fast electrons (in eV) in the anode plane is usually slightly higher than the instantaneous value of the applied voltage to the gap (in V).

Corona discharge in atmospheric pressure air under a modulated voltage pulse of 10 ms

Formation and decay of diffuse “channels” of a corona discharge are studied in atmospheric pressure air, as well as optical and X radiation. Modulated (∼290 kHz) high voltage (∼250 kV) pulses of 10 ms were used. Soft X rays were recorded from a corona discharge in atmospheric pressure air. Bright glowing points were observed in the region of diffuse “channels” and plasma formations, at a distance from the channels. It was ascertained that wriggles appear on the diffuse “channels” of a corona discharge, the length of which increases towards the end of a voltage pulse.

Theoretical simulation of a low pressure gas breakdown in the gap with combined metal-dielectric electrodes

The problem of an electronic devices collapse is particularly relevant for electronics, operated under conditions of significant changes in temperature, pressure, and other critical factors. Currently, the main cause of failure of electrical equipment is microscopic electrical discharges between closely spaced conductive elements of printed circuit board (PCB). The final stages of the development of such micro-discharges are arcs characterized by a large quantity of energy, which leads to the destruction of the circuit elements. This paper considers two-dimensional theoretical model of self-discharge between the current-carrying PCB elements for a wide range of gas pressures (from sub-atmospheric pressure to closed vacuum conditions), and initial concentration of electrons, which are characteristics of the operating conditions of spacecrafts and other large vacuum systems. The basic advantages of the proposed model are demonstrated (such as a wide variety of boundary conditions types and geometric of the discharge gap shapes, the scalability of the critical parameters of the environment, simple representation of surface reactions, etc).

The effect of phase stabilization of microwave oscillations in nanosecond Gunn oscillators

The effect of the semiconductor structure of an oscillator diode on the phase stabilization of microwave oscillations in a nanosecond Gunn oscillator by using a modulating voltage pulse edge is investigated. Numerical simulation is employed to determine phase deviations depending on the scatter of pulseedge duration and pulse amplitude. The standard deviation of phase-delay time of microwave oscillations in the oscillator with regard to a constant level at the modulating pulse edge and the standard deviation of phase difference of microwave oscillations in two electrodynamically insulated oscillators connected in parallel to one and the same modulator have been measured.

Radiation from a diffuse corona discharge in atmospheric-pressure air

Optical and X-radiation from a corona discharge in atmospheric-pressure air is investigated. Spectra of the optical radiation in the range 200–850 nm are obtained under various parameters of the voltage pulse. It was shown that an increase in the voltage pulse changes the corona discharge mode so that the discharge becomes a source of UV radiation, not only from nitrogen 2+ bands, but also from the cathode material. It was also shown that the formation of diffuse corona discharges in a non-uniform electric field under high pressure is conditioned by fast electrons and X-ray generation. It was determined that fast electrons originating from discharges in air under atmospheric pressure generate 525-eV photons from the K-shell of oxygen. Calculations have shown that the photons can effectively initiate new electrons near areas of strong fields. This process explains the formation of types of diffuse discharge for a positive-polarity electrode with a small radius of curvature at atmospheric pressure, and of a fast-moving cathode streamer.

Phase stabilization of nanosecond microwave oscillations in Gunn-diode-based oscillators

The “intrusion” of the phase of a Gunn-diode nanosecond microwave oscillator by applying a modulating voltage pulse is numerically simulated. The dependences of the microwave oscillation phase on the spread of the pulse rise time and modulating pulse amplitude are revealed. The standard deviation of the phase lag time in a 3-cm-range oscillator relative to a fixed level at the leading edge of the modulating phase is measured. Phase synchronization between two electrodynamically uncoupled oscillators that are simultaneously excited by a single modulator is studied experimentally.