Ionization Waves in Glow Discharges with Non-Uniform Magnetic Fields

The properties of ionization waves self-excited in glow discharges with a non-uniform axial magnetic fields are investigated experimentally. The fundamental frequency remains almost constant over the tube for the variable magnetic fields, while the amplitude decreases with increasing the field. The wavelength becomes longer at the cathode side of the magnetic coil and shorter at the anode side with increasing the local magnetic field. The dependence of the wavelength on the magnetic field is explained by the changes of the axial electric field in the non-uniform magnetic field.     

辉光放电等离子体镁电离的研究

以铝镁合金作阴极,采用吸收光谱测定了辉光放电放电等离子体中镁离子和原子的相对密度。提出了在近似条件下,由镁离子和原子吸光度比法求算镁电离度的方法。探讨了电离对常规分析的干扰与校正,以及影响镁电离的因素。     

Experimental Study of Ionization Waves in the contracted Discharge in Neon

It is proved experimentally that there exist constriction ionization waves propogating in the form of current pinch neckings. Dynamics of abrupt contraction and strate arising is investigated by current modulation near the critical value. Dispersion laws are determined depending on discharge conditions.     

Investigations about the Influence of the External Circuit Elements on the Propagation of Ionization Waves in the Positive Column of a Neon Glow Discharge

Our investigations have been motivated by former works of Michel and Achterberg [1]. They described the important influence of the external circuit elements and connected therewith the mechanism of feedback (Barkhausen k · v ≧ 1). The properties of external and self-excited moving striations (threshold current, fundamental frequency) are strongly influenced by the feedback. This paper demonstrates the differences occuring either a voltage or a current source in the external circuit is used in order to perturb the discharge and to realize different degrees of feedback by changing the external resistor R_ext. of the discharge. It is shown the impact on the fields of existence of self excited striations in a non driven discharge. Furthermore our investigations yield differences in the width of Arnol'd tongues [2] of periods one and two in the perturbed discharge depending on a varied degree of feedback. Last not least its influence on the behaviour of quasiperiodic and chaotic states is demonstrated. The investigations permit first information concerning the sensivitity of one parameter variation (feedback controll by external resistor) which might be used e.g. for a stabilization of unstable periodic orbits (controlling chaos).     

The Theory of Ionization Waves in the Contracted Discharge of Noble Gases

Positive column plasma in noble gases at middle pressures is analysed for stability in the frames of the linear hydrodynamic theory. At critical values of pressure and current the discharge becomes unstable to radial contraction (contraction) and to wave disturbances of the type of current pinch constrictions (contraction ionization waves). Ionization waves in the contracted discharge are three-dimensional formations with electron concentration oscillations on the axis in the opposite phase with current pinch cross section. The discharge diffuse-recombination theory was used for analysing the problem of instability arising.     

大功率脉冲氙灯的放电研究

利用转镜式高速摄影机分幅摄影技术,对脉冲氙灯放电中的沟道扩展和熄灭过程进行了摄影和分析.放电时沟道扩展速度很快,呈树枝状,沟道熄灭过程长于扩展过程,且呈斑状.同时研究了预电离放电对沟道扩展和熄灭过程的影响,当预电离存在时,脉冲氙灯放电的沟道扩展的时间要长.结果表明,预电离有利于放电沟道的形成,提高氙灯的发光效率,且有助于减小主放电能量对管壁材料的冲击.     

氮气中空心阴极放电条纹的发光特性

利用发射光谱法,在氮气环境下研究了圆柱型空心阴极放电条纹的特性。测量得到了气压为20 Pa,放电电流为1.3 mA时条纹区的发射光谱,结果表明发射光谱主要为氮分子的第一正带系(B3П_g →A3П_u)和 第二正带系(C3П_u→B3П_g )。利用双原子光谱发射理论,计算得到了氮分子振动温度的空间分布特性。结果表明光谱线强度呈周期性分布,明纹中心处的谱线强度高于暗纹中心处的谱线强度。明纹中心处的N₂分子振动温度为3 500～4 400 K,并且从阴极到阳极,明纹中心处光谱线强度和分子振动温度逐渐下降。同时测量得到了放电电流为1.0和1.5 mA时的发光条纹特性,研究了放电电流对条纹特性的影响。随着放电电流的增加,明纹中心处的分子振动温度升高,条纹间距增加。另外,利用测量得到的发光条纹,计算得到了条纹区的平均约化电场强度为44～49 m-1·Pa-1,并且由阴极向阳极逐渐降低。对于揭示气体放电中发光条纹的形成机理和促进空心阴极放电的稳定性有重要的参考价值。     

Quenching Effect of Microwave to DC Glow Discharge in Gas Lasers

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Negative Ions in a Glow Discharge of Tetrafluoromethane

The Langmuir — probe measurements in a CF₄ — glow discharge reveal a large number of negative ions (10¹⁰ cm^?3) in the plasma between the planar C-electrodes. Under special conditions the density of them exceeds the electron density at several orders of magnitude and sustains a quasi — electron free plasma. The ratio depends on the residence time of the molecular gas in the discharge reactor. It is due to dissociative electron attachment to highly molecular gas components arising from the plasmachemical conversion of CF₄. F^? and CF₃^? are the most important negative ions.     

Self-Consistent Stationary Distributions of the Electric Field and Plasma Density in the Process of Ionization Self-Channeling of Quasielectrostatic Waves

Radiophysics and Quantum Electronics - We find self-consistent stationary distributions of the electric field and plasma density in the process of ionization self-channeling of quasielectrostatic...     

