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.     

Electron beam formation in an anomalous glow discharge

Scaling parameters that account for the efficient formation of electron beams in sources based on an anomalous glow discharge are considered, and the processes leading to the violation of scaling laws are analyzed. Estimates show that the working pressure range in such sources can be increased significantly. The results obtained can be used to optimize discharge regimes with required electron beam parameters. It is demonstrated that sources with plane-parallel continuous electrodes can operate at pressures as high as 100 Torr (which is one to two orders of magnitude higher than that in similar existing electron beam sources), provided that parasitic spark breakdowns at the insulator near the discharge cathode are suppressed. The sources designed can be used for direct excitation of laser working media or their preionization by soft X-rays.     

Behavior of the spatial phase of modulated ionization waves in a glow discharge

Work is described in which it was shown experimentally that a modulated glow discharge with striations acquires an additional characteristic which can be called spatial phase of the oscillations. In fact, this characteristic reflects the spatial distribution of the maxima of the time-averaged integrated plasma luminescence on the tube axis which arises due to the influence of the current modulation on traveling striations. It was discovered that for fixed discharge conditions such a distribution remains constant when the discharge is switched off and on, i.e., it is not random. An experimental investigation was made of the influence of a magnetic field on the spatial phase of the modulated ionization waves. It was found that in a low-pressure glow discharge with small currents the striations are initiated in the cathode region. The anode region does not directly initiate the striations but it influences their spatial phase characteristics through a feedback mechanism. State University, St. Petersburg. Ukhtinskii Industrial Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 108–113, January, 1997.     

Some properties of ionization waves of varietyR in a neon glow discharge

The parameters of ther-ionization waves in a neon discharge were measured at two neutral gas temperatures (298°K and 77°K). The experimental results of the measurements of the artificially excitedr-ionization waves over the region of the homogeneous positive column in discharge tubes with different radius (from 0·5 cm to 1·2 cm) are reported. The results are arranged as simple functions of pressure, electric field and discharge tube radius. The product of the wave-length and the electric field and the ratio of the group and phase velocities are independent of the temperature. The temperature changes of the dependences of the frequency and phase and group velocities are connected with the temperature changes of the atomic ion life-time in neon discharge. The validity of the dependences for wave parameters is confined to the artificially excited waves in a homogeneous positive column.Authors express their gratitude to M. Novák, L. Láska, K. Rohlena and V. Krejí for helpful discussions and valuable remarks on this work.     

Spherical striations in a glow discharge

The stratification of a volume glow discharge is observed experimentally. Spherically symmetric stationary striations are detected. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 11, 679–682 (10 December 1997)     

Numerical analysis of glow discharge in oxygen

Computational analysis of the positive column in a dc oxygen glow discharge was performed. Considering the discharge plasma as a mixture of electrons, positive molecular ions, negative atomic ions, metastable molecules O ₂ ^* (a¹_g), atoms and molecules particle balance equations were solved. As a result the particle concentrations in a dependence on discharge parameters were obtained and the mechanism of the discharge was discussed.     

On the shape of the glow discharge channel

Examples of the shapes of the glow discharge channel are presented. The discharge has been initiated in air at a pressure of 0.1 atm. The effective value and frequency of the discharge current are 30–70 mA and 50 Hz, respectively. It has been shown that, for these values of the current and pressure, thermal convection in a vacuum chamber and buoyancy (Archimedes force) are not major reasons for the specific parabolic shape of glow discharge.

