Ar-Xe Mixtures Research Articles

Rapid ionization of Xe/Ar mixtures in nanosecond discharges exploiting post-pulse field reversals

Enhanced post-pulse electric field reversals of Ar, Xe, and XeAr mixture gases in capacitively coupled nanosecond discharges are investigated with Particle-In-Cell simulations in the context of maximizing electron density. The electric field reversal occurs at the falling edge of the voltage pulse and induces electron oscillatory movement in the plasma bulk region. The amplitude of field reversals is affected by driven voltage and the ratio of bulk length to gap distance. Exploiting the field reversal with a so called Plasma frequency dependent Square Wave (PSW) in an optimal gas mixture leads to the highest electron density. Specifically, for a 250 V PSW XeAr mixture case, the electron density is 2.2 times higher compared to a 1 kV DC pure Xe case even if the driven voltage is 4 times less than DC voltage. In 250 V PSW cases, XeAr mixture plasma has 1.2 times higher average electron density and 1.2 times electron temperature in the sheath region than a pure Xe plasma. With a narrower bulk region, the XeAr plasma has an enhanced field reversal and this leads to higher and faster growing electron density and electron temperature than a Xe plasma. For applications using Xe plasmas, XeAr mixture plasmas with PSW can be exploited for high electron density and temperature at reduced costs.

Emission of Noble Gases Binary Mixtures under Excitation by the Products of the 6Li (n, α)3 H Nuclear Reaction

The luminescence of Kr-Xe, Ar-Kr, and Ar-Xe mixtures was studied in the spectral range 300–970 nm when excited by 6Li (n, α)3 H nuclear reaction products in the core of a nuclear reactor. Lithium was deposited on walls of experimental cell in the form of a capillary-porous structure, which made it possible to measure up to a temperature of 730 K. The temperature dependence of the radiation intensity of noble gas atoms, alkali metals, and heteronuclear ionic noble gas molecules was studied. Also, as in the case of single-component gases, the appearance of lithium lines and impurities of sodium and potassium is associated with vaporization during the release of nuclear reaction products from the lithium layer. The excitation of lithium atoms occurs mainly as a result of the Penning process of lithium atoms on noble gas atoms in the 1s states and subsequent ion-molecular reactions. Simultaneous radiation at transitions of atoms of noble gases and lithium, heteronuclear ion molecules of noble gases allows us to increase the efficiency of direct conversion of nuclear energy into light.

Automated Cryogenic Unit for Xenon Extraction from Concentrated Mixtures

Recycling to recover Xe from its mixtures is proposed because of its shortage and high price. The simplest recycling scheme involves several consumers connected to a common centralized Xe enrichment and purification complex. However, such a scheme has limited applicability because it can cover only small regions. A versatile recycling scheme is based on deployment of a network of cryogenic separators operating in unison with rare-gas consumers. Such a solution can be implemented using fully automated units and remote control of their operation, possibly over the internet. Introduction into the rectification column of an intermediate gas, the boiling point of which is between those of the mixture components to be separated, is proposed to prevent Xe from freezing on contact with the low-temperature component. Control methods that ensure stable rectification of Ar–Xe mixtures in the presence of Kr as an intermediate are developed and tested.

VUV radiation of heteronuclear dimers and its amplification in the plasma of high-voltage nanosecond discharges initiated by runaway electrons in Ar–Xe mixture

Narrowband VUV radiation (near a wavelength of 147 nm), corresponding to the optical transition of a heteronuclear dimer ArXe*, was recorded from plasma formed during the excitation of an Ar–Xe mixture at a pressure of 400 mbar by a high-voltage nanosecond discharge initiated by runaway electrons. Amplifying properties of the discharge plasma related to this radiation were found.

An accelerated discrete velocity method for flows of rarefied ternary gas mixtures in long rectangular channels

An accelerated discrete velocity method is presented for rarefied three-component gas mixtures flowing through long rectangular ducts. The scheme is developed on the basis of the McCormack linearized kinetic model. Diffusion equations are derived for the velocity and the heat flow vector. The kinetic and diffusion equations are solved in a coupled iteration. Simulations are carried out for He–Ar–Xe mixture to test the computational performance of the scheme for pressure driven flow. It is shown that the accelerated method requires a fewer number of iterations and smaller computational time in a large part of the gas rarefaction from the transition region to the hydrodynamic limit than the non-accelerated one. These quantities are studied as a function of the convergence parameter also. The flow rates as a function of the rarefaction parameter and representative velocity profiles are shown. A good agreement is found between the total flow rate and the corresponding slip flow value at large rarefaction parameters. The present approach can be useful for fast computation of flows of ternary gas mixtures in long rectangular channels.