Asymptotic Models of Diffusion Effects due to Nonlinear Resonant Interaction of Waves with Flows

We develop an asymptotic theory describing nonlocal effects caused by weak-diffusion processes in the case of resonant interaction of quasi-harmonic waves of small but finite amplitudes with flows of various physical nature in the case of an arbitrary relation between the nonlinearity and diffusion.We analyze the interaction of internal gravity waves with plane-parallel stratified shear flows in the nonlinearly-dissipative critical layer (CL) formed in the vicinity of the resonance level where the flow velocity is equal to the phase velocity of the wave. It is shown that the combined effect of the radiation force in the inner region of the CL and vorticity diffusion to the outer region results in the formation of a flow in which the asymptotic values of average vorticity at different sides of the CL are constant but different. If the criterion of the linear dynamic stability is satisfied (the Richardson number Ri>1/4), the resulting vorticity steps are comparable to the unperturbed vorticity. As a result, a wave reflected from the vorticity inhomogeneity in the CL is formed. As the amplitude of the incident wave increases, the average vorticity at the incidence side approaches the linear-stability threshold (Richardson number Ri > 1/4), and the reflection coefficient tends to -1.In the regime of nonlinear dissipative CL, we study the quasi-stationary asymptotic behavior of the flow formed by an internal gravity wave incident on a dynamically stable flow with velocity and density stratification, whose velocity at some level is equal to the phase velocity of the wave. It is shown that the vorticity diffusion results in the formation of a nonlocal transition region between the CL and the unperturbed flow, which we call the diffusive boundary layer (DBL). In this case, the CL is shifted toward the incident wave. We obtain a self-similar solution for the average fields, which is valid in the case of a constant vorticity step in the CL, and determine its parameters depending on the inner Reynolds number in the CL which describes the relation between the nonlinear and diffusive effects for the wave field in the resonance region. We determine the structure and temporal dynamics of the DBL formed by a rough surface streamlined by a stratified fluid whose velocity changes direction at some level.It is shown that in the case of the nonlinear resonance interaction of plasma electrons with a Langmuir wave, the electron diffusion in the velocity space leads to a significant nonlocal distortion of the electron distribution function outside the trapping region. We determine the distorted distribution function and calculate the rate of the nonlinear Landau damping of a finite-amplitude wave for an arbitrary ratio of the electron collision rate and the oscillation period of trapped electrons.     

辉光放电光谱分析技术在金属材料分析中的应用

本文主要介绍了辉光放电光谱仪的基本原理，分析特点以及在金属材料分析中的应用，并从理论上推导出辉光放电光谱分析技术用于金属材料分析的理论依据。着重介绍了基板分析、深度逐层分析。对磷青铜镀银层逐层分析；渗碳、氮钢板分析；彩涂钢板分析进行了探讨。     

Atmospheric Pressure DC Glow Discharge in Semiconductor Gas Discharge Electronic Devices

The stabilization of dc glow discharges in a dc plasma is studied experimentally in air and neon media functions of pressure $p$, interelectrode distances $d$, and diameter $D$ of the cathode areas in the semiconductor gas discharge electronic devices (SGDED) with GaAs cathode. Comparision of current and discharge light emission (DLE) from SGDED are used for the determination of the stabilization under low- and atmospheric-pressure glow microdischarge conditions. It is found that uniform DLE can be generated in Ne up to atmosphere pressure different from the case in air under specific conditions. Apart from the homegeneous results, nonhomogeneous current–voltage characteristic forms are also observed for some parameter sets. The experimental results reveal different discharge behaviors in both gas media at atmospheric pressure.      

Above-Threshold Ionization of Xenon by Chirped Intense Laser Pulses

We experimentally investigate above-threshold ionization of xenon subject to chirped intense laser pulses. While for few-cycle laser pulses free of chirp, the Freeman resonance narrow peaks in the photoelectron spectra become strongly suppressed, they will re-emerge for laser pulses with a certain chirp. Moreover, the position of the resonant peaks exhibits a strong dependence on the direction of the chirp. The experimental features can be understood by a two-step ionization process; that is, a multi-photon excitation plus subsequent ionization process.     

Atomic Emission Spectrometry of Microsamples in a Glow Discharge

A glow discharge system for atomic emission spectrometry is evaluated for physical and analytical characteristics. Lead (as the nitrate) is the model element used for these studies. The sputtering characteristics of several electrode designs are studied with the best system tried resulting in total sample vaporization in less than 1 s. Discharge currents up to 200 mA at a discharge voltage of 1200 V and a pressure of 2 torr are found to give the best results. The detection limit for lead is 0.9 ng and the linear dynamic range of response is greater than 2 orders of magnitude. Sodium chloride at a 100-fold excess amount causes a 50% decrease in the signal level.     

Ionization yield in neon due to electron impact

A theoretical study of the ionization yield in neon due to electron impact has been performed. With a given set of collision cross sections, a comparison of the Fowler equation (which takes into account the discrete nature of energy loss) and the continuous-slowing-down approximation (CSDA) has been made by applying the two methods for energies from ionization threshold to 1 keV. The CSDA is found to be very poor at low energies. A hybrid model consisting of the Fowler equation for low energies and CSDA for high energies is found to be quite satisfactory throughout the energy range. The mean energy dissipated per ion pair formed (W value) is finally calculated in this model for electron energies up to 10 keV taking into account the multiple ionization and the effect of Auger electrons. The results are in good agreement with the available experimental data.     

Simulation of an Ultrahigh-Pressure Short-Arc Xenon Discharge Plasma

Technical Physics - We have studied a high- (ultrahigh-) pressure short-arc discharge in xenon with thoriated tungsten cathodes. A system of equations formulated based on earlier experimental data...