Showing papers on "Buffer gas published in 1984"

Ion–molecule association reactions: A study of the temperature dependence of the reaction N+⋅2+N2+M → N+⋅4+M for M=N2, Ne, and He: Experiment and theory

Abstract: The temperature dependence of the N+⋅2+N2 → N+⋅4 association has been investigated using a mass spectrometer source with coaxial electron entrance and ion exit apertures. The source resembles a miniature drift tube in that a small electric field is used to move the ions through the source. The effect of the field on the ion energy is discussed. Thermal reaction rate coefficients are obtained over the temperature range of 80 to 450 K, using He, Ne, and N2 as buffer gases. The experimental data reported here are compared with literature data as well as with the predictions of phase space theory calculations. Good agreement was found for the pure N2 system between the present results, previous experiments and theoretical calculations. Less good agreement was found between previous and present experiments when He was used as the buffer gas. In this case, the calculations tended to support the present results. The theoretical calculations also indicate a significant pressure dependence in the third‐order rate coefficient which may account at least in part for the discrepancy between results.

Electron-beam-controlled atomic Xe infrared laser

Abstract: A study was made of a high-power high-pressure electron-beam-controlled laser utilizing the 5d-6p and 7p-7s transitions of the Xe atom and having an active volume of 9 liters. The dependences were obtained of the electrical parameters of an electron-beam-controlled discharge and of the energy parameters and spectral composition of the output radiation on the type of buffer gas, the discharge circuit parameters, and the composition and pressure of the active mixture. When the medium was pumped by an electron beam alone, having a current density of ~ 6 A/cm2 and a pulse duration of O.7 μsec, the laser output energy was ~ 6/J (efficiency ~ 1.5%), but for electronbeam- controlled pumping it was roughly 20 J. The physical lasing efficiency, in terms of the electric field, was ~5%. An analysis was made of the mechanism of the establishment of the active medium conductivity and of the population kinetics of the active transition levels.

Procedure for creating an inert gas atmosphere with constant composition of nitrogen and carbon dioxide in a refrigerated container

Abstract: An inert gas atmosphere of nitrogen and carbon dioxide is created in a refrigerated container having a diesel engine. A lower oxygen content is maintained by an oxygen limit control while the nitrogen is led into the interior of the container from a gas bottle connected with the container when the predetermined oxygen limit value is exceeded. While the inert gases are being supplied, a constant flow of cold gaseous nitrogen is produced by an electrical evaporator in the liquid nitrogen storage tank and connected to the generator of the diesel engine while carbon dioxide is removed from the gas bottle, heated, released to a constant pressure and fed into the container via throttle points constituting a parallel-switched group of such throttle points which can be individually activated.

Shortening of electron conduction pulses by electron attachers O2, N2O, and CF4

Abstract: A uniform electron density is produced by two‐photon ionization of trace trimethylamine in the N2 buffer gas of atmospheric pressure using ArF laser photons. The transient conduction pulses induced by the electron motion between parallel electrodes under various applied electric fields are observed. The duration of the electron transient pulse is shortened when the electron attacher O2, N2O, or CF4 is added to the buffer gas. Electron attachment rate constants are obtained from the ratios of the transient current with and without attachers at various times after the laser pulses. For O2 and N2O, the electron attachment rate constants measured in this experiment agree with previous values measured by different methods. The apparent rate constants for the attachment of low‐energy electrons by CF4 are measured. The electron drift velocity is found to increase when CF4 is added to N2. The present method is applicable for the measurement of the electron attachment rate associated with the production of short‐lived negative ions.

The atmosphere of Mars - Resources for the exploration and settlement of Mars

Abstract: This paper describes methods of processing the Mars atmosphere to supply water, oxygen and buffer gas for a Mars base. Existing life support system technology is combined with innovative methods of water extraction, and buffer gas processing. The design may also be extended to incorporate an integrated greenhouse to supply food, oxygen and water recycling. It is found that the work required to supply one kilogram of an argon/nitrogen buffer gas is 9.4 kW-hr. To extract water from the dry Martian atmosphere can require up to 102.8 kW-hr per kilogram of water depending on the relative humidity of the air.

Characteristics of a wire preionized nitrogen laser with helium as buffer gas

Abstract: The operation of a small N2 laser using wire preionization and He as a buffer gas is discussed. The preionization is found to increase the output power and energy by 50% while the addition of helium can increase fourfold the output power.

