Ion-cluster reactions initiated by an electron beam in mixtures of argon with methane and monosilane

The excitation of argon radiation in condensing supersonic jets of argon mixtures with methane, monosilane, and carbon dioxide upon electron-beam activation of the flow is investigated experimentally. It is found that, at certain condensation stages, the radiation intensity at some atomic argon lines increases anomalously. It is shown that the effect appears at the initial stages of condensation and is damped upon the formation of large mixed clusters.     

Formation of mixed clusters in a pulsed supersonic helium-oxygen-isoprene jet

An experimental study of the formation of mixed van der Waals oxygen-isoprene complexes, generated in an expanding supersonic helium-oxygen-isoprene jet at various stagnation pressures and at diverse oxygen and isoprene concentrations, has been performed. To measure the composition and distribution of the partial densities of the individual components, molecular beam mass spectrometry was adapted to pulsed modes of gas source operation. The particularities of applying mass spectrometry to studying clustered isoprene streams in a pulsed mode have been discussed. The composition of small clusters generated in a free supersonic jet has been checked for dependencies upon the initial mixture composition and stagnation pressure. The mechanism of nucleation has been identified for different partial concentrations of impurities in the helium stream. It has been shown that, even at a 0.3% concentration of isoprene in the mixture, nucleation starts with the formation of hydrocarbon complexes. The specific features of the dissociative ionization of van der Waals complexes, consisting of pure isoprene and mixed complexes, have been discussed. The conditions needed for the formation of binary oxygen-isoprene van der Waals complexes have been identified.     

Acoustic characteristics of interacting supersonic jets

This study was intended primarily to reveal more information about the noise producing mechanisms of supersonic jets. Two identical, small, cold air, supersonic, overexpanded jets were tested at selected angles, varying from parallel to 90 degrees intersecting, and at various distances apart. Schlieren photographs of the jet structure and far field sound data were obtained. Close spacing of the parallel jets caused acoustic attenuation, which reached a maximum at one diameter centerline spacing, where the sound of two jets nearly equals that of a single jet. In every case the intersecting jets merged into a single supersonic jet.The overall sound power level of intersecting jets is generally higher than that of two independent jets, because of the turbulent mixing of the two jet flows. A maximum level is reached when the jets intersect at a point near the middle of the flow region containing repetitive shocks. For the parallel jets and intersecting jets at large separation, the sound levels are lower in the plane containing the jet centerlines. For intersecting jets at small separation, however, this shielding effect is reversed.     

HL-2A托卡马克超声分子束注入深度和加料效果研究

超声分子束注入深度与加料效率是分子束加料研究中的基本课题.在近期开展的超声分子束注入实验中，发现分子束注入深度与等离子体电子温度和密度、分子束源的气压和温度有直接关系，获得了分子束注入深度的定标律.在低温气体源(液氮冷却)的分子束注入实验中，发现分子束流中形成了团簇，其注入深度超过30 cm，分析了在低温气源分子束注入实验中的团簇现象. 关键词： 超声分子束注入 注入深度 加料效率 团簇     

Spectroscopy of mixed Ar-Xe clusters: Formation of a xenon core

The spectra of vacuum ultraviolet luminescence of heteroatomic Ar-Xe clusters condensed in supersonic jets of a mixture of these gases at a xenon impurity concentrations of 0.001–2% are measured. A new group of molecular luminescence bands of argon-xenon centers is recorded, which allows a highly sensitive detection of xenon in the argon matrix of a cluster. The phenomenon of phase separation into pure components with formation of a sharp interface between the xenon core and argon shell of the cluster is found.     

Electron-induced fluorescence of carbon dioxide clusters. I. Free jet of condensing gas

In measurements in jets of condensing gases, problems arise in interpreting the results obtained with the use of electron-beam fluorescence diagnostics, in particular due to the possible contribution of clusters to the radiation from the jet. Data on the fluorescence are obtained by comparing the optical and x-ray emission excited by an electron beam with calculations of the amount of condensate. Studies are made on the fluorescence of CO₂ clusters excited by an electron beam in a free jet of the condensing carbon dioxide gas. It is found that the clusters radiate at wavelengths of the monomers extremely effectively per molecule, almost as much as the free molecules, and the dependence on size is quite weak. It is shown that with electron-impact excitation the emission of the clusters comes about as the result of the ejection of excited molecules from the cluster as the latter fragments. The results of this investigation of the fluorescence of CO₂ clusters lead to conclusions regarding the use of electron beam fluorescence diagnostics for measurements in free jets with CO₂ clusters. Zh. Tekh. Fiz. 67, 43–52 (March 1997)     

Properties and applications of cold supersonic gas jet

By analyzing the formation mechanism of a supersonic gas jet, a set of equations which describe the atomic beam properties were established. The influence of initial temperature, initial pressure, background gas pressure and pumping speed was discussed in detail. A simulation program was developed based on the equations, and the results under different initial conditions were obtained. The results are in good agreement with the experimental data, and suggest that, in order to get much smaller transverse momentum in collision experiments, it is necessary to lower the initial temperature and the initial pressure of the supersonic gas jet, together with increasing the pumping speed. These results are very instructive for construction of a new generation of cold supersonic gas jets.     