Heat transfer in ternary rarefied gas mixtures between two parallel plates

An approach is presented to calculate the heat transfer problem in ternary rarefied gas mixtures between two parallel plates. The study is based on the McCormack linearized kinetic model, which is solved by the discrete velocity method. The heat flux is determined and tabulated for He–Ar–Xe and Ne–Ar–Xe mixtures in a wide range of the gas rarefaction at various values of the mole-fractions by using the experimental potential. Results with the hard-sphere model are also delivered for the first mixture. The heat flux is sensitive to the mole-fractions and the intermolecular potential. Representative distributions of the perturbations of the density and the temperature of the components are shown. The results indicate that the deduction of the heat flux should be based on the full treatment of the three component gas mixture.

ВУФ-излучение гетероядерных димеров и его усиление в плазме высоковольтного наносекундного разряда, инициируемого убегающими электронами, в смеси Ar-Xe

ВУФ-излучение гетероядерных димеров и его усиление в плазме высоковольтного наносекундного разряда, инициируемого убегающими электронами, в смеси Ar-Xe

A fast iterative discrete velocity method for ternary gas mixtures flowing through long tubes

An accelerated discrete velocity method is presented for flows of three-component gas mixtures through long tubes. The gas is modeled by the McCormack linearized kinetic equation. Two diffusion equations are derived from the kinetic one. These equations are solved during the kinetic iteration by a linear algebraic approach. Test simulations are performed for flows of He–Ar–Xe mixture driven by pressure or temperature gradients in a wide range of the gas rarefaction. The accelerated method requires fewer number of iterations and smaller computational times than the non-accelerated one in the early transition, slip and near-hydrodynamic domains. The efficiency of the accelerated scheme compared to the standard one increases with increasing rarefaction parameter. The computational performance in terms of the iteration criterion is also analyzed. In typical simulations, the convergent results can be reached in approximately less than two minutes by using the new method in a wide range of the gas rarefaction on a present-day computer.

Viscous velocity, diffusion and thermal slip coefficients for ternary gas mixtures

An approach is presented to determine the viscous velocity, diffusion and thermal slip coefficients for three-component gaseous mixtures. The gas is described by the McCormack linearized kinetic model. It is shown that two diffusion slip coefficients exist for a ternary mixture. The boundary problem is solved by the discrete velocity method. The slip coefficients are calculated and tabulated for He–Ar–Xe mixture at various values of the mole fractions for the hard-sphere and experimental potentials. It has been found that the diffusion and thermal slip coefficients are more sensitive to the interaction potential than the viscous one. Representative velocity profiles of the Knudsen layer are also shown. Furthermore, a test calculation is presented for pressure and mole fraction driven flows in a tube. The flow rates obtained by the slip solution are compared to the kinetic results. It is revealed that the slip flow approximation provides a relatively good estimation of the flow rates at higher rarefaction parameters. The present methodology and the tabulated data can be useful to determine the gaseous flow in the slip region for the ternary mixture.

Intense infrared scintillation of liquid Ar-Xe mixtures

Intense infrared (IR) light emission from liquid Ar-Xe mixtures has been observed using 12 keV electron-beam excitation. The emission peaks at a wavelength of and the half-width of the emission band is . Maximum intensity has been found for a 10 ppm xenon admixture in liquid argon. The conversion efficiency of electron-beam power to IR light is about 1% (10000 photons per MeV electron energy deposited). A possible application of this intense IR emission for a new particle discrimination concept in liquid noble gas detectors is discussed. No light emission was found for perfectly purified liquid argon in the wavelength range from 0.5 to on the current level of sensitivity.

