Spatial distribution of plasma parameters in a hollow cathode discharge not limited by walls: Experiment and modeling.

Based on the results of numerical simulation of the development of a streamer discharge in CO 2 in a gap with an external longitudinal magnetic field, the possibility of self-focusing of such discharges is demonstrated. The self-focusing is caused by a sharp slowdown in the speed of the radial ionization wave due to a change in the EEDF, a decrease in the average electron energy, electron mobility, and the rate of electron impact ionization in the crossed electric and magnetic fields as compared with the case of the discharge development without magnetic field. Simultaneously with the deceleration of the radial ionization wave, the ionization wave accelerates along the axis of the discharge gap due to a decrease in the radius of the streamer head and an increase in the electric field on it. Since the electric and magnetic fields are parallel to each other on the axis of symmetry, for the longitudinal wave there is no decrease in the average electron energy and ionization rate with an increase in the magnetic field value.

In this work, diagnostics and comparative analysis of microhollow cathode discharges with an open and covered external surface of the cathode in helium at atmospheric pressure were carried out. It is shown that by covering the external surface of the cathode, it is possible to achieve the effect when the current–voltage characteristics of the discharge grows in a wider range of discharge currents. Obviously, in this case, the negative glow (NG) plasma of the hollow cathode occupies a significant part of the discharge cell, as evidenced by the measurements carried out with the additional electrode. The electron temperature values determined from the I–U characteristic of the additional electrode are 0.3–0.4 eV for a microhollow cathode discharge with a covered external surface, which indicates that the plasma of such discharge is similar to NG plasma of glow discharge. The fast parts of the second derivatives of the I–U characteristic of the additional measuring electrode demonstrate the detection of the spectra of fast electrons produced as a result of Penning ionization reactions. Moreover, by covering the external surface of the cathode, conditions are created under which the entire discharge volume is occupied by a NG plasma, which makes it possible to achieve a better resolution for recording the spectra of fast electrons.

We report plasma parameters of laser ablated silicon plasma using the fundamental (1064 nm) and second harmonics (532 nm) of a Nd : YAG laser. The electron temperature and electron number density are evaluated using the Boltzmann plot method and Stark broadened line profile, respectively. The electron temperature and electron number density are deduced using the same laser irradiance 2–16 GW cm−2 for 1064 nm and 532 nm as 6350–7000 K and (3.42–4.44) × 1016 cm−3 and 6000–6400 K and (4.20–5.72) × 1016 cm−3, respectively. The spatial distribution of plasma parameters shows a decreasing trend of 8200–6300 K and (4.00–3.60) × 1016 cm−3 for 1064 nm and 6400–5500 K and (5.10–4.50) × 1016 cm−3 for 532 nm laser ablation. Furthermore, plasma parameters are also investigated at low pressure from 45 to 550 mbar, yielding the electron temperature as 4580–5535 K and electron number density as (1.51–2.12) × 1016 cm−3. The trend of the above-mentioned results is in good agreement with previous investigations. However, wavelength-dependent studies and the spatial evolution of plasma parameters have been reported for the first time.

Наведено результати дослідження спектральних, інтегральних і ресурсних характеристик випромінювання газорозрядної плазми атмосферного тиску на багатокомпонентних сумішах дийодиду кадмію з гелієм і малої добавки молекулярного азоту. Створення газорозрядної плазми і збудження компонент робочої суміші здійснювалося імпульсно-періодичним (частота проходження імпульсів 18–20 кГц, тривалість імпульсів 150 нс) бар’єрним розрядом. Виявлено випромінювання у видимій області спектру ексиплексних молекул монойодиду кадмію, атомів кадмію. Встановлено закономірності в змінах оптичних характеристик плазми в залежності від частоти проходження імпульсів накачки, компонентного і кількісного складу сумішей. Представлено обговорення результатів досліджень. Дані досліджень представляють інтерес для створення ексиплексних газорозрядних джерел видимого випромінювання з максимумом випромінювання на довжині хвилі λ=650 нм.

Model of microsecond pulsed glow discharge in hollow cathode for mass spectrometry

Semiempirical model for analysis of inhomogeneous optically thick laser-induced plasmas

Summary form only given. The buildup of a thin (about 1 mm diameter) plasma column on the axis of a hollow cathode leads to a distortion of the electric field distribution in such a way that there is a substantial increase in the radial component of the electric field at the orifice. For sufficiently high fields in this region, a second breakdown can be expected from the walls of the cathode to the center of the axial plasma column. This will rapidly lead to the establishment of a high current hollow cathode discharge. The mechanism of this initially radial discharge is assumed to be determined by pendel electrons. These are electrons which are excited from the walls of the cylindrical cathode, are accelerated in the radial electric field, traverse the negative glow region on the axis, and are reflected back from the cathode fall in front of the opposite cathode surface. In order to study the effect of these pendel electrons on the sustainment of a hollow cathode discharge, one-dimensional steady-state Monte Carlo calculations, in a hollow linear cathode region have performed

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 cathode). The nozzle (hollow cathode) 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.