Design Analysis of Rayleigh-Step Floating-Ring Seals

Abstract: The analysis and design of a 50-mm diameter floating-ring helium buffer seal are described. The seal rings incorporated Rayleigh-step lift pads to provide hydrodynamic forces to separate the rings from the shaft. Maximum surface speed is 183 m/s (600 fps) and maximum buffer gas pressure is 1389 kPa (200 psia). An operating range map was computed as a function of speed and pressure. Contradictory problems arise due to excessive friction preventing ring tracking at low-speed, high-pressure conditions and insufficent friction to retard inertia driven motions at high-speed, low-pressure conditions. Steady-state and dynamic analyses and performance are described, as well as the results of thermal studies.

The effects of wavelength, temperature, and trifluoromethane‐H buffer gas pressure on the infrared multiphoton decomposition of trifluoromethane‐D

Abstract: The isotopically selective infrared multiphoton dissociation of trifluoromethane‐d (CF3D) has been studied as a function of trifluoromethane‐h (CF3H) buffer gas pressure at three temperatures and two wavelengths. The measurements revealed that the isotopic selectivity in dissociation (ratio of probabilities of CF3D and CF3H dissociation) was high even under conditions where many collisions took place between CF3D and CF3H molecules during the laser pulse. For example, this selectivity was >220 under conditions where approximately 50 gas kinetic collisions would occur. It was also found that the laser fluence required to cause CF3D dissociation was a relatively slow function of collision number. The number of collisions at room temperature required to double the fluence required for dissociation, calculated assuming a simple threshold model for the dependence of yield on fluence, was ∼60 and ∼140, respectively, at the CO2 laser transitions R(26) and R(12). The implications of these results on economic production of deuterium are discussed.

Production of carbon fiber

Abstract: PURPOSE: To obtain a carbon fiber having high generation density and long fiber length, in high efficiency, by a vapor-phase process, by reacting a hydrocarbon at a specific temperature to effect the formation of fiber, and treating the fiber in an inert gas at a temperature within the ordinary fiber-forming temperature zone. CONSTITUTION: A hydrocarbon such as benzene is introduced together with a carrier medium (preferably hydrogen gas, etc.) into a reaction system, and made to react by heating at 650W950°C in the presence of a metal (compound) catalyst, and the produced carbon fiber is grown by the treatment with an inert gas such as N 2 gas or a mixture of an inert gas and an active gas at 1,000W1,300°C to obtain the objective fiber. The gas used in the growing process is preferably an inert gas or a mixture composed mainly of an inert gas. The metal (compound) catalyst is preferably a transition metal (compound) such as Fe, ferrocene, etc. COPYRIGHT: (C)1986,JPO&Japio

Thermal gas lens in a copper vapor laser

Abstract: A description is given of the method and results of investigations of a thermal gas lens in the active medium of a copper vapor laser. This medium exhibited defocusing properties, the focal length being inversely proportional to the buffer gas pressure and to the input power. The gas temperature in the discharge channel was estimated from the focal length.

High‐energy optically pumped iodine laser. I. Kinetics in an optically thick medium

Abstract: The operation of a high‐energy atomic iodine laser pumped by high‐intensity broadband radiation is described theoretically. Nonlinear transport of pump radiation into an optically thick medium is specifically taken into account. Integrodifferential formulations are made for both planar and cylindrical geometries. The model obtains the temporal and spatial dependences of the various chemical species, gas temperature, pump radiation, and stimulated emission in the laser medium. For an active gas of n‐C3F7I, relevant temperature‐dependent rate constants, absorption cross sections, and line‐broadening coefficients were selected after a critical review of the literature. The model is used to interpret recent laser experiments performed in the nonlinear regime using an intense (∼22 000 K) flash lamp to pump a n‐C3F7I medium with and without buffer gas. The theoretical results are in excellent agreement with the experimental measurements. The relative importance of the various kinetic processes is evaluated, and the spatial and temporal dependence in the optically thick medium is exhibited. Heating of the medium leads to major changes in the lasing kinetics. It is also observed that a gas‐dynamic perturbation wave from the flash‐lamp surface significantly limits laser output in some cases. Under some conditions this source drives a pyrolysis wave into the medium, but it is not strong enough to drive a faster photolysis wave.

Influence of the gas mixture composition and cathode material on the output power of a copper vapor laser

Abstract: The highest output powers and lasing efficiencies for self-heated active elements in copper vapor lasers, containing electrodes mounted in the high-temperature zone and employing a longitudinal discharge, were achieved using neon as the buffer gas and refractory metals as the cathode material. In this case the discharge on the cathode surface was localized in a spot of about 1 mm diameter, the cathode material had no influence on the discharge and lasing characteristics, and the lowering of the laser output power on increase in the neon pressure to 50-80 kPa was relatively slight. The addition of impurity gases with ionization potentials below that of neon reduced markedly the efficiency of the laser cycle.

