Dynamics and correlated performance of a photo-triggered discharge-pumped HF laser using SF6 with hydrogen or ethane

3 , has been performed in Ne/SF₆/H₂ and Ne/SF₆/C₂H₆ mixtures. Parameters involved have been the storage line capacitance and the circuit inductance, the capacitors charging voltage, the RH-molecule type and partial pressure, and the X-ray dose for the preionization. High laser performance has been achieved with C₂H₆: an output energy up to 3 J corresponding to a specific energy of 9.6 J/l at an efficiency of 4.7%, which strengthens the advantage of the photo-triggering technique to energize high-power HF lasers. However the optimum performance achieved with H₂, 5.75 J/l and 3.5%, are lower. It is shown, through a time-resolved study of the electrical discharge and spatial dynamics correlated to laser power and energy measurements, that discharge instabilities are responsible for the poor laser performance of the mixture with H₂. These instabilities, which lead to arc development, are characteristics of the discharge in Ne/SF₆. It is demonstrated for the first time that addition of a heavy hydrocarbon, such as C₂H₆, to that mixture induces the discharge stabilization so that the laser emission arises in a homogeneous active medium. This effect allows us to achieve better laser performance than with H₂. Received: 17 March 1998/Revised version: 13 July 1998     

Excited state positronium formation in low density gases

Excited state Ps atoms formed in low density Ne, Ar and H₂ gases have been observed for the first time. The maximum yield was estimated to be ≈ 5.7 × 10^?2 excited Ps atoms per stopped positron of energy ≈ 16 eV in H₂. This is about 14 times greater than previous maximum yields.     

Generation of H− ions in a low-pressure xenon-hydrogen discharge. I

A theory of a low-pressure discharge in a xenon-molecular hydrogen mixture is developed. It is shown that, in such a discharge, at an interelectrode distance of L = 1 cm and a total plasma pressure of p ₀ ～ 1 Torr, the density of negative hydrogen ions produced via the dissociative attachment of thermal electrons to vibrationally excited molecules H₂ can reach a value as high as N_H ^? ≥ 10¹² cm^?3. According to calculations, the electron temperature in discharge operating regimes under study attains T _e ≈ 1?2 eV, which corresponds to the maximum of the e-v exchange rate constant of H₂ molecules. This ensures a relatively high rate of vibrational pumping of H₂ molecules in the discharge.     

Intensification of shock-induced combustion by electric-discharge-excited oxygen molecules: numerical study

Mechanisms of combustion enhancement in a supersonic H₂–O₂ reactive flow behind an oblique shock wave front are investigated when vibrational and electronic states of O₂ molecule are excited by an electric discharge. The analysis is carried out on the base of updated thermally nonequilibrium kinetic model for the H₂–O₂ mixture combustion. The presence of vibrationally and electronically excited O₂ molecules in the discharge-activated oxygen flow allows to intensify the chain mechanism and to shorten significantly the induction zone length at shock-induced combustion. It makes possible, for example, to ignite the atmospheric pressure H₂–O₂ mixture at the distance shorter than 1 m behind the weak oblique shock wave at a small energy E_s = 1.2 × 10^–2 J · cm^–3 input to O₂ molecules. At higher pressure it is needed to put greater specific energy into the gas in order to ignite the mixture at appropriate distances. It is shown that excitation of O₂ molecules by electric discharge is much more effective for accelerating the hydrogen–oxygen mixture combustion than mere heating the gas.     

The double M-effect induced by noble gases activated with negative ions

The M-effect (monochromatization-effect) is a powerful tool which can give high intensity monochromatic spectra with a certain wavelength depending on the type of used gas mixtures to generate plasma state. The effect consists in the emission of a single spectral line of plasmas ignited in certain gas mixtures. The main condition to obtain the M effect is the presence of an electropositive and an electronegative gas mixture. For example, in the case of Ne+H₂ monochrome radiation was obtained, the wavelength of Ne being 585.3 nm (1s²–2p⁵). In this paper we prove the general character of this effect, i.e. if the optical emission spectra reduced to nearly one line can be observed also in other gas mixture discharges, for example in the case of one electronegative gas and two electropositive gases. Different other mixtures, as Xe+Ne+H₂ and Xe+Ar+H₂ have been studied. In all these cases, the M-effect appeared without doubt.     

