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We describe the recently discovered phenomenon of the formation of an extended luminous structure at the bend of the channel of a high-voltage pulse discharge. It is called the apokamp (from the Greek words απó — ‘from’ and κάμπη — ‘bend’), and the discharge as a whole is referred to as apokampic. In the course of experimental and theoretical studies, it is shown that the apokamp is a narrow streamer channel that propagates at a characteristic speed of tens to hundreds of km/s, depending on the applied voltage, pressure, and gas type. The necessary conditions for apokamp formation are established. The apokamp discharge is used for laboratory studies of conditions for the formation of blue jets and red sprites — large-scale transient luminous events (transients) observed in Earth’s atmosphere above areas with thunderstorm activity. The revealed signs of similarity between apokamps and blue jets are described. The proposed experimental setup can also be used for meaningful testing of hypotheses about the conditions of formation of transients in Earth’s atmosphere and in the atmospheres of other planets.

The use of stationary solvers instead of approximate solution methods or time-dependent solvers, which are standard tools in gas discharge modeling, allows one to develop a very fast and robust numerical model for studying the time-averaged characteristics of dc corona discharges. Such an approach is applied to dc corona discharges in point-plane gaps in ambient air. A wide range of currents of both voltage polarities and various gap lengths are investigated, and the simulation results are validated by comparing the computed current–voltage characteristics and spatial distributions of the radiation intensity with experimental results. Specific features of the numerical and experimental results at both polarities are discussed.

The principle of operation and technical parameters of excilamps with a small-diameter output window from a series of portable narrow-band ultraviolet and vacuum ultraviolet radiation sources are described. An example of using a KrCl excilamp to excite photoluminescence of crystalline materials is given.

It is ascertained that heating of volcanic material from the Etna volcano (Italy) by an apokampic discharge reduces the voltage at which a positive streamer (apokamp) starts from the discharge channel and increases its propagation speed. The luminescence spectra show these processes to be accompanied by the emission of easily ionizable K and Na, which is consistent with data on the elemental composition of Etna samples. A hypothesis is suggested about an increase in the appearance probability of blue jets and starters over sites of high volcanic activity at altitudes of 10–18 km (at the level of the troposphere).

Experimental and theoretical investigations of a new form of pulsed periodic discharge burning in the form of a thin plasma jet – apokamp – have been carried out. It is shown that for sustainable apokamp formation, the presence of a weak external electric field is required which is enhanced near the head of a growing streamer at the expense of good conductivity of the plasma trace. It is experimentally demonstrated that the apokamp formation is initiated by external electric field strength of ~1 kV/cm.

It is shown that the channel of apokampic discharge is a source of streamers at low air pressure and low frequencies (7–16 Hz) of high-voltage positive-polarity pulses and voltage amplitudes from 26 to 35 kV. The maximal starting speed of laboratory streamers was 560 km/s. A hypothesis about blue jet origination in nature is suggested based on experimental data. For their start, high frequencies of voltage pulses are not required, breakdowns in the Hz range are sufficient, but the discharge channel should bend and the field intensity should be high at the bending point.

The experimental and theoretical investigations of a new form of burning of a repetitively-pulsed discharge – apokamp – are performed. It is shown that an apokampic discharge represents a narrow streamer channel, growing from the point of plasma channel bending, having a characteristic propagation velocity of tens and hundreds of meters per second, depending on the applied voltage and gas pressure and type. The conditions necessary for an apokamp to evolve are formed in a comparatively weak macroscopic electric field. The channel bend ensures a local field enhancement, which prescribes the starting orientation of the growing streamer channel. The pulse-frequency power supply regime of the discharge reproduces the streamer channel in every pulse, but the preceding framework of the ion-ion plasma ensures reproduction of the channel shape from pulse to pulse.

It is observed that the formation of an apokamp is preceded by the appearance of streamer coronas starting from the channel of a repetitively pulsed discharge. It is shown that the streamer coronas under experimental conditions alleviate the development of an apokamp, acting as a preionization source.

Laboratory simulation of the conditions for the occurrence of blue jets in the Earth’s atmosphere has been carried out. For this purpose, the diffuse formation of jets and plasma buildup in corona and apokampic discharges in air has been studied. It is shown that the jets are formed due to streamer breakdown and their color depends on air pressure. At atmospheric air pressures of 30–120 Torr, streamers starting from different parts of a repetitively pulsed discharge are recorded in a nonuniform electric field. It has been ascertained that a spherical corona discharge is formed before a breakdown between pointed electrodes, near a metal high-voltage electrode of positive polarity, from which streamer coronas start as the voltage increases. Data on the streamer head size and streamer propagation speed in the corona and apokampic discharges are presented.

