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.     

Experimental Measurements on the Current Balance at the Cathode of a Cylindrical Hollow Cathode Glow Discharge

The contribution of positive ions, photons and metastable particles to the secondary emission of electrons from the cathode of an argon glow discharge with cylindrical cathode is measured by sampling the plasma species through a small orifice in the cathode wall and analyzing them in a high vacuum region. Additional experiments are made with a second apparatus which enables the sampling fo plasma species from the negative glow and the dark space. The paper describes the experimental techniques used in both cases and presents estimates on the validity of the results obtained. The positive ions are found to be the dominant contribution to the discharge current at the cathode. The secondary emission of electrons is — in decreasing order of importance — due to impact fo singly charged ions, doubly charged ions and metastable atoms.     

直流大气压辉光放电高能电子密度的空间分布

利用针阴极和水阳极,在6 mm的空气隙产生了大气压空气辉光放电。该大气压辉光放电具有明显的负辉区、正柱区和阳极辉区等明亮的发光区。通过研究放电的电压电流特性,发现该放电处于亚辉光放电到正常辉光放电阶段。由于氮分子第二正带系337.1 nm的光谱强度反映高能电子密度,对337.1 nm谱线的强度进行了空间分辨测量。结果发现高能电子在针尖附近密度最大,而其他区域相差不多。随电压升高,高能电子密度减少。增大限流电阻,高能电子密度也减少。氧原子对杀菌消毒具有重要作用,利用发射光谱法对氧原子谱线强度的空间分布进行了测量,发现氧原子谱线强度与高能电子的空间分布及其随参数的变化关系一致。     

H2对N2直流辉光放电电子行为的影响

通过用Monte Carlo方法模拟N₂-H₂ 混合气体直流辉光放电等离子体快电子行为，从不同H₂浓度的电子能量分布函数，电子密度以及e_f-N₂碰撞率等方面，研究了加H₂对氮辉光放电等离子体过程的影响. 研究结果表明: 随着H₂浓度的升高，电子的平均能量增加, 电子密度及e_f-N₂的各种非弹性碰撞率减小; 但在 关键词： 2-H₂辉光放电')" href="#">N₂-H₂辉光放电 Monte Carlo模拟 2碰撞率')" href="#">e-N₂碰撞率     

介质阻挡均匀大气压辉光放电数值模拟研究

通过数值求解一维电子、离子连续性方程和动量方程，以及电流连续性方程，计算了氦气介 质阻挡大气压辉光放电电子、离子密度和电场在放电空间的时空分布，以及放电电流密度和 绝缘介质板充电电荷密度随时间的变化. 分析讨论所加电压频率、幅值及介质板性质等对均 匀大气压辉光放电性质的影响. 当外加电压频率足够高时，大量离子被俘获在放电空间，空 间电荷场又引起足够多的电子滞留在放电空间. 这些种子电子使得在大气压下发生汤森放电 ，放电空间结构类似于低气压辉光放电，即存在明显的阴极位降区、负辉区、法拉第暗区和 等离子体正柱 关键词： 大气压辉光放电 介质阻挡 数值模拟 等离子体     

Electron impact ionization and excitation rate coefficients in the negative glow region of a glow discharge

Some easy to use reasonable approximations for electron impact rate coefficients have been considered. The most important rate coefficients for electron collisions in noble gases are electron-neutral ionization and electron impact excitation. Electron-neutral ionization besides electron impact excitation of some states of the argon and helium atom in direct current (dc) glow discharge plasma has been calculated. The plasma parameters of electron are significant factors for computing the rate coefficients. We present first results of probe diagnostic that includes the double probe measurements of the plasma parameters, namely, electron temperature (T_e) and electron density (n_e). Electron properties obtained from the double probe characteristic curves including T_e and n_e as well as the calculated rate coefficients (ionization and excitation) were studied as a function of the axial distance from the cathode while the discharge operating parameters of voltage and pressure were varied. Two regions of the glow discharge were investigated: cathode fall region and negative glow. Particular emphasis was placed on the negative glow region.     

