Microdischarges in ceramic foams and honeycombs

Microdischarges in spatially confined geometries, such as microcavities and micropores of various materials, present a promising method for the generation and maintenance of stable discharges at atmospheric pressure. They have been successfully used in many biomedical, environmental and industrial applications. The paper presents two relatively new types of discharges in confined volumes – a capillary microdischarge in ceramic foams and a sliding discharge inside the capillaries of ceramic honeycombs – and describes their basic physical properties and mechanisms. Microdischarges inside the microporous ceramic foams develop from the surface barrier discharge if the amplitude of the applied voltage reaches given threshold, but only for a specific pore size. Sliding discharge inside the honeycomb capillaries is produced by a combination of AC barrier discharge inside catalytic pellet bed coupled in series with DC powered honeycomb monolith. Both discharges produce relatively cold microplasmas with high level of non-equilibrium. The basic characteristics of the microdischarges, addressing the effects of the applied voltage, discharge power, pore size, length and diameter of the capillaries are discussed.     

Supersonic flow in ablative discharge capillaries

The Mach number equation for plasma flow in ablative discharge capillaries was derived from a set of 1-D flow equations which incorporate the ablation and Ohmic dissipation processes. By examining this equation it is concluded that, while in the case of a capillary with a constant cross section the flow is subsonic and the sound velocity can be reached only at the open end, there is a possibility to reach supersonic plasma velocities inside a capillary with a monotonically increasing cross-sectional area.     

介质阻挡放电系统中带晕蜂窝六边形发光斑图

为了丰富介质阻挡放电系统中斑图的多样性,利用双水电极介质阻挡放电装置,在空气和氩气按一定比例混合的气体中（氩气含量χ=25%）,发现了带晕蜂窝六边形斑图。通过观察用普通相机拍摄的斑图照片,可以发现斑图是由中心点、晕和蜂窝框架构成,且中心点位于晕的中心,中心点和晕嵌套在蜂窝框架的中心。采用带有3个通道的高速照相机对斑图进行分脉冲瞬态拍摄,结果显示带晕蜂窝六边形斑图的3套子结构在外加电压的半周期内,总是按照晕-蜂窝框架-中心点这样的顺序放电。运用光电倍增管对这3套子结构进行研究,发现晕的放电在时间和空间上具有局部选择性。利用发射光谱法,根据氮分子第二正带系（C³Π_u→B³Π_g）谱线计算了中心点、晕和蜂窝框架的分子振动温度,结果显示:中心点的分子振动温度为2 632 K,晕的分子振动温度为2 679 K,蜂窝框架的分子振动温度为2 720 K。本文利用壁电荷理论解释带晕蜂窝六边形斑图的形成机制和时空结构。     

Non-thermal plasma generation by using back corona discharge on catalyst

This paper discusses a novel plasma catalysis generation method based on back-corona discharge along porous catalyst bed reactor. The reactor consists of a high-voltage needle electrode, one floated mesh electrode, one catalyst bed and one grounded mesh electrode. Typical plasma current density is 11.88 μA/cm². It can be used for ozone generation and volatile organic compounds decomposition. By using a home-made AgMnOx/Al₂O₃-1 catalyst, 90% of toluene is removed at the specific plasma energy density of 123 J/L. At the same time, aerosol byproducts are collected and then decomposed on the catalyst bed. Moreover, the catalyst is regenerated because of the back-corona discharge.     

介质阻挡放电蜂窝斑图形成过程的光谱研究

采用光谱法, 研究了氩气/空气混合气体介质阻挡放电中蜂窝斑图形成过程中等离子体参量的变化。实验发现,随着电压的增加,放电经历六边形点阵斑图及疏密点同心圆环斑图后,形成了蜂窝斑图。利用氮分子第二正带系(C3Π_u→B3Π_g)的发射谱线、氩原子763.26 nm(2P₆→1S₅)与772.13 nm(2P₂→1S₃)两条谱线强度比法和氩原子696.57 nm(2P₂→1S₅)谱线的展宽,分别研究了上述三种斑图的分子振动温度、电子激发温度和电子密度。结果发现：蜂窝斑图的分子振动温度和电子激发温度均高于六边形点阵斑图相应的温度,但其电子密度却比后者的电子密度低。实验还通过电容法,测量了放电斑图的放电功率,发现蜂窝斑图的放电功率远远高于六边形点阵斑图的放电功率。工作结果对于研究介质阻挡放电自组织斑图的形成机制具有重要意义。     

