[en] Interaction of femtosecond laser pulses with the intensities 10²¹, 10²²W/cm² with CH plastic foils is studied in the framework of kinetic theory of laser plasma based on the construction of propagators (in classical limit) for electron and ion distribution functions in plasmas. The calculations have been performed for real densities and charges of plasma ions. Protons are accelerated both in the direction of laser pulse (up to 1 GeV) and in the opposite direction (more than 5 GeV). The mechanisms of forward acceleration are different for various intensities

[en] Ignition of hydrocarbon-containing gaseous mixtures has been studied experimentally and numerically under the action of a high-voltage nanosecond discharge at elevated temperatures. Ignition delay times were measured behind a reflected shock wave in stoichiometric C_nH_2n+2 : O₂ mixtures (10%) diluted with Ar (90%) for n = 1-5. It was shown that the application of the gas discharge leads to more than an order of magnitude decrease in ignition delay time for all hydrocarbons under consideration. The measured values of ignition delay time agree well with the results of a numerical simulation of the ignition based on the calculation of atom and radical production during the discharge and in its afterglow. The analysis of simulation results showed that a non-equilibrium plasma favours the ignition mainly due to O atoms produced in the active phase of the discharge. (fast track communication)

[en] Plasma decay after a high-voltage nanosecond discharge has been studied experimentally and numerically behind incident and reflected shock waves in high temperature (600-2400 K) air and N₂ : O₂ : CO₂ mixtures for pressures between 0.05 and 1.2 atm. Time-resolved electron density history was measured by a microwave interferometer for initial electron densities in the range (1-3) x 10¹² cm^-3 and the effective electron-ion recombination coefficient was determined. A numerical simulation was carried out to describe the temporal evolution of the densities of charged and neutral particles under the conditions considered. It was shown that the loss of electrons in this case is determined by dissociative recombination with O₂⁺ ions, whereas the effect of complex ions is negligible. Electron attachment to O₂ to form negative ions is not important because of fast electron detachment in collisions with O atoms produced in the discharge. In the absence of O atoms the electron density could decay as if the loss of charged particles were governed by electron-ion recombination with the effective rate coefficient being much higher than the dissociative recombination coefficient.

[en] Plasma decay after a high-voltage nanosecond discharge was studied experimentally and numerically in room temperature N₂, CO₂ and H₂O for pressures between 1 and 10 Torr. The time-resolved electron density was measured by a microwave interferometer for initial electron densities in the range 8 x 10¹¹-3 x 10¹² cm^-3 and the effective electron-ion recombination coefficient was determined. It was shown that this coefficient varies in time and depends on pressure. A numerical simulation was carried out to describe the temporal evolution of the densities of charged particles under the conditions considered. A good agreement was obtained between the calculated and the measured electron density histories. It was shown that the loss of electrons is governed by dissociative recombination with complex ions, their density being dependent on pressure. In N₂ at low pressures, a hindered electron thermalization in collisions with molecules led to a delay in the plasma decay. This effect was observed both experimentally and theoretically

[en] The results of the experimental and numerical study of a high-voltage nanosecond discharge developing through a shock wave in air and combustible mixtures were presented for various neutral density jumps across the wave. The discharge uniformity was investigated using ICCD camera images in a shock tube. The results demonstrated that the discharge plasma became more uniform when the ionization wave moved from a high-density region to a low-density region. The radiation intensity emitted by the plasma in the low-density region was higher than that emitted by the plasma in the high-density plasma. The results of a zero-dimensional simulation in the case of quasi-uniform plasma agree well with the measured ratios of the intensities radiated by the plasmas before and after the shock front. A two-dimensional simulation of the development of a steamer intersecting the shock wave showed that the streamer characteristics change drastically during the transition from the high-density region to the low-density region. Streamer penetration into the low-density region was accompanied by the formation of primary and secondary ionization waves. (paper)

