Argon-xenon Mixtures Research Articles

Performance enhancement of an argon-based propellant in a Hall thruster

Finding alternatives to xenon as a propellant is essential for reducing the launching cost of all-electric satellites and for achieving low-cost electric propulsion, especially using Hall thrusters. Argon is a candidate as such a low-cost propellant, but it has never been used practically owing to its poor performance. We attempted two methods to improve the thruster performance: (1) by mixing xenon in argon propellant and (2) by modifying the thruster structure for the argon propellant. Modifying the thruster structure yielded an increase in the specific impulse from 482 to 1500 s using pure argon. Also, when we used an argon-xenon mixture gas as propellant, the thruster performance increased under argon-rich conditions using the modified thruster.

Attenuation of vacuum ultraviolet light in pure and xenon-doped liquid argon —An approach to an assignment of the near-infrared emission from the mixture

Results of transmission experiments of vacuum ultraviolet light through a 11.6 cm long cell filled with pure and xenon-doped liquid argon are described. Pure liquid argon shows no attenuation down to the experimental short-wavelength cut-off at 118 nm. Based on a conservative approach, a lower limit of 1.10 m for the attenuation length of its own scintillation light could be derived. Adding xenon to liquid argon at concentrations on the order of parts per million leads to strong xenon-related absorption features which are used for a tentative assignment of the recently found near-infrared emission observed in electron-beam excited liquid argon-xenon mixtures. Two of the three absorption features can be explained by perturbed xenon transitions and the third one by a trapped exciton (Wannier-Mott) impurity state. A calibration curve connecting the equivalent width of the absorption line at 140 nm with xenon concentration is provided.

Performance of a gas electroluminescence x-ray detector filled with an argon-xenon mixture

The performance characteristics of a gas electroluminescence X-ray detector (DELG) filled with an Ar + Xe mixture in a range of Xe concentrations of 5–100% were investigated. For a mixture of 80% Ar + 20% Xe, an improvement of the energy resolution is observed with an increase in the gaseous-mixture pres-sure. The best result obtained at a pressure of 3 atm is 7.25% (MnKα, 5.9 eV), which is higher than the data known from the literature by 0.5%. The peak/valley parameter for the same mixture amounts to a value of 650 for an energy of 5.9 keV compared to a value of 200 for pure Xe. The energy resolution of the DELG is suitable for use in X-ray diffractometry for effective suppression of Kβ lines of characteristic radiation of the main anodes of X-ray tubes.

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.

Application of the microhole and strip plate detector for neutron detection

We introduce the microhole and strip plate (MHSP) detector as a micropattern detector for the detection of thermal and epithermal neutrons. Detection sensitivity is obtained by filling these detectors with /sup 3/He at high pressures. We propose the use of argon-xenon penning mixtures as the stopping gas as opposed to the usual carbon based stopping gases. These argon-xenon mixtures provide suitable gas gains for the high pressure/high resolution neutron detector applications. With these mixtures it is possible to obtain a sealed detector with only rare-gas filling which is simple to purify and not subject to ageing. An MHSP gas detector filled with a 3-bar argon/50-mbar xenon/6-bar helium mixture can achieve gains above 2/spl times/10/sup 3/. This mixture allows neutron detection efficiencies of about 70% at 1 /spl Aring/ for a 2.5-cm thick absorption region and intrinsic position resolution (full-width at half-maximum) of about 1.8 mm. The sensitivity to /spl gamma/-rays of the present mixture will be the same when compared to that of 2.6-bar CF/sub 4/.

Noble-gas operation of Micro-Hole and Strip Plate electron multipliers at atmospheric-to-high pressures

We present the performance of a Micro-Hole and Strip Plate (MHSP) electron multiplier in argon–xenon mixtures, at pressures of 1–7 bar. This microstructure can operate at high pressures without significant reduction of the maximum achievable gain. Absolute gains of 1–4×10 3 were reached in Ar/50 mbar Xe over this pressure range; the maximum gain is imposed by the discharge limit, dropping at higher pressures. Energy resolutions between 14% and 16% were reached for 6 keV X-rays; they do not degrade significantly with increasing pressure. Better performances are expected by improved manufacturing of the MHSP.

The performance of the GPSC/MSGC hybrid detector with neon-xenon gas mixtures

The performance for X-ray spectrometry of neon-xenon gas proportional scintillation counters using a CsI-coated microstrip plate in direct contact with the scintillation gas as a VUV photosensor is investigated for different neon-xenon mixtures. At best operation conditions, the detector gain can reach values about 50% higher than those achieved with pure xenon filling. The highest gains and the best energy resolutions are achieved for xenon contents around 40%. However, the achieved energy resolutions are similar to those achieved with pure xenon. As in pure xenon and argon-xenon mixture gas fillings, the detector performance is limited by optical positive feedback resulting from additional scintillation produced in the electron avalanche processes around the MSP anodes. The best energy resolutions are achieved for positive feedback gains in the range of 1.1 to 1.2. The performance achieved with neon-xenon mixtures is inferior to that achieved with argon-xenon mixtures.

