The influence of a radial magnetic field on current-voltage characteristics of toroidal glow discharge

The present paper deals with the influence of a radial magnetic field on different regions of the toroidal glow discharge and with the subsequent changes of the current-voltage characteristics. From the above it is clear that when studying the influence of a transverse magnetic field on the glow discharge it is necessary to understand that the discharge is not a homogeneous unit and the change of current-voltage characteristics involves the total sum of changes of the properties in different regions of the discharge.     

The influence of a transverse magnetic field on a subnormal glow discharge in air

In subnormal glow discharge under d.c. excitation at different pressure in a varying transverse magnetic field (0 to 30 G) some measurements have been carried out for various initial average tube currents. The voltage across the discharge increases and average tube current and residual current decreases in the magnetic field. With the help of Beckman’s expression [4] for the axial field and the electron density distribution in a transverse magnetic field the observed variation of current and voltage can be satisfactorily explained. The variation of axial electric field with transverse magnetic field can be represented to a fair degree of accuracy by the derived equation. The behaviour of residual current with magnetic field has been observed in these oscillations.     

Two types of spherical stratified gas discharge

Results on experimental investigation of a volume low-pressure gas discharge between the walls of a metal chamber and the small anode in the center of the chamber are represented. The discharge current-voltage characteristics in the range of currents corresponding to Townsend and glow discharges are measured. The experiments were carried out in nitrogen, argon, helium, carbon dioxide, and argon-acetone mixture. Hysteresis of current voltage characteristics is observed for some gas media in the link area of Townsend and glow discharges. It is found that the Townsend spherical discharge plasma is always stratified. Contrary to the glow discharge, stratification in this case is observed in all gases and remains for an arbitrary length of time.     

针-板和针-水电极大气压直流辉光放电的光谱特性

利用光谱学方法,对针-水电极和针-板电极直流辉光放电特性进行了比较研究。结果发现两种装置产生的放电都有明显的分区现象, 从阴极到阳极分别为负辉区、阴极暗区、正柱区和阳极辉区。针-板电极放电中可以清晰地观测到阳极暗区, 而针-水电极放电阳极暗区不明显。对比两种放电的伏安特性曲线,发现放电电压均随电流增大而减小,但相同电流下针-水电极间的电压大于针-板电极间的电压。由于伏安特性具有负斜率,且放电电流密度介于10-5～10-4 A·cm-2,说明两种装置中的放电均处于正常辉光放电阶段。在正常辉光放电的范围内比较两种放电的发射光谱, 发现发射光谱中都包含N₂的第二正带系(含波长为337.1 nm的谱线)和N+₂的第一负带系(含波长为391.4 nm的谱线),但相对强度不同。利用光谱学方法对放电发射谱的谱线强度比I_391.4／I_337.1和振动温度进行了空间分辨测量,发现相同位置处针-水电极放电的谱线强度比要比针-板电极放电的大,并且相同位置处针-水电极放电的振动温度高。     

气压对微束射频容性放电模式调制的研究

微束射频容性放电在纳米晶体颗粒等离子体增强气相合成有着潜在的应用前景.本论文利用ICCD、单反相机、高压探头和电流探头等对微束射频容性放电特性进行了实验诊断研究.结果发现:在纯氩气微束射频放电中,随着气压的增加,放电从辉光放电模式向多通道丝状放电模式转换;在99%氩/1%氢混合气体微束射频放电中,丝状放电模式消失,而是从低气压全空间分布的辉光放电模式,到中等气压向轴心收缩的辉光放电模式,最后到高气压的“环状”辉光放电模式;而在纯氢气微束射频放电中,随着气压的增加,放电模式直接从全空间分布的辉光放电模式向“环状”辉光放电模式转换.最后通过射频电场中电子加热、趋肤效应和气体热传导的共同作用解释了产生不同放电模式的物理机制.     

An Electrodeless Discharge at 60 Hz

Inductive glow discharges have been generated in argon at pressures between 0.6 and 3.0 Torr in an 80-mm wide toroidal tube that was threaded by a magnet core system of 400 cm2 cross section. The fields required to maintain the discharges were produced by exciting the core at 60 Hz. Starting was accomplished either by a capacitor discharge through auxiliary electrodes or in an electrodeless manner by exciting the core at 9600 Hz. Plasma currents at 1 Torr exceeded 100 A andc were slightly trailing the voltage. Mean electron densities at this condition were estimated to be 5 × 1013/cm3. Power dissipation in the discharge was between 0.5 and 1.9 kW at an average conversion efficiency of 60%.     

