[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)

No abstract available

[en] New modes of spin precession have been observed in superfluid ³He-B with a precessing magnetization M=pM_eq, where p=1, (1)/(2), and ∼0. These dynamic order parameter states are the first examples of stable precession with a magnetization different from the equilibrium value M_eq. The p=(1)/(2) mode is the second example of a phase-coherent state of a spin superfluid. The new states can be excited close to T_c in the range 1-T/T_c approx-lt 0.02 where dissipation is low and the energy barriers between the different local minima of the spin-orbit energy are small. copyright 1996 The American Physical Society

[en] Self-assembled InGaAs quantum dots with In content 80% grown on vicinal GaAs substrates by MOVPE method have been investigated by photoluminescence technique in a wide range of temperatures and excitation densities. Multimodality of distribution of size and (or) shape in array of vertically stacked quantum dots synthesized under different growth conditions as well as in a single layer structure was found on the ground of appearance of a set of peaks in photoluminescence spectra at lowered temperatures. Influence of growth conditions on density and radiation wavelength of quantum dot modes has been analyzed. Investigation of photoluminescence of samples as a function of temperatures has allowed determining activation energies of three channels of the losses that were attributed to different modes of quantum dots. (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