Evgenii Kh. Baksht

Diffuse discharge, runaway electron, and x-ray in atmospheric pressure air in an inhomogeneous electrical field in repetitive pulsed modes

This letter reports on experimental studies of a pulsed discharge in an inhomogeneous electric field at a pressure of 1 atm for varying voltage pulse parameters. The amplitude of voltage pulses applied to point-to-plane and point-to-point gaps was 12–140 kV and the full width at half maximum was 1–40 ns. It is shown that in a wide range of experimental conditions, a diffuse discharge is ignited due to preionization of the gap by runaway electrons and x-rays. With all gaps, the runaway electrons are produced in response to electric field amplification near the electrodes and in the gap.

Supershort Avalanche Electron Beams and X-rays in Atmospheric-Pressure Air

The conditions for the generation of runaway electron beams with maximum amplitudes and soft X-rays with maximum exposure doses in a nanosecond discharge in atmospheric-pressure air were determined. A supershort avalanche electron beam (SAEB) with a current of amplitude ~50 A, a current pulse of full-width at half-maximum (FWHM) ~ 100 ps, and a current density up to 20 A/cm2 was recorded downstream of the gas diode foil. It is shown that the maximum of the SAEB current amplitude shifts in time relative to the voltage pulse rise as a collector is displaced over the foil surface. A source of soft X-rays with an FWHM of less than 200 ps and an exposure doze of ~3 mR per pulse was designed based on a SLEP-150 pulser (maximum voltage amplitude ~140 kV, FWHM ~1 ns, and pulse rise time ~0.3 ns). It is demonstrated that X-ray quanta with an effective energy of ~9 keV make a major contribution to the exposure dose.

Modes of Generation of Runaway Electron Beams in He,

In this paper, the characteristics of runaway electron beams downstream of a foil anode were studied at a pressure of helium, hydrogen, neon, and nitrogen of 1-760 torr. High-voltage pulses (~150 and ~250 kV) with pulse rise times of ~300 and ~500 ps were applied to the tubular cathode-plane anode gap. It is shown that the highest amplitudes of a supershort avalanche electron beam (SAEB) of 100-ps pulse duration are attained in helium, hydrogen, and nitrogen at pressures of ~60, ~30, and ~10 torr, respectively. It is demonstrated that further decreasing the pressure changes the mode of generation of runaway electron beam and increases the beam current amplitude and the voltage pulse duration across the gap. It is found that increasing the pressure of helium, hydrogen, and nitrogen to hundreds of torr decreases the delay time between the instants the voltage pulse is applied to the gap and the SAEB is generated, as well as the maximum voltage across the gap.

\hbox{H}_{2}

The generation of runaway electron beams in gases at atmospheric pressure has been studied with a real picosecond accuracy. Their main parameters have been determined. It has been found that three groups of electrons can be separated at a subnanosecond voltage pulse in a runaway electron beam generated in air at atmospheric pressure. It has been proven that the duration of a beam pulse in air at atmospheric pressure behind an anode foil is ~100 ps.

, Ne, and

The pulsed diffuse discharge in air at 1 atm in an inhomogeneous electric field at repetitive pulsed mode is investigated. The discharge was formed at voltage pulse amplitude of 12 kV in incident wave and a pulse repetition rate of 100-1000 Hz. It is shown that, in a wide range of experimental conditions, including those with a positive point electrode and small gaps, a diffuse discharge occurs. It is shown that, for time about 1 ns, light spots on the needle electrode and diffuse discharge in the gap were formed.

\hbox{N}_{2}

Runaway electron (RAE) with extremely high-energy plays important role on the avalanche propagation, streamer formation, and ionization waves in nanosecond-pulse discharges. In this paper, the generation of a supershort avalanche electron beam (SAEB) in SF6 and air in an inhomogeneous electric field is investigated. A VPG-30-200 generator with a pulse rise time of ∼1.6 ns and a full width at half maximum of 3–5 ns is used to produce RAE beams. The SAEBs in SF6 and air are measured by using aluminum foils with different thicknesses. Furthermore, the SAEB spectra in SF6 and air at pressures of 7.5 Torr, 75 Torr, and 750 Torr are compared. The results showed that amplitude of RAE beam current generated at the breakdown in SF6 was approximately an order of magnitude less than that in air. The energy of SAEB in air was not smaller than that in SF6 in nanosecond-pulse discharges under otherwise equal conditions. Moreover, the difference between the maximum energy of the electron distributions in air and SF6 dec...

