Electric field enhancement during gap breakdown by ionization waves in nitrogen at elevated pressure

The breakdown of an interelectrode gap filled with nitrogen and some other gases at elevated pres- sure has been studied in an inhomogeneous electric field generated by high-voltage pulses applied to sharp blade electrodes. It is established that the gap breakdown is produced by counterpropagating diffuse plasma jets originating from the two electrodes. The jets merge together and shorten the gap in the axial direction and at angles relative to the electric field lines. The measurements of the laser generation in nitrogen at λ = 337.1 nm showed that, at elevated gas pressures, the electric field in the region of breakdown between coun- terpropagating jets is enhanced, while the intensity of the discharge plasma glow in this region is lower than in the other parts of the gap.     

Filamentation and Self-Focusing of Electron Beams in Vacuum and Gas Diodes

Technical Physics Letters - In this paper, we experimentally studied pulsed electron beams with a high local density. The conditions in which the energy density cumulation is observed during the...     

Note: Measurement of extreme-short current pulse duration of runaway electron beam in atmospheric pressure air

This note reports the time-amplitude characteristic of the supershort avalanche electron beam with up to 20 ps time resolution. For the first time it is shown that the electron beam downstream of small-diameter diaphragms in atmospheric pressure air has a complex structure which depends on the interelectrode gap width and cathode design. With a spherical cathode and collimator the minimum duration at half maximum of the supershort avalanche electron beam current pulse was shown to be ～25 ps. The minimum duration at half maximum of one peak in the pulses with two peaks can reach ～25 ps too.     

A coaxial chopping gap filled with air at atmospheric pressure with a pulse decay time ≤100 ps

The results of experimental studies of a coaxial chopping gap filled with air at atmospheric pressure are presented. At a pulse rise time of 100–300 ps and a voltage pulse amplitude of 30–145 kV, the obtained duration of the voltage-pulse decay time is ≤ 100 ps. The high stability of the gap operation is attained in the presence of the edge with a small radius of curvature on one of the electrodes. The fast voltage decay across the gap is determined by the preionization of the gap by runaway electrons.     

Effective regimes of runaway electron beam generation in helium,hydrogen, and nitrogen

Runaway electron beam parameters and current-voltage characteristics of discharge in helium, hydrogen, and nitrogen at pressures in the range of several Torr to several hundred Torr have been studied. It is found that the maximum amplitudes of supershort avalanche electron beams (SAEBs) with a pulse full width at half maximum (FWHM) of ∼100 ps are achieved in helium, hydrogen, and nitrogen at a pressure of ∼60, ∼30, and ∼10 Torr, respectively. It is shown that, as the gas pressure is increased in the indicated range, the breakdown voltage of the gas-filled gap decreases, which leads to a decrease in the SAEB current amplitude. At pressures of helium within 20–60 Torr, hydrogen within 10–30 Torr, and nitrogen within 3–10 Torr, the regime of the runaway electron beam generation changes and, by varying the pressure in the gas-filled diode in the indicated intervals, it is possible to smoothly control the current pulse duration (FWHM) from ∼100 to ∼500 ps, while the beam current amplitude increases by a factor of 1.5–3.     

Effect of nitrogen pressure on the energy of runaway electrons generated in a gas diode

The energy spectra of runaway electrons generated in a gas diode under the action of voltage pulses with a front width of ∼300 ps and amplitude of ∼140 kV have been studied using a time-of-flight spectrometer at nitrogen pressures in a range of 0.1–760 Torr. The delay of runaway electron beam pulse relative to the driving voltage pulse has been determined. The electron energy depends in a complicated manner on the nitrogen pressure in the gas diode and on the cathode geometry. A minimum breakdown voltage for a gap between tubular cathode and flat anode has been observed at a nitrogen pressure of ∼100 Torr. A decrease in the nitrogen pressure below 100 Torr leads to an increase in the maximum of voltage drop on the gap and the energy of the main fraction of electrons.     

Generation of subnanosecond electron beams in air at atmospheric pressure

Optimum conditions for the generation of runaway electron beams with maximum current amplitudes and densities in nanosecond pulsed discharges in air at atmospheric pressure are determined. A supershort avalanche electron beam (SAEB) with a current amplitude of ∼30 A, a current density of ∼20 A/cm², and a pulse full width at half maximum (FWHM) of ∼100 ps has been observed behind the output foil of an air-filled diode. It is shown that the position of the SAEB current maximum relative to the voltage pulse front exhibits a time shift that varies when the small-size collector is moved over the foil surface.     

The temporal structure of a runaway electron beam generated in air at atmospheric pressure

Supershort avalanche electron beams (SAEBs) generated in air at atmospheric pressure have been studied with picosecond time resolution. It is established that an SAEB has a complicated structure that depends on the interelectrode gap width and cathode design. In a gas-filled diode with a small gap width, an SAEB current pulse with a full width at half maximum (FWHM) of ??25 ps has been observed behind a collimator with a hole diameter of 1 mm. As the gap width is increased or decreased relative to the optimum value that corresponds to the maximum beam current, the SAEB current pulse shape changes and pulses with two peaks are more likely detected. The two-peak SAEB current pulse shape is retained behind aluminum foil with a thickness of 60 and 110 ??m.     

Pulsed cathodoluminescence of diamond,calcite, spodumene,and fluorite under the action of subnanosecond electron beam

Amplitude and temporal characteristics of pulsed cathodoluminescence (PCL) of diamond (natural and synthetic), calcite, spodumene, and fluorite have been studied at a temporal resolution of ∼0.3 ns. The PCL was generated by electron beam pulses with a full width at half maximum (FWHM) of 0.1, 0.25, and 0.65 ns. The PCL spectra have been measured for the emission induced by 0.1- and 0.25-ns pulses at a beam current density of ∼90 A/cm².