OES analysis in a nonthermal plasma used for toxic gas removal: Rotational and excitation temperature estimation

Nonthermal plasma technologies are often used for cleaning toxic gases. In this work, we will present an optical emission spectroscopy (OES) study in a dielectric barrier discharge (DBD) used to remove NO _x specifically. Rotational temperatures are calculated from the UV-OH band (A ²Σ, ν = 0 → X ²Π ν′ = 0) situated between 306–310 nm; for the rotational temperature, a fitting method was employed (comparison between experimental data with a synthetic molecular spectrum). Excitation temperatures were calculated using OII atomic lines situated in a wavelength range of 300–700 nm using a Boltzman’s plot method. From calculated temperatures, a thermal inequity characteristic of nonthermal plasma discharges has been high-lighted. The influence of the percentage of water added to the DBD reactor is also studied in the removal efficiency and in the OH band intensities and temperatures.     

Lack of partial thermal equilibrium in pinch discharges

Measurements of the deuterium Balmer line intensities in the early phase of a theta pinch discharge show strong deviations from steady state population of levels considerably above the collision limit, even if criteria for the relaxation times of these levels are well satisfied. Solutions of time dependent rate equations for a hydrogen plasma confirm these observations. In cases of rising electron temperatures and rising degree of ionization the population of the ground level deviates by orders of magnitude from the steady state population of the momentary electron temperature and density. The population rates from the highly overpopulated ground level into levels above the collision limit then successfully compete with population rates from other levels and the continuum. Under such circumstances the relaxation time of excited levels above the collision limit into thermal equilibrium is determined by the relaxation time of the ground level into its steady state population.     

低温等离子体灭菌实验装置研究

相对于传统的灭菌方法,利用常压低温等离子体灭菌有许多优点.简单介绍了一个常压低温等离子体灭菌实验装置,该装置主要由电源、匹配测量电路、放电电极和真空系统及光谱检测系统等4个部分组成,并给出了运行调试的结果.     

Multi-spike structure of ion pulses generated by plasma focus discharges

Space- and time-resolved studies of high-energy (> 50 keV) deuteron beams emitted from 3 different Mather-type plasma focus facilities of energy capacity ranging from about 10 kJ to above 200 kJ are presented. In deuteron beams space-resolved with a pinhole camera a spike structure is observed. In quasi-monoenergetic, e.g. 305±20 keV deuterons chosen from a Thomson-spectrograph image there appear up to 3 separate pulses of 8–10 ns FWHM, separated by 30–40 ns intervals. Some pulses demonstrate a fine spike structure with FWHM < 2 ns.     

Observations of extreme ultraviolet emission from plasma produced by capillary discharges

This study reports the results of a pilot experiment concerning observations of extreme ultraviolet emission from plasma produced by the capillary discharges. A few kA current was applied across the gas-filled alumina capillary (1 mm diameter and 8 mm long) to generate radiation in the EUV region (12–63 nm). Spectroscopic studies were carried out by means of a XEUV spectrometer which was upgraded for special lithography purposes. The results obtained from the EUV spectroscopic measurements provided information about the radiation processes from xenon and argon plasma and testifies that given capillary is an effective source of EUV emission. Additionally we showed a simulation which describes plasma dynamics parameters and dynamics of various ionization stages in capillary discharge. Our computer simulation confirmed the presence of ions, which spectra was registered in the experiment.     

空气放电非平衡等离子体的模拟计算

基于空气放电非平衡等离子体动力学,对空气放电进行了数值计算,分析了放电后等离子体中的主要粒子（N2(v6),N2(A3),O2(a1),O和O3）数密度随起始温度、电子数密度和约化场强的变化趋势。计算结果表明,随着初始温度的升高,空气放电产生的粒子数密度增加。温度为300 K时,放电产生的O原子数密度最大值约为4.90×7 cm-3,而当温度升高到400 K和500 K时,O原子数密度的最大值则相应地增加到5.2×1010 cm-3和5.51×1010 cm-3。约化场强的影响与温度类似,其中氮气的振动激发态N2(v6)数密度随约化场强的变化幅度不明显。电子数密度增加,粒子数密度大幅增加,氮分子的激发态N2(A3)粒子数密度与电子数密度保持严格的线性关系。     

空气放电非平衡等离子体的模拟计算

 基于空气放电非平衡等离子体动力学,对空气放电进行了数值计算,分析了放电后等离子体中的主要粒子（N₂(v6),N₂(A3),O₂(a1),O和O₃）数密度随起始温度、电子数密度和约化场强的变化趋势。计算结果表明,随着初始温度的升高,空气放电产生的粒子数密度增加。温度为300 K时,放电产生的O原子数密度最大值约为4.90×⁷ cm^-3,而当温度升高到400 K和500 K时,O原子数密度的最大值则相应地增加到5.2×10¹⁰ cm^-3和5.51×10¹⁰ cm^-3。约化场强的影响与温度类似,其中氮气的振动激发态N₂(v6)数密度随约化场强的变化幅度不明显。电子数密度增加,粒子数密度大幅增加,氮分子的激发态N₂(A3)粒子数密度与电子数密度保持严格的线性关系。     

火花光源发射光谱法测定钢中微量铌

研究了火花光源光谱仪测定钢中微量铌的方法 ,确定了制样和分析条件 ,校正了共存元素的干扰。方法简便、快速 ,具有良好的准确度和精密度 ,结果令人满意     

Filamentary structure of the pinch column in plasma focus discharges

The fine structure of a soft (0.8–3 keV) X-ray emitting zone in a 280 kJ neutron optimized plasma focus is investigated. Distinct continuous filaments are registered during the pinch phase. Time-resolved X-ray measurements show that the filamentation exists to ≈ 20–50 ns after the maximum compression. A comparison of these observations with those performed previously with a 56 kJ plasma focus device is also presented.     