The paper presents research data on positive and negative coronas in atmospheric pressure air in a highly inhomogeneous electric field. The data show that irrespective of the polarity of pointed electrodes placed in a high electric field (>200 kV/cm), this type of discharge develops via spherical streamers even if the gap voltage rises slowly (£0.2 kV/ms). The start voltage of first positive streamers, compared to negative ones, is higher and the amplitude and the frequency of their current pulses are much lower: about two times and more than two orders of magnitude, respectively. The higher frequency of current pulses from negative spherical streamers provides higher average currents and larger luminous regions of negative coronas compared to positive ones. Positive and negative cylindrical streamers from a pointed to a plane electrode are detected and successive discharge transitions at both polarities are identified.

The share of UVB spectrum range (290-320 nm) in the solar radiation flux accounts for an average of about 1.5% of the radiant flux on the planet. Taking into account the fact that plants adapt to living conditions in the course of evolution, it can be assumed that the flow of UVB radiation is also used by plants, but at the level of subdoses that reach the Earth's surface. The aim of current work is to study the growth and development of spring wheat (“Irgina” cultivar) when treated with subdoses of UVB radiation. For processing, XeCl-excilamp (High Current Electronic Institute SB RAS) radiation was used. The spectrum of this lamp is a narrow band with a maximum at a wavelength of 308 nm, which corresponds well to the UVB range. In the course of study, the pre-sowing UVB radiation dose values for seeds were found, under the influence of which wheat sprouts had an increase in such indicators as the length and dry weight of the root, the length of the leaf and the ratio of the root/shoot masses. It was shown, that as plants developed, the nitrogen balance index was always higher in the experiment with radiation in plants whose seeds were subjected to pre-sowing treatment with UVB radiation. This indicates the activation of growth and development processes in plants, as well as the accelerated absorption and assimilation of nitrogen compounds. Under the action of dose 0.5 J/cm2 the weighting parameters grain productivity such as weight of grains per ear, spike weight, weight of 1000 pcs seeds and the grain yield exceeded the check by 10.2%. The UVB processing did not affect the quality of the wheat grain. Based on the obtained data, it is concluded that the use of XeCl-excilamp UVB radiation for pre-sowing stimulation of wheat is promising.

Dielectric barrier discharge XeCl-excilamps can be used for detecting of surface defects in case of the luminescent liquid penetrant inspection method (LLPI). In case of LLPI, surface defects are detected by brightly glowing indications formed on the developing coating (developing agent) in the locations of discontinuities. This method differs from the color one that the inspection is performed under darkening conditions and requires ultraviolet irradiation, so it is more sensitive, since the visual luminescence of the display is detected better than the color contrast. This article experimentally compares the results of LLPI using different UV-light sources (two barrier discharge excilamps (portable and front-mounted), a mercury UV lamp and an led UV lantern). It is shown that the XeCl-excilamp gives a good detection and fixation of indicator traces in comparison with other sources of UV radiation.

Atmospheric pressure plasma jets generated by apokamp discharge (APPJ AD) in ambient air was investigated for the improvement of growth parameters of spring wheat seeds («Irgina» cultivar) and for inhibition of potentially phytopathogenic fungi on seeds surface. In case of APPJ AD, active forms of oxygen and nitrogen (as well as the radiation of molecules) are formed in the air of atmospheric pressure, which increases their concentration in the streamer head by orders of magnitude, compared to traditional APPJ based on inert gases. Owing to this, we believe to concentrate action of active forms of oxygen and nitrogen in situ, on the biological target. In our case, this can intensify the processes of inactivation of microscopic mold fungi on the surface of seeds. We tested our hypothesis on wheat seeds infected with helminthosporiosis ( Bipolaris sorokiniana Shoemaker ) with a degree of infection of 50% and early blight ( Alternaria sp. ), whose infection rate was 10%. In the first case, the seeds were treated by apokamp plasma for 1 and 10 minutes. It provided a significant reduction in the degree of infection of seeds with helminthosporiosis by 1.7 and 2.3 times. In comparison with check variant, the treated seeds maintained high rates of viability and germination energy. In the second case, it was possible to completely inactivate alternariosis pathogens within 3 min of treatment. In addition, it is shown that the action of APPJ AD caused a statistically valid elongation of the roots of wheat seedlings. A hypothesis is proposed to explain the found effects. The potential advantages of APPJ AD in the task of seed surface treatment in comparison with other known atmospheric plasma techniques are discussed.

