Bipolar atmospheric-pressure corona discharge in a He/H2 mixture

Results are presented from a study of the characteristics of a steady-state plasma in a He/H₂ mixture at high pressures. The plasma is formed in the outer region of a multielectrode corona discharge. It is shown that molecules of helium hydride form in such a medium, and their decomposition is accompanied by continuum emission in the 350–650 nm region. The corona discharge is distributed over the length and can be used in systems for the transverse electric circulation of the working medium of atmospheric-pressure plasma radiation sources. The reference spectra of the plasma emission and the dependence of the relative intensity of the lines and the brightness of the bands of He ₂ ^* on the value of the discharge current, pressure, and composition of the working mixture are investigated. Zh. Tekh. Fiz. 69, 33–37 (July 1999)     

Numerical simulation of corona discharge in N2

A numerical study of a negative corona discharge in nitrogen in a point-plane gap using a Monte Carlo method is presented. The simulation provides a detailed structure of avalanches, propagation of successive avalanches and ion distribution can be discerned. The development of electron avalanches is due to ionization and photoionization in the high-field region, while the quenching of the avalanches is due to the low electric field near the plane electrode. Also the accumulation of electrons and positive ions are displayed in detail. The space charge field distortion is studied.     

Positive point-to-plane corona discharge forms in O2-N2 mixtures

An extensive survey has been made of positive point-to-plane corona discharges with 0–100% O₂ in O₂-N₂ mixtures in the pressure range 0.5–100 kPa. Selected results are presented in the form of pressure-voltage diagrams. They show the regions of existence for the different point-plane discharge forms observed: burst pulses, glow corona with oscillations, streamers, sparks, and a pulse- and oscillationless glow-spike corona. The latter positive corona discharge form has formerly only been observed in very pure nitrogen. The main aim of the paper is to give a short account of these different forms of positive coronas and their stability or oscillations, and to guide experimenters in establishing experimental conditions for future studies of these phenomena. Dedicated to Prof. Jan Janča on the occasion of his 60th birthday.     

The influence of NH3 on NO2 conversion in a dc corona discharge in N2:O2:CO2:NO2:NH3 mixture

The aim of this paper is to investigate the influence of NH₃ additive (540–1470 ppm) on the conversion of NO₂ and the creation of NO and N₂O in a mixture of N₂:O₂:CO₂: NO₂:NH₃ subjected to the so-called direct current (dc) corona discharge. The dc corona discharge was generated in a needle-to-plate reactor. Seven positively polarized needles were used as one electrode and a stainless steel plate as the other. The time-averaged discharge current was varied from 0 to 7 mA. It was found that the dc corona discharge decomposed NO₂ and produced NO and N₂O. The reduction of NO₂ was higher without NH₃ additive if the residence time of the operating gas was relatively short. However, in a longer corona discharge processing the NH₃ additive may be useful for reduction of NO₂.Supports from the Research and Development Commitee (KBN) under Programme KBN 0889/P4/93/04 and the Polish Academy of Sciences within IMP 3.1 project are gratefully acknowledged.     

Sulfur dioxide (SO2) gas transfer process enhanced by corona discharge

The sulfur dioxide (SO₂) gas transfer process in a corona discharge field has been studied. The experiments were conducted to investigate the effects of voltage, length, and height of the discharge area on the electric transfer of SO₂ as well as on the desulphurization efficiency. Experimental results show that corona discharge can facilitate the SO₂ gas transfer process. The rate and efficiency of desulphurization increase with increasing voltage, length of discharge area, and input power. The addition of a uniform electric field to the corona-discharge field improves the electronic transfer of SO₂. Measured desulphurization efficiency was as high as 95%, and the augmentation of desulphurization efficiency due to corona discharge was nearly 50% under the conditions tested.     

The characteristics of a negative corona discharge in He/Xe/SF6 mixture

The results of investigation of the electrical and optical characteristics of a negative corona discharge in the electrode system of the type needle-grid lit in a He/Xe/SF₆ mixture under the pressure of 100–300 kPa are presented in this paper. The given medium is working for a pulse-periodic excimer lamp on = 351 nm XeF(B–X). Distributed on the length of a lamp active media a bipolar corona discharge is intended for using in the electric circulation of the XeF-lamp working medium. It is shown that the given discharge is ignited steadily in the He/Xe/SF₆ mixture, containing 0, 5kPa SF₆ molecules and is characterised by a low power consumption; the current of the discharge is limited to the development of instability by increasing the voltage on the needles; in hot zones of corona discharge SF₆ molecules cause the effective population 6s of XeI state.     

