Heat flux and temperature and density profiles in a gas

Summary Starting from Boltzmann's equation, a method is developed for calculating temperature and density profiles and heat flux in a neutral gas in the presence of a temperature gradient and an external force. A generalized barometric law is obtained. The influence of different cross-section models is also investigated. This work was supported in part by MPI (60%) grants of the Italian Ministry of Education.     

Influence of the gas mixture temperature on the efficiency of synthesis gas production from ethanol in a nonequilibrium plasma

The mechanism behind the plasma conversion of a mixture of ethanol vapor, water vapor, air, and carbon dioxide CO₂ in the nonequilibrium plasma of a tornado discharge is studied. The influence of the CO₂ flow rate, the current through the discharge, and the gas temperature in the discharge on the concentrations of molecular hydrogen and carbon monoxide CO is studied. Comparison between the concentrations of the gaseous mixture’s main components at the output from the reactor obtained experimentally and by numerical simulation shows that the adopted kinetic mechanism adequately describes the plasma kinetics in the mixture.     

Influence of the gas density on the motion of a free plasma piston in the railgun channel

The influence of the gas density on the acceleration of a plasma armature inside the railgun channel filled with various gases (xenon, air, or helium) under atmospheric pressure is investigated experimentally and theoretically. It is shown that, after the discharge current has reached a steady value, the velocity of the glowing plasma front ceases to grow and remains constant as long as so does the current. The length over which the velocity saturates is equal to a few centimeters, i.e., is much shorter than the railgun channel length. The maximum velocity of the plasma piston meets a predicted limit, which is determined by the drag of the medium and a decrease in the acceleration of the plasma armature when a fraction of the material evaporated from the rails is involved into motion. The plasma composition depends on the electrode material. The velocities measured when the channel is filled with helium (V = 17.5 km/s) or air (V = 9.8 km/s) noticeably exceed the sound speed inside the plasma piston (5–7 km/s).     

Propagation of electron cyclotron waves in a weakly relativistic plasma with steep density and temperature profiles

Summary A detailed analysis is made of the deduction of systems of differential equations describing the propagation of both ordinary and extraordinary waves in the electron cyclotron frequency range in a stratified plasma, perpendicularly to the magnetic field and across the electroncyclotron fundamental resonance layer. The equations are derived under conditions of not too large electron temperature (the so-called weakly relativistic condition) and of very weak nonuniformities of the confining magnetic field. The effects of the nonhomogeneities of the equilibrium plasma density and temperature are carefully examined. It is shown that the propagation equations derived previously in the literature can be extended with only a moderately larger effort in computations to take account also of very strong density and temperature gradients.     

Cathodic-arc plasma density, radial profile, and total plasmainventory as measured by microwave interferometer and Faraday cup

The total amount of plasma, peak plasma density, and plasma density radial profile are derived from a series of measurements of ion current density (with a Faraday cup) and integrated electron line density (with a microwave interferometer) for a cathodic arc derived plasma. Comparisons are made between cathode material (erbium and titanium), arc current, background gas pressure, and the presence or absence of a series magnetic solenoid around the coaxial anode and cathode     

Influence of noise on the nature of synergetic systems

We have studied the stationary states of a homogeneous synergetic system in the presence of noise. In the framework of the subordination principle it is shown that, as a function of noise intensity in the system, transitions of both first and second order may be observed. The corresponding phase diagrams are presented.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 75–82, April, 1996.     

Evolution of the density profiles and flows of charged particles during the diffusive decay of an electronegative gas plasma

Different scenarios of the spatiotemporal evolution of the parameters of the diffusive decay of a pulsed electronegative gas plasma in the absence of plasma chemical processes are studied. It is shown that nonlinear diffusion in a plasma with negative ions occurs in several stages. The rate of electron density decay increases with time and, in the beginning of the second stage, almost all the electrons escape from the discharge volume. On the other hand, the ion density profile is smoothed out due to ion-ion ambipolar diffusion and the flow of negative ions toward the wall is absent in the first stage of decay. In the second stage, the main diffusion mode is first established and then the ion-ion (electronless) plasma decays exponentially with a characteristic time determined by ion-ion ambipolar diffusion.     

等离子体针放电的振动温度和气体温度研究

大气压等离子体针空气放电产生的低温等离子体由于脱离了真空装置,在工业上具有广泛的应用前景。本文采用等离子体针装置在空气中产生了稳定的大气压等离子体羽,并利用光谱法对等离子体羽的振动温度和气体温度进行了研究。结果发现大气压空气等离子体羽的放电区域分为强光区和弱光区。放电发光信号是宽度为几个微秒的脉冲。研究结果表明等离子体振动温度随空间位置不同在2 500～3 000K范围变化。振动温度在强光区随着远离针尖距离的增大振动温度呈上升趋势,在5mm左右存在极大值,在弱光区随着远离针尖距离的增大振动温度呈下降趋势。与其相似,弱光区放电的气体温度随着远离针尖距离增大,从640K降低到540K。这些结果对大气压空气放电的工业应用具有重要意义。     

空心针板放电等离子体气体温度和振动温度研究

使用空心针板放电装置,以氩气作为导入气体,在大气环境下产生了1.6~3 cm波长的等离子体炬。利用发射光谱法,研究了等离子体炬弧根和弧梢处的气体温度和振动温度,以及它们随气体流量的变化。等离子体气体温度通过对OH基309 nm附近的谱带进行拟合得到,等离子体振动温度由氮分子第二正带系C3Πu—B3Πg计算得到。实验发现弧根和弧梢处的气体温度相等,并随着气体流量的增大而下降。当气体流量从3.0 mL.min-1增大到6.5 mL.min-1时,气体温度由350 K下降到300 K。当气体流量较小(如3.0 mL.min-1)时,弧梢处的振动温度(1 950 K)高于弧根处的振动温度(1 755 K)。随着气体流量的增大,弧梢处与弧根处的振动温度均下降,但弧梢处下降速率较快。当气体流量较大时,二者趋于相等。     

