Model of pulsed electric discharge expansion in dense gas taking into account electron and radiative thermal conductivity. III. Limit discharge temperature

Based on the energy conservation law for the shell of a pulsed high-current electric discharge in dense gas (Xe, Kr, Ar, Ne, He, N₂, air) an equation for the relative temperature of the discharge channel was derived taking into account electron and radiative thermal conductivities and the energy expended to ionization of gas involved in the discharge. The condition under which the limit channel temperature T _LIM is achieved was determined by solving this equation, and the universal dependence between the temperature T _LIM and the ionization potentials of the above gas atoms was obtained. It was shown that this universal dependence is in agreement with experimental data.     

Multiparameter dimensionless complex determining the compression dynamics of a cylindrically symmetric Z-pinch in a gas

For the initial compression stage of a cylindrically symmetric Z-pinch in a gas, on the basis of the energy balance of the discharge we derived a dimensionless equation of the relative radius of its plasma cord, containing a generalized variable, i.e., a multiparameter complex Ξ which determines the discharge compression dynamics and is a result of generalization of experimental data. It is shown that the experimental dependence of the relative plasma cord maximum temperature on the complex Ξ has a tendency to saturation, which is due to the rapid increase in Z-pinch radiation intensity in deuterium upon cord compression.     

Numerical investigation of a fast-axial-flow CW CO2 laser

This paper presents the results of the calculation of the parameters of the active medium of a fast-axial-flow CO₂ laser using numerical methods in the framework of a one-dimensional approximation of the set of continuity equations, Bernoulli equation, equation of gas state, energy equation and multi-temperature rate equations with regard to diffusion for the gas flow in the cylindrical discharge tube. The spatial distribution of the small-signal gain and gas temperature along the gas flow direction have been calculated for a given set of initial conditions, namely, gas flow velocity, gas pressure and the tube diameter. In addition, the dependence of small-signal gain, the asymmetric stretch vibrational temperature of CO₂ (T₃) and the gas temperature on the discharge current were studied.     

大气压介质阻挡放电中的自组织斑图结构

采用水作为电极,对大气压介质阻挡放电中的自组织斑图结构进行了研究,观测到了规则的斑图结构(包括准六边形斑图和条带状斑图)和不规则的斑图结构.实验发现斑图中放电丝的密度随着电介质层厚度的增加及放电气隙宽度变大而减小,而随外加电压及频率增大而增大.采用空间相关函数的方法分析了准六边形斑图结构中的放电丝分布与驱动电源电压的关系 关键词： 介质阻挡放电 自组织斑图 放电丝密度 空间相关函数     

氮气交流放电光谱强度和电压及气压的关系

利用浓度调制光谱技术,测量了玻璃管中放电频率20 kHz时N2的介质阻挡放电光谱.实验记录了N2的C3∏u-Bb∏g357.7nm和B2∑ u-X2 g391.4 nm的跃迁谱线光谱强度随小同电压和气体压强变化规律.实验数据显示,保持气体压强p=130 Pa不变,在电压较低时,光谱强度随电压增长较快,在电压较高时,光谱强度增长较慢;保持放电电压U=6.4 kV不变,光谱强度随气压增长逐渐变小.根据电子和分子碰撞激发函数和电离函数,建立光强随放电参数变化的物理理论模型和公式,并对实验数据进行数学拟合,拟合曲线与实验结果符合较好,相关系数R>0.9.进一步明确了等离子体发射光谱强度随不同电压和气体压强变化的机理.     

Model of pulsed electric discharge expansion in dense gas, taking into account electron and radiative thermal conductivities. IV. Limiting brightness of discharge radiation

Based on the relation between the radiation brightness B _R of the pulsed high-current electric discharge in dense gas (Xe, Kr, Ar, Ne, He, N₂, and air at atmospheric pressure and above) and its temperature, the dependence of the limiting brightness B _LIM of discharge channel radiation on ionization potentials of atoms of mentioned gases was obtained, and the condition under which the brightness saturation is achieved was determined. It was shown that this dependence is in agreement with experimental data of various researchers.     

