Neon Glow Discharge Research Articles

Study of UV Ne II line shapes in the cathode sheath of an abnormal glow discharge

We report results of an experimental and theoretical study of complex UV line shapes of Ne II 369.421 nm, Ne II 370.962 nm, Ne II 371.308 nm, and.Ne II 372.711 nm lines in the cathode sheath (CS) region of an abnormal DC glow discharge in pure neon. Two sets of experimental profiles and electric field distributions, one for discharge with tungsten and the other with titanium cathode, were obtained by means of the optical emission spectroscopy (OES) and theoretically studied by the iterative CS kinetic model. It is shown that our theoretical model enables the determination of the most important CS parameters (e.g. the thickness of the CS region, and the theoretical distributions of electric field and gas temperature) and thereupon based accurate theoretical predictions of the experimentally observed profiles of the studied lines.

Theoretical Study on Characteristics of Glow Discharged Neon Gas and Its Interaction With Terahertz Waves

Discharge gases have been used to detect terahertz (THz) waves, however, there are few relevant theoretical studies. The neon glow discharge model is established by COMSOL Multiphysics software, the characteristics of glow discharged neon and the interaction of the discharged gas with THz waves were investigated. The results show that with the increase of THz wave’s frequency, the transmittance increases, the change of plasma discharge characteristics caused by THz wave can be used for THz wave detection. The results provide a theoretical basis for the development of cheap, room temperature THz wave detector with fast response speed, and high sensitivity.

Design of pulsed neon injection in the synthesis of W-B-C films using magnetron sputtering from a surface-sintered single powder cathode

The surface sintering approach was examined in the present manuscript to obtain single cathode material consisting of multiple elements. Design of electromagnetic discharge without the use of a mechanical press was utilized for this purpose at pulsed pressure oscillations, ranging from 25 to 125 Pa. Meanwhile, each pulsed plasma flux provided absolute energy varying from 87.8 to 279.5 J, resulting in a well-sintered tungsten boride crust within carbon matrix (WBx-C). Its application in sense of sintering degree was estimated by measuring thermal diffusivity, with a maximum value of 3.65 mm2/s achieved at the mid-range neon injection (75–100 Pa). Further, as-surface-sintered cathode material provided suitable contribution to the promising deposition rate (54 nm/min) of W-B-C films by employing gas injection magnetron sputtering in the single magnetron cycle. The quantitative analysis examined using photoelectron X-ray spectroscopy showed that W-B-C films are composed of four elements, of which the W/B ratio was differed prior to prepared cathode materials stoichiometry. The chemical bonding state study revealed the C-W, B-W, B-C and B-O bonds, of which W2BC nanocrystallites (~ 2 nm) were formed in the amorphous structure under the arrangement of neon pulsed glow discharge, and as indicated results of fast Fourier transform and Raman spectra. Nucleation of those ternary nanoclusters promoted a Vickers microhardness result of 26.3 GPa, emphasizing a sensitive response to the mechanical performance of deposited W-B-C films.

Electrophysical Parameters of Plasma with a Charged Dust Cloud

The parameters of a low-pressure glow discharge in neon with solid microparticles are experimentally and numerically studied in order to determine the region of the existence of charged dust clouds that most strongly affect the electrophysical parameters of a gas-discharge plasma in neon. It is shown that dust clouds with the maximum total negative charge are formed at the average electron density of 108 cm–3 over the volume of the discharge. The obtained values of the plasma parameters with dust clouds are close to the values characteristic of the disturbed states of the ionosphere.

Complex UV Ne II line shapes in the cathode sheath of an abnormal glow discharge

We report results of an experimental and theoretical study of complex UV line shapes of Ne II 369.421 nm, Ne II 371.308 nm and Ne II 372.711 nm lines in the cathode sheath (CS) region of an abnormal glow discharge in pure neon. The experimental profiles were studied by means of the optical emission spectroscopy (OES) in conjunction with an iterative CS kinetic model. It is shown that our theoretical model describes the experimental line shapes and that, with the aid of the measured Stark shifts of atomic neon lines, it can be used for the determination of the most important CS parameters (e.g. the thickness of the CS region, distribution of electric field, and the gas temperature). We draw attention to the possibility of determining the electric field strength in CS from the width of the pedestal of the complex line profiles.