Stability test and EXAFS characterization of plasma prepared Pd/HZSM-5 catalyst for methane combustion

Pd/HZSM-5 catalysts prepared via glow discharge plasma reduction followed by calcination thermally show excellent enhanced stability for methane combustion. EXAFS characterization confirms that argon glow discharge reduces Pd/HZSM-5 catalyst effectively at close to room temperature. After thermal calcination of argon plasma reduced Pd/HZSM-5 catalyst under air, specific tetragonal PdO species are formed. This kind of active PdO species keeps stable during methane combustion, which leads to the observed excellent stability of plasma prepared Pd/HZSM-5 catalyst. EXAFS characterization also shows argon plasma reduction can help to remove Cl, which has a negative effect on catalysts properties.     

电子回旋共振离子推力器放电室等离子体数值模拟

电子回旋共振离子推力器属于静电型推力器,具有寿命长、比冲高、结构简单、可靠性高等优点,适用于深空探测等长时间空间飞行任务.放电室是一个关键部件,其内部通过电子回旋共振产生等离子体.针对放电室内等离子体流场建立飘移-扩散近似模型,采用迎风格式有限差分法对该模型进行数值求解,得到了放电室内不同时刻的等离子体流场分布及其演化规律.数值模拟结果可以为推力器的设计和实验研究提供有用信息.     

Generation and investigation of a parallel-plate DBD driven at 1.6 MHz with flowing helium

The development of a new driven circuit that can drive a parallel-plate dielectric barrier discharge with flowing helium at atmospheric pressure is presented. The operating principle is based on the capability of a Tesla coil to generate high voltages with high oscillating frequencies. The discharge is generated inside a one open end parallelepipedic plasma chamber made of glass, using two outside parallel-plate electrodes. Depending on the helium flow-rate the plasma has three developing stages. In the homogeneous developing stage (1 l/min helium flow-rate) the plasma is characterized by using an electric model and based on its emission spectrum.     

冷等离子体强化制备金属催化剂研究进展

冷等离子体属于非热平衡等离子体,具有较高的电子能量和较低的气体温度,是一种制备金属催化剂的绿色新方法.等离子体强化制备金属催化剂包含复杂的物理和化学多相反应.一方面,等离子体提供的高活性环境不但可以加速化学反应,使反应时间从数小时缩短至数分钟,还可以使热力学或者动力学上不可行的反应发生,实现非常规制备;另一方面,等离子体强化制备过程中,在介观尺度上等离子体对相接触行为的影响,可使获得的金属催化剂结构区别于传统方法制备的催化剂.本综述总结了冷等离子体制备金属催化剂的反应器结构、物理化学机理、获得金属催化剂的结构特性、制备面临的挑战,并对未来发展进行了展望.重点阐述了冷等离子体反应器、制备机制及其对金属催化剂结构和性能的影响.     

Ferro-electric pellet shape effect on C/sub 2/F/sub 6/ removal by a packed-bed-type nonthermal plasma reactor

Ceramic dielectric material pellet shape effects on the performance of perfluoroethane (C/sub 2/F/sub 6/) gas removal from simulated semiconductor process gas using packed-bed reactor are experimentally investigated. The bench-scale cylindrical shaped (plasma part: 30-mm inner diameter and 20-mm length) plasma reactor consists of two metal mesh electrodes packed with spherical, cylindrical, or hollow cylindrical shaped ferro-electric pellets with various dielectric constants. The 60-Hz ac high voltage was applied to the mesh electrode. The 3000 ppm C/sub 2/F/sub 6/ gas diluted with nitrogen was used as simulated gas with flow rate of 30 mL/min. The C/sub 2/F/sub 6/ concentration was monitored using Fourier transform Infrared absorption spectroscopy measurements. The results show that the packed-bed plasma reactor with the hollow cylindrical-shaped pellets removed the C/sub 2/F/sub 6/ gas with energy efficiency of 3.7 g/kWh. This value was almost 1.5 times higher than the efficiency 2.5 g/kWh in case of the spherical pellets. The discharge characteristics in the reactor were also changed with the pellet shape. The discharge onset voltage decreases by changing the pellets shape from sphere to hollow cylinder. The quantity of charges accumulated with the microdischarge currents increases by changing the pellet shape from sphere to hollow cylinder in spite of fact that the energy consumed in the reactor decreases.     