Experimental studies of the heat release processes in the apokamp discharge were carried out via the plotting of intensity charts. The procedure was verified with measurement techniques similar to those used in the operation of a disappearing filament pyrometer. A criterion was formulated for its applicability for the study of apokamp discharge in air. The intensity charts obtained at different stages of the formation of discharge confirm the need for gas heating near the discharge channel to form streamers.

Emission spectra of apokamp discharge plasma jets in CO2, Ar, Kr, N2, and their mixtures have been studied. It has been shown that the emission spectra of the Kr–N2 mixture contain N2 and $$\rm{N_2^+}$$ bands, as well as Kr lines. The spectrum of the Ar–CO2 mixture is presented by bands of the Fox–Duffendack–Barker system and lines of the exited argon atom. In all gas media under study, the reduction of the molecular gas quantity leads to the transition from an apokampic discharge in the form of a diffusion jet developing from the current channel to a volume discharge with a strong transverse glowing. The experimental apparatus described in this work is proposed for use in laboratory investigations of spectral characteristics of transient luminous events observed in atmospheres of planets of the Solar System.

The modern level of research on the inactivation of viruses, bacteria, and living cells under the influence of ultraviolet radiation from excilamps is presented. Special attention is paid to the inactivation of viruses, which is relevant in connection with the spread of coronavirus infections. It has been shown that UVC excilamps, emitting in the wavelength range of 200-240 nm, are an alternative to classical sources of ultraviolet radiation for inactivating viruses. They can be used alone or in combination with known sources (e.g., LEDs, low pressure mercury lamps). A forecast was made for the development of a new technology for disinfecting air and surfaces from infectious agents of various etiologies. (C) 2021 Optica Publishing Group

Results of investigations of UV and VUV radiation sources (excilamps) based on inert gases and mixtures of inert gases with halides are presented. Conditions are described in which maximum radiation parameters are attained. Photoreactors and irradiators promising for application in medicine, agriculture, and gas industry have been developed based on the excilamps.

Experimental and theoretical investigations of a diffuse jet (streamer) of apokampic discharge are carried out for various values of air pressure. It is established experimentally that this regime of pulse-periodic discharge is formed stage by stage. At the first stage, in a microsecond discharge of a voltage pulse of positive polarity, a potential spark channel formed during the first pulses between two needle electrodes is transformed into a diffuse channel. At the second stage, a weakly glowing halo is formed near the discharge channel, and a bright offshoot arises near the bending point. Finally, at the third stage of discharge in the steadystate mode, for frequencies of a few to tens of kilohertz in each pulse, the offshoot becomes a source of plasma bullets (streamers) moving with a velocity of up to 200 km/s. As a result of simulation of a streamer in atmospheric pressure air under conditions corresponding to the experimental data, a propagation velocity of up to 400 km/s is obtained for the streamer. It is shown that the formation of a jet significantly depends on the air temperature.

Miniature analogs of starters and blue jets that are observed in the upper atmosphere of the Earth and have dimensions of tens of kilometers are formed and studied in air and nitrogen at pressures of tens and hundreds of Torr. Ministarters and mini blue jets have been obtained in laboratory experiments owing to the application of a pulse-periodic discharge with a plasma jet referred to as apokamp. The velocities of propagation of apokamps have been measured at various pressures. It has been found that the average values of these velocities are about the velocities of propagation of starters and blue jets in the atmosphere of the Earth. It has been shown that jets (apokamps) with the maximum length are observed in the pressure range corresponding to the altitudes of appearance and propagation of starters and blue jets.

The formation of blue jets in air at low pressures is simulated using an apokamp discharge. The field strength is measured in the discharge channel. Assuming the applicability of similarity laws to gas discharges, the field strength in a storm cloud during the formation of blue jets is assessed to be from 6 × 1010 to 1.9 × 109 V/m, which is much higher than the values characteristic of the development of cloud-to-ground lightning discharges. A hypothesis is suggested that excess magnitudes of characteristic fields is among features of high-voltage pulsed discharge within a cloud, which results in the formation of blue jets at altitudes of about 12–18 km.

