The work is devoted to the study of a high-pressure short-arc xenon discharge, namely, its modeling taking into account the evaporation of thorium into the discharge volume with a different shape of the working surface of electrodes. The reason for the presence of thorium atoms in the discharge plasma is tungsten cathodes doped with thorium, which are used in high and ultrahigh pressure xenon arc light sources. The strong influence of thorium atoms and the shape of the electrode surface on the electrokinetic characteristics of plasma is shown, manifested in changes in the composition and spatial distribution of plasma particles, in particular, xenon and thorium ions, which also significantly affects the generation of optical radiation. The presented results allow us to obtain radiation mainly in the ultraviolet, visible and/or infra-red regions of the spectrum.

The dynamics of the structure of an infinite vortex tube in ideal gas under explosive external energy deposition near its axis is studied. With neglect of viscosity and heat conduction, it is discovered that the tube is destroyed under arbitrarily small power of energy release and the time of vortex destruction decreases as the total power of energy release increases. The physical model of the flow explaining the revealed relationships is constructed. The analytical relations assessing the problem parameters for the practical use of explosives in destruction of large-diameter vortices are obtained. The estimates show that the proposed method can be applied in practice.

The problem of the infinite vortex tube structure dynamics in an ideal gas with an explosive external supply of energy near its axis solution is considered. It was found that, neglecting viscosity and heat conductivity, the tube collapses at an arbitrarily low power of energy release, while the decay time of the vortex decreases with increasing total power of energy release. A physical flow pattern that explains the discovered patterns is constructed. Analytical relations for the practical use of explosives in the destruction of large-diameter vortices are obtained. Estimates show that the proposed method is practically feasible.

AbstractWe have studied a high- (ultrahigh-) pressure short-arc discharge in xenon with thoriated tungsten cathodes. A system of equations formulated based on earlier experimental data indicating possible emission of cathode material (thorium) into the discharge gap has made it possible to determine the electric field strength, plasma temperature, and concentration of thorium atoms as well as thorium and xenon ions in the plasma. The problem has been solved for a model discharge between planar electrodes. The results indicate the key role of thorium atoms in the cathode region. Thorium atoms determine the ionization balance and other electrokinetic properties of plasma. Emission of thorium atoms reduces the plasma temperature at the cathode, which turns out to be noticeably lower than the plasma temperature near the anode; this is a new result that agrees with experimental data. Other electrokinetic characteristics of the plasma (in particular, charged particle concentration and electric field strength) are also in good agreement with the experiment.

Впервые показано, что при изменении временных параметров возбуждающего импульса лазера (величина чирпа, длительность импульса и его амплитуда) можно управлять величиной и знаком эффекта " конденсации спектра" импульса на частоте резонансного перехода плотной резонансной среды.Важно отметить, что

For the first time, it is demonstrated that the magnitude and sign of the effect of spectral condensation of a laser pulse at the resonant-transition frequency of a dense medium can be controlled by changing the driving-pulse parameters (chirp, pulse width, and pulse amplitude). In the process of this, importantly, the driving-pulse energy and spectrum remain unchanged. Direct time-resolved measurements revealed an oscillatory character of the induced superradiance of rubidium vapors representing a long train of decaying short pulses. The width and repetition rate of the pulses in the train are determined by atomic density N-0 of the medium, while the width of an entire superradiance pulse (10 ps) is considerably larger than that of the driving laser pulse (50 fs).

Comparison of electronand photon-impact processes as a method for determination of photo-ionization cross sections is described, discussed and shown to have many attractive features. Keywords—Transition probability, cross section, photoionization, electron-ionization, multi-photon process.

Electronic spectra of the Xe2 molecules in the energy range of 77700–89300 cm −1 are recorded. The method of resonance enhanced multiphoton ionization of molecules in a supersonic molecular beam was used, in which excitation of the molecules by three photons was followed by ionization caused by a fourth photon (the (3+1) REMPI method). Analysis of the vibrational structure of observed systems of bands yielded information about the dissociation energy and the molecular constants for ungerade states of molecules. On the basis of the Franck-Condon principle, the equilibrium distances for potential curves were estimated from the relative intensities in vibrational progressions. Data on 16 new electronic states of diatomic xenon molecules with the dissociation limits Xe 2 * → XE(5 p 6 1 S 0 ) + Xe*(5 p 5 6 p ,5 d , 7 s , 7 p ) were obtained.