Composition of a non-self-sustained discharge plasma in an N2: O2: H2O mixture at atmospheric pressure

The plasma composition of a discharge sustained by a pulsed ionization source of μs duration is computed. It is shown that, within a time interval of ∼10⁻⁶ s after the ionization pulse, the dependences of the ion densities on the electric field and ionization source power show features that should be taken into account when developing laser systems for controlling electric discharges in long air gaps. The effect of the plasma composition on the efficiency of electron photodetachment from negative O ₂ ⁻ ions is investigated by the example of a discharge initiation system consisting of two lasers with different pulse durations and wavelengths. Plasmochemical processes under conditions of enhanced electron photodetachment from negative O ₂ ⁻ ions are simulated. It is shown that photodetachment can increase the electron density for a time of <10⁻⁵ s.     

Conversion of nitrogen oxides in N2:O2:CO2 and N2:O2:CO2:NO2 mixtures subjected to a dc corona discharge

This paper concerns the influence of a direct current (dc) corona discharge on production and reduction of NO, NO₂ and N₂O in N₂:O₂:CO₂ and N₂:O₂:CO₂:NO₂ mixtures. The corona discharge was generated in a needle-to-plate reactor. The positively polarized electrode consisted of 7 needles. The grounded electrode was a stainless steel plate. The gas flow rate through the reactor was varied from 28 to 110 cm³/s. The time-averaged discharge current ranged from 0 to 6 mA. It was found that in the N₂:O₂:CO₂ mixture the corona discharge produced NO, NO₂ and N₂O. In the N₂:O₂:CO₂:NO₂ mixture the reduction of NO₂ was between 6–56%, depending on the concentration of O₂, gas flow rate and corona discharge current. The NO₂ reduction was accompanied by production of NO and N₂O. The results show that efficient reduction of nitrogen oxides by a corona discharge cannot be expected in the mixtures containing N₂ and O₂ if reducing additives are not employed.     

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.     

An analytical approach to discharge circuits in gas lasers

Summary An analytical method for solving equations applied to circuits whose resistance varies according to an exponential decay law is proposed and applied. The solution is given in terms of generalized hypergeometric functions. To speed publication, the authors of this paper have agreed to not receive the proofs for correction.     

Electron kinetics in dc CF4 + O2 mixture discharge

The electron distribution function, transport coefficients and rate coefficients for the dissociation of CF₄ and the excitation of a¹ _g and b¹ _g ⁺ states of oxygen have been calculated for a CF₄ + O₂ mixture discharge. The two-term approximation was used in solving the electron Boltzmann equation. The influence of the dissociation was ignored, so that the results are parametric in the density reduced electric fieldE/N and the ratio of the mixture components. Only slight dependence of the calculated quantities on the composition of the gas mixture has been observed. The critical electric field for the onset of the discharge was found to beE/N=1.1–1.25 × 10^–15 Vcm² and it is weakly decreasing with growth of the oxygen content. With a small amount of oxygen added to CF₄ the electron distribution function and the mean kinetic energy remain practically unchanged.     

An empirical model for ionic wind generation by a needle-to-cylinder dc corona discharge

We present the results of an experimental study on ionic wind generation by a needle-to-cylinder dc corona discharge. A strong electrical field in the air generates air flow driven by the motion of ionized gas molecules along electric field lines. We measured the ionic wind velocity and discharge current with respect to various electrode geometries, distances between electrodes, and applied voltages. Our measurements suggest an empirical model for the ionic wind velocity as a function of the geometric factors of the collector electrode and the applied electric potential, which is useful for designing ionic wind cooling systems for small electronics.     

Multiwalled carbon nanotubes mass-produced by dc arc discharge in He–H2 gas mixture

Uniform cathode deposits (longer than 15 mm), containing multiwalled carbon nanotubes (MWNTs) inside, were produced by dc arc discharge evaporation with a computer-controlled feeder of a pure-carbon electrode without a metal catalyst in a He–H₂ gas mixture. The purification of MWNTs was carried out to remove amorphous carbon and carbon nanoparticles. High-resolution transmission electron microscopy observations and Raman scattering studies show that the MWNTs possess a high crystallinity and a mean outermost diameter of ∼ ∼10 nm. It has been confirmed that the current density in the electron field emission from a purified MWNT mat can reach 77.92 mA/cm², indicating that the purified MWNTs are a promising candidate electron source in a super high-luminance light-source tube or a miniature X-ray source.     

多间隙气体开关电晕均压结构优化

电晕针均压的多间隙气体开关,其各间隙电晕电流一致性会直接影响开关的耐压稳定性。在工作气压0.1,0.2,0.3,0.4 MPa条件下,实验测量了六间隙气体开关在不同电压下的各间隙电晕电流。结果显示,针-板间隙电晕电流明显高于针-杆间隙电晕电流。对针-板间隙进行结构调整并进行三维静电场仿真。对调整结构后的针-板间隙进行电晕电流测试,测试数据的变化趋势与仿真结果相符。基于实验和仿真结果,优化了针-板间隙中电晕针的高度,充电25 kV时,开关各间隙电晕电流的相对标准偏差最大为8%。     

Emission characteristics of a barrier discharge in an Ar-H2O mixture

We have experimentally studied the UV radiation of a low-temperature barrier discharge plasma in an Ar-H₂O mixture. The spectral interval 300–400 nm has been examined in detail. Addition of argon with a pressure of 24 kPa to a barrier discharge in water vapor at a pressure of ～0.1 kPa leads to a ninefold increase in the UV radiation power of excited hydroxyl molecules. An increase in the duration of the UV radiation pulse of the mixture in the longitudinal discharge decay has been achieved for the first time, which may be direct evidence of energy transfer from metastable argon atoms to water molecules. An estimate of the upper boundary of the dissociative excitation rate constant of hydroxyl molecules OH*(A ²Σ⁺) upon interaction of metastable argon atoms with water molecules has been obtained.     