Stability of the H2–(He,Ne, Ar) fluid mixtures

A theory of mixtures based on a statistical mechanical perturbation scheme is used to compute the excess free energy of mixing, the excess entropy of mixing and the concentration fluctuations in the long wavelength limit as functions of composition (c) over a wide range of temperature (T = 150 to 350 K) and pressure (p = 10 MPa to 10 GPa). This has been utilized to investigate the effects of c, T and p on the solubility of H₂ (the first element of the periodic table) to He, Ne and Ar (the first three elements of the last group) and the thermodynamic stability of the mixture. The long-range correlations among the constituent species are included through the double Yukawa potential which acts as a perturbation to the hard sphere reference mixture. The non-additivity of the potentials of the constituent species is linked to the second virial coefficients which can be determined from the experimental data. Necessary corrections to the equation of state for dimerisation of H₂ molecule and quantum effects are included. At a given T = 150 K and p = 100 MPa, H₂–Ar mixture exhibits greater thermodynamic stability than H₂–Ne and H₂–Ar.     

Der Einfluß der Stoßkenndaten auf die Elektronenkinetik in schwachionisierten Mischplasmen

The Influence of the Characteristic Quantities of the Collision Processes on the Electron Kinetics in the Low Ionized Mixture Plasm Starting from former investigations concerning the electron kinetics in the pure molecular plasma of N₂ and H₂ and in the mixtures of N₂/Ne and N₂/H₂ the influence of the important characteristic quantities of the collision processes on the isotropic distribution function and the energy balance of the electrons was studied for binary mixtures. The conclusions obtained were verified by results calculated numerically for the energy balance in the three mixtures He/Ne, N₂/H₂ and N₂/Ne which were investigated in the relevant range of the normalized electric field strength E/p₀ as a function of the mixture ratio. This analysis demonstrates the sensitive dependence of the macroscopic properties of the binary mixtures on the characteristic quantities of the collision processes of the electrons with the two components of the binary mixture.     

High-efficiency,high-energy performance of a pulsed HF laser pumped by phototriggered discharge

A comparison of the performance of pulsed infrared HF lasers pumped by phototriggered discharges using either Ne/SF₆/H₂ or Ne/SF₆/C₂H₆ mixtures are presented. For an active volume of 50 cm³, a specific output energy as high as 11 J/ has been achieved with an efficiency higher than 3% when C₂H₆ is used as H atom fuel. The replacement of ethane by molecular hydrogen reduces the laser performance by 40%. The investigation of the temporal evolution of the laser intensity shows that this dramatic decrease results from a shortening of the laser pulse duration rather than from a decrease of the peak power. Indications are given that this behavior is correlated to a very different temporal evolution of the discharge parameters, especially at low reduced electric field E/N.     

Multiple M‐Effect Signal in Noble Gases and Hydrogen Mixture Discharge

The M‐effect (monochromatization‐effect) is a powerful process which can give high intensity monochromatic spectra with a certain wavelength depending on the type of used gas mixtures to generate the plasma state. The effect consists in the emission of a single spectral line emerging from plasma under specific experimental conditions involving one electropositive gas and one electronegative gas mixture. For example, in the case of Ne‐H₂ mixture, a clear monochrome radiation was obtained, corresponding to the λ_Ne =585.3 nm wavelength at 2p₁‐1s₂ transition in the Paschen notation, the pressures ranging between 10‐100 torr. In this paper we prove the general character of this effect, i.e. if the optical emission spectra (OES) reduced to selective lines can be noticed also in other multiple gas mixture discharges. The Ne‐Ar‐Xe mixture discharges with different percentages of H2 as electronegative gas added in has been investigated. The triple M‐effect, means three specific monochromatic lines, could be revealed in the OES at 50% of H2 addition in Ne‐Ar‐Xe mixture (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

H2O2–Ng dynamics predictions using an accurate potential energy surface

ABSTRACT

Based on ab initio calculations, our research group has built an analytical ground-state potential energy surface (PES) for hydrogen peroxide– noble gas (Ng) interactions, such as H₂O₂–He, H₂O₂–Ne, H₂O₂–Ar, H₂O₂–Kr, and H₂O₂–Xe complexes. From this PES, it was verified that the Ng presence does not affect the equilibrium values of the H₂O₂ dihedral angles. This happens because the H₂O₂ intramolecular barriers have much higher energies than the atom–bond interaction within these complexes. From this point of view, it is indeed reasonable to consider the H₂O₂ system as a rigid rotor, frozen at its equilibrium configuration. We present in this work the torsional motion for the H₂O₂ isolated system, the vibration–rotation energy levels and spectroscopic constants for hydrogen peroxide–noble gas by using the aforementioned PES. The predicted H₂O₂ torsional motions are in good agreement with both theoretical and experimental results available in the literature. Regarding H₂O₂–Ng ro-vibrational energies and spectroscopic constants, it is the first time that these calculations are presented in the literature. The current theoretical predictions are expected to be useful in the future experimental investigations.     