空气中空心阴极不同放电模式下的发光特性

为了进一步揭示空心阴极放电中放电模式的转换机制,特别是空心阴极放电过程中自脉冲的形成机理,利用柱型空心阴极放电结构,在空气环境下研究了放电处于不同模式时的发光特性。测量得到了不同放电模式下的伏安特性曲线、放电发光图像、自脉冲阶段的脉冲波形等。实验结果表明随着放电电流的增加放电分为汤生放电模式、自脉冲放电模式、正常辉光放电模式和反常辉光放电模式。虽然所用电源为直流电源,但在自脉冲放电阶段电流和电压随时间呈周期性变化。实验结果表明在不同的放电模式下具有不同的发光特性。在由汤生放电转换为自脉冲放电模式和由自脉冲模式转换为正常辉光放电模式过程中,放电腔的径向中心处和轴向孔口附近均存在光强的突变。实验同时在200～700 nm范围内测量得到了不同电流时的发射光谱。结果表明发射光谱主要集中在330～450 nm,主要包括氮分子的第二正带系(C3Π_u→B3Π_g )和氮分子离子的第一负带系（B2Σ+_u→X2Σ+_g）。其中氮分子离子第一负带系具有较强的发射光谱。由于B2Σ+_u激发电位较高,因此该谱带较强发射光谱的存在表明空心阴极放电较其他放电形式更容易获得高激发态粒子和高能量电子。在650～700 nm附近存在一弱的发光谱带,主要为氮分子的第一正带发射谱（B3Π_g→A3Σ+_u）。在此基础上根据双原子光谱发射理论,结合氮分子第二正带系的三组顺序组带：Δν=-1,-2和-3,利用玻尔兹曼斜率法计算得到了不同放电模式下氮气的分子振动温度。结果表明在实验电流范围内分子振动温度在3 300 K左右,随着电流的增加而升高,并且在自脉冲消失时存在一突变迅速增强。由于电子能量、电子密度与分子振动温度密切相关,因此该结果也表明随着放电电流的增加电子平均能量和电子密度不断增加,当脉冲消失时,电子平均能量和电子密度出现跃变升高。最后,对空心阴极放电中自脉冲的形成机理进行了讨论,结果表明自脉冲放电源于放电模式的转换。     

Profile of spectral-line intensity along a negative glow

The longitudinal profile of the spectral-line intensity has been measured in a plasma of a negative glow in helium, neon, and mixtures of these gases. Under the conditions of a normal glow discharge, the intensities of several spectral lines fall off exponentially toward the anode. The decay of the line intensity was used to evaluate the effective cross section for attenuation of the electron beam from the cathode dark space. There is a discussion of the mechanism for the change in the profile of the line intensity in the discharge gap at the transition on a normal glow discharge to an anomalous discharge.     

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。     

细长金属管内产生的直流辉光等离子体发射光谱诊断

利用发射光谱法对金属管内形成的稳定氩氮直流辉光等离子体进行了诊断。通过对等离子体发射光谱谱线的研究确定了等离子体中的活性粒子成分;根据氩原子的玻尔兹曼曲线斜率法计算了等离子体中的电子激发温度;采用氮分子第二正带系跃迁(C3Π_u→B3Π_g)的发射谱线计算了等离子体中的氮分子振动温度;研究了电子激发温度和氮分子振动温度随压强的变化特征。研究结果表明,在20 Pa下产生的Ar60%+N₂40%直流辉光等离子体中,活性成分主要是Ar原子、Ar离子、N₂的第二正带系跃迁(C3Π_u→B3Π_g)和N+₂的第一负带系跃迁(B2Π+_u→X2Σ+_g);电子激发温度约为(15 270±250)K;氮分子(C3Π_u)振动温度约为(3 290±100)K;随着压强的增加电子激发温度、分子振动温度逐渐降低。文章的研究结果对细长金属管内表面改性研究具有重要的意义。     

Role of nonlocal ionization in formation of the short glow discharge

An analytical model for estimating basic characteristics of short (without a positive column) glow discharges is suggested that allows for electron generation both in the cathode sheath and by nonlocal ionization in the plasma negative glow. The model is based on a previously developed approach according to which the discharge gap is divided into space-charge layers and a quasi-neutral plasma. The plasma region includes part of the negative glow, Faraday dark space, and positive column (if it exists). Simple expressions for basic characteristics of the glow discharge (I–V characteristic, cathode sheath thickness, position of the point of electric field reversal, etc.) are derived, and plasma concentration distributions are presented. The results obtained in terms of our model are in good agreement with experimental data, while local approximations based on the classical Engel-Steenbeck model diverge considerably from the experiment.     

The excitation of spectral lines in the cold cathode region of a glow discharge in argon

Calculations on the excitation of spectral lines emitted by the cathode fall and the negative glow regions of a glow discharge in argon have been performed using space-dependent electron velocity distributions allowing for electron impact excitation and ionization of atoms.     

Energieverteilungsfunktionen im Fallraum von Glimmentladungen

Energy distribution functions of electrons, ions and neutrals in the one-dimensional cathode fall region of anomal glow discharges in Hydrogen are derived by numerical integration of simplified Boltzmann equations for two values of the dark space voltage (5 kV and 0,45 kV). Molecular and atomic ions and neutrals are treated separately. Charge exchange, ionization, excitation and dissoziation are taken into account. The first part of this investigation is still published [1].     

