Radiation of the Plasma of a Transverse Discharge in a Helium–Krypton–Elegas Mixture

We carried out a spectroscopic investigation of the degradation of the active medium of a pulsed-periodic KrF emitter based on a He/Kr/SF₆ mixture (P = 10–150 kPa) with pumping by a transverse volumetric discharge. The plasma radiation spectra in the range 200–620 nm at different stages of degradation of the working mixture and the dynamics of the radiation of inert gases as well as of the products of decomposition of SF₆ molecules in the plasma are studied. It is shown that since the number of discharge pulses is 10⁴, rather effective formation of excited sulfur molecules is observed which decompose with emission in the spectral range 260–550 nm. This can be employed for developing a wideband lamp based on the system of KrF(B–X; D–X), S₂(B–X), and S₂(f–a) bands.     

The characteristics of a negative corona discharge in He/Xe/SF6 mixture

The results of investigation of the electrical and optical characteristics of a negative corona discharge in the electrode system of the type needle-grid lit in a He/Xe/SF₆ mixture under the pressure of 100–300 kPa are presented in this paper. The given medium is working for a pulse-periodic excimer lamp on = 351 nm XeF(B–X). Distributed on the length of a lamp active media a bipolar corona discharge is intended for using in the electric circulation of the XeF-lamp working medium. It is shown that the given discharge is ignited steadily in the He/Xe/SF₆ mixture, containing 0, 5kPa SF₆ molecules and is characterised by a low power consumption; the current of the discharge is limited to the development of instability by increasing the voltage on the needles; in hot zones of corona discharge SF₆ molecules cause the effective population 6s of XeI state.     

A Pulsed-Periodic, Low-Pressure Volume Discharge in Chlorine and in a Xenon/Chlorine Mixture

The electrical and optical characteristics of a self-initiated, low-pressure, pulsed-periodic discharge in chlorine and in a xenon/chlorine mixture are investigated. A volume discharge not bounded by dielectric walls was triggered in a spherical anode–plane cathode system of electrodes on supply of a constant positive-polarity voltage to the anode. The discharge existed in the form of a unit domain. The spatial, spectral (in the range 150–350 nm), and time characteristics (voltage, current, and photocurrent of total radiation of plasma in the spectral range 200–700 nm) of the volume discharge are investigated. Optimization of the pressure and of the structure of the working medium is carried out to obtain the maximum brightness of UV–VUV radiation of the bands of the Cl₂(D–A), Cl₂ ^**, and XeCl(D, B–X) molecules. The results obtained are of interest for being used in a pulsed-periodic, excimer-halogen low-pressure lamp.     

Multiwave Low‐Pressure Excimer Radiator

The excitation conditions and characteristics of a longitudinal glow discharge in a short tube of small diameter in Kr/Cl₂ and Ar/Kr/Cl₂ mixtures are investigated. It is shown that this discharge is a multiwave radiation source on systems of the 199/222/258 and 175/199/222/258 nm bands. Optimization of the pressure and composition of working mixtures most applicable for obtaining the approximately equal intensity of the ArCl(B X), KrCl(D, B X), and Cl₂(DA) radiation bands is carried out in the discharge investigated. A multiwave UVVUV radiation source is of interest for use in photometry, microelectronics, photochemistry, and medicine.     

UV Radiation Source Based on the Plasma of a Glow Discharge in a Mixture of Helium with Water Vapors

The results on the optical characteristics of the glow–discharge plasma in an He/H₂O mixture are presented. It has been established that it is a source of UV radiation in the region 306–315 nm (_max = 309.6 nm). Radiation lines of the atoms of hydrogen (H 486.1 nm and H 656.3 nm) and helium (491.1, 501.1, 587.6, and 667.8 nm) were recorded in the visible region of the spectrum; they can be used as diagnostic lines in measuring the parameters of this plasma (n _e, T _e) by the method of emission spectroscopy. The intensity of the UV bands and of the spectral lines HI and HeI have been optimized depending on the partial pressure of helium and the discharge current. The results obtained are of interest for the development of an ecologically pure source of UV radiation on the basis of chemiluminescence of water vapors in a longitudinal glow discharge.     

