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The conditions for the generation of subnanosecond and picosecond electron beams with a tunable pulse width are studied on an SLEP-150 generator with a tubular cathode at a voltage pulse rise time of 0.3 ns. The width and shape of the beam current pulse are 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 ${\sim}{0.5}$ to ${\sim}{\rm 0.2}~{\rm ns}$ as the interelectrode gap is decreased from 12 to ${\sim}{\rm 2}~{\rm mm}$ . 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 full width at half maximum (FWHM) of the current pulse from ${\sim}{1}$ 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. It is confirmed that with a nanosecond voltage pulse, the residual pressure of helium, nitrogen, and air in the diode ( ${\sim}{0.1}$ torr or less) does not affect the beam current amplitude and pulse width. At low pressure of air in the gas diode, the attained beam current density at a beam current pulse FWHM of 0.18-1 and ${\sim}{\rm 0.1}~{\rm ns}$ is ${\sim}{500}$ and ${\sim}{100}~{\rm A}/{\rm cm}^{2}$ , respectively.

The dependences of the electron beam intensity and X-ray dose on the thickness of metal foils (Al, Cu) in a nanosecond discharge initiated in atmospheric-pressure air are studied theoretically and experimentally. Calculated curves of electron beam attenuation in aluminum and X-ray dose attenuation in copper agree well with experimental data. It is found that the amplitude of a super-short avalanche electron beam and the X-ray exposure dose reach maximal values at different values of the interelectrode gap. When the length of the cathode’s edge with a small radius of curvature increases, an interelectrode gap maximizing the amplitude of the runaway electron current shrinks.

A high-pressure CO{sub 2} laser with a discharge initiated by an electron beam of sub-nanosecond duration in the laser gas mixture at a pressure up to 5 atm is fabricated. For the 20-ns pulses the energy from the active volume {approx} 4 cm{sup 3} amounted to 40 mJ. The laser operation at a pulse repetition rate up to 5 Hz is demonstrated. In the gas mixture CO{sub 2}:N{sub 2}:He = 1:1:6 at a pressure 5 atm, the specific energy deposition of {approx} 0.07 J cm{sup -3} atm{sup -1} is obtained in the process of a non-self-sustained discharge with ionisation amplification.

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.

Luminescence of crystals of natural spodumene and natural diamond of the type IIa is studied upon excitation by a laser at a wavelength of 222 nm and by a subnanosecond avalanche electron beam (SAEB) formed in air at the atmospheric pressure. The photoluminescence spectra of spodumene and diamond are shown to exhibit additional bands, which are absent upon SAEB excitation. It is demonstrated that SAEB excitation allows one to analyse various crystals under normal conditions without using any vacuum equipment.

It is shown that a volume discharge is formed in a nonuniform electric field for the short leading edge of a voltage pulse and nanosecond pulse duration without any additional preionisation source in various gases at pressures higher than atmospheric (6 atm in helium and 3 atm in nitrogen). Lasing at atomic transitions in Xe is obtained in an Ar—Xe mixture under a pressure of 1.2 atm for an active length of 1.5 cm. A record-high specific power input (more than 0.8 GW cm-3 under a pressure 1 atm in air) is realised in the volume discharge stage. The volume discharge is formed due to preionisation of the discharge gap by fast electrons accelerated due to amplification of the electric field in the cathode region and in the gap. In a nonuniform electric field, volume discharge is realised under a quasistationary voltage from 10 to 180 kV across the gap, at a pulse repetition rate of up to 160 Hz and for various discharge gap geometries.

Conditions are studied under which an electron beam and a volume discharge with a subnanosecond rise time of a voltage pulse are produced in air under atmospheric pressure. It is shown that the electron beam appears in a gas-filled diode at the front of the voltage pulse in ∼0.5 ns, has a half-intensity duration of ≤0.4 ns and an average electron energy of ∼0.6 of the voltage across the gas-filled diode, and terminates when the voltage across the gap reaches its maximum value. The electron beam with an average electron energy of 60 to 80 keV and a current amplitude of ≥70 A is obtained. It is assumed that the electron beam is formed from electrons produced in the gap due to gas ionization by fast electrons when the intensity of the field between the front of the expanding plasma cloud and the anode reaches its critical value. A nanosecond volume discharge with a specific power input of ≥400 MW/cm3, a density of the discharge current at the anode of up to 3 kA/cm2, and specific energy deposition of ∼1 J/cm3 over 3 to 5 ns is created.

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.

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.

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.

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.

An atmospheric-pressure CO2 laser with an electron-beam-initiated discharge produced in a working mixture is developed. The laser output energy of 18 mJ from a ~6-cm3 active volume is achieved. The laser operation with a pulse repetition rate of up to 5 Hz is demonstrated. The specific energy deposit of ~0.1 J cm-3 is obtained in the CO2:N2:He = 1:1:4 gas mixture at the atmospheric pressure during a pulsed nonself-sustained discharge with ionisation amplification.

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.

