Effect of the scheme of plasmachemical processes on the calculated characteristics of a barrier discharge in xenon

The dynamics of a repetitive barrier discharge in xenon at a pressure of 400 Torr is simulated using a one-dimensional drift-diffusion model. The thicknesses of identical barriers with a dielectric constant of 4 are 2 mm, and the gap length is 4 mm. The discharge is fed with an 8-kV ac voltage at a frequency of 25 or 50 kHz. The development of the ionization wave and the breakdown and afterglow phases of a barrier discharge are analyzed using two different kinetic schemes of elementary processes in a xenon plasma. It is shown that the calculated waveforms of the discharge voltage and current, the instant of breakdown, and the number of breakdowns per voltage half-period depend substantially on the properties of the kinetic scheme of plasmachemical processes.     

Study of the surface barrier discharge generated by electrodes in the form of a series of parallel metal strips

A surface discharge in a system where metal electrodes in the form of a series of parallel strips are positioned on the dielectric surface is studied. Analytical formulas for calculating the spatial distribution of the potential and the electric field in a discharge cell are derived. It is shown that the geometry of the metal electrodes should be taken into account (along with physical and chemical characteristics of the dielectric, the voltage applied to the electrodes, and other parameters of the system) for generation of the electric field with optimal configuration in the discharge cell. The obtained results are also applicable for analysis of discharge cells with a coplanar barrier discharge where metal electrodes are positioned in the dielectric at small depths. The results are of interest since a barrier discharge is one of the efficient methods for generating non-equilibrium plasma at high pressures for a variety of technological applications.     

Electrical and chemical properties of XeCl*(308 nm) exciplex lamp created by a dielectric barrier discharge

The aim of this work is to highlight, through numerical modeling, the chemical and the electrical characteristics of xenon chloride mixture in XeCl* (308 nm) excimer lamp created by a dielectric barrier discharge. A temporal model, based on the Xe/Cl₂ mixture chemistry, the circuit and the Boltzmann equations, is constructed. The effects of operating voltage, Cl₂ percentage in the Xe/Cl₂ gas mixture, dielectric capacitance, as well as gas pressure on the 308-nm photon generation, under typical experimental operating conditions, have been investigated and discussed. The importance of charged and excited species, including the major electronic and ionic processes, is also demonstrated. The present calculations show clearly that the model predicts the optimal operating conditions and describes the electrical and chemical properties of the XeCl* exciplex lamp.     

Study of low-temperature plasma between rotating electrodes

Results are presented from experimental studies of the electrophysical and spatiotemporal characteristics of a dielectric barrier discharge operating in atmospheric-pressure air in a discharge cell with a dielectric barrier in the form of a rotating disc. One of the electrodes of the discharge cell was stationary and placed at a certain distance from the dielectric surface, and the following two versions of the second electrode were used: (i) a metal disc electrode was attached to the surface of the rotating dielectric disc, while on the opposite surface of the disc, there was a rectangular strip electrode that was at the same potential as a metal disc electrode and had a sliding contact with the dielectric; (ii) only the strip electrode with the sliding contact was connected to the high-voltage source, while the metal disc electrode was disconnected. Due to barrier rotation, the discharge operated in a pulse mode, although it was supplied from a dc voltage source. The current-voltage characteristic of such a dielectric barrier discharge was measured and analyzed. The number of microdischarge channels arising at the stationary electrode, the geometrical parameters of the microdischarge channels, and the discharge current were studied as functions of the supplied voltage, the distance between the stationary electrode and the dielectric surface, and the rotation velocity of the barrier disc.     

Numerical simulation of a surface barrier discharge in air

The development of a surface barrier discharge in air at atmospheric pressure under the action of a constant voltage of different polarity is simulated numerically. When the polarity of the high-voltage electrode is negative, the discharge develops as an ionization wave that moves along the dielectric surface. When the polarity is positive, the discharge develops as a streamer that first moves above the dielectric surface and then comes into contact with and continues to develop along it. In the case of a high-voltage electrode of positive polarity, the discharge zone above the dielectric surface is approximately five times thicker than that in the case of negative polarity. The characteristic aspects of numerical simulation of the streamer phase of a surface barrier discharge are discussed. The numerical results on the density of the charge stored at the dielectric surface and on the length of the discharge zone agree with the experimental data.     

Prebreakdown stages of a barrier discharge in air

The initial stages of a barrier discharge in a short air gap at atmospheric pressure are investigated by means of numerical simulations. A highly nonuniform electric field caused by the residual surface charges on the dielectric surfaces was taken into account. The results of calculations of the two-dimensional dynamics of the discharge radiation are in good agreement with the experiment.     