The characteristics of multiple-photon absorption of SF6 molecules cooled in free jet expansion from a pulsed supersonic nozzle

The multiple-photon absorption of pulsed TEA CO₂ laser radiation by SF₆ molecules cooled toT _R40K andT _v160K in the free jet expansion from a pulsed supersonic nozzle has been investigated at energy fluences of 0.1 to 3.0 J·cm^–2.For practically all laser lines which coincide with the linear absorption spectrum of thev ₃ vibrational mode of SF₆ [P(12)...P(28), 10,6 m], the dependence of the absorbed energyE _ab on the exciting energy fluence was found to be steeper than linearE _abⁿ, wheren=(1.1 to 1.8). Considerable increases of the absorption cross sections with increasing energy fluence were observed.The fraction of the molecules interacting with the laser radiation is estimated.     

Fine Structures of the Permittivity and Characteristic Losses of Electrons in Fluorite

Experimental-computational spectra of the permittivity and characteristic losses –Im^–1 for energies in the range 5–21 eV at a temperature of 4.2 K and theoretical spectra of and –Im^–1 of a fluorite crystal are resolved into elementary transition bands. The parameters of transition bands (energies of their maxima E _i, band halfwidths H _i and areas S _i, and oscillator forces f _i) are determined. A correlation of the spectral bands of and –Im^–1is established, and their specific features are elucidated.     

Self-diffusion in simple models: Systems with long-range jumps

We review some exact results for the motion of a tagged particle in simple models. Then, we study the density dependence of the self-diffusion coefficientD _N() in lattice systems with simple symmetric exclusion in which the particles can jump, with equal rates, to a set ofN neighboring sites. We obtain positive upper and lower bounds onF _N()=N{(1–)–[D_N()/D_N(0)]}/[(1–)]x for [0, 1]. Computer simulations for the square, triangular, and one-dimensional lattices suggest thatF _N becomes effectively independent ofN forN20.     

Electron kinetics in dc CF4 + O2 mixture discharge

The electron distribution function, transport coefficients and rate coefficients for the dissociation of CF₄ and the excitation of a¹ _g and b¹ _g ⁺ states of oxygen have been calculated for a CF₄ + O₂ mixture discharge. The two-term approximation was used in solving the electron Boltzmann equation. The influence of the dissociation was ignored, so that the results are parametric in the density reduced electric fieldE/N and the ratio of the mixture components. Only slight dependence of the calculated quantities on the composition of the gas mixture has been observed. The critical electric field for the onset of the discharge was found to beE/N=1.1–1.25 × 10^–15 Vcm² and it is weakly decreasing with growth of the oxygen content. With a small amount of oxygen added to CF₄ the electron distribution function and the mean kinetic energy remain practically unchanged.     

Influence of inert and molecular gas impurities on the lasing efficiency of a neon-hydrogen plasma laser operating at λ=585.3 nm He

A study has been made of the effect that inert and molecular gas impurities (He, Ar, Kr, Xe, N₂, CO₂) have on the lasing efficiency of a Penning plasma laser operating at =585.3 nm Hel in an Ne-H₂ mixture excited in a longitudinal discharge. The optimal compositions found for ternary mixtures can substantially increase the laser output parameters. The lasing power gain obtained in an Ne-H₂-Ar mixture is more than an order of magnitude higher than that in an Ne-H₂ mixture.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 54–59, April, 1996.     

Note on the interfacial tension of phase-separated polymer solutions

Earlier theoretical calculations of the interfacial tension of phase-separated polymer solutions as a function of the degree of polymerizationN and the temperatureT, based partly on the mean-field approximation, had led toN ^–1/4(1–T/T _c )^3/2 for fixedN1 andT approaching the critical solution temperatureT _c It is here remarked that the scaling procedure of de Gennes then modifies this toN ^–0.37(1–T/T _c )^1.26, which is in close accord with the experimentalN ^–0.44(1–T/T _c )^1.26. The simplest mean-field picture yieldsN ^–1/2(1–T/T _c )^3/2.     