A technique for determining the amplitude and time parameters of pulsed electron beams is proposed. Using this technique, it is possible to measure weak currents. It is based on the non-self-sustained discharge initiated by the electron beam under investigation. The experimental results are presented for two electron beams formed in a gas-filled diode at the atmospheric pressure of air, nitrogen, a mixture of CO2 : N2 : He = 1 : 1 : 3, or helium and ejected through a foil or grid.

It has been shown that a volume discharge is forming in a non-uniform electric field at a short voltage pulse rise and pulse nanosecond duration without preionization in different gases under pressures above atmospheric (helium 6 atm, nitrogen 3 atm).

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 at FWHM 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. With a diode filled in with air under atmospheric pressure, beam current amplitude over 240 A at a pulse duration at FWHM of 0.2 ns and current density of 40 A/cm 2 was obtained. It has been also shown that at a smal l gas diode inductance the subnanosecond electron beams are formed in various gases in a wide pressure range (up to 6 atm in helium, and up to 4 atm in nitrogen). It has been established that with the new method an electron beam is formed due to critical field reached between an anode and plasma propagating from a cathode. Key words: e-beam, running electrons, gas diode, volume discharge

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. The experimental data results indicate that the electron beam is generated either at a large strength of electric field, when the fraction of runaway electrons is large, or in the field of low strength, where intensive electron multiplication takes place. In the latter case, cathode plasma propagates to anode at high velocity, at that with electrical field distribution in gas diode area the critical value of E/p is reached either due to geometric quotient leading to formation of nanosecond and subnanosecond electron beams. The electron beams obtained in the helium-filled diode had the current amplitude of up to 200 A (corresponding to the current density above 20 A/cm2) at electron energy of ~130 keV.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

This paper reports on experimental study of subnanosecond e-beam formed in air under atmospheric pressure. An electron beam with amplitude of ~ 170 A with duration at FWHM ~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 cathode type and plasma protrusions occurred on the cathode. It is shown that in order to get maximum e-beam in gas diode, the discharge in gas diode should be volume.

Properties of plasma produced in volume nanosecond high-pressure discharge and its formation conditions under elevated pressure in air, nitrogen, krypton, argon, neon and gas mixtures Ar-N2, Ar-Xe, CO2-N2-He in the gap with the cathode having small curvature radius have been investigated. Time-amplitude characteristics and radiation spectra of plasma in different gases in the range of 230-600 nm were defined. Lasing in the gas mixture Ar-Xe at active length of 1.5 cm has been achieved by excitation through volume nanosecond high-pressure discharge. Comparison of spectral radiation in nitrogen, krypton, argon, and neon under pumping of mentioned gases by volume discharge in non-uniform electric field, by nanosecond e-beam, and by volume pulsed discharge in the uniform electric field with high initial voltage was made. Lasing has also been obtained in the gas mixture CO2-N2-He under pumping by e-beam initiated discharge. The electron beam was formed in a gas diode filled the same gas mixture.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Introduction. Investigation of the luminescence of crystals caused by various external factors is an important stage in the spectral analysis of solids, which allows the chemical composition and structure (including the presence of defects and internal stresses) to be determined [1]. Measuring the emission induced by electron beams (cathodoluminescence, CL), it is possible to perform the room-temperature spectral analysis of almost all nonmetallic solids. However, the classical CL measurements require placing the sample in vacuum and ensuring leakage of the electron-beaminduced current from the sample surface [2], which complicates the experimental procedure. It was demonstrated [2‐5] that, using high-current pulsed electron beams of nanosecond duration for the excitation of CL pulses, it is possible to perform the investigations in air at atmospheric pressure. The CL spectra measured under such conditions, as well as the PL spectra measured at cryogenic temperatures, are characterized by high resolution and reveal the fine structure [4]. However, along with this advantage, the pulsed CL technique has a significant drawback, since accelerated electron beams were obtained using vacuum diodes requiring continuous pumping, while sealed-off electron tubes had a short working life. This circumstance limited the implementation of pulsed CL techniques for rapid diagnostics of solid samples.

The repetitively pulsed regime of an atomic xenon transition laser pumped by an electron beam with various pulse durations and an electron-beam-initiated discharge is studied experimentally. An average radiation power of 2.5 W has been achieved in a quasi-stationary regime for a pulse repetition rate of 5 Hz in a laser pumped by a radially convergent electron beam of duration 100 μs without circulation of the Ar — Xe working mixture. The average output power for a laser pumped by a planar electron beam in quasi-stationary regime is 2 W. It is shown that for a specific energy contribution not exceeding 50 J L-1 and laser excitation by a train of electron-beam pulses at a repetition rate of 50 Hz, the amplitude and duration of the second lasing pulse virtually coincide with those of the first. For a laser pumped by a discharge initiated by a nanosecond electron beam, an average lasing power of 380 mW is achieved under steady-state conditions upon transverse circulation of the working mixture and a pump pulse repetition rate of 25 Hz. Pumping by an electron beam from two accelerators with a pulse duration of a few tens of microseconds under an Ar — Xe mixture pressure of about 1 atm and a specific pump power of 1 — 3 kW cm-3 per pulse is proposed for the development of 1.73-μm repetitively pulsed Xe lasers with a high average output power.