     

Mechanisms controlling the transition from glow silent discharge tostreamer discharge in nitrogen

Low-energy dielectric-barrier controlled discharges in nitrogen are studied by undertaking electrical measurements to determine mechanisms controlling the transition from glow to streamer-like discharge. The highest and the lowest values of the frequency and the amplitude of power supply voltage leading to a glow discharge have been found dependent on the gas flow and the nature of the surface in contact with the discharge. These boundary values have been related to the criteria necessary for initiating a Townsend breakdown rather than a streamer breakdown commonly observed under such conditions. This implies: (1) that the seed electron density just before the breakdown is high enough to allow the development of numerous small avalanches under a low field avoiding the formation of only one large avalanche mechanism at the origin of the streamer formation; and (2) to let the time for ions issued from the first avalanches to reach the cathode before the electrical field becomes large enough to induce the formation of large avalanches. Practically, the transition from a Townsend breakdown to a streamer breakdown is analyzed from electrical measurements data coupled to the visual aspect of the discharge. Without any gas flow, the obtaining of an atmospheric pressure glow discharge (APGD) is mainly limited by the species etched from the surface in contact with the gas. Indeed, these species can be quenchers of the nitrogen metastable molecules, which are the species at the origin of the formation of seed electrons via the Penning effect. This limitation can be overcome by the use of a laminar gas flow. However, this type of gas flow through the discharge induces a depletion of N₂ metastables and, consequently, influences the electron density at the entrance of the discharge, leading to a tendency on this part of the discharge to transit to a streamer-like one     

Plasma sterilization using the RF glow discharge

In the present work, glow discharge oxygen plasma was used to sterilize the Pseudomonas aeruginosa on the polyethylene terephthalate (PET) sheets. In a self-designed plasma reaction equipment, active species (electron, ion, radical, UV light, etc.) were separated effectively, and the discharge area, afterglow area and remote area were plotted out in the plasma field. Before and after plasma treatment the cell morphology was studied by scanning electron microscopy (SEM). The results showed that after treatment of 30 s the germicidal effect is 4.26, 3. 84, 2.61, respectively in the three areas on the following conditions: discharge power was 40 W and gas flux was 20 cm³/min. SEM results revealed the cell morphology before and after plasma treatment. The walls or cell membrane cracking was testified by determining the content of protein using coomassie light blue technique. The results from electron spin resonance spectroscopy (ESR) and double Langmuir electron probe showed that electron, ion and oxygen free radical played important roles in sterilization in the discharge area, but only oxygen radicals acted to sterilize the bacteria in the afterglow area and the remote area.     

Energy model of glow discharge nitriding

A new model of nitriding is proposed on the basis of the energy initial conditions.     

Plasma-dust structures in He-Ar DC glow discharge

The gas mixture discharge has a number of features which can appear in experiments with dusty plasma. For example, in the case of a significant difference in atomic masses of ions and atoms, strong anisotropy of the distribution function over ion velocities takes place, which in turn can cause a significant change in properties of dust structures. In this work, experiments on the study of the dust structures in the gas discharge of a mixture of light and heavy gases, i.e., helium and argon, are analyzed. The results of numerical simulation of ion and electron drift in the mixture of these gases and dust particle charging processes are presented.     

Electron collision rates in oxygen glow discharge

The calculations of the distribution function of electrons and the collisional rates were carried out on the basis of a numerical solution of the Boltzmann equation for a weakly ionized discharge in O₂ rangingE/N from 5 Td to 200 Td. The distribution function, Townsend ionization and dissociative attachment coefficients calculated were found to be in good agreement with experiments. A comparison of the results on the collisional rates with the values available in the literature was performed as well.     

GDP/D-GDP化学结构与力学性能的研究

利用低压等离子体增强化学气相沉积技术制备碳氢辉光放电聚合物(GDP)和全氘代辉光放电聚合物(D-GDP)薄膜。利用表面轮廓仪、傅里叶红外光谱仪和纳米压痕技术对制备的样品进行表征,讨论了GDP/D-GDP薄膜的沉积速率、化学结构和力学性能在ICF物理实验用靶应用中的优缺点。结果表明：GDP/D-GDP薄膜的沉积速率都随反应气体流量比例近线性增加,GDP的沉积速率达到2.6 m,D-GDP的沉积速率达到1 m,GDP的沉积速率远大于D-GDP的沉积速率;D-GDP薄膜内部的交联化程度较弱,D-GDP更有利于靶丸内燃料的红外均化;GDP的力学性能明显优于D-GDP,更有利于ICF物理实验用靶的燃料填充与装配操作。