Process for the separation of krypton from a radioactive waste gas mixture and arrangement for implementing the process

Abstract: A process for the separation of krypton from a radioactive waste gas mixt which is released during the chemical dissolution of burned-down nuclear fuel particles, and which in a carrier gas such as air, in addition to krypton, also contains xenon, argon, nitrous oxide and residual gas components. The waste gas mixture flowing out from a resolver has xenon removed therefrom after purifying the waste gas of nitrous oxides and radioactive residual gas components, such as aerosols, iodine, tritium and carbon(C-14) dioxide; and wherein krypton is finally withdrawn from the residual gas mixture and then stored. The invention also relates to an arrangement for the implementation of the inventive process. Subsequent to the purifying of the waste gas mixture from nitrous oxides and radioactive residual gas components, such as aerosols and iodine, a portion of the waste gas mixture is reconveyed into the resolver, and wherein the remaining portion of the waste gas mixture is purified of tritium and carbon(C-14) dioxide, and after an adsorptive removal of xenon discontinuously flows through a preparative gas chromatograph in which the krypton is separated from the residual gas. The remaining portion of the waste gas mixture is thereafter purified of tritium and carbon(C-14), which are removed in the form of HTO or, in essence, 14CO 2 , and thereafter adsorptively freed from xenon. The remaining waste gas mixture containing krypton is discontinously conveyed to a preparative gas chromatograph in which the krypton is separated from the residual gas.

A study of radiative and collisional decay of Pb atoms by time-resolved laser spectroscopy

Abstract: The 6p7s state of atomic Pb was populated by irradiation of Pb vapor by the frequency-doubled output of a pulsed nitrogen laser–pumped dye laser at the resonance wavelength λ = 2833 A, and the resulting fluorescent decay was monitored using the method of delayed coincidences. A least squares fit to the observed time-decay spectrum yielded the decay constant and gave the radiative lifetime of the state, τ = 5.85 ± 0.20 ns. The dependence of the decay constant on buffer gas pressures was also investigated, yielding the total depopulation (quenching) cross sections Q = 0.31 ± 0.10 A2 and 12.2 ± 1.0 A2 for collisions with H2 and N2, respectively. An upper limit (Q < 0.2 A2) for the He quenching cross section was also determined.

Dynamics of the optically pumped midinfrared NH 3 laser at high pump power - Part II: Raman gain and ac stark shifts

Abstract: Coherent effects produced by high-intensity pumping on aR (6, 0) in NH 3 are investigated for both the pure gas and for mixtures with an inert buffer gas. Two different Raman transitions are observed. One is the usual directly pumped Raman transition, and the other is pumped indirectly since it first requires a large population transfer to the upper vibrational level. This population transfer also creates inversion gain, shifted away from line center due to ac Stark shifts, on both transitions. Raman gain coefficients of 10 percent ċ cm-1and inversion gain coefficients > 2 percent ċ cm-1are observed, and compared to a combined density-matrix and rate-equation model.

Time-dependence study of radiation trapping by time-delayed two-photon absorption

Abstract: The transport of resonance radiation through an optically thick vapor of Sr atoms is studied. A pulsed dye laser tuned to the 461-nm resonance line excites a narrow (about 250-micron-diameter) column of Sr atoms along the axis of a cylindrical oven containing Sr vapor and Ar buffer gas. After a delay of no greater than 80 ns, a second dye laser excites the atom from the first excited state (5s5p) to a higher excited state (5s7s). The fluorescence from this latter transition is monitored as the second laser is translated parallel to the first. Since the excited-state-excited-state fluorescence is not trapped, the result is a plot of density of atoms in the 5s5p state as a function of position from the originally excited volume. The results are discussed qualitatively. 23 references.

Relaxation of the 4s2 2D5/2 metastable level of the copper atom in the afterglow of a pulsed discharge in a copper vapor laser

Abstract: The method of resonance absorption of the 510.6 nm line was used to determine the density n/sub m/ of the 4s/sup 2/ /sup 2/D/sub 5//sub ///sub 2/ metastable level of the copper atoms during the interpulse periods of a Cu laser, in the neon buffer gas pressure range of 10--50 kPa. At pressures exceeding 10 kPa an increase in n/sub m/ was observed (following rapid decay) over a period 5--10 ..mu..sec after the current pulse. A numerical solution of the problem of relaxation of the plasma parameters showed that the complex nature of the variation in n/sub m/ can be explained by a combination of a number of processes including recovery of the concentration of the copper atoms in the ground state and relaxation of the temperature and density of the electrons.