The Radio Frequency Hollow Cathode Discharge Induced by the RF Discharge in the Plasma‐Jet Chemical Reactor

In the recent decade an RF driven, low‐pressure plasma reactor with supersonic plasma jet was developed (RPJ). This reactor was successfully used for deposition of thin films of various materials. The deposition of thin films indicates that the properties of the deposited films are dependent on the sputtering or reactive sputtering processes appearing inside the nozzle (hollow athode). The nozzle (hollow athode) fabricated of different kinds of materials and alloys works both as a cathode of the radio frequency (RF) hollow cathode discharge and as a nozzle for plasma jet channel generation as well. The RF hollow cathode discharge is a secondary discharge, which is induced by the primary RF plasma generated in the reactor chamber. The present paper deals with the experimental study of this RF hollow cathode discharge. The stress is laid on the investigation of the axial distribution of discharge parameters and sputtering processes inside the nozzle. On the base of experiments, the simple model of the axial distribution of the investigated RF hollow cathode discharge has been developed.     

Understanding hydrogen plasma processes based on the diagnostic results of 2.45 GHz ECRIS at Peking University

Optical emission spectroscopy(OES), as a simple in situ method without disturbing the plasma, has been performed for the plasma diagnosis of a 2.45 GHz permanent magnet electron cyclotron resonance(PMECR) ion source at Peking University(PKU). A spectrum measurement platform has been set up with the quartz-chamber electron cyclotron resonance(ECR) ion source [Patent Number: ZL 201110026605.4] and experiments were carried out recently. The electron temperature and electron density inside the ECR plasma chamber have been measured with the method of line intensity ratio of noble gas. Hydrogen plasma processes inside the discharge chamber are discussed based on the diagnostic results. What is more, the superiority of the method of line intensity ratio of noble gas is indicated with a comparison to line intensity ratio of hydrogen. Details will be presented in this paper.     

Novel concept of electric discharge oxygen-iodine laser

A novel concept of discharge oxygen-iodine laser (DOIL) is presented. The supersonic DOIL includes a discharge singlet oxygen generator (DSOG) and discharge atomic iodine generator (DAIG). The operation of DSOG is based on a fast mixing of hybrid argon plasma jet of DC electric arc and RF discharge with a neutral molecular oxygen stream. The goal of our effort is achievement of DOIL oscillations by this new discharge technique, which should provide the singlet oxygen yields exceeding 30% at the total pressures higher than 10 torr. The DAIG operation is based on a cw/pulse RF discharge dissociation of iodine donors directly inside a laser iodine injector. This method substitutes the classic dissociation of molecular iodine by energy of singlet oxygen, which saves its energy for laser generation and so can increase the laser efficiency. The laser power could be thus enhanced by up to 25% if this method is employed in a chemical oxygen-iodine laser (COIL) operation, and even 3 times in DOIL without increase in the iodine laser pumping by singlet oxygen.     

Influence of the Inner Diameters of Capillary on the Z‐Pinch Plasma of the Capillary Discharge Soft x‐ray Laser

In this paper, the effects of inner diameters on the Z‐pinch plasma of capillary discharge soft x‐ray laser were investigated with the 3.2 mm and 4.0 mm inner diameter alumina capillaries. The intensities of the laser emitted from the 3.2 mm and 4.0 mm inner diameter alumina capillaries were measured under different initial pressures. To understand the underlying physics of the experimental measurements, the Z‐pinch plasma simulations had been conducted with a one‐dimensional cylindrical symmetry Lagrangian magneto‐hydrodynamics (MHD) code. The parametric studies of Z‐pinch plasma, such as the electron temperature, the electron density and the Ne‐like Ar ion density, were performed with the MHD code. With the experimental and the simulated results, the discussions had been conducted on the Z‐pinch plasma of Ne‐like Ar 46.9 nm laser with the 3.2 mm and 4.0 mm inner diameter alumina capillaries. The analysis had been made on the difference of the gain coefficients under the optimum pressures with both capillaries. Then, the effects of inner diameters on the optimum pressure and the pressure domain were analyzed. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A collisional-radiative model for helium and its application to a discharge plasma

