I. D. Kostyrya

Supershort electron beam from air filled diode at atmospheric pressure

The properties of an electron beam (e-beam) formed in air under atmospheric pressure are reported. The nanosecond generators RADAN-303 (two devices) and RADAN-220, producing nanosecond voltage pulses with amplitude of up to 400 kV and subnanosecond rise time were used in the experiments. It was shown for the first time that the duration of e-beam current of gas diode behind the foil does not exceed 0.1 ns. The maximum amplitude of current of a supershort avalanche electron beam (SAEB) behind the foil was ∼400 A. The data on the influence of various parameters on e-beam current amplitude measured behind the foil were obtained. An electron beam with energy less than 60 keV and powerful X-ray radiation were formed in discharge gap simultaneously with SAEB.

Runaway-electron-preionized diffuse discharge at atmospheric pressure and its application

The paper presents the results of experimental research on nanosecond high-pressure diffuse discharges in an inhomogeneous electric field with a time resolution of ~100?ps. It is shown that decreasing the voltage pulse duration enhances the feasibility of the diffuse discharge with no additional ionization. In particular, with a narrow interelectrode gap, a diffuse discharge in atmospheric pressure air with preionization by runaway electrons, called a runaway-electron-preionized (REP) diffuse discharge (DD), was realized. It is found that most of the energy is deposited to the REP DD plasma once the voltage across the gap reaches its maximum. It is demonstrated that the REP DD holds promise for producing high-power VUV pulses. The radiation power attained with xenon at a wavelength of ~172?nm is 8?MW. The treatment of an AlBe foil with an REP DD in atmospheric pressure air provides cleaning of its surface layer from carbon and penetration of oxygen atoms into the foil to a depth of 450?nm per 300 pulses.

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.

Supershort avalanche electron beam generation in gases

This paper reports on the properties of a supershort avalanche electron beam generated in the air or other gases under atmospheric pressure and gives the analysis of a generation mechanism of supershort avalanche electron beam, as well as methods of such electron beams registration. It is reported that in the air under the pressure of 1 atm, a supershort ( 6 and Xe under the pressure of 2 atm, and in He, under the pressure of about 15 atm. It is shown that in SF 6 under the high pressure (>1 atm) duration (full width at half maximum) of supershort avalanche electron beam pulse is about 150 ps.

Runaway electron preionized diffuse discharges in atmospheric pressure air with a point-to-plane gap in repetitive pulsed mode

This paper presents the results of the experimental studies of a pulsed discharge in atmospheric pressure air in an inhomogeneous electric field for various parameters of voltage pulses. It is shown that in a wide range of experimental conditions, including those with a positive electrode of small curvature radius, a diffuse discharge is ignited in the gap. In particular, a diffuse discharge is ignited at a pulse repetition frequency of 1 kHz and a voltage pulse amplitude of ∼25 and ∼40 kV across a high-resistance load. With voltage pulses of ∼ 220 kV in amplitude and low repetition frequencies, an extended (∼70 cm) diffuse discharge is observed in gaps of 13–40 mm. It is confirmed that the diffuse form of discharges in an inhomogeneous electric field at increased pressures is attributed to the generation of runaway electrons and x-rays.

Supershort Avalanche Electron Beams in Discharges in Air and Other Gases at High Pressure

In this paper, the generation of supershort avalanche electron beams (SAEBs) from the plasmas of nanosecond diffuse discharges in air and other gases at atmospheric pressure was investigated. It is shown that, in the mode of SAEB generation, the plasma in the discharge gap with an inhomogeneous electric field can be produced in a time no greater than 100 ps with the charged-particle density sufficient to force out the electric field from the discharge-gap region occupied by the dense plasma. It is demonstrated that decreasing the voltage pulsewidth in the discharge gap (to ~100-ps FWHM) reduces the optimum gap for SAEB generation. It is also found that the difference in electron path toward the foil center and the foil edge affects the SAEB current pulsewidth. For lower voltages across the gap (~25 kV), the SAEB pulsewidth at half maximum is ~200 ps.

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.

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.

SLEP-150m compact supershort avalanche electron beam accelerator

A SLEP-150M gas-diode runaway electron accelerator was designed to produce supershort avalanche electron beams (SAEBs) at increased gas pressures. The cathode and gas-diode used in the design made it possible to greatly increase the current amplitude of the runaway electron beam produced in atmospheric pressure air. The number of electrons downstream of the gas diode foil was ~5 × 1010 electrons, and this corresponds to a SAEB amplitude of ~80 A at a FWHM of ~100 ps.

Application of dynamic displacement current for diagnostics of subnanosecond breakdowns in an inhomogeneous electric field.

The breakdown of different air gaps at high overvoltages in an inhomogeneous electric field was investigated with a time resolution of up to 100 ps. Dynamic displacement current was used for diagnostics of ionization processes between the ionization wave front and a plane anode. It is demonstrated that during the generation of a supershort avalanche electron beam (SAEB) with amplitudes of ~10 A and more, conductivity in the air gaps at the breakdown stage is ensured by the ionization wave, whose front propagates from the electrode of small curvature radius, and by the dynamic displacement current between the ionization wave front and the plane electrode. The amplitude of the dynamic displacement current measured by a current shunt is 100 times greater than the SAEB. It is shown that with small gaps and with a large cathode diameter, the amplitude of the dynamic displacement current during a subnanosecond rise time of applied pulse voltage can be higher than 4 kA.