Condensation of monosilane-argon and monosilane-helium mixtures in free jets

Condensation of gaseous monosilane-argon and monosilane-helium mixtures was investigated in free jets by a Rayleigh scattering laser diagnostic technique. The condensation of a SiH₄-Ar mixture begins to develop at a lower stagnation pressure and at a shorter distance from the nozzle, and proceeds at a higher rate, as compared to condensation in monosilane-helium and pure argon jets. The results of Rayleigh scattering measurements in condensing monosilane-argon jets scale with the parameter P ₀ d ^0.8. An analysis of the results obtained in this study and found in literature suggests that simultaneous monosilane-argon condensation lead-ing to the formation of mixed clusters takes place in the monosilane-argon mixture.     

Water condensation kinetics on a hydrophobic surface

Employing thermal desorption spectroscopy, we show that the effective probability of water condensation at low water vapor pressure on an octane film is much below unity at 100-120 K. This unusual finding is related to a small binding energy of H2O monomers on octane (approximately equal to 0.08 eV), requiring the formation of critical water clusters for condensation to occur. This results in strong temperature and impingement-rate dependencies of the water condensation rate and a nonlinear uptake as a function of dose time. All these features are rationalized quantitatively by a kinetic model of water condensation.     

水下超声速气体射流气液两相复杂流动研究

本文实验研究了水下超声速气体射流气液两相复杂流动。利用高速摄影仪和电子相机分别实时记录了过膨胀超声速工况水下气体射流的喷射状态和整体形貌,显示了不同工况水下高速气体垂直射流的演化过程和动态不稳定性形貌。研究结果表明:在射流的初始段存在与射流内部复杂波系相关的激波反馈特性,激波反馈特性发生之前存在能量积聚的高频低幅的胀鼓过程,二者均随机发生;在射流的主体段,在气水掺混和卷吸大规模能量交换作用下,射流呈现随机的偏摆效应,并且偏摆受环境流场影响明显。     

A1等离子体与甲醇团簇的反应

利用激光烧蚀-分子束法(LA-MB)对激光烧蚀金属铝靶产生的Al等离子体与脉冲分子束超声膨胀产生的(CH3OH)n团簇在气相条件下的反应进行了研究.烧蚀激光相对于脉冲分子束之间的延时不同,观测到团簇离子序列及团簇尺寸的变化,反映出脉冲分子束状态对反应条件及激光烧蚀等离子体状态的影响.在激光烧蚀发生于脉冲分子束的前段,主要反应产物为Al (CH3OH)n,但团簇尺寸较小;在烧蚀发生于脉冲分子束的中段,主要产物为H (CH3OH)n,团簇尺寸增大,强度减弱;在烧蚀发生于脉冲分子束的后段,观测到尺寸更大的水合质子化团簇H (H2O)m(CH3OH)n.结合团簇离子速度分布的特征,对团簇的产生机理进行了讨论.     

Flow characteristics of the large scale wave-like structure of a supersonic round jet

A model is developed for the large scale coherent structure of subsonic and supersonic axisymmetric jets. A fluctuation in the jet flow is regarded as being separable into a time-averaged component, a periodic wave-like component and a random small scale component. The small scale fluctuation is viewed as both the driving and dissipative mechanism for the wave-like component. An energy balance model is developed which examines thinterchange of energy between the mean flow and the large scale motion. The effect of wave-like fluctuation amplitude on its own and the mean flow development is examined. Calculations of contours of equal pressure level in the jet near field are made. A model for the mechanism by which locally subsonic components of the wave-like structure may radiate noise to the far field is examined. The method for calculating the radiated noise is discussed.     

Supersonic flow characteristics in laser grooving

The gas flow structure in laser grooving has been evaluated by numerical simulation and experiments in this study. A nozzle designed with a specific arrangement of compound jets for laser grooving has been tested. For this nozzle configuration the compressible flow structure of a shock wave induced by a supersonic side jet has been predicted in a numerical simulation using FLUENT, a computational fluid dynamics code and visualized in the experiment where the wall pressure on the grooving zone was evaluated and measured for jets impinging on the substrate at varying attacking angles of the side jet. The results obtained numerically and experimentally were comparable. In addition, the relationships between the material removal efficiency and the flow structure have also been established. It transpired that the attacking angle made a significant and dramatic improvement on the flow structure and grooving appearance and that a large wall pressure with a clear grooving profile can be obtained for attacking angles between 40° and 50° in the present test setup.     

