Plasma Properties and Neutral Gas Densities in Hg-Rare Gas Discharges

The density of the neutral gases in Hg-rare gas discharges and their spatial distribution is controlled by the discharge parameters as well as by the externally adjustable partial pressures. Essential quantities in this context are the gas temperature produced by elastic collisions, the ion transport by the discharge current, the processes governing the wall temperature, and ambipolar diffusion. Despite equal partial pressures different densities may occur, which, in turn, will influence the parameters of the discharge. This has effects on the assessment of the methods of Hgvapour pressure adjustment and on the evaluation of the measured values. These effects are demonstrated, especially by field strength measurements, for a wide parameter range.     

激光支持等离子体爆轰波温度的实验测量

 高能量激光聚焦空气产生等离子体,等离子体进一步吸收激光能量会形成激光支持等离子体爆轰波。等离子体爆轰波温度是表征爆轰波的一个重要参数,研究等离子体爆轰波温度对于深入了解激光支持等离子体爆轰波形成机理有重要意义。分析了激光聚焦空气形成等离子体爆轰波过程和影响等离子体爆轰波温度的主要因素。采用多通道瞬态光学高温计,测量了不同激光发射能量下空气中形成的激光支持等离子体爆轰波的辐射强度,获得了一系列等离子体爆轰波温度动态变化曲线。测量结果表明：等离子爆轰波温度在随时间演化过程中出现3个峰,最高温度在7 000～10 000 K范围内;激光能量与等离子体爆轰波温度没有明显的相关性。     

NO激光诱导荧光对高焓气流温度的测量

由于真实气体效应,高超声速流场的研究仍然依赖于大量的实验.流场温度是实验的重要参数,目前只能通过具有非入侵性质的光学测量手段获得,然而,由于多方面的难题,鲜有对高焓流场参数测量的报道.文章介绍了利用激光诱导荧光（laser-induced fluorescence,LIF）技术对JF-10氢氧爆轰激波风洞产生的高焓实验气流温度的测量工作.搭建了用于脉冲式风洞的LIF测量系统,使用了NO分子作为荧光组分.因为高焓流场实验条件苛刻,本实验对传统的激光设置进行了调整,使用了平行于拍摄方向的竖直平面激光激发NO,使荧光信号更为集中,获得了清晰的LIF图像.利用双线测温法（two-line thermometry,TLT）测量高焓自由流中NO分子的转动温度,从而确定气流的平转温度.测量结果表明,JF-10实验气流的平转温度为600 K.      

Electron Temperatures and Electron Densities in Microwave Helium Discharges with Pressures Higher than 0.1 MPa

We adopted laser Thomson scattering for measuring the electron density and the electron temperature of microwave plasmas produced in helium at the pressures higher than the atmospheric pressure. The electron density decreased while we observed the increase in the electron temperature with the pressure. These are reasonable results by considering the decrease in the reduced electric field, the dominant loss of electrons via three‐body recombination with helium as the third body, and the production of electrons with medium energy via heavy particle collisions at the high gas pressure. The temporal variation of the electron temperature had the rise and the fall time constants of approximately 10 ns. The rapid heating and cooling of the electron temperature are due to the fast energy transfer from electrons to helium because of the high collision frequency in the high‐pressure discharge. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

激光等离子体温度测量方法设计

为了获得高时间和空间分辨率的激光等离子体温度测量结果,基于等离子体温度测量的二谱线法,设计了一种激光等离子体温度测量方法。介绍了该方法的测量原理及时间空间分辨率实现方法。利用这种方法获得了空间分辨率微米量级、时间分辨率纳秒量级的激光等离子体温度测量结果,测量得到的激光等离子体温度为10^4K量级。实验结果表明,该方法能够获得具有很高时间空间分辨率的温度测量结果,具有较好的可行性。     

脉冲电子束荧光技术测量稀薄流场速度研究

脉冲电子束荧光测速技术是一种直接测量稀薄流场速度的非接触手段,以Φ0.3 m高超声速低密度风洞Ma=12型面喷管为对象,在总压2 MPa、总温650 K的状态下,测量了喷管出口150 mm截面的径向速度分布,各点的7次测量结果表明重复性偏差约为10％,最大相对不确定度为4％,中心位置的速度与Pitot管测压技术、Ray...     

激光诱导荧光技术测量OH自由基的建立和研究

氢氧自由基（ＯＨ）在对流层大气化学中起着重要的作用,因此,对其浓度的测量具有重要意义。本文利用气体扩张激光诱导荧光技术（ＦＡＧＥ）建立了ＯＨ测定系统,对其进行了标定,得到归一化荧光信号（Ｓ）与ＯＨ自由基浓度的较好的相关关系,并对可能存在的干扰进行了分析。     

Effect of Analyte Concentration on the Laser-Induced Plasma Temperature and Electron Density in Liquid Matrix

In the present work, we report spectroscopic studies of laser-induced plasmas produced by focusing the second harmonic (532 nm) of a Nd:YAG laser onto the laminar flow of a liquid containing chromium. The plasma temperature is determined from the coupled Saha–Boltzmann plot and the electron density is evaluated from the Stark broadening of an ionic line of chromium [Cr(II)] at 267.7 nm. Our results reveal a decrease in plasma temperature with an increase in Cr concentration up to a certain concentration level; after that, it becomes approximately constant, while the electron density increases with an increase in analyte (Cr) concentration in liquid matrix.     

Boundary Conditions in the Source of an Electron Beam on the Surface of the Anode Plasma with a Supersonic Ion Flow

Russian Physics Journal - A solution for the one-dimensional Poisson problem for a layer on the surface of a plasma ion emitter is obtained. The case of plasma with a directed ion velocity greater...     