Analytic study of power spectra of the tent maps near band-splitting transitions

Successive band-splitting transitions occur in the one-dimensional map x_i+1=g(x_i),i=0, 1, 2,... withg(x)=x, (0 x 1/2) –x +, (1/2 <x 1) as the parameter is changed from 2 to 1. The transition point fromN (=2ⁿ) bands to 2Nbands is given by=(2)^1/N (n=0, 1,2,...). The time-correlation function _i=x_ix₀/(x₀)²,x_i x_i–x_i is studied in terms of the eigenvalues and eigenfunctions of the Frobenius-Perron operator of the map. It is shown that, near the transition point=2, _i–[(10–42)/17] _i,0-[(102-8)/51]_i,1 + [(7 + 42)/17](–1)ⁱe^–yi, where2(–2) is the damping constant and vanishes at=2, representing the critical slowing-down. This critical phenomenon is in strong contrast to the topologically invariant quantities, such as the Lyapunov exponent, which do not exhibit any anomaly at=2. The asymptotic expression for _i has been obtained by deriving an analytic form of _i for a sequence of which accumulates to 2 from the above. Near the transition point=(2)^1/N, the damping constant of _i fori N is given by _N=2(^N-2)/N. Numerical calculation is also carried out for arbitrary a and is shown to be consistent with the analytic results.     

Statistical mechanics of the isothermal lane-emden equation

For classical point particles in a box with potential energy H^(N)=N ^–1(1/2) _ij=1 ^N V(x _i,x _j) we investigate the canonical ensemble for largeN. We prove that asN the correlation functions are determined by the global minima of a certain free energy functional. Locally the distribution of particles is given by a superposition of Poisson fields. We study the particular case =[–L, L] andV(x, y)=}- cos(x–y),L}>0, }>0.References     

Long-wave optical absorption in electron-bombarded GaAs

The absorption spectra of n- and p-type GaAs bombarded with 2-MeV electrons at T=300K were studied in the spectral range from 0.2 eV to Eg. It was found that shallow radiation-defect levels E_c – 0.01 eV and E_c + (0.06–0.1) eV were formed. The structureless character of the absorption in the region h < Eg in electron-bombarded gallium arsenide specimens was shown to be due to the distinctive features of photoionization of deep levels and the strong electron-phonon interaction in this material.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 93–97, July, 1981.     

Removal of NOx from NO2∶NO∶N2 mixture by a pulsed and dc streamer corona in a needle-to-plate reactor

The results of laboratory experiments on reduction of NO _x in the oxygen free gas mixture NO₂NON₂ simulating exhaust gas, by means of pulsed and dc streamer corona discharges generated in a needle-to-plate reactor have been presented. The results show that the dc corona discharge is more efficient in De-NO _x process than the pulsed corona discharge. This is in contrast to the results obtained in the wire-to-cylinder reactors where the pulsed corona discharge removes NO _x more efficiently. The results also lead to the conclusion that in the dc streamer corona discharge the short pulses and long interelectrode distances are recommended in order to increase the NO _x conversion rate.Presented at 17^th Symposium Plasma Physics and Technology, Prague, June 13–16, 1995.This work was financially supported by the Polish Academy of Sciences (projects IMP 3.1 and 3.3) and by the Polish Committee for Scientific Research (KBN Grant No. P40103304).     

Plasma radiation emitted by dense mixtures of rare gases excited by an electron beam and by a discharge

An experimental investigation was made of the radiation emitted from a plasma formed by rare gases (He, Ne, Ar, Kr, Xe) excited by a beam of electrons with different parameters and by discharge pulses (P= 0.1–0.5 atm, I=1 kA, U=10–15 kV, C=0.25 F). An investigation was made of the spectral composition and time characteristics of the radiation, and of their dependences on the excitation conditions. New molecular bands were observed in the near-ultraviolet and visible ranges. The uniquely large widths of these bands could be of interest in the amplification of light in a wide spectral range.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 56–73, January, 1992.     

Multiwave excimer lamps using XeF/XeCl/KrF/KrCl molecules

Results are presented of an investigation of the spectral and temporal characteristics of an electricdischarge excimer lamp emitting simultaneously on the 351 nm XeF, 308 nm XeCl, 249 nm KrF, and 222 nm KrCl transitions. The He/Kr/Xe/SF₆/HCl working mixtures were excited in a transverse discharge with ultraviolet spark preionization at a total pressure of 25–100 kPa. In order to obtain the same brightness the concentration ratio [Kr]/[Xe] for the excimer molecular transitions was 8/0.8 kPa, and that for the halogen-containing molecules was [SF₆]/[HCl][=[0.06–0.12]/[0.08–0.16] kPa. The duration of the radiation pulses for the excimer molecular transitions at atmospheric pressure was 100–200 ns and when the total mixture pressure was reduced to 250 kPa, this was doubled or trebled. The service life of the spontaneous radiation for B-X transitions in excimer molecules was 10⁵ pulses. Zh. Tekh. Fiz. 68, 64–67 (December 1998)