Now, agriculture strives for advanced technologies that would speed up the seed germination, reduce the plant disease incidence, and enhance the crop yield. In this connection, more and more studies address ultraviolet irradiation of seeds and plants as a way to increase their sowing quality. In this paper, XeCl-excilamp (λ~ 300-320 nm) ‒ as a simulator of solar short-wave radiation ‒ is used in the quality of source of ultraviolet radiation. A new data on morphometric and morphological indicators of development of a number of economically valuable crops (parsley, cucumber, pumpkin, zucchini) exposed to XeCl-excilamp are presented. In particular, it is shown that the ultraviolet treatment increases the number of zucchini fruits ("Tsukesha" sort) by an average of 40%, compared to untreated control samples and increases the area of the assimilating surface of leafs (in the first week after germination and further in a month and two months) by an average of one and a half times. Compared with the control 90-second treatment of seeds zucchini led to a higher content of vitamin C in fruits and more than a twofold reduction of nitrate to 64±7 mg/kg. Similar results were obtained for the pumpkins. First processing radiation of XeCl-excilamp were subjected parsley seeds. Found processing conditions in which you can increase the yield by an average of 20%. The obtained indicators allow us to draw a conclusion about the economic feasibility of XeCl-excilamp seeds illumination and confirm our conclusions about the prospects of such a procedure for pre-sowing plant seeds.

The paper demonstrates the possibility of studying blue jets in laboratory apokamp discharges as a source of blue streamers that move upward from the discharge channel. Research data are presented on the formation of such streamers in low-pressure air at a voltage of tens of kilovolts, showing for the first time that they do arise at low (∼8 Hz) pulse repetition frequencies under pressures at which gigantic blue jets develop 10–20 km above the Earth. At a voltage of positive polarity with an amplitude of 33 kV, the streamer velocity in a pulsed apokamp discharge reaches 560 km/s. When applying microsecond voltage pulses of amplitude 15 kV with a repetition frequency of 50 kHz, the length of streamers ranges to more than 120 cm.

Results of experimental and computational study of the dynamics and structure of atmospheric-pressure air plasma jets formed by barrier discharge in a thin dielectric tube are presented. Formation of plasma bullet-guided streamers, moving along the jet with velocity varying in the range (1–3) $\times 10^{{\mathrm {7}}}$ cm $\text{s}^{{\mathrm {-1}}}$ , is observed. Simulation, for conditions of the experiment, gives the streamer radius, velocity, and propagation length in reasonable agreement with the experimental data.

A new phenomenon is observed in a spark discharge developing under normal conditions in air in a discharge circuit with a capacitive decoupling. It consists in the current channel bending becoming a source of a 4–6 cm long plasma jet directed across the channel. The phenomenon is termed an apokampic discharge or an apokamp. Its emission spectrum contains the bands of electron-vibration transitions from the second positive group of molecular nitrogen. The conditions of formation of an apokamp are experimentally determined. A conclusion is drawn that in order construct a physical model of an apokamp, one has to take into account: 1) the presence of a local gas overheating in the site of the current channel bending, 2) the similarity of the current and voltage time dependences in the corona discharge and in the current channel (becoming a source of an apokamp), and 3) the length of the apokamp plasma jet.

The energy redistribution in barrier-discharge Xe2 excilamp in various excitation regimes is investigated using the pressure jump method. Analytic expressions are derived for calculating power W dissipated in the excilamp discharge plasma in the form of heat and for calculating total discharge heat power PT spent on heating the excilamp. It is shown that the mechanism of the thermal energy dissipation gradually changes upon an increase in the xenon pressure in the excilamp. The conditions for generating the maximal radiation power of the excilamp are determined. It is shown that the maximum of the average radiation power is attained for an excitation pulse duration of 500 ns and the maximal pulse power is attained for a pulse duration of 100 ns. It is found that the optimal operation regime for the excilamp corresponds to the maximal values of the PT–W difference.

A new phenomenon has been discovered where a bend of a plasma channel becomes of a source of one or several diffuse jets that have a length (at a given voltage) up to 4–6 cm and are directed across the plasma channel at a pulse-periodic spark discharge in air under normal conditions. The phenomenon is called apokamp discharge (apokamp). The spectrum of radiation of the apokamp includes primarily the bands of electron-vibrational transitions of the second positive system of molecular nitrogen. The conditions of the formation of apokamp have been experimentally revealed and it has been established that it consists of plasma bunches moving from the plasma channel at each pulse at a velocity of about 220 km/s.

