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This paper deals with the phenomenon of runaway electrons generation in fast discharges under atmospheric pressures. For the first time we explain the existence of runaway electrons having so-called “anomalous” energies (above the applied voltage value) according to physical kinetics principles. The model we consider provides comprehensive information on the formation and development of runaway electron...
Pulsed discharges, especially with fast rise time and high over-voltage, usually accompany by some specific pheromones in the nonuniform electric field. In this paper, the appearance of bright spots on the electrodes in air breakdown and the inversion of polarity effect in SF6 breakdown are investigated. Experiments were carried out by using three experimental setups with a full width at half maximum...
Diffuse discharges were formed in a highly nonuniform electric field by point-plane gaps in atmospheric pressure air, nitrogen, CH4, SF6, xenon, krypton, argon and helium by two nanosecond-pulse generators. The rise time of generators were 0.3 (SLEP-150) and 1 ns (RADAN-220), and a full width at half maximum (FWHM) were 1 and 2 ns, respectively. The variables affecting the discharge characteristics,...
In this work, we performed experiments to examine the conditions under which a runaway electron beam moves not only toward the anode but also backward (to the space downstream of the cathode). For recording a backward runaway electron beam, a positive voltage pulse was applied to the highvoltage electrode of the gas diode. The breakdown of atmospheric pressure air gaps with a special cathode design...
The aim of the work was to take measurements during subnanosecond breakdowns with a time resolution no worse than 100 ps. The current through gaps filled with atmospheric pressure air was investigated during the generation of runaway electrons and X-rays. Three generators, when ensuring the formation of a runaway electrons preionized diffuse discharge (REP DD), were used. It is confirmed that during...
In this work, an experiment to examine the conditions under which a runaway electron beam moves not only toward the anode but also backward (to the space downstream of the cathode) was performed. For recording a backward runaway electron beam, a positive voltage pulse was applied to the high-voltage electrode of the gas diode. The breakdown of atmospheric pressure air gaps with a special cathode design...
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...
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...
In this paper, characteristics of the runaway electron beams downstream of a foil anode were studied at a pressure of helium, hydrogen, and nitrogen from vacuum to tens of 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 demonstrated that increasing the pressure from vacuum to 10 of torr and more changes...
The plasma formed by XeCl∗ laser on the metal targets has been studied. The plasma formation thresholds and expansion velocities have been. It was shown that long-lived plasma objects can be formed near a target in Xe or air at pressure 0, 1–1 atm. Non-symmetric current passing through the laser plasma and the effect of current interruption in the plasma stream were obtained. It is shown that the...
Summary form only given. Breakdown of the gaps with a non-uniform electric field filled with nitrogen and air as well as with other gases under high-voltage nanosecond pulses was investigated. It is shown that conditions of obtaining a diffuse discharge without a source of additional ionization are extended at the voltage pulse duration decreasing. A volume discharge is formed due to the gap preionization...
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 were applied to the tubular cathode — plane anode gap. The SLEP-150 generator, with no transmission line, produced voltage pulses of amplitude ∼160 kV across a high-resistance load; the incident wave amplitude in the transmission...
The spectra of electron beams produced in air-filled diodes at atmospheric pressure were studied. The feasibility of correct reconstruction of the electron beam spectrum from an experimental dependence of its attenuation factor in foils of different thickness was demonstrated. The electron energy distributions were calculated on minimum a priori assumptions by regularization of an ill-posed problem...
X-ray radiation characteristics from a diode filled with atmospheric pressure air were investigated. A source of soft X-ray radiation with the FWHM less than 200 ps and exposure dose of about 3 mR per pulse has been created.
Generation of a supershort avalanche e-beam (SAEB) in nitrogen and helium at quasi-continuous gap voltage has been shown. SAEB duration at generator voltage of 25 kV is ∼200 ps at a half-height, and its delay time with respect to the voltage pulse risetime may be tens of nanoseconds. The beam current waveforms, having several subnanosecond peaks have been recorded. It was established that at SAEB...
This paper reports on experimental studies on generation of sub-nanosecond electron beams and X-rays in gas discharges under atmospheric pressure. The properties of the runaway electrons and X-ray radiation produced using a nanosecond volume discharge are examined. An electron beam with amplitude of ∼ 100 A has been obtained. Current pulse duration (FWHM) of the fast electrons beam formed in an atmospheric...
Generation time of supeshort avalanche electron beam (SAEB) with respect to discharge current front has been established at nanosecond breakdown of air under atmospheric pressure in non-uniform electric field and volume discharge formation. It has been shown that SAEB current maximum is registered at the leading edge of the discharge current before the peak of discharge current of the gas diode capacitance,...
Two-dimensional particle-in-cell simulations were carried out to study the sub-nanosecond electron-beam extraction from a diode gap filled with helium. The simulation code «MAGIC» was used, where gas ionization and secondary electrons are considered. The simulation results have given the behavior of the diode and the characteristics of the output electron beam.
New understanding of mechanism of the runaway electrons beam generation in gases is presented. It is shown that the Townsend mechanism of the avalanche electron multiplication is valid even for the strong electric fields when the electron ionization friction on gas may be neglected. The non-local criterion for runaway electrons has been proposed. This criterion leads to the universal two-valued voltage...
It has been shown that the use of gas diodes with cathode electric field enhancement and voltage pulses having a short leading edge allow to form high-current subnanosecond electron beams. An electron beam appears at voltage pulse leading edge with duration not more than 0.3 ns. On the beam current termination the discharge is usually continued in a quasi-stationary mode having a volume character...
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