Modeling of a Ne/Xe dielectric barrier discharge excilamp for improvement of VUV radiation production

This work is devoted to excimer lamp efficiency optimization by using a homogenous discharge model of a dielectric barrier discharge in a Ne?Xe mixture. The model includes the plasma chemistry, electrical circuit, and Boltzmann equation. In this paper, we are particularly interested in the electrical and kinetic properties and light output generated by the DBD. Xenon is chosen for its high luminescence in the range of vacuum UV radiation around 173 nm. Our study is motivated by interest in this type of discharge in many industrial applications, including the achievement of high light output lamps. In this work, we used an applied sinusoidal voltage, frequency, gas pressure, and concentration in the ranges of 2–8 kV, 10–200 kHz, 100–800 Torr, and 10–50%, respectively. The analyzed results concern the voltage V _p across the gap, the dielectric voltage V _d, the discharge current I, and the particles densities. We also investigated the effect of the electric parameters and xenon concentration on the lamp efficiency. This investigation will allow one to find out the appropriate parameters for Ne/Xe DBD excilamps to improve their efficiency.     

A powerful electrohydrodynamic flow generated by a high-frequency dielectric barrier discharge in a gas

Theoretical and experimental studies of an electrohydrodynamic flow induced by a high-frequency dielectric barrier discharge distributed over a dielectric surface in a gas have been conducted. Dependences of the ion current, the gas flow velocity, and the spatial distributions thereof on the parameters of the power supply of the plasma ion emitter and an external electric field determined by the collector grid voltage have been described.     

Inactivation of Microorganisms on Plane Surfaces by a Dielectric Barrier Discharge

Plasma Physics Reports - Inactivation of spore microorganisms on a dielectric surface by a dielectric barrier discharge with plane electrodes was studied experimentally. It is shown that, at an...     

Structure of the surface streamers of an AC barrier corona in argon

Results are presented from experimental studies of the structure of an ac surface discharge excited by a metal needle over a plane dielectric surface. A barrier corona discharge was ignited in atmospheric-pressure argon at frequencies of the applied sinusoidal voltage from 50 Hz to 30 kHz. In experiments, the area of a dielectric covered with the discharge plasma increased with applied voltage. The discharge structure in diffuse and streamer modes was recorded using a digital camera and a high-speed image tube operating in a frame mode. It is found that, in the positive and negative half-periods of the applied voltage, the structure of the surface discharge is substantially different. The statistical characteristics of the branching surface streamers in the positive and negative half-periods are determined as functions of the voltage frequency. The most intense lines in the emission spectrum of the barrier corona are determined for both half-periods. The correlation between the dynamics of the emission intensity and the dynamics of the discharge current and voltage is investigated.     

Study of spatiotemporal dynamics of a nanosecond atmospheric-pressure dielectric barrier discharge in millimeter-long air gaps

The spatiotemporal dynamics of a nanosecond atmospheric-pressure dielectric barrier discharge in 1- to 3-mm-long air gaps was studied experimentally. By using a segmented electrode, data on the time evolution of the discharge in different regions of the discharge gap were obtained. The uniformity of the discharge over the cross section is estimated by analyzing the spatial distribution of its glow.     

The Memory Effect of Microdischarges in the Barrier Discharge in Airflow

Plasma Physics Reports - The paper devoted to the research of the microdischarge dynamics in the dielectric barrier discharge. The discharge between rail electrodes in airflow along the electrodes...     

Study of the homogeneity of the current distribution in a dielectric barrier discharge in air by means of a segmented electrode

The current distribution in a dielectric barrier discharge in atmospheric-pressure air at a natural humidity of 40–60% was studied experimentally with a time resolution of 200 ps. The experimental results are interpreted by means of numerically simulating the discharge electric circuit. The obtained results indicate that the discharge operating in the volumetric mode develops simultaneously over the entire transverse cross section of the discharge gap.     

Comparison of the AC barrier corona with DC positive and negative coronas and barrier discharge

Results are presented from experimental studies of ac corona discharges between a point electrode and a dielectric-coated plate in nitrogen, argon, helium, and air in the voltage frequency range f=50 Hz–50 kHz. The characteristic features of this type of discharge are compared with the well-known features of dc positive and negative coronas and a barrier discharge between plane electrodes. It is shown that the presence of a dielectric barrier on the plane electrode significantly changes the electric characteristics and spatial structure of the corona, whereas the main phases of the discharge evolution remain unchanged as the voltage increases. With a point electrode, the breakdown voltage of the barrier corona decreases substantially as compared to the breakdown voltage of a barrier discharge with plane electrodes. This leads to softer conditions for the streamer formation in a barrier corona, which becomes more stable against spark generation.     