About the mechanism of modification of melamine formaldehyde particles in dusty plasmas

The article presents the previously obtained results of the modification of spherical microparticles of melamine-formaldehyde injected as a dust component of complex plasma formed in stratified glow discharge in neon. Particular attention is paid to changing the particle size depending on the residence time in the plasma. A mechanism is proposed for heating particles by ion flow sustaining a stable charge of their surface. Calculations of the heat balance are presented, confirming the results obtained in the experiment.

Charge transfer from doubly charged ions of transition elements in a neon glow discharge: evidence based on emission spectra

An extensive study of Mn II, Fe II, Ti II, Cr II and Cu II emission spectra from a Grimm-type glow discharge in neon was performed, using the formalism of transition rate (TR) diagrams. In this method, radiative depopulation rates of individual excited levels of a species under study are established based on the emission spectrum, prospective contributions from radiative decay of higher excited levels (cascade excitation) are subtracted and the resulting net depopulation rates are plotted as function of energy of the levels involved. A peak at a particular energy in such a diagram reflects a collisional process in operation, selectively populating levels in a narrow interval around that energy. By comparing net TR diagrams of ionic spectra of the elements listed above, a common pattern was found indicating that singly charged ions of these elements are created, in addition to other mechanisms, by charge transfer between doubly charged ions of the element under study and metastable neutral neon atoms. This mechanism appears to be significant and needs to be taken into account in collisional–radiative models describing excitation and ionization of some elements in neon glow discharges.

Glow discharge excitation and ionization of chromium, comparison with iron

Cr I and Cr II emission spectra from a Grimm-type glow discharge (GD) in argon and neon were analyzed. Intensities of strong resonance Cr I lines were corrected for self-absorption and population functions (experimental Boltzmann plots) of the Cr I system were established. A prevailing excitation mechanism in Cr I is the electron impact (EI) excitation. Cr II spectra in both discharges were described by transition rate (TR) diagrams, under the model of radiatively-dominated deexcitation. The contribution of cascade excitation was subtracted and the resulting net-TR diagrams of Cr II were analyzed. Unlike ionic spectra of some other transition elements, asymmetric charge transfer (ACT) between the ions of the discharge gas and ground state Cr atoms does not play a role in the excitation of the Cr II spectrum, because of the absence of suitable states in Cr II that would allow simultaneous conservation of energy and total angular momentum. Cr II states below ≈17 eV are populated largely by EI excitation from long-lived low Cr II states. In a neon discharge, ACT reactions between neutral neon metastables and doubly charged Cr ions and between neutral chromium and neon molecular ions were identified. The findings reported here were compared with the excitation of Fe I and Fe II systems at similar conditions. A well-known ‘hydrogen effect’, an enhancement of the Cr II line at 267.7165 nm in the presence of hydrogen in a GD plasma, was explained by charge transfer reaction between H+ ions and neutral chromium.

QPSK detection using glow discharge detector and a photodiode for millimeter‐wave and terahertz communication

AbstractThe terahertz gap (0.1‐10 THz) is an attractive frequency band for new applications. In wireless communication, it can serve as a high capacity link. The lack in use of that gap exists due to a lack of available commercial communications technology systems in that region. We have found that neon indicator lamps or glow discharge detectors (GDD) can be used as simple and very inexpensive detectors in that frequency gap. In modern modulation techniques, the signal phase should be recovered. This article is a proof of concept of detection of quadratic amplitude modulated millimeter‐wave signals by a GDD and photodiode using a heterodyne detection method.

Excitation and ionization of iron in argon and neon glow discharges: towards the true picture

A systematic detailed analysis of calibrated Fe I, Fe II emission spectra from an argon- and a neon glow discharge was performed, involving a large number of Fe I and Fe II levels. The relevant excitation and ionization processes of iron in those discharges are described and discussed, based on experimental population functions of Fe I and transition rate diagrams of Fe II in both discharges. The Fe I spectrum reflects electron impact excitation occurring at conditions far from local thermodynamic equilibrium. Some processes involving heavy particle collisions were considered also as potentially responsible for the features observed in the Fe I population function. Charge transfer between neutral iron atoms and the ions of the discharge gas is the prevailing ionization mechanism of iron in both discharges and the decay of the charge transfer-excited ionic levels dominates the Fe II spectrum. In a neon discharge, the decay proceeds step-wise, causing a massive cascade excitation of lower Fe II levels on the way. Emission associated with electron impact excitation of ground state iron ions was also observed. A simple semi-quantitative empirical collisional-radiative model is presented for iron atoms and ions in an argon glow discharge.