Submicrosecond Pulsed Electron Beam Formation in Electron Sources and Accelerators with Plasma Emitters

The most popular methods for submicrosecond electron beam generation and physical processes underlying electron extraction from plasma in plasma emitters are considered. Electron sources and accelerators developed on the basis of plasma emitters allow pulsed beams with currents from tens to 10³ A and current densities of several amperes per square centimeter, pulse durations of hundreds of nanoseconds, and high repetition rates to be generated.     

On the Plasma Beam Instability of the Space Limited Electron Beam in a Magnetic Field

The present paper considers the plasma-beam instability of a space limited electron beam in a strong magnetic field (ω_H ? ω_o). The form of the beam was taken to be both cylindrical and plane. The threshold of the non-linear regime turned out to be weakly dependent on the beam form and independent of the magnetic field intensity. It is defined by the current and the directed velocity of the beam particles.     

Study of the Z-Pinch Plasma Initiated by the Electron Beam

A lot of activities are carried out to develop compact laser accelerators. The transportation and focusing of beams in Z-pinch-type discharges, which requires thorough investigations into methods for the formation of these discharges, are important problems to be solved. At the ITEP, an experimental setup [1] is constructed to study Z-pinch plasma dynamics when the discharge is initiated by an electron beam. The first results of the experimental and numerical investigations show that development of the discharge initiated by an electron beam differs considerably from the ordinary Z-pinch formation process.     

Finding of Optimal Calcium Ion Probes for Fluorescence Lifetime Measurement

We have investigated the fluorescence lifetime properties of 8 calcium ion probes, calcium-green-1, calcium green-2, calcium green-5N, calcium orange, oregon green 488 BAPTA-6F, fluo-3, fluo-4, and fluo-5N. We found that the decay time of calcium green-5N varied more sensitively with calcium concentration than calcium green-1 which was known to be a highly sensitive probe. We have also found that the center of observable range of calcium concentration by fluorescence lifetime measurement is lower than that by fluorescence intensity measurement.     

Laser-Induced Fluorescence Molecular Beam Investigation of New Singlet and Triplet Electronic States of Yttrium Monohydride

The yttrium monohydride spectrum in the range 12 500-25 000 cm⁻¹ has been studied by various laser-induced fluorescence (LIF) techniques. YH (YD) molecules have been produced in a free jet molecular beam apparatus by a laser vaporizing yttrium metal in the presence of He doped with H₂ (D₂) or NH₃ (ND₃). Low-resolution (∼0.04 cm⁻¹) excitation spectra have been recorded in the entire studied range. Four green bands (19 300-19 900 cm⁻¹) of the YH isotopomer have been studied in more detail: (1) high-resolution (∼120 MHz, ∼0.004 cm⁻¹) excitation spectra have been recorded, (2) dispersed fluorescence spectra have been obtained, and (3) lifetimes of the selected rotational levels of the upper states have been measured. Our observations have confirmed that the ground state of yttrium monohydride has ¹Σ⁺ symmetry and have provided a link between the singlet and triplet manifolds. The upper states of the observed transitions have been tentatively assigned to five electronic states, d0⁺, f³Π, f′1, D¹Π, E0⁺, and Fl. The low-energy excited electronic state observed in the dispersed fluorescence experiment has been assigned as the a³Δ state.     

Optimal Control of Trapped Electron Instability by a Modulated Neutral Beam

Equivalent lumped parameter system representation for dissipative trapped electron instability involving many modes is obtained. Optimal control theory in the presence of noise is used to design a stabilizing feedback network, with a modulated neutral beam as a remote suppressor. The optimality criterion is the minimization of the total energy of control and instability fluctuations. It is shown that the control power does not depend on the level of instability fluctuations in the absence of feedback, but on the noise level in plasma.     

Interaction of a Relativistic Electron Beam with a Plasma

The dispersion relation for the interaction of a relativistic electron beam in a thermal plasma, in the absence of an external magnetic field, is studied. It is shown that there are two distinct beam-plasma branches present, and that one of them couples to the electromagnetic eigenmode of the beam-plasma system with a magnetic field and a Poynting flux associated with it. It is also shown that these branches can couple together.     

Device for Producing and Investigating an Electron Beam Plasma Discharge

A survey on the properties and applications of the beam plasma discharge is given. A device for the experimental investigation of this discharge is described in which a magnetically guided (H = 0.05?0.1 T), ribbonlike electron beam (eU = 0.5–5 KeV, I = 10^?3?1 A) passes through a working chamber (p = 0.1–10 Pa; l = 10 cm, ø = 22 cm). The beam plasma discharge is sustained by collective beam plasma interaction. First results concerning the wall current and the ignition of the discharge as dependent on beam parameters are presented.     

Collisionless Currents for Cylindric Probes in a Plasma with non-Maxwellian Distribution of the Electron Energy

The radial model developed by Allen, Boyd, Reynolds and Chen [1, 2] for the ion collection of Langmuir probes is extended to describe the case of a non-Maxwellian distribution of the electron energy. Assuming standard distributions, showing with respect to the Maxwell distribution an increasing deficite of fast electrons as the parameter k of the distribution increases, the electron-retarded current characteristic, the potential distribution and the density profiles for electrons and ions in the probe sheath, ion-current characteristics as well as graphs for the ion-density determination are calculated for different k. It is shown, that the application of the Chen model (k = 1) in plasma with k > 1 leads only to a small error in the ion-density measurement.