Isothermal flows of rarefied ternary gas mixtures in long tubes

A method is presented to determine isothermal flows of three-component rarefied gaseous mixtures in long tubes. The flow is subject to arbitrary but small local density gradients, when linearization can be applied. The mixture is described by the McCormack kinetic model, which is solved by discretizing the spatial and velocity spaces. Results are presented for the realistic and hard-sphere molecular interactions. The dimensionless kinetic coefficients are presented and commented for He–Ar–Xe mixture in a wide range of the rarefaction and numerous values of the mole fractions. The velocity profiles of the components are also shown. An additional method is also developed to solve the flow problem of the mixture driven by a global pressure difference between the two ends of the tube. The flow rates and the distributions of the mole fractions and the pressure along the axis of the tube are presented for pressure-driven flows of He–Ar–Xe mixture. The flow of the ternary mixture exhibits the separation phenomenon. The profiles of the mole fractions are non-uniform.

High-order harmonic generation from Xe–Ar gas mixture in the tight focusing laser

Abstract We report on the harmonics radiation and spectrum properties in the Xe–Ar gas mixture by using tight focusing laser pulses. The cutoff position is extended from the harmonic H33–H37 in mixed gases. The extended orders are attributed to the harmonic radiation from Xe+. We observe that the harmonics are decreased in the plateau region. The result is attributed to the destructive interference of the harmonics generated from the different atoms. Our results suggest that using the Xe–Ar mixture as nonlinear can obtain the coherent XUV source.

Density-induced modifications of the IR emission spectrum of Xe2 excimers in dense gas

The infrared emission spectrum of Xe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> excimers produced by irradiating Xe gas with high-energy electrons has been monitored as a function of density up to 3.3 MPa at room temperature. Excimer decay yields a broad continuum centered around 7800 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> of width 900 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> at 0.1 MPa. The spectrum shape is consistent with a bound-free molecular transition between 0 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">u</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> and 0 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> states correlated with 6p and 6s atomic limits. Upon increasing density, the spectrum is strongly red-shifted and broadened. The present measurements confirm preliminary results obtained in a smaller density range. The shift is explained by the dielectric screening exerted by the gas atoms on the optically active electron-ionic molecular core interaction, and by quantum multiple scattering effects of the electron scattered off the gas atoms. The latter effect links this experiment to electron transport experiments in non-polar gases. The different spectrum broadening in pure Xe and in an Ar-Xe mixture is believed to be due to quantum indistinguishability of identical particles.

Performance of Argon-Xenon Mixtures in a Gas Proportional Scintillation Counter for the 0.1–10 keV X-Ray Region

The performance of a gas proportional scintillation counter filled with either pure Xe or Ar-Xe mixtures is described for the 0.1-10 keV X-ray energy range. It is shown that the spectra tail distortion exhibited by Xe filled gaseous detectors for soft X-rays below 2 keV is reduced if Ar-Xe mixtures are used. The peak-to-valley ratio increases by a factor of about 2 or 3 as the Xe concentration is reduced from 100% to 5%. Moreover, the energy resolutions for such mixtures are similar to the ones for pure Xe.

Ar–Xe mixtures and their use in curved grid gas proportional scintillation counters for X-rays

An experimental study of the scintillation properties of Ar–Xe mixtures has been carried out with a gas proportional scintillation counter instrumented with a photomultiplier tube. Energy resolutions of 7.7, 7.8, 7.8, 8.3, 8.5, 9.1 and 11.5% were obtained for 5.9 keV X-rays respectively for the 100% Xe, 60%Ar–40%Xe, 80%Ar–20%Xe, 90%Ar–10%Xe, 95%Ar–5%Xe, 97%Ar–3%Xe and 99%Ar–1%Xe mixtures at 800 Torr. Thresholds for scintillation and ionization were also determined. The performance of Ar–Xe mixtures as detection media in large detection area applications has been studied for a 52 mm diameter photomultiplier and a 38 mm diameter radiation window. The curved grid technique was used to minimize spectra distortion due to solid angle effects.

Experimental Study of the $w$-Values and Fano Factors of Gaseous Xenon and Ar-Xe Mixtures for X-Rays

An experimental study of the w -values and Fano factors for Ar-Xe gaseous mixtures at atmospheric pressures for 5.895 keV X-rays was carried out with two experimental set-ups based on gas proportional scintillation counter techniques. For the 100% Xe, Ar-40% Xe, Ar-20% Xe and Ar-10% Xe mixtures at 800 Torr the measured w-values were 21.61 eV, 21.63 eV, 21.64 eV and 21.42 eV, respectively, within an accuracy of plusmn0.21 eV. For the same mixtures the Fano factors were 0.254, 0.258, 0.250 and 0.256, respectively, within an accuracy of about plusmn0.004. For lower Xe concentrations of 5%, 3% and 1% the Fano factors were ap0.24, ap0.23 and ap0.22, respectively. These experimental results are compared with those available in the literature.