Detection of SF<Subscript>6</Subscript> molecules sublimating from the surface of (CO<Subscript>2</Subscript>)<Subscript><Emphasis Type="Italic">N</Emphasis></Subscript> nanoparticles in a cluster beam by the infrared multiphoton excitation method

It has been found that SF₆ molecules captured by large van der Waals clusters (CO₂) _N (where N ≥ 10² is the number of monomers in a cluster) in intersecting molecular and cluster beams sublimate from the surface of clusters after a certain time and carry information on the velocity and temperature (internal energy) of clusters. Experiments have been carried out for detecting these molecules by means of a pyroelectric detector and the infrared multiphoton excitation method. The multiphoton absorption spectra of molecules sublimating from the surface of clusters have been obtained. The temperature of the (CO₂) _N nanoparticles in the cluster beam has been estimated using these spectra and comparing them with the infrared multiphoton absorption spectra of SF₆ in the initial molecular beam.     

Vibrational predissociation of UF6 clusters in supersonic Laval nozzle flow

The time-dependent change in the concentration of UF₆ monomers populated in the ground state was monitored in a supersonic Laval nozzle flow with an infrared diode-laser spectrometer in which the frequency of the laser beam was fixed at the = 1 0 transition (627.7 cm^–1) of the ₃ vibrational mode of the²³⁸UF₆ monomer. The concentration of UF₆ monomers in the ground state increased immediately after a single shot from a Raman laser tuned to a vibrational mode of UF₆ clusters (614.8 cm^–1) was applied to the gas in the nozzle. Subsequently, this concentration leveled off and slowly returned to the previous level. These results indicate that the population of UF₆ monomers in the ground state increased as a result of the predissociation of UF₆ clusters vibrationally excited with Raman laser radiation. It is demonstrated that one can utilize this procedure for vibrational predissociation of UF₆ clusters as a technique to increase the concentration of UF₆ monomers in an irradiation zone for molecular laser isotope separation of uranium.     

Research on the mechanics of underwater supersonic gas jets

An experimental research was carried out to study the fluid mechanics of underwater supersonic gas jets. High pressure air was injected into a water tank through converging-diverging nozzles (Laval nozzles). The jets were operated at different conditions of over-, full- and under-expansions. The jet sequences were visualized using a CCD camera. It was found that the injection of supersonic air jets into water is always accompanied by strong flow oscillation, which is related to the phenomenon of shock waves feedback in the gas phase. The shock wave feedback is different from the acoustic feedback when a supersonic gas jet discharges into open air, which causes screech tone. It is a process that the shock waves enclosed in the gas pocket induce a periodic pressure with large amplitude variation in the gas jet. Consequently, the periodic pressure causes the jet oscillation including the large amplitude expansion. Detailed pressure measurements were also conducted to verify the shock wave feedback phenomenon. Three kinds of measuring methods were used, i.e., pressure probe submerged in water, pressure measurements from the side and front walls of the nozzle devices respectively. The results measured by these methods are in a good agreement. They show that every oscillation of the jets causes a sudden increase of pressure and the average frequency of the shock wave feedback is about 5–10 Hz.     

Modelling of the flow structure in a composite jet behind two thrusters located near the spacecraft case

The gasdynamic flow structure is studied experimentally and numerically in the zone of jet interaction flowing with considerable underexpansion from two supersonic nozzles located near the spacecraft case. Longitudinal and transversal distributions of the density are obtained by the method of electron beam. They are compared with calculation results for inviscid gas. Generalized dependencies for determination of gas density within the zone of two jets interaction and boundary of this zone are obtained.     

Absolute electron scattering cross sections for the CF2 radical

Using a crossed electron-molecular beam experiment, featuring a skimmed nozzle beam with pyrolytic radical production, absolute elastic cross sections for electron scattering from the CF2 molecule have been measured. A new technique for placing measured cross sections on an absolute scale is used for molecular beams produced as skimmed supersonic jets. Absolute differential cross sections for CF2 are reported for incident electron energies of 30-50 eV and over an angular range of 20-135 deg. Integral cross sections are subsequently derived from those data. The present data are compared to new theoretical predictions for the differential and integral scattering cross sections, as calculated with the Schwinger multichannel variational method using the static-exchange and static-exchange plus polarization approximations.     

Formation and measurement of cluster beams at gasdynamic cooling of CF2HCl molecules

The clustering of CF₂HCl (Freon-22 refrigerant) molecules is found to take place when these molecules are dynamically cooled in a pulsed supersonic beam. A method of CF₂HCl cluster beam diagnostics is developed that combines UV multiphoton ionization, time-of-flight mass spectroscopy, and cluster IR photodissociation. The velocity of directed motion of (CH₂HCl)_n clusters, as well as the longitudinal and transverse velocities of their thermal motion, are measured at different stagnation pressures P ₀. The cluster mean size and the degree of clustering in the flow are estimated depending on supersonic flow conditions.