Interaction-induced absorption in liquid argon–xenon mixture cluster: MD simulation

When two dissimilar rare gas atoms interact, a dipole moment is generated, due to mutual distortion of the atomic charge clouds. The many-body time-correlation functions and interaction-induced spectra for the small cluster composed of binary argon–xenon Ar 13Xe 6 mixture in the liquid phase have been calculated using molecular dynamic simulation.

The performance of the GPSC/MSGC hybrid detector with argon-xenon gas mixtures

The performance for X-ray spectrometry of argon-xenon gas proportional scintillation counters (GPSCs) using a CsI-coated microstrip plate in direct contact with the scintillation gas as a vacuum ultraviolet photosensor is investigated for different argon-xenon mixtures. The GPSC/microstrip gas chamber hybrid detectors filled with argon-xenon mixtures present superior performance when compared to those with pure argon and pure xenon fillings. For these mixtures, the signal amplification due to the scintillation processes and the detector energy resolution may achieve values of 15-18 and 11-10%, respectively. The best energy resolutions can be achieved for mixtures with a broad range of xenon concentration, 20-70% Xe, and for lower reduced electric fields in the scintillation region as the xenon concentration is reduced. As in pure argon or pure xenon gas-filling, the detector performance is limited by optical positive feedback resulting from additional scintillation produced in the electron avalanche processes around the microstrip plate anodes. The best energy resolutions are achieved for positive feedback gains of about 1.1.

Two-fluid computational model for a binary gas mixture

This work is devoted to the derivation of moment equations for the description of a gasdynamic flow of a binary non-reacting gas mixture. The equations are based on the kinetic model in a relaxation approximation and they are a generalization of the quasigasdynamic equations studied before. As an example of applicability of the system proposed, we present calculations of flows in a shock wave for an argon-xenon mixture and of a binary diffusion problem for argon and helium, in comparison with the results of modeling these problems using the Direct Simulation Monte-Carlo method. A comparison with experimental results is also presented.

A Comprehensive Approach to Critical Phenomena and Phase Transitions in Binary Mixtures

The hierarchical reference theory of fluids (HRT) combines a first-principles description of the system from the knowledge of the microscopic interaction with some of the basic concepts of the renormalization group. The application of HRT to binary mixtures has provided a theoretical justification of the critical behavior predicted by the phenomenological approach. Moreover, the reason for the strong crossovers that make it difficult to detect experimentally the asymptotic critical regime has been attributed to the competition between two different fixed points. On the basis of this analysis, the most favorable conditions that lead to an enhancement of the asymptotic region are identified: mixtures close to a change in the topology of the phase diagram are good candidates for the direct experimental observation of features like the renormalization of the critical exponents or the weak divergence of the isothermal compressibility. This theory gives information not only on critical phenomena but it is able to treat the full phase diagram in the fluid region and the static correlation functions at long as well as at short distances. Some predictions for the phase diagram and the structure factors of an argon-xenon mixture are shown.

Attenuation length measurements of scintillation light in liquid rare gases and their mixtures using an improved reflection suppresser

The attenuation lengths for scintillation photons in liquid argon, krypton, xenon, argon-xenon (3%) mixture, and krypton-xenon (3%) mixture, have been measured by using a newly designed reflection suppresser. The obtained values are 66±3 cm for argon, 82±4 cm for krypton, 29±2 cm for xenon, 170±23 cm (first experiment) and 118±10 cm (second experiment) for argon-xenon (3%) mixture, and 136±11 cm for krypton-xenon (3%) mixture. The reason why the attenuation lengths in the mixtures are longer than those in the pure liquids is attributed to the reduced Rayleigh scattering in the mixtures.

Low temperature ultrasonic properties of vapour condensed films of argon-xenon mixtures

Using surface acoustic waves we have studied the elastic properties of thin solid films of pure Argon and Xenon and of Ar−Xe mixtures condensed at 4.4 K. From our results we conclude that in all samples low energy excitations are present. They give rise to a relaxation absorption and to related changes of the sound velocity. An important difference to conventional glasses is, that even below Helium temperatures relaxation occurs not only via tunneling but also via thermally activated processes. The density of states of the low energy excitations is comparable to that of vitreous silica and increases continually with Xenon concentration.

A study of an electron-beam excited atomic xenon laser at high energy loading

Operation of an electron-beam excited atomic xenon laser was investigated at pump rates between 40 W/cm/sup 3/ and 1 kW/cm/sup 3/ with pump times of 1 ms. Effects of cavity loss, gas mixture, and pump rate on laser performance were studied under selected conditions. The variation in laser power in 99.5% argon and 0.5% xenon selectively lasing at 1.73 or 2.6 mu m was investigated as a function of pump power. It was found that the laser pulsewidth was shorter than the pump pulse and increased as the pump rate decreased, consistent with a temperature-induced effect. Lasing with broadband optics was investigated as the xenon concentration was varied and as helium or neon was combined with argon-xenon mixtures. Strong lasing was observed for xenon concentrations up to 20%. Addition of helium resulted in a slight increase in laser pulsewidth and caused lasing at 2.03 mu m to increase at the expense of lasing at 1.73 and 2.6 mu m.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A 650 J e-beam-pumped atomic xenon laser