Multipactor discharge on a dielectric at different inclination angles of the microwave electric field relative to the dielectric surface

Multipactor discharge on a dielectric is studied numerically and analytically for different inclination angles α of the microwave electric field with respect to the dielectric surface. The power absorbed in the discharge is calculated, and analytic estimates for the average current density of secondary electrons and the average energy of electrons bombarding the dielectric surface are obtained as functions of the angle α and the electron oscillation energy in the microwave field. It is found that the dependence of the absorbed power on the inclination angle of the external microwave field has a minimum at α ～20°–30°.     

Diffuse and constricted modes of a dc discharge in neon: Simulation of the hysteresis transition

Results are presented from theoretical studies of high-pressure (～100 Torr) dc discharges in neon. The diffuse and constricted discharge modes are studied using a model including the equation of balance for charged and excited particles, heat conduction equations for the neutral gas and plasma electrons, and Poisson’s equation for the radial electric field at a fixed total discharge current. A specific feature of the constricted mode in the investigated range of low fields and high degrees of ionization is that the excitation and ionization rates in the center of the discharge tube and at the periphery differ by several orders of magnitude. This implies that, in the constricted mode, the region where the electron energy distribution function is Maxwellian due to electron-electron collisions may adjoin the region (beyond the constriction zone) where the high-energy part of the distribution function is depleted. The hysteresis transition between the diffuse and constricted modes is analyzed. A transition from the constricted to the diffuse mode can be regarded as a manifestation of the nonlocal character of the formation of the electron distribution function, specifically, the diffusion of high-energy electrons capable of producing gas ionization from the central (constricted) region toward the periphery. The nonlocal formation of the distribution function is described by a nonlocal kinetic equation accounting for electron-electron collisions and electron transport along the radius of the discharge tube. Since only high-energy electrons produce gas ionization, the effect of the nonlocal formation of the electron distribution function is taken into account by introducing the effective temperature of the high-energy part of the distribution function and solving the equation for the radial profile of the high-energy part of the distribution function. This approach allows one to approximately take into account the nonlocal character of the electron distribution function without substantial expenditure of computer resources. The nonlocal model makes it possible to numerically simulate the hysteresis transition between the diffuse and constricted modes, which is impossible in the local approximation.     

Study of electric discharges between moving electrodes in air

A barrier electric discharge excited between a fixed electrode and a rotating electrode covered with a dielectric layer in atmospheric-pressure air is studied experimentally. A distinctive feature of this type of discharge is that it operates at a constant voltage between the electrodes. An advantage of the proposed method for plasma generation in the boundary layer of the rotating electrode (e.g., for studying the influence of plasma on air flows) is the variety of forms of the discharge and conditions for its initiation, simplicity of the design of the discharge system, and ease of its practical implementation     

Frequency Effects on Helium–Oxygen Dielectric Barrier Discharges from Multibreakdowns to Single Breakdown per Half-Cycle

Plasma Physics Reports - In this work, a one-dimensional fluid model is established to study the effects of frequency on (He + O2) dielectric barrier discharge. As the frequency increases...     

Numerical analysis of similarity of barrier discharges in the 0.95 Ne/0.05 Xe mixture

Established dynamic regimes of similar (with a scale factor of 10) barrier discharges in the 0.95 Ne/0.05 Xe mixture are simulated in a one-dimensional drift-diffusion model. The similarity is examined of barrier discharges excited in gaps of lengths 0.4 and 4 mm at gas pressures of 350 and 35 Torr and dielectric layer thicknesses of 0.2 and 2 mm, the frequencies of the 400-V ac voltage applied to the discharge electrodes being 100 and 10 kHz, respectively.     

Probing biological interfaces by tracing proton passage across them.

The properties of water at the surface, especially at an electrically charged one, differ essentially from those in the bulk phase. Here we survey the traits of surface water as inferred from proton pulse experiments with membrane enzymes. In such experiments, protons that are ejected (or captured) by light-triggered enzymes are traced on their way between the membrane surface and the bulk aqueous phase. In several laboratories it has been shown that proton exchange between the membrane surface and the bulk aqueous phase takes as much as about 1 ms, but could be accelerated by added mobile pH-buffers. Since the accelerating capacity of the latter decreased with increase in their electric charge, it was suggested that the membrane surface is separated from the bulk aqueous phase by a barrier of electrostatic nature. In terms of ordinary electrostatics, the barrier could be ascribed to dielectric saturation of water at a charged surface. In terms of nonlocal electrostatics, the barrier could result from the dielectric overscreening in the surface water layers. It is discussed how the interfacial potential barrier can affect the reactions at interface, especially those coupled with biological energy conversion and membrane transport.