介质阻挡放电中单个新型放电丝放电特征和光谱测量

在放电间隙较大(d=3.8 mm)的介质阻挡放电(DBD)中,通过减小放电区域(S=1 cm×1 cm),首次观察到了单个新型放电丝。与其他实验小组所观察到的单个放电丝相比,该单个新型放电丝由体放电(VD)和沿面放电(SD)二部分构成,其放电稳定性和持续性极好。利用高速照相机和光谱仪,研究了单个新型放电丝在外加电压半周期单次放电中的放电特征和单个新型放电丝侧面放电柱不同位置的等离子体状态。在高速照相机不同曝光时间条件下拍摄得到了单个新型放电丝端面和侧面放电的瞬时照片,并对其外加电压半周期单次放电的放电特征与辉光放电进行了对比。利用发射光谱法,采集了单个新型放电丝侧面放电柱不同位置的氩原子763.26 nm(2P₆→1S₅)和772.13 nm(2P₂→1S₃)发射谱线,并通过两条谱线强度比法,估算出了相应的电子激发温度。实验结果得出：单个新型放电丝由体放电和沿面放电构成,且沿面放电在体放电四周呈枝状扩散;单个新型放电丝在外加电压半周期单次放电中与辉光放电特征相似,且在阴极呈现出漏斗状放电;氩原子谱线强度及其相应的电子激发温度从极板两端到中间均呈减小的变化趋势,表明单个新型放电丝侧面放电柱不同位置的等离子体状态不同。     

On the similarity law in picosecond gas discharges

It has been shown that the product of the gas pressure p and the discharge formation time τ is unambiguously related to the reduced electric-field strength E/p for air and argon in the picosecond range of τ. This dependence was previously found for the nanosecond range. The available experimental data are satisfactorily explained in the framework of the theory of the multielectron initiation of pulsed gas discharges that was proposed in my previous works.     

流动氩气放电系统中条纹斑图形成的实验研究

采用双水电极介质阻挡放电装置, 在大气压下流动氩气中产生了稳定的条纹斑图, 并采用拍照和电学方法对其产生机理进行了研究. 研究发现, 条纹斑图仅出现在外加电压较低的情况下, 在较高电压下放电会过渡到均匀模式. 低电压下的条纹斑图是由于放电丝沿着气流方向定向移动形成的, 该定向移动速度几乎与电压无关, 主要由气体流量决定. 分析发现放电空间中活性粒子的记忆效应对条纹斑图的形成起决定作用. 电学测量发现放电电流和放电的气隙起始电压都随着气流的增加而减小, 本文对这一现象进行了定性解释. 本文结果对斑图动力学研究和介质阻挡放电的工业应用都具有很重要的意义.     

Functional form of the repulsive potential in the high pressure region

The present work is devoted to the analysis of the functional form of the repulsive potential in the framework of soft-sphere model. We used two different approaches which were based on the treatment of an equation of state and spectra of molecular light scattering at large shifts of frequencies. In particular, it has been shown that the density dependence of pressure at P>10³ MPa allowed to calculate the steepness exponent of the repulsive potential as a fitting parameter of the equation of state which possesses reliable extrapolation properties under extrapolating experimental PVT data in the high-pressure region. Processing of experimental data on a base of the statistical equation of state reveals the temperature dependence of the steepness parameter. The similar situation is also typical for the light scattering spectra. So for argon the value of this parameter varies from 15 to 10 in the gas phase and up to 24–28 in the liquid phase. The results obtained with the help of the equation of state and molecular light scattering spectra correlate well.     

Amplification and saturation in a CO2 waveguide amplifier

An ir CO₂, dc current pumped, optical waveguide (WG) amplifier has been built, and its active medium optical parameters measured for several CO₂ emission lines, and their dependence from active medium total pressure, discharge current and temperature was investigated.High gain is found which, coupled with relatively high saturation power in the WG fundamental mode and ease of fabrication with this technology in long (up to 1.5 m) lengths, indicates promising use to efficiently amplify high spectral and spatial purity output of a short, highly tunable WG laser up to power levels suited for nonlinear spectroscopy and optical pumping. The dependence of the small signal gain coefficient and of the saturation parameter for individual rotational lines on the radiation intensity was computed using experimentally known parameters of the discharge plasma. The computation was carried out using the two mode rate equation approach for CO₂–N₂–He gas mixtures. A satisfactory agreement between theoretical and experimental results was obtained.Work supported by G.N.S.M.-C.N.R. and M.P.I.     

Ionization waves (moving striations) in a low pressure helium discharge — results of measurements compared with a direct solution of the electron Boltzmann equation

The Boltzmann equation expanded in the angular dependence in the velocity space is solved numerically in one-dimensional approximation to obtain the perturbed distribution function. This perturbed distribution is integrated to construct the rate coefficients entering the atomic ion and the metastable continuity equations. From these balance equations the dispersion equations of the fast as well as slow ionization wave varieties are recovered. The space resonances of the electron gas described earlier give rise to the fast s and slow s' wave varieties observed in the positive column of the low current helium DC discharge. The existence regions of these waves are numerically evaluated and compared with experiment. Furthermore, the results on the wave phase velocities and dependence of the characteristic potential on the electric field are confronted with the experimental data. The theory, which involves no free or adjustable parameters, renders a resonable agreement in some points. Possible reasons for the observed discrepancies are also discussed.     