The atomic xenon laser has been scaled from the 80-J per pulse output-energy level reported by N.G. Basov et al. (1986) to 650 J using a large two-sided e-beam-pumped device. The extraction volume dimensions were 0.5 m*0.65*3 m. The gas was pumped at a temporally and spatially averaged rate of 70 kW/cm/sup 3/, and the spatially averaged specific input energy was 115 J/L. Output-energy measurements were made with a full-aperture calorimeter, and the temporal pulse shape of the 1.73- mu m laser radiation was recorded with a spectrally filtered germanium photodiode. The device was operated with argon-xenon gas mixtures at pressures ranging from 20 to 40 psia at a temperature of 23 degrees C, and the xenon mole fraction was empirically optimized. The maximum output energy of 650 J was obtained at an intrinsic efficiency (output energy divided by energy deposited to gas) of 0.57%. A higher efficiency of 0.85% was achieved by using a shorter e-beam pulse, at a reduced laser output energy of 495 J. A possible explanation for the observed laser pulse shape is given.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

High-pressure infrared xenon laser with X-ray preionization

The first experimental results are presented of an X-ray preionized argon-buffered xenon laser. The X-rays are generated by a simple electron-beam device located below the 23-cm inner diameter laser chamber. The advantages of X-ray preionization for high-pressure discharge-pumped lasers include the long X-ray penetration depth, high preionization density, and spatial uniformity. The combination of X-ray preionization and techniques to eliminate surface flashover allows energetic operation in 4 atm of argon buffer for the first time in a photopreionized discharge laser. The argon-xenon mixtures lased primarily at 1.73 mu m and 2.63 mu m with a peak energy of 340 mJ at 4 atm, and a specific energy output of 0.85 J/liter.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

X- ray diffraction of krypton and xenon mixtures adsorbed on graphite

Mixtures of xenon and krypton adsorbed on graphite at 45 K are studied by X ray diffraction. Two kinds of incommensurate and one kind of commensurate solids were observed The coexistence of each incommensurate with the commensurate structure indicates first order C - I transitions. Diffraction spectra with low coverage (about 0.1) show that small platelets are first covered and that they favour an incommensurate solid The limit of the incommensurate xenon-like structure seems inconsistent with results on an argon-xenon mixture. Explanation could be a less ordered structure for the latter mixture.

Equation of state of an equimolar dense argon and xenon mixture

The density of an equimolar dense argon-xenon mixture has been measured at 25°C and up to 8000 bar. A constant-volume method is used. The representation of the interactions by a Lennard-Jones-type potential is discussed.

Spectroscopic and kinetic analysis of the VUV emissions of argon and argon-xenon mixtures. II. Energy transfer in Ar-Xe mixtures

For pt.I see ibid., vol.15, p.2935 (1982). Spectroscopic and kinetic study of ultraviolet emissions from argon-xenon mixtures brings to light very large energy transfers from argon and xenon. When small amounts of xenon (a few ppm) are added to argon, the argon continua disappear and simultaneously Xe resonance lines can be seen. At higher Xe concentrations (of the order of a few per cent), the spectra of mixtures are similar to those obtained in pure xenon. Kinetic analysis of the main VUV emissions of the two gases allows a complete kinetic scheme of the transfer phenomena to be established. Excited radiative xenon states are created from Ar2* molecules and atomic precursor states. The 1P1 state of xenon is excited by two-body collisions with the excimer Ar2*(3 Sigma u+) which is responsible for the second argon continuum (k=1.5*107 Torr-1 s-1). The transfer is also observed from the Ar*(3P1) state towards highly excited xenon levels (configuration 5f) (k=2.4*107 Torr-1 s-1). Both these paths lead, directly or indirectly, to the production of the 3P1 and 3P2 states of xenon which, through three-body heteronuclear collisions, are involved in the formation of the radiative Xe2* states responsible for the emission of the second continuum at 173 nm. The lifetime of this state, tau =106 ns, is not modified by the presence of argon.

Spectroscopic and kinetic analysis of the VUV emissions of argon and argon-xenon mixtures. I. Study of pure argon

The VUV luminescence spectra of argon excited by alpha particles at a few hundred Torr present two continua, at 180 and 127 nm. The 127 nm emission is very intense, it corresponds to transitions from the lowest vibrational levels of the A 1y(3 Sigma u+) and B Ou+(1 Sigma u+) states of Ar2 towards the dissociative X Og+(1 Sigma g+) ground state. The shape of the pulse corresponding to the emission of the second continuum was reconstituted by time amplitude conversion. Three exponential terms can be seen. The variation of the time constants with pressure allows a kinetic scheme for the formation and decay of the radiative molecule species to be established. The excited states of the argon molecule are created by three-body collisions, from the (1)()J=1 and (1)()J=2 states of the 3p54s configuration, the collision constants being 1.6 and 13.8 Torr-2 s-1 respectively. The radiative lifetime of the A 1u(3 Sigma u+) state is 2.86 mu s.