Continuous radiation from a dense,weakly non-ideal,argon plasma

Continuum radiation from the argon plasma generated by a cascade arc has been investigated over the pressure range 1–10 atm and the temperature range 12?16×10³⁰K in the visible, near i.r. and u.v. spectral regions. Plasma temperatures were found from absolute intensities of the argon atom and ion lines; the concentrations of charged particles were determined from the ion-line half-widths.The results obtained on the continuum radiation intensity are compared with theoretical and experimental data obtained by other authors. At elevated pressures, the experimental data have been found to exceed theoretical values in the spectral region under investigation. The dependence of the recombination-threshold-shift in the plasma on azimuthal quantum number appears to be worthy of special attention. Possible reasons for excess radiation are discussed.     

New possible laser media in the UV and XUY in high current heavy ion beam induced plasmas

Mixtures of rare gases with alkali-metal vapour were excited by a high power argon ion beam in a windowless gas target system. Narrow emission continua were observed in the vacuum ultraviolet region between 60 and 200 nm. The observed emission was assigned to the decay of a new class of excited ionic molecules Rg⁺ A formed by the combination of a rare gas ion Rg⁺ with an alkali atom A. These excimer-like ions are of great interest for possible short-wavelength lasers, because the ground state consisting of a rare gas atom and an alkali ion is only weakly bound. The observed decay energies and fine structure splittings agree well with the prediction of calculations. A summary of previous results is presented.Supported by the German Government Department for Research and Technology (BMFT), Bonn, Germany.     

Laser interferometric measurements of electron density in an arc plasma

The paper describes the application of a laser interferometric technique to arc discharges operating at atmospheric pressure. The limitations of this method are discussed in detail. Results are given for the axial electron density in an argon arc, tube 5 mm diameter, over a current range 30–75 A. In addition the decay of the electron density following rapid arc interruption is also given. It is shown that the time constant of the conductance decay which can be derived from the preceeding measurements is in very good agreement with experimental values determined directly.     

Das Neutralgasprofil und die Elektronentemperatur in der Freifallsäule bei hohem Ionisationsgrad

The formula for the ion density is corrected. Furthermore, for different accommodation coefficients at the wall numerical values of the neutral atom velocities in argon ion lasers are estimated. The neutral gas heating by electron collisions is relatively small in argon ion lasers.     

Decay of inert-gas-discharge plasma in the expansion mode. Part 1: Dynamics of the plasma ionization state,criterion of recombination nonequilibrium,and experimental study of argon plasma decay

The influence of expansion of a pulsed arc plasma on its decay is studied theoretically and experimentally with allowance for deviation from the equilibrium state. The dynamics of the ionization state during the decay of a dense expanding plasma is traced, and a criterion of its recombination nonequilibrium is determined. The results of calculation are compared with experimental data by the example of a pulsed arc in argon.     

Simulation study of argon adsorption on (0 0 1) faces of phyllosilicates

Grand Canonical Monte Carlo molecular simulations have been performed for argon and nitrogen adsorption on the basal surfaces of phyllosilicates without surface cations. The results have been compared with derivative isotherms analysis of experimental data. An optimization of the surface-Ar interaction has been performed by varying the oxygen atom LJ ?/k_B parameter and the optimized value was used to perform the nitrogen adsorption simulations. The analysis of the argon adsorption simulation indicates that adsorption mechanisms are more complex than may be suggested by experimental results obtained by low-pressure adsorption. The structure of the adsorbed film has a marked dynamic behaviour and the monolayer capacity strongly depends on the equilibrium relative pressure. For nitrogen adsorption, while high pressure behaviour is simulated adequately, some deviation is observed in low-pressure region of the isotherms suggesting that additional simulation and perhaps the use of a more sophisticated potential to model the nitrogen molecule can be necessary to understand fully the behavior of this gas on clay minerals.     

仪器展宽对大气压等离子体电子密度测量的影响

实验使用两台不同的单色仪,采用光谱线型法测量了大气压氩气介质阻挡放电中的电子密度.诊断结果表明,由于不同的单色仪其仪器加宽不同,仪器加宽对总的光谱线型有较大影响.通过考虑等离子体中的各种加宽机制,采用卷积和反卷积的方法对氩原子发射谱线线型进行了分析,从整个光谱线型中分离出Stark线型,排除了仪器加宽对最终诊断结果的影响.从而最终测量了大气压氩气介质阻挡放电中的电子密度.测量得到在大气压氩气介质阻挡放电中单个放电丝存在时,电子温度为10000K时,电子密度约为3.05-3.26×1021 m-3.此方法不仅可以应用在大气压介质阻挡放电中,还可以用于测量其它大气压等离子体电子密度.     