We analyzed the atmospheric pressure plasma jet excited in air and nitrogen by a barrier discharge. The source forming stable plasma jets of length up to 4 cm in air and nitrogen is constructed, and its energy and spectral characteristics are measured.

The ignition of a corona discharge on a tip electrode with a small radius of curvature in air at atmospheric pressure is studied. It is established that the initiation of the corona discharge in a highly nonuniform electric field at any voltage polarity is due to the formation of ball streamers at high (≥10 kV/µs) and low (≤0.2 kV/ms) rates of the tension increase in the tip—plane gap. It is shown that the current amplitude through the gap of the first streamers at a positive tip electrode polarity is approximately half of that at a negative polarity, and the frequency of their appearance differs by two or more orders of magnitude. It is established that the high pulse repetition frequencies at the same voltage across the gap lead to higher average currents through the gap and a larger observed glowing area in the case of the negative polarity tip electrode in the formation region of ball streamers.

A laboratory setup has been created for modeling certain aspects of the initiation process of blue jets in the Earth’s atmosphere. With its help, the influence of an electric field on the apokamp discharge in air at pressures of 180-260 Torr was established. It is shown that the formation of a negatively charged zone located above the channel of a pulse-periodic discharge with a positive potential leads to both initiation and lengthening of the apokamps starting from the channel, and also reduces the voltage amplitude necessary for their formation.

The recent hypothesis about the initiation of red sprites in the Earth atmosphere in presence of metal atoms was verified. We have tested this hypothesis using Al, Cu, Fe, and W electrodes in laboratory apokamp discharges in air at a pressure of 45 and 760 Torr. Our experiments show that the electrode material does influence the apokamp dynamics. However, for Fe and W, compared to Al and Cu, the start voltage of an apokamp in pulse-repetition mode is higher and its length is shorter. The emission spectrum of apokamp discharges reveals lines of their metal electrodes. Thus, the experiments confirm the hypothesis on the contribution of metal vapors from burnt meteors to the initiation of red sprites in the Earth atmosphere.

Experimental study of a diffuse jet propagation of apokampic discharge is carried out at air pressure of 120 Torr, which corresponds to start altitudes of nature transient luminous events - blue jets and starters. A new data about apokamp medium-velocity dependence on voltage pulse characteristics are obtained. While pulse frequency decreasing from 56 to 10kHz the medium-velocity of plasma bullets is almost doubled to ~220 km/s. They are testifies that there is no need for increased breakdown frequencies in atmospheric cloud layers for producing extended jets.

Formation of a diffuse discharge at a short front of voltage pulse (less than 1 ns), as well as when placing water, water solutions, and dielectric film inside the discharge, is studied. A volumetric discharge was observed in water on the anode when placing dielectric film (polyethylene, vinyl chloride-methyl methacrylate (VCMMA), etc.), water, or aqueous solutions of 3% hydrogen dioxide or 18% KMgO4 inside the discharge. The change in the absorption spectrum of substance was found after multiple discharge switching on. Fourier analysis of the infrared absorption spectra showed the difference between the spectra of exposed and unexposed polyethylene film. The changes in the absorption spectra of water, 3% hydrogen dioxide and 18% KMgO4 aqueous solutions are related with expansion of the band of valence oscillations of OH-groups without clearly expressed maxima (for the studied liquids). Therefore, volumetric diffuse discharge in molecular and atomic gases can be used in modifying dielectrics, water and aqueous solutions.

The decomposition products of pulse-periodic discharge atmospheric pressure plasma in apokamp, diffuse and corona modes were determined by optical and chemical methods. It is shown that apokamp discharge formation starts at a critical value of dissipation power in a discharge channel. Simultaneously, due to the thermochemical reactions, plasma starts to efficiently produce nitrogen oxides.

The object of this work is the apokamp—a new type of plasma jet, which is formed from a bright offshoot emerging at the bending point of a channel of a high-voltage pulse-periodic discharge under conditions where the electrodes have a capacitive decoupling with the ground. The aim of this work is the identification of distinctive properties of the offshoot in comparison with the apokamp. The differences in the spectra of the offshoot and plasma jet (apokamp) were detected experimentally in air under normal conditions. The results of the previous studies, according to which the apokamp is a wave of ionization, were confirmed. The launch of a helium plasma jet from the offshoot of the pulse-periodic discharge in a mode of the apokamp forming was demonstrated experimentally. It was shown that the offshoot of high-voltage pulsed discharge in the mode with the apokamp is a medium that is strongly heated and conducting electric current.