[en] We study experimentally and numerically the kinetics of ignition in lean and stoichiometric C₂H₂ : O₂ : Ar mixtures after a high-voltage nanosecond discharge. The ignition delay time is measured behind a reflected shock wave with and without the discharge using detection of CH radiation. Generation of the discharge plasma is shown to lead to a decrease in ignition delay time. Discharge processes followed by chain chemical reactions with energy release are simulated during ignition in the C₂H₂ : O₂ : Ar mixtures. The generation of atoms, radicals and excited and charged particles in the discharge phase is numerically simulated. The calculations are based on the measured time-resolved discharge current and electric field. The calculated densities of the active particles produced in the discharge on a nanosecond time scale are employed as input data to simulate plasma-assisted ignition on a microsecond scale. The calculated ignition delay times are compared with the experimental data. It is shown that the effect of the discharge plasma on ignition of the acetylene-containing mixtures is associated with active species production in the discharge phase rather than with gas heating during the discharge and in its afterglow. A sensitivity analysis is made to determine limiting reactions in acetylene autoignition and ignition after the discharge under the conditions studied. (paper)

[en] The influence of nonlinear interference effects (NIEF) on line shape is investigated. Ion dynamics is taken into account within the frame of Model Microfield Method. The present research is performed within atomic density matrix formalism. Numerical calculations of both lifetimes of radiating states and line shapes are performed for the spectral doublet (1s-2s)2¹S-(1s-4p)4¹P, (1s-2s)2¹S-(1s-4d)4¹D of helium-like multicharged ions in hot dense plasmas. It is found that ion microfield essentially influences on the difference of populations of radiating 4¹P, 4¹D states NIEF is contribution in both allowed and forbidden components is calculated at various plasma conditions. Results demonstrate that account of NIEF essential in the calculation of line shapes of multicharged ions

[en] The decay of air plasma produced by a high-voltage nanosecond discharge at room temperature and gas pressures in the range of 1–10 Torr was studied experimentally and theoretically. The time dependence of the electron density was measured with a microwave interferometer. The initial electron density was about 10¹² cm⁻³. The discharge homogeneity was monitored using optical methods. The dynamics of the charged particle densities in the discharge afterglow was simulated by numerically solving the balance equations for electron and ions and the equation for the electron temperature. It was shown that, under these experimental conditions, plasma electrons are mainly lost due to dissociative and three-body recombination with ions. Agreement between the measured and calculated electron densities was achieved only when the rate constant of the three-body electron-ion recombination was increased by one order of magnitude and the temperature dependence of this rate constant was modified. This indicates that the mechanism for three-body recombination of molecular ions differs from that of the well-studied mechanism of atomic ion recombination.

[en] This paper presents the results of experimental and theoretical studies of an afterglow in room temperature air and O₂ excited by a high-voltage nanosecond discharge for pressures between 1 and 10 Torr. We measured time-resolved electron density by a microwave interferometer for initial electron densities in the range (2-3) × 10¹² cm^-3. Discharge uniformity was investigated by optical methods. The balance equations for charged particles and electron temperature were numerically solved to describe the temporal evolution of the densities of electrons and ions in the discharge afterglow. It was shown that the loss of electrons is governed by dissociative and three-body electron recombination with O₂⁺ ions under the conditions considered. Good agreement between the calculated and measured electron density histories could be obtained only when the rate of three-body recombination was increased by an order of magnitude and when the dependence of the recombination rate on electron temperature was changed. This could testify that the well-understood mechanism of three-body electron recombination with atomic ions could be noticeably modified in the case of molecular ions. (paper)

[en] We study a nanosecond surface dielectric barrier discharge (SDBD) initiated by negative or positive polarity pulses 10–15 kV in amplitude in a cable, 25–30 ns FWHM, 5 ns rise time, in the regime of a single shot or 3 Hz repetitive frequency. Discharge parameters, namely spatial structure of the discharge and time- and space-resolved electric field are studied in a N₂ : O₂ = 4 : 1 mixture for P = 1–5 atm. The possibility of igniting a combustible mixture with the help of an SDBD is demonstrated using the example of a stoichiometric C₂H₆ : O₂ mixture at ambient initial temperature and at 1 atm pressure. Flame propagation and ignited volume as a function of time are compared experimentally for two discharge geometries: SDBD and pin-to-pin configurations at the same shape and amplitude of the incident pulse. It is shown that the SDBD can be considered as a multi-point ignition system with maximum energy release near the high-voltage electrode. Numerical modeling of the discharge and subsequent combustion kinetics for the SDBD conditions is performed. The discharge action leads to the production of atoms and radicals as well as to fast gas heating, due to the relaxation of electronic and vibrational degrees of freedom. The calculated ignition delay time is in reasonable agreement with the experimental results. (paper)