氩原子基态波函数和能量的解析计算

以第一性原理和变分原理为基础,给出了氩原子基态波函数的一种解析表达式,计算了基态氩原子(含类氩离子)的能量,导出了所涉及的所有积分的解析表达式.对氩原子,所得到的能量理论值与实验值的相对误差为0.22%.     

Die Erzeugung von negativen polarisierten Deuteriumionen aus metastabilen Deuteriumatomen im 2S 1/2-Zustand

An experimental method to produce polarized negative hydrogen ions is discussed and compared with other methods. The method makes use of the different lifetimes of the metastable 2S 1/2 state and the 2P 1/2 state of the hydrogen atom. Polarized ion beams are obtained by using a selective quenching process followed by selective ionisation. Experimental results are given for the intensity and polarization of the polarized negative ion beam of deuterons. These results were obtained as a function of the quenching-field, the magnetic field in the argon-cell and the density of argon and cesium. The yield of negative ions can be expressed by the cross sections for the different charge exchange reactions in argon. The measured tensorpolarisationP ₃₃ can be interpreted as a function of the cross sections, the argon-density and the magnetic field along the beam axis. Beams of 50 nA intensity were produced with a polarization ofP ³³=?0.250±0.006. The main advantage of this method is a low beam emittance, values of 0.7 cm rad eV^1/2 were achieved. The production of a polarized positive deuteron beam seems to be possible.     

Determination of static dipole polarizabilities of Yb atom

We determine the static values of the scalar and tensor dipole polarizabilities of the ground, 6s6p~3P_0~o, and 6s6p~3P_1~o states of the Yb atom. These results can be useful in many experiments undertaken using this atom. We employed a combined configuration interaction(CI) method and a second-order many-body perturbation theory(MBPT) to evaluate energies and electric dipole(E1) matrix elements of many low-lying excited states of the above atom. These values are compared with the other available theoretical calculations and experimental values. By combining these E1 matrix elements with the experimental excitation energies, we estimate the dominant valence correlation contributions to the dipole polarizabilities of the above states. The core contribution is obtained from the finite field approach. We also compare these values with the other theoretical results as there are no precise experimental values that are available for these properties.     

Spontaneous emission of an atom placed near the aperture of a scanning microscope

Analytic expressions in the quasi-static approximation are obtained for the spontaneous decay rates of an atom placed near the circular aperture of a scanning microscope. The results obtained show not only that the spontaneous decay rates increase substantially near the aperture edge but also that the atomic decay appreciably slows down near the aperture center if the vector of dipole transition moment lies in the aperture plane.     

Line shape and lifetime in argon 2p electron spectroscopy

The argon 2p photoelectron spectrum and the argon L₃M₂₃M₂₃ ¹S₀ Auger spectrum have been measured at several photon energies between 6 and 80 eV above the 2p_3/2 threshold with an instrumental line width significantly smaller then the natural line width. The spectra are described well by the theory of van der Straten et al. [Z. Phys. D 8 (1988) 35] provided that allowance is made for the instrumental resolution and measurements are made at a sufficiently low pressure. The lifetime (Lorentzian) line width determined from these measurements for the core-ionized atom is 112±3 meV, in good agreement with the line width for the 2p_3/2→4s core-excited state, 114±2 meV, indicating that the 4s electron has little influence on the Auger decay rate. Remeasurement of the line width for the carbon 1s hole in carbon dioxide gives values in good agreement with the previous measurement of 99 meV.     

Kinetic simulations of argon dusty plasma afterglow including metastable atom kinetics

The afterglow of a dusty plasma of rf discharge in argon is simulated by the particle-in-cell-Monte Carlo collision (PIC-MCC) method. The experimental observation that heavy dust contamination of plasma leads to an anomalous increase in the electron density at the beginning of afterglow is explained by release of electrons from the dust surface. Under the assumption that the floating potential of particles is in equilibrium with plasma conditions, the fast cooling of electrons in afterglow plasma due to a rapid escape of hot electrons from the volume leads to a decrease in the magnitude of the floating potential and hence to a loss of charge by dust. The intensive desorption of electrons from nanoparticles is the origin of anomalous behavior of the electron density. At the next stage of afterglow, when the electrons become cool, the plasma decay is defined by ambipolar diffusion. The effect of metastable argon atoms is also considered. Additional ionization due to metastable atom collisions affects the electron temperature but does not change the behavior of the electron density qualitatively.     