Perturbative analysis of the probability of the nonthermal transfer of an electron

The probability of the nonthermal transfer of an electron of an excited donor-acceptor complexes was calculated from the electron coupling parameter within the framework of time-dependent perturbation theory. Using the analysis of the two first corrections of the perturbation theory series for the standard spinboson model with the Debye spectral density of thermostat oscillators as a basis, we revealed the structure of higher corrections. This allowed us to sum up the series and obtain a new analytical expression distinct from the widely used Padé-approximation for the probability of the nonthermal transfer of an electron. The stochastic approach was shown to allow overestimation of the probability of nonthermal electron transitions by 40.0% in the solvent-controlled regime.     

Spatial characterization of H 2 :CH 4 dissociation level in microwave ECR plasma source by fibre-optic OES

Spatially resolved optical emission spectroscopy (SR-OES) was used to investigate microwave activated H₂/Ar/CH₄ plasma under conditions of the electron cyclotron resonance (ECR). The chemistry and composition of the gas phase were studied using self-designed fibre-optic system with echelle type spectrometer during CVD deposition of polycrystalline diamond. One-dimensional intensity profiles of the main species were collected along the vertical axis of chamber. The dominant species in the flux, originating from excited hydrogen and hydrocarbons, were identified as H, H⁺, CH and CH⁺; they are crucial for the diamond deposition process. The effect of ECR on the spatial distribution of H₂ and CH₄ dissociation profiles was studied in depth. The influence of processing parameters (gas flow rates, input power, pressure and magnetic field level) on species excitation as a function of the distance above substrate was asessed. The obtained data can be used for the ECR system optimization.     

Review of relaxation oscillations in plasma processing discharges

Relaxation oscillations due to plasma instabilities at frequencies ranging from a few Hz to tens of kHz have been observed in various types of plasma processing discharges. Relaxation oscillations have been observed in electropositive capacitive discharges between a powered anode and a metallic chamber whose periphery is grounded through a slot with dielectric spacers. The oscillations of time-varying optical emission from the main discharge chamber show, for example, a high-frequency (\sim 40~kHz) relaxation oscillation at 13.33Pa, with an absorbed power being nearly the peripheral breakdown power, and a low-frequency ( \sim 3 Hz) oscillation, with an even higher absorbed power. The high-frequency oscillation is found to ignite plasma in the slot, but usually not in the peripheral chamber. The kilohertz oscillations are modelled using an electromagnetic model of the slot impedance, coupled to a circuit analysis of the system including the matching network. The model results are in general agreement with the experimental observations, and indicate a variety of behaviours dependent on the matching conditions. In low-pressure inductive discharges, oscillations appear in the transition between low-density capacitively driven and high-density inductively driven discharges when attaching gases such as SF₆ and Ar/SF₆ mixtures are used. Oscillations of charged particles, plasma potential, and light, at frequencies ranging from a few Hz to tens of kHz, are seen for gas pressures between 0.133 Pa and 13.33 Pa and discharge powers in a range of 75--1200 W. The region of instability increases as the plasma becomes more electronegative, and the frequency of plasma oscillation increases as the power, pressure, and gas flow rate increase. A volume-averaged (global) model of the kilohertz instability has been developed; the results obtained from the model agree well with the experimental observations.     

Long plasma channels and high-voltage discharges induced by strong picosecond laser pulses

The formation of long plasma channels and laser-induced high-voltage discharges are demonstrated by focusing infrared picosecond laser pulses in air. Based on measurements of the channel conductivity, the maximum electron density in excess of 1014cm-3is estimated. The plasma channels are good conductors, through which long-air-gap high-voltage discharges are triggered. The breakdown voltages show large drops but the discharging paths are not well guided: in this, the plasma spots distributed along the channel might play an important role.     

Analysis of dusty plasma in the positive column of glow discharges

The radial distributions of ions,electrons and dust particles in the positive colum of glow discharges are investigated in a tripled-pole diffusion model.The dust particles are mainly trapped in the region around the column axis where the electrostatic potential is the highest.The presence of the dust particles results in the ion density increasing and the electron density decreasiung in the dust-trapped region.The dust-trapped region is wider for a higher dust temperature or a smaller particulate redius.The ions and electrons in the dust-free region away from the column axis are in ambipolar diffusion.     

Tokamak plasma equilibrium analysis based on the relaxation method with a specified magnetic axis

In this contribution, we have presented two techniques for the determination of plasma equilibrium position in IR-T1 tokamak: relaxation and optical methods. An analysis method of tokamak plasma equilibrium by a relaxation method with a specified magnetic axis is presented. The degrees of freedom due to designated positions of the magnetic axis are possible by using poloidal field coil currents. Stable steady-state tokamak plasma equilibria are calculated along with the magnetohydrodynamic potential energy. The plasma generates a plasma current which partially or fully cancels the magnetic field from the poloidal field coils. For low-temperature plasmas, the plasma current distribution is centrally peaked; for high-temperature plasmas, the plasma current has a hole. A centrally peaked current distribution in a low-temperature plasma is evolved into a current distribution with a hole by increasing the plasma pressure by Ohmic heating, radio frequency heating, or by neutral beam injection heating. In the second technique, an image-processing technique was used for the output signal of the charge coupled device camera and plasma emission intensity profile and then the plasma position was obtained. Results are compared and discussed.