Electron temperature and plasma density in surface-discharged alternating-current plasma display panels

The electron temperature and plasma density at the lateral distance of 125 /spl mu/m from the center of sustaining electrode gap have been investigated by a Langmuir probe along with the high-speed discharge image in coplanar alternating current plasma display panels. The plasma density at the lateral distance of 125 /spl mu/m from the center of sustaining electrode gap is shown to be maximum value of 3.7/spl times/10/sup 11/ cm/sup -3/, whereas the electron temperature is measured to be decreased from 1.8 to 0.8 eV as the gas pressure increases from 150 to 400 torr in this experiment. It is noted that the electron temperatures measured by the Langmuir probe and high-speed image camera are in good agreement with each other within 5% error limit.     

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介绍了一种对等离子体边缘进行径向扫描的往复静电探针系统,该系统由高压气源、传输杆、光栅尺、探针组件构成。它在一次放电中能测量主等离子体边缘的温度、密度、悬浮电位、空间电位、离子饱和电流、极向电场、粒子通量等参数的径向分布以及电子温度和密度的衰减长度。测量结果表明,利用该系统测量的主等离子体边缘参数分布与JT-60U、TEXT、HT-7等装置上测量的结果一致。     

Signature of quantum criticality in the density profiles of cold atom systems

In recent years, there has been considerable experimental effort using cold atoms to study strongly correlated many-body systems. One class of phenomena of particular interest is quantum critical (QC) phenomena. While prevalent in many materials, these phenomena pose notoriously difficult theoretical problems due to the vanishing of energy scales in the QC region. So far, there are no systematic ways to deduce the QC behavior of bulk systems from the data of trapped atomic gases. Here, we present a simple algorithm to use the experimental density profile to determine the T=0 phase boundary of bulk systems, as well as the scaling functions in the QC regime. We also present another scheme for removing finite-size effects of the trap. We demonstrate the validity of our schemes using exactly soluble models.     

Influence of the electron density profile on surface plasmons: Retardation effects

Hydrodynamics effects when used in conjunction with a diffuse surface are found to result in qualitatively new surface plasmon behavior in the optical region ($\text{q≈}\text{ω}\text{c}$).     

XPS analysis of down stream plasma treated wool: Influence of the nature of the gas on the surface modification of wool

A microwave plasma treatment in a down stream configuration was used to modify the natural hydrophobocity of untreated wool fibers. This property is a consequence of the presence of a Fatty acid monolayer (F-layer) on the outermost part of the fiber surface. The wool fibers treated with plasma were analyzed by means of X-ray photoelectron spectroscopy (XPS) without previous exposure to the air. Experiments have been carried out with air, water vapor, oxygen and nitrogen as plasma gas. The “in situ” analysis of the treated samples has permitted to differentiate between the plasma effects and those other linked to the exposure of the fibers to the air after their treatment. The results have evidenced the effects induced by the different active species generated by plasma from the different components of the air. In general, the intensity of CC peaks decreases and that of the CO, CO and OCO increases when using a gas containing oxygen species. Simultaneously, the intensity of the SS groups decreases and that of the sulphonate (SO₃⁻) increases. Other changes are also detected in the intensity of the N 1s level. The extent and characteristics of the oxidation and functionalisation of the hydrocarbon chains of the F-layer depend on the nature of gas. Thus, whereas treatments with plasmas of air and water vapor strongly affect the hydrocarbon chains of the F-layer, oxygen is less effective in the oxidation process. It has been also noted that the active species formed in the nitrogen plasma do not induce any significant change in the surface composition of the wool fibers.     

Intensity radial profiles of VUV line radiation near the solid target in a hot plasma

An investigation of hot plasma interaction with solid target is carried out at the CASTOR tokamak (IPP Prague) and the GOL-3 multi-mirror magnetic trap faccility (Budker Institute, Novosibirsk) [1], [5]. In both experiments, the Imaging Seya-Namioka Spectrometer based on a spherical dispersion grating has been upraded to monitor the radial profiles of the chord-integrated low-Z impurity line intensities in VUV spectral range. Such spatial resolved intensity monitoring in radial direction together with application of the radiation code simulation allows obtaining a radial distribution of ions of different ionization stages near the target immersed in edge plasma. The energy release from plasma to the target is order of 100 J/m² in the CASTOR tokamak and 30 MJ/m² int he GOL-3 magnetic open confinement system.     

Influence of the electron-hole density profile on the reflectivity of laser irradiated silicon

We study the influence of the spatial extension of the electron-hole plasma created by a pump pulse on the reflectivity of a probe pulse. We show that the density deduced from reflectivity measurements is the surface density value with a very good accuracy, except very close to the plasma resonance. We also show that the resonance broadening due to the spatial inhomogeneity can be larger than the one due to free carriers absorption and has to be included in the usual experimental determination of the plasma relaxation time.     

温度对气体折射率的非线性影响

对测量群折射率的迈克耳孙白光干涉技术进行了改进,采用光栅线位移传感器提高反射扫描镜的位移精度. 实验确定了空气折射率对温度的非线性曲线拟合方程,其拟合因子的精度达到10-5℃-1.