The effect of magnetic field on plasma particles in dusty plasma

In this work, we present the investigation of the formation features and internal structure of dust clouds created in plasma of glow discharge in the external magnetic field corresponding to a range of moderate and strong fields, at which the ion component is magnetized. The analysis of the plasma magnetization in the presence of dust components is carried out. We defined the values of magnetic induction at which the changes in dynamics of plasma particles in magnetic field in light inert gases are expected. The experimental setup was built in two versions. For the purpose of generating of magnetic field, the first setup was equipped with ordinary magnetic coils, and the second one included a superconducting solenoid. The discharge tubes, the main chambers where plasma was ignited and maintained in a glow discharge in lowered pressure, also have certain peculiarities, which we describe below. While using helium as a bulk gas, our study focused only on the dust trap in the region of narrowing discharge current. For neon, we used two traps: the striation trap and one just mentioned above placed in the narrowing of the discharge tube. As a result, the steady dust structures in a glow discharge under the magnetization of ions and electrons were obtained for the first time. Dust structures were rotated and tended to form a dust cluster and shell structure. A number of parameters of magnetization achieved in experiments were calculated.     

Low pressure toroidal glow discharge in the radial magnetic field

The behaviour of the plasma of a low pressure toroidal glow discharge in a radial magnetic field is studied experimentally. Results concerning the plasma velocity as a function of the magnetic field for different pressures are given.The author wishes to express his thanks to Prof. J. Kracík DrSc for valuable advice and suggestions and Mr. K. Kavalier for his active assistance.     

Conversion of an atomic to a molecular argon ion and low pressure argon relaxation

The dominant process in relaxation of DC glow discharge between two plane parallel electrodes in argon at pressure200 Pa is analyzed by measuring the breakdown time delay and by analytical and numerical models. By using the approximate analytical model it is found that the relaxation in a range from 20 to 60 ms in afterglow is dominated by Ar+2ions,produced by atomic-to-molecular conversion of Ar+ions in the first several milliseconds after the cessation of the discharge.This conversion is confirmed by the presence of double-Gaussian distribution for the formative time delay, as well as conversion maxima in a set of memory curves measured in different conditions. Finally, the numerical one-dimensional(1D)model for determining the number densities of dominant particles in stationary DC glow discharge and two-dimensional(2D) model for the relaxation are used to confirm the previous assumptions and to determine the corresponding collision and transport coefficients of dominant species and processes.     

Self-consistent structure of a dc discharge with a closed hall current in crossed electric and magnetic fields

A dc glow discharge with a closed Hall current in crossed electric and magnetic fields in helium is investigated. It is shown that the main features of an unmagnetized dc discharge [1] (such as the separation of the discharge into a space charge sheath and a quasineutral plasma, the formation of a cathode fall region and a negative glow, the appearance of a region with a reversed electric field producing a potential well for low-energy electrons and resulting in the formation of a Faraday dark space, and the formation of three pronounced groups of electrons in the electron distribution function) are also retained in a discharge in crossed fields. It is found that the sheath length is almost independent of the magnetic field, while the length of the negative glow region decreases appreciably with increasing magnetic field. The measured electron distribution function agrees well with the nonlocal theory, according to which the current in the Faraday dark space is carried by the intermediate electrons that are not trapped in the potential well and the energies of which are lower than the first excitation energy.     

The Influence of Parasitic Capacities on Measurements of the Dynamic Behaviour of a Gas Discharge

Measurements of the impedance behaviour of the positive column of a glow discharge are falsified by parasitic capacities. A model, which respects these capacities, was developed and tested by computer simulations and experimental data. Using this model it is possible to correct the influence of parasitic capacities on experimental measured impedance curves. The efficiency of this method is demonstrated on some measurements in a neon discharge.     

Interaction of a surface glow discharge with a gas flow

A surface glow discharge in a gas flow is of particular interest as a possible tool for controlling the flow past hypersonic aircrafts. Using a hydrodynamic model of glow discharge, two-dimensional calculations for a kilovolt surface discharge in nitrogen at a pressure of 0.5 Torr are carried out in a stationary gas, as well as in a flow with a velocity of 1000 m/s. The discharge structure and plasma parameters are investigated near a charged electrode. It is shown that the electron energy in a cathode layer reaches 250–300 eV. Discharge is sustained by secondary electron emission. The influence of a high-speed gas flow on the discharge is considered. It is shown that the cathode layer configuration is flow-resistant. The distributions of the electric field and electron energy, as well as the ionization rate profile in the cathode layer, do not change qualitatively under the action of the flow. The basic effect of the flow’s influence is a sharp decrease in the region of the quasineutral plasma surrounding the cathode layer due to fast convective transport of ions.     

伪火花放电开关电压跌落过程实验研究

 设计了典型参数下的伪火花放电开关，进行了空气介质下的电压特性实验，给出了伪火花开关放电电压与气压变化的关系曲线；测量了产生伪火花放电的气压范围（1~29Pa）和单间隙伪火花放电开关耐受电压的最大值(40kV)，测得了伪火花放电与辉光放电的转折点气压(29Pa)，并对实验结果进行了理论分析。研究了伪火花放电开关电压跌落时间与放电电压的关系，首次将开关电压跌落过程分为暂态阶段和稳态阶段，讨论了放电电路参数，气体压力，开关结构和放电电压对电压跌落时间的影响。实验表明，在气压和开关结构不变的条件下，暂态过程时间由放电电压决定，电压越高，则所需时间就越短；稳态过程时间由放电电路参数决定，不受放电电压影响。     

Loss factor study

In the present paper the so-called “loss factor” for the case of toroidal plasma accelerator is determined on the basis of the law of momentum conservation. This factor characterizes the influence of the remaining gas on the plasma movement. The magnitude of this factor is determined also experimentally. The low-pressure toroidal glow discharge situated in the moving magnetic field was used for experiments.     