The excited electronic states of ArXe molecules in the region 77 000-80 200 cm(-1) were studied using the (2+1) and (3+1) resonance-enhanced multiphoton ionization methods. The use of different methods of multi-photon excitation and Ar+ ion registration allowed us to obtain some new data. Molecular constants were obtained for previously unknown excited states of molecules with the following dissociation limits: ArXe* -> (ArS0)-S-1+Xe*6p[5/2](3) with Omega = 2, 3 symmetry; (ArS0)-S-1+Xe*6p[3/2](2) with Omega = 1, 2 symmetry; (XeS1)-S-0 -> Xe*6s'[1/2](1)(0) with Omega = 0(+) symmetry.

The electronic spectra of ArXe molecules in the 80 300-89 500 cm(-1) region were recorded by (2 + n) and (3 + n) REMPI methods. The vibrational progressions attributed to transitions of molecules from the ground state to the bounded excited state and wide unstructured bands related to transitions to the continuous upper state were obtained. The molecular constants of ArXe* were calculated for all the observed progressions in the 80 300-87 000 cm(-1) region as an approximation of an anharmonic oscillator and the Morse potential. For different excited states the energy of harmonic oscillator and the dissociation energy are changed from 10 to 100 cm(-1) and from 70 to 750 cm(-1), respectively.

The electronic spectra of XeNe molecules in the range of 77100-90100 cm-1 are measured by the method of laser resonance multiphoton ionization in a supersonic jet. The photoionization spectra are obtained upon two- and three-photon excitations of molecules and their ionization by the next photon. In the range of 80300-90100 cm-1 near Xe*(5d, 6p’, 6d, 7s, and 7p), the spectra are obtained for the first time. A whole number of vibrational systems are measured in this range. The majority of vibrational systems near Xe* (5d, 6d, 7p, and 7s) are located in the red range with respect to their dissociation limits. In the blue range with respect to the dissociation limits, continua corresponding to transitions of molecules from the ground state to repulsive potential curves of excited states are detected. For a number of excited states of XeNe molecules, the vibrational analysis is performed and molecular constants are estimated.

The excitation cross-sections of the OH-radical band A(2) Sigma(+) -> X-2 (v' = 0 -> v '' = 0, v' = 1 -> v '' = 1) were measured. OH-radicals were formed during dissociation of water molecules by electron impact in the conditions of crossing of supersonic molecular and electron beams in the energy range 10-120 eV. Measurements were conducted at temperatures of 50, 80 and 200 K. It was shown that the excitation function had a sharp maximum in the region of low energies (at 16 eV) and an extended plateau up to 120 eV. It is proved that there are two channels of molecule dissociation with formation OH (A(2) Sigma(+)) through excitation of either the triplet b(3)A(1) or the singlet B(1)A(1) states of H2O molecules. The form of the excitation function essentially depends on the temperature of water vapours in the beam. With the decrease of the water molecule temperature the height of the plateau in the region 30-120 eV decreases in comparison with that of the peak at 16 eV. The absolute value of the excitation cross-section of the OH band at the temperature 50 K has been measured. It is equal to (1.6 +/- 0.5) x 10(-18) cm(2) in the maximum at 16 eV. The ratio of cross-sections of bands 1-1 and 0-0 weakly depends on the energy of the exciting electron in the range 12-120 eV and is equal to 0.28 +/- 0.05. The appearance threshold is equal to (9.1 +/- 0.5) eV.

Signals from ions forming in a supersonic molecular beam consisting of an argon-water vapor mixture are measured as functions of the exciting electron energy in the range to 120 eV. The thresholds of electron impact excitation of (H2O) n − 1H+ and Ar n (H2O m + clusters are determined for the first time. It is found that the proton-hydroxyl group binding energy decreases considerably both in the case of water molecule clustering and when mixed Ar n (H2O) m clusters arise.