Determination of gas temperature of high-frequency low-temperature electrodeless plasma using molecular spectra of hydrogen and hydroxyl-radical

In this study we determine gas temperature of He+H₂, Ar+H₂ and Ne+H₂ high frequency electrodeless lamps using intensity distribution in rotational spectra of hydrogen molecule and hydroxyl radical. The measurement results show that OH rotational spectra can be successfully used for estimation of gas temperature of the high-frequency electrodeless lamps at very small amounts of hydrogen present in plasma. The analysis of the measurement results leads to the conclusion that in “pure” plasma the applied energy is used to heat plasma, while for the plasma with hydrogen addition the energy is used in chemical reactions.     

含氢气氛下区熔硅单晶中缺陷的研究

利用化学腐蚀和X射线投影貌相方法研究了含氢气氛下区熔无位错硅单晶中的缺陷,发现异常腐蚀现象、缺陷密度与气氛中氢含量紧密相关,观测了纯氢气氛下无位错硅单晶退火后的缺陷,找到了貌相与蚀象的对应关系,还观察了二次退火效应,最后,综合所观测到的结果,讨论了氢在硅单晶中的集聚、沉淀和位错环列的发射、运动及交互作用。 关键词：     

H1+,H2+,H3+和He,Ne,Ar碰撞过程中的巴耳末系Hα,Hβ,Hγ发射

实验利用TN-1710光学多道分析系统(OMA),对H₁⁺,H₂⁺,H₃⁺和He,Ne,Ar碰撞过程中产生的巴耳末系H_α,H_β,H_γ发射进行了测量,入射离子H₁⁺,H₂⁺,H₃⁺的 关键词：     

The electronic structure of carbon films deposited in rf argon–hydrogen plasma

The electronic structure of C films deposited by sputtering a graphite target in rf. Ar–H₂ plasma is investigated by photoemission, Auger emission and electron energy loss spectroscopy (EELS) as a function of the H₂ concentration in the feed gas, referred to as [H₂]. Adding hydrogen to the plasma causes the films to change from a graphite-like unhydrogenated structure to a non-graphitic hydrogenated structure. The film mass density, as derived from the π + σ plasmon energy, decreases upon H₂ addition to the gas mixture, goes through a minimum at low [H₂] and increases with increasing [H₂]. It reveals a non-monotonous behavior of the film H content as a function of [H₂], the maximum H incorporation occurring at low [H₂]. This appears to be a characteristic of C deposition via graphite sputtering in Ar–H₂ plasma and it is discussed in connection with previous results on the subject.     

Numerical study of tip opening of hydrogen/air Bunsen flame

To understand tip opening of a hydrogen–air Bunsen flame, the detailed flow, temperature and concentration fields of the flame were studied based on numerical calculations that use the exact transport properties and the full chemical reaction mechanism. The study has revealed that the local chemical reactions along the flame cone portion do not remain uniform; the H₂ consumption rate decreases in the downstream direction. The lowering H₂ concentration of the mixture coming into the cone, caused by the radial outward diffusion of mobile H₂ molecules, leads to the slowdown of the main H₂-consuming reactions downstream and causes the breakdown of the reaction at the downstream end of the cone. This is the tip opening.     

Electrical and optical characterization of pulsed plasma of N<Subscript>2</Subscript>–H<Subscript>2</Subscript>

This paper considers the electrical and optical characterization of glow discharge pulsed plasma in N₂/H₂ gas mixtures at a pressures range between 0.5 and 4.0 Torr and discharge current between 0.2 and 0.6 A. Electron temperature and ion density measurements were performed employing a double Langmuir probe. They were found to increase rapidly as the H₂ percentage in the mixture was increased up to 20%. This increase slows down as the H₂ percentage in the gas mixture was increased above 20% at the same pressure. Emission spectroscopy was employed to observe emission from the pulsed plasma of a steady-state electric discharge. The discharge mainly emits within the range 280–500 nm. The emission consists of N₂ (C-X) 316, 336, 358 nm narrow peaks and a broad band with a maximum at λ_max = 427 nm. Also lines of N₂, N₂ ⁺ and NH excited states were observed. All lines and bands have their maximum intensity at the discharge current of 0.417 A. The intensities of the main bands and spectral lines are determined as functions of the total pressure and discharge current. Agreement with other theoretical and experimental groups was established.     