For the collisional-radiative model applied to helium, two alternative formulations are presented in which non-linear process such as ionization due to metastable-metastable collisions may be included. The atomic data, including dielectronic,recombination, employed in the calculations are summarized. The collisional-radiative calculation is applied to a positive-column plasma for which both the nonlinear processes and radiation trapping are taken into account. The calculated population densities of excited levels for a low-pressure and low-current discharge plasma show good agreement with a measurement made using the hook method. The population density distribution among excited levels is interpreted in terms of excitation-ionization mechanisms in the plasma. This leads to a grouping of the excited levels into two phases for the discharge plasma considered: the corona phase applies to the lower-lying levels and the quasi-saturation phase to the higher-lying levels. The importance of the ladder-like excitation-ionization mechanism is noted for this class of plasmas.     

Liquid crystal alignment in cylindrical microcapillaries

A variety of alignment configurations of liquid crystals (LCs) inside the glassy cylindrical capillaries is realized by using alignment materials providing different anchoring. The radial configuration with central disclination line is obtained for homeotropic boundary conditions. In turn, the axial, transversal and tilted alignment structures are realized by using materials for planar anchoring. The uniformity and controlling of the latter structures were provided by photoalignment method. This approach can be further used to control LC alignment in the photonic crystal fibers recognized as advanced elements for different optical devices.     

RF discharges at atmospheric pressure

The described plasma source is based on the RF torch discharge. The powered RF electrode of the torch discharge plasma source is made from the thin metal pipe with an inner diameter of 1–2 mm and with a length of several cm. The working gas (argon pure or with an admixture of reactive components) flows through the RF electrode as the nozzle. The electrode is connected through the matching unit to the RF generator of the frequency of 13.56 MHz.The advantage of this described plasma source consists in the fact that the torch discharge remains stable up to the atmospherical pressure of the working gas even in the liquid environments. Up to now the torch discharge has been used only for treatment in liquid environment only for archaeological artefacts. For further applications it is necessary to additional study of this phenomenon. While in previous papers we presented a measurement of different temperatures from spectra emitted by plasma, there is drawn attention to equiintensity maps inside the nozzle.     

A theoretical study on the effect of a permeable membrane in the air cavity of a double-leaf microperforated panel space sound absorber

A double-leaf microperforated panel absorber (DLMPP) is composed of a two microperforated panel (MPP) with a air cavity in-between, and without any backing structure. It shows a Helmholtz-type resonance peak absorption and additional low frequency absorption, therefore it can be used as a wideband space sound absorber. In this study, a theoretical study is made to examine the effect of a permeable membrane inside the air-cavity. Permeable membranes are studied in our previous studies and proved to be effective to improve the sound absorption performance of various type MPP sound absorbers. We investigate the absorption characteristics of a DLMPP with a permeable membrane in the cavity through numerical examples, and also studied the effect of honeycomb in the cavity of the same sound absorption structure.     

Development of a new atmospheric pressure cold plasma jet generator and application in sterilization

This paper reports that a new plasma generator at atmospheric pressure, which is composed of two homocentric cylindrical all-metal tubes, successfully generates a cold plasma jet. The inside tube electrode is connected to ground, the outside tube electrode is connected to a high-voltage power supply, and a dielectric layer is covered on the outside tube electrode. When the reactor is operated by low-frequency (6 kHz--20 kHz) AC supply in atmospheric pressure and argon is steadily fed as a discharge gas through inside tube electrode, a cold plasma jet is blown out into air and the plasma gas temperature is only 25--30℃. The electric character of the discharge is studied by using digital real-time oscilloscope (TDS 200-Series), and the discharge is capacitive. Preliminary results are presented on the decontamination of E.colis bacteria and Bacillus subtilis bacteria by this plasma jet, and an optical emission analysis of the plasma jet is presented in this paper. The ozone concentration generated by the plasma jet is 1.0×10¹⁶cm^-3 which is acquired by using the ultraviolet absorption spectroscopy.     

Modulation of the photonic band structure topology of a honeycomb lattice in an atomic vapor

In an atomic vapor, a honeycomb lattice can be constructed by utilizing the three-beam interference method. In the method, the interference of the three beams splits the dressed energy level periodically, forming a periodic refractive index modulation with the honeycomb profile. The energy band topology of the honeycomb lattice can be modulated by frequency detunings, thereby affecting the appearance (and disappearance) of Dirac points and cones in the momentum space. This effect can be usefully exploited for the generation and manipulation of topological insulators.