Influence of nanoparticles and metal vapors on the color of laboratory and atmospheric discharges

Currently, electrical discharges occurring at altitudes of tens to hundreds of kilometers from the Earth’s surface attract considerable attention from researchers from all over the world. A significant number of (nano)particles coming from outer space burn up at these altitudes. As a result, vapors of various substances, including metals, are formed at different altitudes. This paper deals with the influence of vapors and particles released from metal electrodes on the color and shape of pulse-periodic discharge in air, nitrogen, argon, and hydrogen. It presents the results of experimental studies. The discharge was implemented under an inhomogeneous electric field and was accompanied by the generation of runaway electrons and the formation of mini-jets. It was established that regardless of the voltage pulse polarity, the electrode material significantly affects the color of spherical- and cylindrical-shaped mini jets formed when bright spots appear on electrodes. Similar jets are observed when the discharge is transformed into a spark. It was shown that the color of the plasma of mini-jets is similar to that of atmospheric discharges (red sprites, blue jets, and ghosts) at altitudes of dozens of kilometers and differs from the color of plasma of pulsed diffuse discharges in air and nitrogen at the same pressure. It was revealed that to observe the red, blue and green mini-jets, it is necessary to use aluminum, iron, and copper electrodes, respectivel

Luminescence of crystals excited by a runaway electron beam and by excilamp radiation with a peak wavelength of 222 nm

This paper presents research data on cathodoluminescence, photoluminescence, and Cherenkov radiation at 200–800 nm excited in crystals with different refractive indices by a subnanosecond runaway electron beam and by KrCl excilamp radiation with a peak wavelength of 222 nm. The data include spectral and amplitude-time characteristics measured with a resolution of up to ∼100 ps for natural and synthetic diamonds of type IIa, sapphire, CsI, ZnS, CaF2, ZrO2, Ga2O3, CaCO3, CdS, and ZnSe. The research suggests that cathodoluminescence and photoluminescence should be accounted for in Cherenkov-type detectors of runaway electrons. The results can be useful for detecting high-energy electrons in tokamak

Generation of neutrons in a nanosecond low-pressure discharge in deuterium

The neutron yield is measured in a high-voltage Townsend discharge in deuterium with a hollow cylinder made of tungsten or steel used as a polarizing anode of electrons. A flat metallic plate covered by a layer of deuterated zirconium is applied as a grounded cathode. The highest yield of neutrons in the reaction 2H(d,n)3He, ∼1.2 × 104 neutrons per pulse, is observed in the case of the tungsten anode at a deuterium pressure on the order of 100 Pa. The pulsed neutron flux duration estimated with data obtained from a scintillation detector is roughly equal to 1.5 ns

Review of supershort avalanche electron beam during nanosecond-pulse discharges in some gases

Supershort avalanche electron beam (SAEB) plays an important role in nanosecond-pulse discharges. This paper aims at reviewing experiments results on characteritics of SAEB and its spectra in different gases in nanosecond-pulse discharges. All the joint experiments were carried in the Institute of High Current Electronics of the Russian Academy of Sciences and the Institute of Electrical Engineering of the Chinese Academy of Sciences. In these experiments, the generation of a SAEB in SF6 in an inhomogeneous electric field was studied on three generators with pulse rise times of 0.3, 0.5 and ∼2 ns. Firstly, the comparison of SAEB parameters in SF6 with those obtained in other gases (air, nitrogen, argon, and krypton) is introduced. Secondly, the SAEB spectra in SF6 and air at pressures of 10 kPa (75 torr), and 0.1 MPa (750 torr) are reviewed and discussed. Finally, 1.5-D theoretical simulation of the supershort pulse of the fast electron beam in a coaxial diode filled with SF6 at atmospheric pressure is described. The simulation was carried out in the framework of hybrid model for discharge and runaway electron kinetics. The above research progress can provide better understanding of the investigation into the mechanism of nanosecond-pulse discharges

Supershort avalanche electron beam in SF6 and krypton

Runaway electrons play an important role in the avalanche formation in nanosecond- and subnanosecond- pulse discharges. In this paper, characteristics of a supershort avalanche electron beam (SAEB) generated at the subnanosecond and nanosecond breakdown in sulfur hexafluoride (SF6 ) in an inhomogeneous electric field were studied. One pulser operated at negative polarity with voltage pulse amplitude of ˜130 kV and rise time of 0.3 ns. The other pulser operated at negative polarity with voltage pulse amplitude of 70 kV and rise time of ˜1.6 ns . SAEB parameters in SF6 are compared with those obtained in krypton (Kr), nitrogen (N2 ), air, and mixtures of SF6 with krypton or nitrogen. Experimental results showed that SAEB currents appeared during the rise-time of the voltage pulse for both pulsers. Moreover, amplitudes of the SAEB current in SF6 and Kr approximately ranged from several to tens of milliamps at atmospheric pressure, which were smaller than those in N2 and air (ranging from hundreds of milliamps to several amperes). Furthermore, the concentration of SF6 additive could significantly reduce the SAEB current in N2-SF6 mixture, but it slightly affected the SAEB current in Kr -SF6 mixture because of the atomic/molecular ionization cross section of the gas had a much greater impact on the SAEB current rather than the electronegativity