at a Pressure of 1–760 Torr

This paper reports an experimental study of luminescence excited in polymethyl methacrylate (PMMA) by a runaway electron beam and by a KrCl excilamp with a wavelength of 222 nm. It is shown that the major contributor to the luminescence of PMMA in both cases is a luminescence band with a maximum intensity at ~490 nm. Based on experiments with the excilamp, it is supposed that Cherenkov radiation with a wavelength shorter than 300 nm is bound to increase the intensity of this band. The luminescence intensity at ~490 nm varies proportionally with the number of beam electrons, allowing the use of this radiation to determine the number of high-energy electrons in electron beams. In PMMA with high absorption at 300–400 nm, one more luminescence band with a maximum intensity at ~400 nm is observed. It is confirmed that in gas diodes at a pressure of 760 torr, the intensity of Cherenkov radiation against the background of luminescence is low and undetectable.

On the parameters of runaway electron beams and on electrons with an “anomalous” energy at a subnanosecond breakdown of gases at atmospheric pressure

This paper presents new experimental data on the generation of runaway electron beams and X-rays in repetitively pulsed discharges in helium and air with an inhomogeneous electric field. Both negative and positive voltage pulses of duration 1-5 ns and amplitude in the incident wave up to 18 kV were applied to a “tube-to-plane” gap at a pulse repetition frequency of up to 1 kHz. It is shown that at a helium pressure of several and tens of torrs, whatever the polarity of the main voltage pulse, an electron beam is generated on arrival of reflected negative voltage pulses in the gap. X-rays were detected over a wide pressure range of helium and air, including atmospheric pressure. The breakdown of atmospheric-pressure air gaps with a special cathode design at a rate of voltage rise of 1014 V/s was studied with subnanosecond and picosecond time resolution. At a voltage amplitude higher than 100 kV, a fast electron beam in atmospheric-pressure air was detected in the space downstream of the cathode, which was made of thin wires arranged parallel to a thin flat foil. The current of the fast electron beam downstream of the cathode depended strongly on the anode material.

Diffuse Discharges in Atmospheric Pressure Air in Repetitive Pulsed Mode With Point-to-Plane and Point-to-Point Gaps

The objective of the work is to study the beam current amplitude and pulse width at a voltage pulse rise time of -0.3 ns for interelectrode gaps of differing width in a diode pumped down to a pressure of about 0.01 Torr and filled with different gases (air, nitrogen, and helium). SLEP-150 generator with a tubular cathode was used. The conducted studies show that with subnanosecond voltage pulse rise times, it is possible to gradually vary the FWHM of the beam current pulse over a wide range. The FWHM and shape of the beam current pulse was varied by varying the pressure and gas kind in the diode. It is shown that in the vacuum diode mode, the beam current rise time decreases from 0.5 to 0.2 ns as the interelectrode gap is decreased from 12 to 2 mm. It is found that with a 3-mm interelectrode gap, increasing the air pressure in the diode of the SLEP-150 generator from 0.1 to 6 Torr decreases the FWHM of the current pulse from 1 to 0.18 ns, with the beam current amplitude greater than 400 A and the beam current rise time less delayed with respect to the voltage pulse rise time. The attained beam current density at a beam current pulse width of 0.18-1 and 0.1 ns is 500 and 100 A/cm2, respectively.

A comparison between spectra of runaway electron beams in SF6 and air

It is shown that the breakdown of a gap with a small-curvature-radius cathode by a voltage pulse with an amplitude of >100 kV and a rise time of about 0.3 ns is accompanied by the generation of runaway electrons with energies from a few keV to several hundred keV. In the electron spectrum, three groups of electrons with different energies can be distinguished. It is shown that the energy spectrum of the beam electrons depends on the voltage rise time, voltage amplitude, and cathode design.