Influence of the Basic Process Parameters on the Ion/Atom Arrival Rate Ratio during Magnetron Sputter Deposition of Thin Carbon Films

The behaviour of the ratio of the argon ion flux and the sputtered atom flux to the substrate with the variation of the basic process parameters was studied in a planar magnetron sputtering system. Finding ways to control this ratio is important with respect to carrying out ion-assisted thin film growth by magnetron sputtering under well-defined conditions. Combined deposition rate measurements and plasma probe measurements were carried out in order to determine the ion/atom arrival rate ratio. In addition calculations of the neutral atom flux were performed on the basis of a simple model and the results compared with the measured values. A considerable change in the values of the ion/atom arrival rate ratio with the variation of the argon pressure and the discharge power was found under operating conditions, at which the back diffusion of the sputtered material is pronounced. The distribution of the ion flux over the substrate surface was found to become more homogeneous with the increase of the working pressure or the target-to-substrate distance.     

Open flavour charmed mesons in a quantum chromodynamics potential model

We modify the mesonic wave function by using a short distance scale r ₀ in analogy with hydrogen atom and estimate the values of masses and decay constants of the open flavour charm mesons D, D _s and B _c within the framework of a QCD potential model. We also calculate leptonic decay widths of these mesons to study branching ratios and lifetime. The results are in good agreement with experimental and other theoretical values.     

惰性气体原子对2500eV电子的绝对弹性散射微分截面

在入射电子能量为2500eV，散射角为4°—15°的条件下测量了氦、氖、氩的相对弹性散射微分截面，并采用非弹性散射的广义振子强度为标准进行刻度，得到了2500eV能量下的绝对弹性散射微分截面值.所得结果与前人的理论和实验结果作了比较. 关键词：     

大气压氩直流微放电光谱研究

微空心阴极放电或微放电是一种能够实现高气压下放电的有效方法。利用不锈钢空心针作阴极,不锈钢网作阳极,进行了大气压氩直流微放电实验研究。测量了大气压氩微放电光谱,发现氩气的发 射谱线主要集中在690～860 nm范围,且全部为氩原子4p—4s的跃迁。实验研究了不同放电电流、气体压强、气体流量与谱线强度之间的关系,发现谱线强度随放电电流、气体流量增加均增加,而谱线强 度随压强变化呈现不同特征：谱线强度随压强的增加先增加后降低,在13.3 kPa时强度最大。此外,选用跃迁波长为763.51和772.42 nm的两条光谱线,利用发射谱线强度比值法测量了氩气微放电等离子 体的电子激发温度。结果显示,其电子激发温度处于2 000～2 800 K之间,且随放电电流的增加而增加,随气体压强和气体流量的增加而降低。     

Systematic studies on α-decay half-lives for super heavy nuclei

Radioactive decay of super heavy nuclei via the emission of α-particles has been studied theoretically in the preformed cluster model (PCM). The nucleus-nucleus (NN) potential is obtained by double folding the density distributions of the α-particle and the daughter nucleus with a realistic effective interaction. The M3Y effective interaction, supplemented by a zero-range pseudo-potential for exchange term, is used to calculate the NN potential. The α decay half-lives for 317 nuclei at Z=102–120 are performed in the PCM framework with the theoretical Q values extracted from the Mller-Nix-Kratz and Liran-Marinov-Zeldes mass tables and are compared with the experimental data. The calculated results are also compared with those obtained by using Q values from the Muntian-Hofmann-Patyk-Sobiczewski and Myers-Swiatecki mass estimates.     

K\rightarrow \pi\pi e^+e^- decays and chiral low-energy constants

The branching ratios of the measured decay and of the still unmeasured decay are calculated to next-to-leading order in chiral perturbation theory (CHPT). Recent experimental results are used to determine two possible values of the combination of weak low-energy couplings (LECs) from the chiral Lagrangian. The values obtained are compared to the predictions of theoretical approaches to weak counterterm couplings to distinguish between the two values. Using the favoured value of the combination and taking into account additional assumptions suggested by the considered models, one obtains the branching ratio of the second decay as a function of the unknown combination of weak low-energy couplings. Finally, using values of the individual LECs derived from a particular model, one predicts the branching ratio of the decay. Received: 27 February 2001 / Published online: 11 May 2001