电场作用下S修饰C24N24从CO2/N2混合气体中选择性吸附

在燃烧后气体中选择性捕获CO2,对减缓因CO2浓度过高引发的环境问题具有十分重要的意义。本文采用第一性原理计算的方法,研究了外加电场作用下S修饰C24N24富勒烯对CO2的选择性吸附性能。首先研究了S@C24N24的结构和性质,发现其具有良好的稳定性。其次,研究了无电场时S修饰C24N24富勒烯对CO2的吸附行为,发现其吸附为弱的物理吸附。另外,进一步研究了外加电场作用下S@C24N24对CO2的吸附行为。结果表明,结合距离（CO2与S）和CO2的键角（O=C=O）随电场的增大而减小;当电场增加到0.018 au时,物理吸附转变为化学吸附。关闭电场时,化学吸附又转化为物理吸附。此外,即使在相同的电场条件下,S修饰C24N24富勒烯对N2的吸附也为弱的物理吸附。这表明,通过控制外加电场的开/关,S@C24N24可以从CO2/N2混合气体中选择性捕获/释放CO2,可作为选择性捕获CO2的优良候选材料。     

气体介质对多间隙气体开关电晕均压与自击穿特性的影响

快脉冲直线变压器型驱动源（FLTD）是近年来快速发展的新型脉冲功率源技术,多采用多间隙气体开关作为开关器件。电晕均压措施有利于提升开关击穿性能,但不同气体中电晕放电有显著区别。本文首先研究了空气中针电极对单间隙电晕放电特性的影响,确定了电晕针电极的尺寸,之后研究了N₂,CO₂,SF₆/N₂混合气体、C₄F₇N/N₂混合气体中的电晕放电特性,研究了电晕均压6间隙气体开关击穿电压及其稳定性随气体种类和气压的变化规律。实验结果表明,N₂中电晕电流较大且不稳定,空气中电晕电流比N₂中低,且电晕放电较为稳定,微量强电负性气体加入会极大降低电晕放电电流。当采用空气和N₂作绝缘介质时,气体开关击穿电压随气压升高线性增加,但存在低值击穿,微量强电负性气体混合N₂可显著提升击穿电压的稳定性。1%SF₆/99%N₂混合气体在0.18 MPa时,击穿电压约为197.33 kV,标准偏差占击穿电压比例为1.50%,1% C₄F₇N /99%N₂混合气体在0.15 MPa时,击穿电压约为190.42 kV,标准偏差为0.55%。这表明,微量环保替代气体C₄F₇N与N₂的混合气体对于提升多间隙气体开关击穿电压稳定性有显著作用。     

电晕均压多间隙串联气体开关特性实验

研制了一种电晕放电均压的小型多间隙串联气体开关,分析了电晕放电在开关工作过程中的作用,开展了开关自击穿特性、电晕放电伏安特性、针尖烧蚀以及开关寿命测试等特性实验。结果表明:老练后开关自击穿电压标准偏差小于3.5%,电晕均压效果明显;随着放电次数增加,电晕针尖逐渐钝化,触发性能变化不大;开关电晕放电电流随耐受电压升高增大,增长趋势逐渐变快;开关充400 kPa干燥空气,100 kV工作电压下开关放电50 000次以上,触发性能稳定,触发击穿时延抖动约4.3 ns,自放电概率低于110-4。     

Experimental pressure dependence of positive corona discharge in N $_\mathsf{2}$

This paper presents the experimental pressure dependence, in the range 1.01 x 10⁵-1.6 x 10⁵ Pa, of the I-V characteristic of a N₂ positive corona discharge. The pressure raise is related to the gas flow increase into the chamber where the corona is ignited. Experimental measurements confirm Townsends I-V characteristic. For a fixed potential difference between the electrodes, corona currents decrease as the gas flow increases (pressure increase): this has been ascribed to a lower ionization rate close to the stressed electrode and a lower charge mobility in the drift region. Both these processes result in a lower current generated by the discharge.Received: 5 February 2003, Published online: 30 July 2003PACS: 52.80.Hc Glow; corona     

Vibrational luminescence of N2O excited by dc discharge: Rotation-vibration constants

High resolution measurements have been performed on 19 emission and absorption bands of the nitrous oxide molecule at 4.7 μm and 2.9 μm. Accurate values of the vibrational and rotational constants of 23 vibration levels were obtained.