In a single-barrier discharge with voltage sharpening and low gas consumption (up to 1 L/min), plane atmospheric pressure plasma jets with a width of up to 3 cm and length of up to 4 cm in air are formed in the slit geometry of the discharge zone. The energy, temperature, and spectral characteristics of the obtained jets have been measured. The radiation spectrum contains intense maxima corresponding to vibrational transitions of the second positive system of molecular nitrogen N2 (C3Π u → B3Π g ) and comparatively weak transition lines of the first positive system of the N 2 + ion (B2Σ + → X2Σ g ). By an example of inactivation of the Staphylococcus aureus culture (strain ATCC 209), it is shown that plasma is a source of chemically active particles providing the inactivation of microorganisms.

Here we present research data demonstrating how crop seeds response to ultraviolet produced by a barrier-discharge XeCl* excilamp with a wavelength of 290–320 nm (82–88 %). The data show that presowing ultraviolet treatment is stimulatory to seed germination and plant growth. Ultraviolet treatment increases the seed germinability by 20–30 % and the plant fresh weight by 54 %, compared to untreated control samples, and provides a developed root system with long twisted segments. The research results are encouraging for upgrading the UV technology to larger-scale seed irradiation.

Pulse-periodic corona discharge in atmospheric air excited by applying a voltage pulse with a subnanosecond or microsecond rise time to a point electrode is studied experimentally. It is shown that, at a voltage rise rate of dU/dt ~1014 V/s, positive and negative ball-shaped streamers with a front velocity of ≥2 mm/ns form near the point electrode. As dU/dt is reduced to 1010−1011 V/s, the streamer shape changes and becomes close to cylindrical. The propagation velocity of cylindrical streamers is found to be ~0.1 mm/ns at dU/dt ~ 2 × 1010 V/s. It is shown that the propagation direction of a cylindrical streamer can be changed by tilting the point electrode, on the axis of which the electric field strength reaches its maximum value. It is established that, for the negative polarity of the point electrode and a microsecond rise time of the voltage pulse, a higher voltage is required to form a cylindrical streamer than for the positive polarity of the point electrode.

The decomposition products of atmospheric pressure plasma of repetitive pulsed discharge in apokamp and corona modes were determined by optical and chemical methods. It is shown, that the decomposition products contain mainly nitrogen oxides NOx. A brief review of the plasma- and thermochemical reactions in the pulsed discharges was made. The review and experimental data allow us to explain the reactive oxygen species formation mechanisms in a potential discharge channel with apokamp. The possible applications of this plasma source for treatment of seeds of agricultural crops are discussed.

New experimental and computational data on apokamps produced by repetitive discharges in air, including a detailed description of the research techniques used, are presented. It has been shown that plasma bullets–streamers in apokamps at low frequencies could start not only from the bright offshoot but also directly from the discharge channel. The experimental and computational data demonstrate that the visual color of apokamp changes from blue to red as the intensity ratio of the second to the first positive nitrogen system decreases with the decreasing pressure.

The apokamp discharge is an atmospheric pressure plasma jet generating from the bending point of the discharge channel between high-voltage and floating potential electrodes. The jet propagates perpendicularly to the interelectrode discharge channel for several centimetres without gas convection. Based on the simplified plasma-chemical model of the discharge, a theoretical explanation of the apokamp phenomenon was obtained for the first time. It is shown that the apokamp is a stable plasma quasi-jet formed by the positive streamer mechanism.

The dynamics of diffuse discharge formation under the action of nanosecond voltage pulses with short fronts (below 1 ns) in the absence of a source of additional preionization and the influence of a dielectric film on this process have been studied. It is established that the diffuse discharge is induced by the avalanche multiplication of charge initiated by high-energy electrons and then maintained due to secondary breakdowns propagating via ionized gas channels. If a dielectric film (polyethylene, Lavsan, etc.) is placed on the anode, then multiply repeated discharge will lead to surface and bulk modification of the film material. Discharge-treated polyethylene film exhibits a change in the optical absorption spectrum in the near-IR range.

The optimal time interval was found for plasma treatment of liquid using distilled water as an example. The positive effect of plasma-active water on the agricultural crops growth is shown. The synchronization task of chemically active particles formation and their entry into the liquid has been revealed.