Average velocity of electrons in the cathode fall region during glow-discharge nitriding

The problem about the average velocity of electrons in the cathode fall region of a glow discharge during nitriding has been solved theoretically and verified experimentally. The technique and analytical apparatus for practical calculations of the average electron velocity have been presented.     

A simple kinetic model of a Ne-H2 Penning-plasma laser

A simple kinetic model of the Ne-H₂ Penning-Plasma Laser (PPL) (NeI 585.3 nm) is proposed. The negative glow of a hollow cathode discharge at intermediate pressures is considered as the active medium. The balance equations for the upper and lower laser levels, electrons, ions and electron energy are solved. The dependences of the laser gain on the discharge conditions (Ne and H₂ partial pressures, discharge current) are calculated and measured. The calculated values are in a good agreement with the experimental data.     

介质阻挡放电点燃大气压直流均匀放电的光谱研究

由于大气压均匀放电等离子体在工业领域具有广泛的应用前景,为了获得大尺寸的大气压均匀等离子体,采用氩气作为工作气体,在大气压空气环境中利用同轴介质阻挡放电点燃了针-板电极间的大气隙(气隙宽度达到5 cm)直流均匀放电。研究发现,同轴介质阻挡放电能够有效降低针-板电极间的击穿电压。该均匀放电由等离子体柱、等离子体羽、阴极暗区和阴极辉区组成。其中等离子体柱和阴极辉区都是连续放电。而等离子体羽不同位置的放电是不同时的。事实上,等离子体羽放电是由从阴极向着等离子体柱移动的发光光层(即等离子体子弹)叠加而成。利用电学方法测量了放电的伏安特性曲线,发现其与低气压正常辉光放电类似,均具有负斜率。采集了放电的发射光谱,发现存在N₂第二正带系、氩原子和氧原子谱线。通过Boltzmann plot方法对放电等离子体电子激发温度进行了空间分辨测量,发现等离子体柱的电子激发温度比等离子体羽的电子激发温度低。通过分析放电机制,对以上现象进行了定性解释。这些研究结果对大气压均匀放电等离子体源的研制和工业应用具有重要意义。     

微空心阴极放电的3维数值模拟

 给出了圆筒形微空心阴极的3维流体方程组及其稳态的差分方程和合理的边界条件,并利用计算机模拟计算,得出了He放电形成的粒子密度、电子能量、 电场及电势分布。讨论了在阴极孔径为240~360 mm,气压6 666.1~13 332.2 Pa的范围内放电参量的变化规律:固定电压和气压时,阴极孔径减小,负辉区重合越多;固定阴极孔径和气压时,气压升高,带电粒子密度随着气压增加而增加。结果表明放电参量强烈依赖阴极孔径和气压。     

Study of Intense Electron Beams Produced by High-Voltage Pulsed Glow Discharges

We report the generation of high-current-density (20 A/cm2) pulsed electron beams from high-voltage (48-100 kV) glow discharges using cathodes 7.5 cm in diameter. The pulse duration was determined by the energy of the pulse generator and varied between 0.2 ?s and several microseconds, depending on the discharge current. The largest electron beam current (900 A) was obtained with an oxidized aluminum cathode in a helium-oxygen atmosphere. An oxidized magnesium cathode produced similar results, and a molybdenum cathode operated at considerably lower currents. A small-diameter (<1 mm) well-collimated beam of energetic electrons of very high current density (>1 kA/cm2) was also observed to develop in the center of the discharge. Electrostatic probe measurements show that the negative glow plasma density and the electron beam current have a similar spatial distribution. Electron temperatures of 1-1.5 eV were measured at 7 cm from the cathode. The plasma density (8.5 · 1011 cm-3 at 450 A) was found to depend linearly on the discharge current. In discharges at high currents a denser and higher temperature plasma region was observed to develop at approximately 20 cm from the cathode. We have modeled the process of electron beam generation and predicted the energy distribution of the electron beam. More than 95 percent of the electron beam energy is calculated to be within 10 percent of that corresponding to the discharge voltage.     

Hysteresis transition between diffuse and constricted modes of dc discharge in argon

The results of theoretical studies of hysteresis transition between the diffuse and constricted modes of a dc glow discharge in argon are presented. It has been shown that the experimentally observed hysteresis of the current voltage characteristic (CVC) at the transition from the constricted to the diffuse mode is caused by the nonlocal formation of the electron energy distribution function (EEDF) while taking into account the heterogeneity of radial fields, namely, the diffusion of high-energy electrons capable of producing gas ionization from the central (constricted) region. The effect of the non-local formation of the EEDF has been described approximately by introducing the effective temperature of the high-energy part of the EEDF and solving the equation for the radial profile of the high-energy part of the EEDF.