Comparison of propagation of a shock wave in a decaying plasma in various gases

The effect of gas humidity and composition on shock wave splitting in the plasma of a decaying glow discharge is investigated in dried and moist air, nitrogen, and argon over various time periods after the discharge termination. The shapes of the signals reflecting the gas pressure distribution behind the shock wave in these media are approximately the same except for some values of decay time comparable to the characteristic time of decay of excited state concentration (including singlet oxygen) after the termination of the discharge (8 ms). The signals in the same four gases are compared quantitatively for different time periods after discharge termination by expanding the signal into a Fourier series. The free term and the second and third modes in the Fourier expansion are compared. Analysis is carried out for up to time periods of 60 ms.     

Electromagnetic Wave Propagation in a Magneto-Plasma Filled Coaxial Structure: II, Experimental

Measurements have been made of electromagnetic propagation in a coaxial electrode structure filled with longitudinally magnetized plasma. The annular plasma region had a 9.55 cm outer diameter, a 3.82 cm inner diameter and was approximately 60 cm long. A magnetic field of 300 gauss was employed. Electromagnetic wave frequencies were in the range .5 to 2.4 GHz. The plasma was generated by a continuous glow discharge. The resulting ? vs. ? curves closely follow the predicted curves for the "quasi-TEM" mode. On the basis of this model, plasma frequencies were 40 - 80% of the cyclotron frequency, depending on magnitude of the glow discharge current.     

实验研究大气压多脉冲辉光放电的模式和机理

采用稍不平行电极进行大气压He气介质阻挡多脉冲辉光放电实验,通过增强电子耦合器件相机短时曝光照片,研究大气压多脉冲辉光放电在不同时刻的放电模式.通过气隙放电电流、表面电荷计算,理论分析了表面电荷、空间电荷、外加电压与气隙电场强度的关系,研究大气压辉光放电形成多脉冲的机理.实验结果表明,放电首先在间隙稍窄的电极左端开始;在第一个脉冲电流峰值,电极右端也开始放电;第一个电流脉冲经历了Townsend放电到辉光放电的过程;电流脉冲之间的时间内,间隙一直维持着微弱的辉光放电;随后的每个电流脉冲均是辉光放电.理论分析表明,大气压辉光放电的多个电流脉冲是表面电荷、空间电荷与外加电压共同演化的结果;除放电伊始出现Townsend放电外,同一半周期内的放电电流脉冲中不会再出现Townsend放电.     

实验研究大气压多脉冲辉光放电的模式和机理

采用稍不平行电极进行大气压He气介质阻挡多脉冲辉光放电实验,通过增强电子耦合器件相机短时曝光照片,研究大气压多脉冲辉光放电在不同时刻的放电模式.通过气隙放电电流、表面电荷计算,理论分析了表面电荷、空间电荷、外加电压与气隙电场强度的关系,研究大气压辉光放电形成多脉冲的机理.实验结果表明,放电首先在间隙稍窄的电极左端开始;在第一个脉冲电流峰值,电极右端也开始放电;第一个电流脉冲经历了Townsend放电到辉光放电的过程;电流脉冲之间的时间内,间隙一直维持着微弱的辉光放电;随后的每个电流脉冲均是辉光放电.理论分析表明,大气压辉光放电的多个电流脉冲是表面电荷、空间电荷与外加电压共同演化的结果;除放电伊始出现Townsend放电外,同一半周期内的放电电流脉冲中不会再出现Townsend放电. 关键词： 介质阻挡放电 增强电子耦合器件 大气压辉光放电 多脉冲     

Emission from a DC glow discharge in a He/H2O mixture

The electrical and optical characteristics of a longitudinal dc glow discharge in a cylindrical discharge tube in mixtures of helium with saturated water vapor at room temperature are investigated. In the UV range, a broad band with a maximum at λ_max=309.6 nm and Δλ=9 nm prevails. The H_α 656.3-nm, H_β 486.1-nm, and HeI lines in the range 440–670 nm are the main diagnostic spectral lines. The helium partial pressure and the glow discharge current are optimized to achieve the maximum intensities of the 309.6-nm band and HeI and HI spectral lines. The results obtained are of interest for the development of an ecologically safe radiation source based on the products of the decomposition of water molecules and clusters in plasma.     

Glow discharge cleaning of vacuum switch tubes

To clean the surfaces of parts inside a vacuum-switch tube (VST) the authors propose a technique which generates a glow discharge between the inner electrodes and the copper grid surrounding it. Photographic observation reveals that the glow discharge spreads out and cleans the whole surface inside the VST. A breakdown test between the inner electrodes shows the effect of the cleaning with this technique. Higher breakdown voltage between the inner electrodes is attained by performing this glow discharge cleaning in argon rather than hydrogen gas. The difference of the cleaning effect seems to be attributed to that of the energy transfer from ion species to the adsorbed molecules and microprotrusions on the surfaces