The influence of the chlorine concentration on the radiation efficiency of coaxial exciplex lamps (excilamps) excited by a dielectric barrier discharge (DBD) in binary Xe-Cl2 mixtures at pressures of 240–250 Torr is investigated experimentally and theoretically. The experiments were carried out at Cl2 concentrations in the range of 0.01–1%. The DBD characteristics were calculated in the framework of a one-dimensional hydrodynamic model at Cl2 concentrations in the range of 0.1–5%. It is found that the radiation intensities of the emission bands of Xe*2(172 nm) and XeCl* (308 nm) are comparable when the chlorine concentration in the mixture is in the range of 0.01–0.1%. In this case, in the mixture, the radiation intensity of the Xe*2 molecule rapidly decreases with increasing Cl2 concentration and, at a chlorine concentration of ≥0.2%, the radiation of the B → X band of XeCl* molecules with a peak at 308 nm dominates in the discharge radiation. The radiation efficiency of this band reaches its maximum value at chlorine concentrations in the range of 0.4–0.5%. The calculated efficiencies of DBD radiation exceed those obtained experimentally. This is due to limitations of the one-dimensional model, which assumes the discharge to be uniform in the transverse direction, whereas the actual excilamp discharge is highly inhomogeneous. The influence of the chlorine concentration on the properties of the DBD plasma in binary Xe-Cl2 mixtures is studied numerically. It is shown that an increase in the Cl2 concentration in the mixture leads to the attachment of electrons to chlorine atoms and a decrease in the electron density and discharge conductivity. As a result, the electric field and the voltage drop across the discharge gap increase, which, in turn, leads to an increase in the average electron energy and the probability of dissociation of Cl2 molecules and ionization of Xe atoms and Cl2 molecules. The total energy deposited in the discharge rises with increasing chlorine concentration due to an increase in the power spent on the heating of positive and negative ions. The power dissipated by electrons decreases with increasing chlorine concentration in the working mixture. Recommendations on the choice of the chlorine content in the mixture for reducing the intensity of VUV radiation of the second continuum of the Xe*2 excimer without a substantial decrease in the excilamp efficiency are formulated.

The properties of apokamps (miniature plasma jets) with length up to 60 cm at low pressures are studied. It is shown that several properties of apokamps resembles that ones for large-scale transient luminous events (sprites, starters and blue jets) observed in the Earth upper atmosphere. The images and spectra of apokamps in these conditions are presented. For the first time red downward directed mini jets in air at pressures of fraction of Torr were obtained.

The paper describes a new discharge source of atmospheric pressure plasma jets (APPJs) in air with no gas supply through the discharge region. In this discharge mode, plasma jets develop from the bending point of a bright current channel between two electrodes and are therefore termed an apokamp (from Greek ‘off’ and ‘bend’). The apokamp can represent single plasma jets of length up 6 cm or several jets, and the temperature of such jets can range from more than 1000 °C at their base to 100–250 °C at their tip. Apokamps are formed at maximum applied voltage of positive polarity, provided that the second electrode is capacitively decoupled with ground. According to high-speed photography with time resolution from several nanoseconds to several tens of nanoseconds, the apokamp consists of a set of plasma bullets moving with a velocity of 100–220 km/s, which excludes the convective mechanism of plasma decay. Estimates on a 100-ns scale show that the near-electrode zones and the zones from which apokamps develop are close in temperature.

A review of studies of thermodynamic processes in KrBr (207 nm), KrCl (222 nm), and XeBr (282 nm) barrier-discharge excilamps and XeBr (282 nm) and XeCl (222 nm) microwave-discharge excilamps is presented. Using various pressure gauges, it was experimentally shown that a pressure jump that occurs upon excilamp switching-on (-off) contains a fast (with a characteristic time of ∼100 ms) and a slow (∼100 s) component. The fast pressure-jump component is associated with gas heating during the discharge and allows evaluation of the fraction of the discharge power that is thermalized in the gas. From the analysis of the pressure decay after the jump, it follows that the gas is heated as a result of two processes: direct gas heating during the discharge (∼100 ms) and the energy dissipation of acoustic waves in the gas (∼10 ms). The slow component of the pressure jump is caused by the general heating of the excilamp and can be used to determine the fraction of the discharge power that is converted to thermal energy and to study various excilamp cooling modes.