Insights into the effect of hollow cathode with external injection of fast ions in a sputter-type negative ion source

The formation of negative ions in conjunction with their effect on SiO2 etching characteristics has been investigated within a CF4/Ar pulsed-power inductively coupled plasma. Electron energy distribution function in the pulsed plasma shows a narrow distribution compared with the CW mode. The average electron energy and electron density decrease greatly with decreasing duty ratio, which indicates that the high-energy electrons can be cooled effectively during afterglow time. By means of threshold ionization mass spectrometry, radical densities including CFx (x=1 to 3) and F are measured as a function of duty ratio and also correlated with the average energy and density of electrons. For negative ions, two major peaks, F- and CF3-, are formed predominantly through the electron attachment reactions during afterglow time. The possible mechanisms for the negative ion formation are proposed in the pulsed plasma. Additionally, the SiO2 etch rate decreases nearly linearly with decreasing duty ratio and microtrenching is suppressed by the reduction of charge accumulation on the sidewalls in the pulsed plasma.

Electron gas heating and cooling effects by microwave electric fields in compensated InSb

The results of investigation of the influence of geometrical dimensions, shape and position of the anode of a high-current non-self-sustained glow discharge with a hollow cathode at low (≈1 Pa) pressure with the current up to 100 A on the degree of inhomogeneity of azimuthal plasma-concentration distributions are presented. The azimuthal measurements demonstrate that upon injection of an electron flow with the current exceeding that of the electrons, formed as a result of the secondary ion-electron emission, the value of the average path length L of electrons before their escape to the anode is much lower than that in a self-sustained discharge burning mode. It is determined that in the case of injection of an electron flow into the hollow-cathode glow discharge the anode position considerably affects the degree of plasma concentration inhomogeneity. It is shown that placing the annular anode in the site preventing the line-of-site between the electron injection and anode surface directions allows achieving the minimum inhomogeneity coefficient value.

Plasma enhanced ignition is an important way in the field of ignition auxiliary. It has got wide attention throughout the researchers both at home and abroad. The plasma is usually added in the form of discharge. It makes a big difference in the discharge form according to different discharge unit, different kinds of electric field and different kinds of discharge medium. Variety of methods could be used to characterize the parameters of the plasma. The electron transport parameter is an important variable during the process of the plasma discharge. The mathematical model was set up to calculate the electron transport parameters in different reduced electric intensity. The electrons meet the Boltzmann equations in plasma system. Reasonable methods were used to simplify the Boltzmann equations. The electron transport parameters of methane-air mixed gas at the same equivalent ratio and pressure in different reduced electric field were calculated. The calculation results show that the EEDF turns to the right with the increasing of reduced electric field. The average electron energy and average electron energy of the mixed gas increases linearly with the increasing of reduced electric field. The increasing of reduced electric field enhances the electronic/energy diffusion effect and the enhancing effect is more apparent when the reduced electric field is high. The increasing of reduced electric field restrains the electron diffusion and energy transference restrains from the trend of the change. The inhibition effect is weakening with the increasing of the reduced electric field.

A comparative study of the effect of the initial composition of the HCl + Ar, H2, O2, and Cl2 binary mixtures on the steady-state physical parameters and composition of direct-current glow-discharge plasma was carried out. Information on the reduced electric field intensity, average energy and concentration of electrons, concentrations and densities of fluxes of atoms and ions were obtained. A simulation analysis of the effect of the initial composition of mixtures on the kinetics of the interaction between reactive species of plasma and the surface in the ion-stimulated chemical reaction mode is carried out.

Although the applications of the Hollow Cathode Discharge (HCD) are not confined to the analytical field, it is here that this low-pressure excitation source has gained most of its popularity. Atomic absorption, atomic fluorescence and atomic emission spectrometry greatly benefit from HCD properties such as high stability of discharge, sharp profile of spectral lines, low background intensity, applicability to samples in various physical forms and ease of determination for non-metals. With the obvious exception for atomic absorption spectrometry, there has not been the expected widespread utilization of the HCD over the years, nor have manufacturers been significantly attracted by the relatively low costs of production and maintainance of HCD-based instruments. One of the factors hampering a wider distribution of this source could be the somewhat limited intensity output achievable when the discharge is operated under conditions which fully preserve its basic features. Thus, the exploitation of the HCD for the analysis of trace and ultratrace elements, is severely limited. No wonder therefore that so much effort has been recently prompted for developing new versions of the HCD capable of promoting radiation intensity enhancement. The most promising of these comprise coupling with magnetic field, boost through auxiliary electric discharge, modifications of the cathode geometry, application of radiofrequency bursts, use of pulse-current regime, superposition of microwave field and separation of the atomization and excitation processes. The consequent increase in signal-tonoise ratio, already very favourable in the HCD as it is not in local thermal equilibrium, further expands its analytical potential. Some representative analytical applications of the improved HCD tubes are illustrated.