Velocity of current filament at the high gain mode of GaAs power photoconductive switches

Many of the characteristics, especially transient turn-on, of high gain mode photoconductive semiconductor switches can be explained by a model similar to a gas streamer model in this paper. Based on the gas discharge theory and photoactivated charge domain model, the mechanism of current filament at the high gain mode of GaAs photoconductive semiconductor switches (PCSSs) was discussed. It is pointed out that both the carrier density and the regional electric field satisfy two critical conditions for the formation and development of streamers. Experimental phenomena indicate that the turn-on time is considerably shorter than the time required for the transit of carriers crossing the electrode gap of the device at saturation transfer velocity. Moreover, the transient turn-on characteristic was analyzed and the ultra-fast velocity of current filament was calculated. The calculated results are in agreement with the experimental results.     

介质阻挡放电系统复合气隙中三种放电丝的光谱研究

介质阻挡放电系统（DBD）作为一个典型的非平衡气体放电系统,不仅在工业生产如低温等离子体生产和发光等方面被广泛应用,而且该系统表现出的非线性现象、自组织现象也吸引人们的关注。DBD系统中放电丝的等离子体参量受诸多因素影响,为了探究DBD系统的放电条件对等离子体参量的影响,该实验重新设计放电单元以保证在其他实验条件相同的情况下,对放电气隙间距和气体组分与等离子体参数之间的关系展开研究。本实验的放电单元为一个平板型玻璃框架气隙,该气隙由三个厚度均为1.2 mm,放电区域边长分别为40,30和20 mm的正方形玻璃框架复合而成,因此该放电气隙有三个放电区域,将此复合气隙放置于可调节气体成分和压强的真空室内,可以同时产生三种放电气隙间距分别为1.2,2.4和3.6 mm的等离子体放电丝。高速录像机拍摄的瞬时照片表明三种放电丝均为随机放电丝,即其放电类型均为流光放电。在垂直于放电气隙平面的方向设置光路,使用聚焦透镜获得清晰的成像,移动光纤探头实现空间分辨并采集数据。实验用光谱仪采集三种等离子体的氮分子第二正带系(C3Π_u→B3Π_u) 谱线,根据谱线强度计算得到各类放电丝的分子振动温度;利用谱线中包含的氮分子离子N+₂第一负带系谱线(391.4 nm)和氮分子第二正带系394.1 nm谱线强度的比值反应放电丝中电子平均能量;改变气室内氩气的含量,得到了三种等离子体的分子振动温度和电子平均能量的变化趋势。实验结果表明：在氩气含量0%~60%区间内,随着氩气含量的增加,三种等离子体的分子振动温度均先升高后降低,整体趋势表现为相同氩气含量下放电气隙间距越小分子振动温度越高,即1.2 mm气隙厚度中的放电丝的分子振动温度最高,2.4 mm气隙厚度次之,3.6 mm气隙厚度的最低;随氩气含量的增加放电丝的平均电子能量先升高后降低,氩气含量相同时气隙厚度越小的放电丝的电子平均能量越高,即1.2 mm气隙厚度中放电丝的电子平均能量最高,2.4 mm气隙厚度的次之,3.6 mm气隙厚度中的最低。实验结果对于研究DBD系统中等离子体参量、工业生产等方面具有重要的参考意义。     

Simulation of shock-wave propagation in the argon plasma of a positive column discharge

The computer simulation of shock-wave propagation in the argon plasma of positive column discharge was performed. A one-dimensional model of the gas-discharge plasma is used, which comprises the continuity equations for the electron and ion plasma components and the equation of electrostatics with allowance for initial and boundary conditions. The distribution of plasma parameters in the shock wave was obtained; the effect of its intensity was evaluated. The simulation results were compared with experimental data.     

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.     

Charge compensation in an insulated target bombarded by a pulsed electron beam in the forevacuum pressure range

We report on the results of computation of the time dependence of the ion flux and the dielectric target potential at the initial stage of bombardment by an electron beam in forevacuum. It is shown that a satisfactory agreement with experimental data is attained with allowance for the possibility of the discharge between the target and the earthed walls of the vacuum chamber.     

Equation of state at the adiabat of unloading

On the assumption that condensed matter at high pressures and temperatures behaves as an ideal gas, a functional dependence of the adiabatic exponent on the Grüneisen constant was obtained, as well as an equation of state that relates the velocity of the shock front and the mass velocity in the shock wave. The calculated estimates of the rate of unloading for cadmium, tin, aluminum, and iron are given as functions of the mass velocities. A comparison with experimental data shows that such an equation of state sufficiently well describes the behavior of the substance and can be used instead of the conventional semiempirical dependences.