Effect of Na?Na spin-exchange collisions on spin relaxation of optically pumped Na in Xe gas

Abstract: We report the first detection of the effect of Na–Na spin exchange collisions on spin relaxation of optically pumped Na in Xe gas by studying the relaxation in the "dark" of the variable Sz in a mixture of dense sodium vapor (number density [Na] ~ 1013 cm−3), and buffer gas helium, xenon and nitrogen as a function of [Na] and xenon pressure

Xe2Cl fluorescence and absorption in self-sustained discharge XeCl lasers

Abstract: Fluorescence at 490 nm from the triatomic excimer Xe2Cl* has been investigated to determine the 308 nm absorption due to this species in an x-ray preionized, self-sustained gas discharge XeCl laser. The dependence of Xe2Cl* density on laser intensity (at 308 nm), buffer gas and Xe and HCl partial pressures has been determined for discharges with a peak electrical power deposition of 2.5 GWl−1. Xe2Cl* absorption is estimated to reach 0.6% cm−1 under non-lasing conditions but decreases to a non-saturable 0.2% cm−1 for intracavity laser intensity>1 MW cm−2. XeCl* and Xe2Cl* fluorescence intensities were found to be a similar for both helium and neon buffer gases but laser output was a factor of two greater with a neon buffer.

Investigation of the broadening of absorption lines of molecular gases by methods of pulsed laser diode spectroscopy

Abstract: A study was made of the use of middle-infrared pulsed laser diodes in investigations of the width and profile of absorption lines of molecular gases. Broadening of the absorption lines of CF2Cl2 and SF6 located in the region of 930 cm-1 was studied by correlation processing of the laser diode spectra. The coefficient representing the broadening of the CF2Cl2 lines in air depended on the buffer gas pressure and it increased from 5.7 to 12.9 MHz/Torr when this pressure was increased from 0 to 100 Torr. The broadening coefficient of the 32SF6 lines by helium was independent of the He pressure in the range 5-100 Torr and amounted to 6 MHz/Torr. The self-broadening coefficients of NH3 and CF2Cl2 were found to be 28.5 and 31.2 MHz/Torr.

Diffusion effects in inelastic processes involving excited atoms

Abstract: Atoms excited to their resonance states, in the presence of an inert buffer gas, undergo elastic and inelastic collisions with the buffer gas atoms or molecules, which affect the properties of the emitted resonance fluorescence. We describe a model which, in addition to the spontaneous radiative decay, also includes collisional quenching and excitation transfer as well as diffusion effects, and which may be employed to interpret the behavior of the atomic fluorescence in relation to buffer-gas pressure. The model, which is particularly useful for the description of 3-level systems including a metastable state, is used to interpret our own Stern-Volmer quenching data for Cd and Zn, as well as phase-shift measurements of the Cd (5 3 P 1 ) lifetime reported elsewhere.

Process for separating a mixed gas into oxygen and nitrogen under low temperature and low pressure conditions

Abstract: @ A process for separating a mixing gas into oxygen and nitrogen under low temperature and low pressure conditions which comprises introducing a mixed gas comprising chiefly oxygen and nitrogen into at least two adsorption towers, each packed with sodium faujasite typical of which is Na-X, at a temperature not higher than room temperature under conditions of an atmospheric pressure to 3 ata thereby causing the nitrogen in the mixed gas to be selectively adsorbed, collecting highly pure oxygen or an oxygen-enriched gas from the outlet of the adsorption towers, and reducing the pressure of the at least two adsorption towers, in which the nitrogen gas been adsorbed, to a level of from 0.08 to 0.5 ata, to cause the nitrogen gas to be desorbed and the sodiumfaujasite to be regenerated.

An efficient and compact discharge-excited XeCl laser

Abstract: The operational characteristics of a discharge-excited XeCl laser utilising a discrete element pulse-forming network (PFN) are reported. A pulse output energy of 0.6 J, an efficiency of approximately 2% and an energy extraction of 4.5 J litre-1 were recorded at a relatively low charging voltage. With neon buffer gas, pulses of 80 ns (FWHM) were measured.

Recombination in a Cu laser plasma with high buffer gas pressures

Abstract: It is shown that an increase in the volume of a copper vapor laser above a certain value must lead to a rise in the optimal buffer gas pressure. There is a corresponding change in the electron cooling mechanism (during the interpulse period) from diffusive to elastic cooling, and recombination processes involving three-body collisions in the plasma become important, setting the upper limit to the pressure and specific output energy of the laser. The results are given of a series of experiments and numerical calculations for a medium excited under these conditions by a transverse discharge.