Environmental influence on the IR fluorescence of Xe2* molecules in electron beam excited Ar–Xe mixture at high density

We report new measurements of the near infrared (NIR) Xe$_2^*$ excimer fluorescence in an electron--beam--excited Ar (90%)--Xe (10 %) mixture at room temperature. Previous measurements up to a density $N\approx 2\times 10^{26}$ m$^{-3}$ discovered a broad excimer fluorescence band at $\approx 7800$ cm$^{-1},$ whose center is red--shifted by increasing $N$ (A. F. Borghesani, G. Bressi, G. Carugno, E. Conti, and D. Iannuzzi, {\em J. Chem. Phys.}, {\bf 115}, 6042 (2001)). The shift has been explained by assuming that the energy of the optical active electron in the molecule is shifted by the density--dependent Fermi shift and by accounting for the solvation effect due to the environment. We have extended the density range up to $N\approx 6\times 10^{26}$ m$^{-3}, $ confirming the previous measurements and extending the validity of the interpretative model. A detailed analysis of the width of the fluorescence band gives a value of 2.85 nm for the size of the investigated excimer state. Such a large value lends credence to the validity of the proposed explanation of the experimental findings.

Pulsed volume discharge in a nonuniform electric field at a high pressure and the short leading edge of a voltage pulse

It is shown that a volume discharge is formed in a nonuniform electric field for the short leading edge of a voltage pulse and nanosecond pulse duration without any additional preionisation source in various gases at pressures higher than atmospheric (6 atm in helium and 3 atm in nitrogen). Lasing at atomic transitions in Xe is obtained in an Ar—Xe mixture under a pressure of 1.2 atm for an active length of 1.5 cm. A record-high specific power input (more than 0.8 GW cm-3 under a pressure 1 atm in air) is realised in the volume discharge stage. The volume discharge is formed due to preionisation of the discharge gap by fast electrons accelerated due to amplification of the electric field in the cathode region and in the gap. In a nonuniform electric field, volume discharge is realised under a quasistationary voltage from 10 to 180 kV across the gap, at a pulse repetition rate of up to 160 Hz and for various discharge gap geometries.

Distinct Diffusion in Binary Mixtures Confined in Slit Graphite Pores

Distinct diffusion coefficients in the barycentric reference frame for equimolar binary mixtures confined in slit-shaped graphite pores have been evaluated using equilibrium molecular dynamics simulations. In all mixtures the ratio of the interaction energies and mass ratios are similar to those of a Xe-Ar mixture with $\sigma_{22}/\sigma_{11}$ varied between 1 and 1.4. When $\sigma_{22}/\sigma_{11}$ = 1.0 both species adsorb in similar layers in the pore and the distinct diffusion is positive. As $\sigma_{22}/\sigma_{11}$ is increased, the distinct diffusion is found to become progressively more negative. This increasing associative tendency as $\sigma_{22}/\sigma_{11}$ is increased is predominantly due to the formation of distinct layers by individual species. In-plane pair correlation functions also reveal the increased association between unlike species with increasing $\sigma_{22}/\sigma_{11}.$ The Xe-Ar mixture is observed to be associative, with negative values of the distinct diffusion when the fluid forms two layers in the pore. At smaller pore widths, where only a single layer is accommodated, the mixture is weakly dissociative. Simulations with a non-Lorentz- Berthelot mixture were carried out to illustrate the effect of the interaction between unlike species.

Complete optimisation of an electron-beam-pumped Xe laser emitting at 1.73, 2.03, 2.65, 2.63, 3.37, and 3.51 μm

The results of complete numerical optimisation of an electron-beam-pumped Xe laser emitting at 1.73, 2.03, 2.65, 2.63, 3.37, and 3.51 μm are presented. At all these wavelengths, the best output parameters are achieved in the Ar—Xe mixture. The maximum lasing efficiency (4.5 %) and the highest specific energy output (19 J L-1) are obtained at a wavelength of 1.73 μm. For wavelengths 2.03, 2.65, 2.63, 3.37, and 3.51 μm, the maximum efficiencies were 2 %, 1.7 %, 1.2 %, 0.6 % and 0.48 %, respectively. These maximum values of output characteristics in the Ar—Xe mixture can be obtained in a certain range of operating parameters.