The solution of Hydrogen in TaV2

TaV₂ may be prepared as a random b.c.c. alloy or as a (C-15) Laves phase. The behavior of hydrogen dissolved in b.c.c. TaV₂ is significantly different than that exhibited by hydrogen dissolved in (C-15) TaV₂. The b.c.c. TaV₂/H₂; system is similar to pure vanadium/H₂; in the region of hydrogen solid solution, the electronic contribution to the thermodynamics of solution is negligible and the system exhibits apparent H-H attractive interactions. A non-stoichiometric f.c.c. dihydride is formed at p_H2 = 10 atm, T = 273 K. (C-15) TaV₂ does not form a hydride phase; hydrogen is continuously absorbed into solid solution to a maximum hydrogen content H/M ? 0.60. The solid solution of hydrogen in (C-15) TaV₂ exhibits trends which are typical of intermetallie/H₂ systems. The dilute hydrogen region is marked by a strong positive deviation from Sieverts' Law, and the relative partial molar enthalpy of solution becomes less exothermic as the hydrogen content is increased. ΔV? vs H/M relationships and ΔS_H vs H/M relationships indicate that hydrogen segregation at the metal surface or at abnormally stable trapping sites does not contribute significantly to the thermodynamic behavior exhibited by hydrogen in (C-15) TaV₂. Analysis of the excess free energy of hydrogen suggests that electronic effects may exert a significant influence on the behavior of hydrogen in (C-15) TaV₂, even at dilute hydrogen contents. It is suggested that the radom substitution of tantalum into the vanadium lattice exerts a significantly greater effect on the vibrational entropy of dissolved hydrogen than does the structural transformation b.c.c. TaV₂ → (C-15) TaV₂.     

Deposition of diamond structures from interacting gas jets

We have reported on the results of experiments on the gas-jet synthesis of diamond from methane and hydrogen flows for various mixing conditions. An original method of separate feed of gas jet has been proposed, which makes it possible to attain a high growth rate for the diamond phase. The synthesis of diamond structures in gas-jet deposition has been studied for separate feeds of two flows (hydrogen and the mixture of hydrogen with methane) in two versions, i.e., with a lateral feed of the methane-containing mixture and axisymmetric feed. Experiments were performed under the following conditions: the temperature of the surface (activating hydrogen) 2400 K, a substrate temperature of 900–1300 K, pressure in the deposition chamber 2 × 10² Pa, gas mixture fluxes (relative to hydrogen) 1500 ncm³/min, CH₄ concentration in H₂ of 0.1–0.7%, and the distance from the substrate to the reactor 10 mm. In the case of a separate feed of the methanecontaining gas and hydrogen, a deposition rate of 20 μm/h was attained. In the case of an axisymmetric separate feed of the gases, a single crystal with a mass of 0.6 mg was grown, which corresponded to the deposition rate of approximately 200 μm/h.     

A Mathematical Representation of Quantizing the Motion of Relativistic Electrons in a Magnetic Field

It is shown that the quadratic component of the kinetic energy of continuous longitudinal motion of relativistic electrons in the external magnetic field is varied continuously between 0 and 2(2m _e c ²_B H) within each Landau energy level, undergoing an abrupt change at the boundaries of the levels. This results in the fact that in the quantum limit of a superstrong magnetic field where all electrons are at the zero Landau level, the maximum quadratic component of the kinetic energy of free longitudinal electron motion along the direction of the magnetic field is twice as high as the maximum quadratic component of the kinetic energy of its bound transverse motion.     

Crystallization of a dusty plasma in the positive column of a glow discharge

The formation of macroscopic ordered structures in the standing striations of a stationary glow discharge in Ne is observed. A Coulomb quasicrystal is formed by spherical glass particles with diameters of 50–63 μm and charge Z _p~7·10⁵ e. The interparticle distance is approximately 300 μm. This corresponds to a nonideality parameter Γ~5·10⁴, which leads to crystallization in the Yukawa model. The factors leading to the formation of a quasicrystal in the striations are discussed. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 2, 86–91 (25 July 1996)