On the nature of radiation of blue and green jets in laboratory discharges initiated by runaway electrons

Spectral and amplitude-temporal parameters of radiation from different regions of discharges initiated by runaway electrons have been studied. The pulse-periodic mode of discharge formation was used. It is shown that the color of a part of jets observed during laboratory discharges is determined by radiation of electrode metal vapors. It is found that blue mini jets from an electrode with a small radius of curvature appear in the cases of stainless steel and aluminum electrodes and are caused by emissions of atomic transitions of these metals. Green mini jets observed near copper electrodes are mainly caused by CuI atomic transitions mainly at wavelengths of 521.8 and 522 nm. It is confirmed that jets of different colors appear during formation of bright spots on electrodes, as well as sparks in the discharge

Features of recording the time profile of single picosecond pulses in the real-time mode

A technique for measuring the time profile of a beam-current pulse of runaway electrons that are generated in atmospheric-pressure air is described. The analysis of changes in the pulse shape depending on the bandwidth of the registration path with a temporal resolution of up to 20 ps was performed. It was shown that the electron beam detected behind small-diameter diaphragms has a complicated structure, which depends on the parameters of the gas diode. The issues related to the interpretation of subnanosecond pulses that are picked off capacitive voltage sensors are discussed

Excilamps and their applications

An innovative class of sources of spontaneous ultraviolet and vacuum ultraviolet radiation, the so-called excilamps, based on the nonequilibrum radiation of exciplex or excimer molecules, is described. The design and some technical characteristics of traditional excilamps excited by a dielectric barrier discharge are presented. The data concerning newly developed types of excilamps excited by runaway-electrons-preionized diffuse discharge both in single and pulse-periodic modes are given as well. Some novel applications of excilamps in photochemistry, the effect of ultraviolet and vacuum ultraviolet radiation on the physiological action of living organisms, photosynthesis, and growth of plants, and the use of excilamps for pre-sowing treatment of seeds are explained in detail

Parameters of REP DDs plasma formed during the pulse and pulse-periodic modes in dense gases

Main parameters of plasma formed during the pulse and pulse-periodic runaway electron preionized diffuse discharge (REP DD) in argon, nitrogen and air at high pressure were measured. An electron concentration in the plasma of pulse and pulse-periodic REP DD in the elevated pressure argon was determined. Average for pulse value of electron density in the argon plasma of pulse REP DD was ~ 3·1015 cm-3. Dynamics of electron density in the atmospheric-pressure plasma of the argon during the REP DD was determined. Measured average values of an electron concentration in the plasma of the pulse-periodic REP DD in atmospheric-pressure air and nitrogen were ~ 3·1014 and ~ 4·1014 cm-3, respectively. In addition, for the plasma formed during the pulse-periodic REP DD in atmospheric-pressure nitrogen and air average values of an electron temperature and reduced electric field, as well their dynamics were determined. Average value of an electron temperature during the pulse duration for nitrogen and air plasmas was ~ 2 eV. Dynamics of an electron temperature and reduced electric field strength was registered. Data on rotational and gas temperatures in the discharge plasma of atmospheric-pressure nitrogen formed in pulse (Tr ≈ 350 K, Tg ≈ 380 K) and pulse-periodic (Tr ≈ 750 K, Tg ≈ 820 K) modes were obtained. In addition, measured value of vibrational temperature in REP DD’s plasma formed in pulse mode in nitrogen at pressure of 1 bar was Tv ≈ 3000 K. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only

Dynamics of ionization processes in high-pressure nitrogen, air, and SF6 during a subnanosecond breakdown initiated by runaway electrons

The dynamics of ionization processes in high-pressure nitrogen, air, and SF6 during breakdown of a gap with a nonuniform distribution of the electric field by nanosecond high-voltage pulses was studied experimentally. Measurements of the amplitude and temporal characteristics of a diffuse discharge and its radiation with a subnanosecond time resolution have shown that, at any polarity of the electrode with a small curvature radius, breakdown of the gap occurs via two ionization waves, the first of which is initiated by runaway electrons. For a voltage pulse with an ∼500-ps front, UV radiation from different zones of a diffuse discharge is measured with a subnanosecond time resolution. It is shown that the propagation velocity of the first ionization wave increases after its front has passed one-half of the gap, as well as when the pressure in the discharge chamber is reduced and/or when SF6 is replaced with air or nitrogen. It is found that, at nitrogen pressures of 0.4 and 0.7 MPa and the positive polarity of the high-voltage electrode with a small curvature radius, the ionization wave forms with a larger (∼30 ps) time delay with respect to applying the voltage pulse to the gap than at the negative polarity. The velocity of the second ionization wave propagating from the plane electrode is measured. In a discharge in nitrogen at a pressure of 0.7 MPa, this velocity is found to be ∼10 cm/ns. It is shown that, as the nitrogen pressure increases to 0.7 MPa, the propagation velocity of the front of the first ionization wave at the positive polarity of the electrode with a small curvature radius becomes lower than that at the negative polarity

Parameters of runaway electron beam generated during excitation by nanosecond voltage pulses in short gaps filled with nitrogen

Parameters of a supershort avalanche electron beam (SAEB) in nitrogen excited by the triangular-shaped voltage pulses with 45kV amplitude in incident wave and full width at half-maximum (FWHM) of ~ 1 ns were investigated. In experiments, cylindrical-shaped cathodes made of aluminum and stainless steel were used. An interelectrode distance in the gas-filled diode was 3, 5, and 8 mm. It was established that the highest values of SAEB's current were registered with an aluminum cathode. It was shown that, in contrast to the case of 8-mm gap length, when the interelectrode distances were 3 and 5 mm, the amplitude of SAEB current pulse in nitrogen began to decrease with high values of the pressure – 100 and 50 kPa, respectively

ICCD-imaging of a plasma glow during the prebreakdown stage of nanosecond discharges at both polarities in nitrogen, air and argon

Dynamics of a plasma glow during the prebreakdown stage of a nanosecond discharge in the «cone-to-plane» gap with length of d = 3 mm was investigated with a HSFC PRO 12-bit four-channel ICCD camera. The gap was filled with nitrogen, air, argon. Gas pressure was ranged from 12,5 to 400 kPa. Voltage pulses of negative (U = 25 kV, τ0,5 = 3 ns, τ0,1–0,9 = 0,7 ns) and positive (U = 25 kV, τ0,5 = 10 ns, τ0,1–0,9 = 3 ns) polarities were applied across the gap. Images of the plasma glow at different stages of streamer formation are presented. It was established that a diffuse discharge is formed due to formation of a large streamer. It was found that plasma appears at a certain distance from the conical electrode at both polarities. These and other features of streamer formation are discussed