Instabilities of a constricted gas discharge with respect to two-dimensional wave perturbations

Modelling of the positive column in the glow discharge of neon was performed under discharge conditions covering the areas of diffuse and constricted states, as well as the transition region between them. An analysis of the stability of the stationary solution for diffuse and constricted regimes of the discharge was made. The spectral problem was solved in order to find the eigenmodes and eigenvalues corresponding to the growth increment of the perturbations of the electron number density and electrical potential. It was shown that the discharge in the diffusion mode is stable with respect to the perturbations under consideration, and the appearance and propagation of essentially two-dimensional spatially periodic perturbations is possible in the constricted mode of the discharge. A two-dimensional structure (topology) of plasma parameters was calculated and illustrated. The results of the theory were compared to the experimental data.

Role of thermal effects in neon and argon constricted discharges

The paper is aimed at investigating the role of inhomogeneous heating of the neutral gas in a constricted glow discharge in neon and argon. It is shown that inhomogeneous heating is not the primary cause of constriction in specified gases at pressures of tens and hundreds Torr cm and reduced currents not exceeding 100–200 mA cm−1. Constriction of the positive column occurs even with an insignificant gas heating in a pulsed regime. An abrupt constriction is caused by the nonlinear dependence of the ionization number on the electron density. In mentioned discharge conditions the frequency of electron–electron collisions is comparable to the electron energy relaxation frequency due to elastic electron-atom collisions. Thermal effects play a secondary role in the formation of a constricted discharge. At the same time, inhomogeneous gas heating in argon is more notable than in neon. Unlike neon, stationary argon discharge loses spatial stability in a vertically oriented tube as the pressure and current increase and a buoyancy effect takes place in a horizontal orientation. Such difference in the behavior of constricted neon and argon discharges is mainly caused by the difference in shape of elastic electron-atom collision cross sections. Interferometric methods allowed to study the temperature field of neutral atoms, dynamics of both gas heating and ascent of constricted cord. Observed effects are interpreted on the basis of the heat equation and the Navier–Stokes equation. Comparison of experimental and theoretical results shows good agreement.

Boundary of the Transition to Hollow Dust Structures in a DC Discharge in Neon with Microparticles

The boundary (line) of the transition from homogenous dust structures to hollow dust structures in the coordinates gas pressure–discharge current in a glow discharge in neon was found experimentally. The experiments were carried out with spherical particles 2.55 and 4.14 μm in diameter. The transition was simulated using the diffusion–drift model of the positive column of a glow discharge in neon with allowance for the radial temperature gradient. Simulations of the experimental data have shown that the thermophoretic force acting on the microparticles in the dust structure depends on the discharge parameters and the dimensions of the microparticles and the dust structure. The results of this work can be used in dusty plasma technologies.

Surface modification of melamine formaldehyde resin particles in a stratified glow discharge in neon

The paper presents the description of the change in size and structure with time of the surface of polymer particles of melamine formaldehyde injected as a dust component of a complex plasma formed in a stratified glow discharge in neon. The experiment was carried out in a specialized discharge chamber, equipped with a device for collecting particles from a dust trap. The analysis of the size and surface structure was carried out by scanning electron microscopy, which gives the original and the resulting surface views of the plasma‐processed particles. These profiles show the variation in surface roughness distribution under the action of the plasma. The time dependence of the particle diameter on plasma exposure was tracked. Data show that 25 min of exposure results in the dust particles losing a substantial part of their volume, which is accompanied by a decrease of the diameter by half. Our results coincide with previous data for smaller particles in similar plasma conditions.The particles used in this work are larger but still are able to levitate in a dust trap, and corresponding processes of size degradation and surface modification are extremely intense.

Dusty plasma of a dc glow discharge in different noble gases

A self-consistent non-local model of the positive column of a dc glow discharge in helium, neon and argon with dust particles is presented. A kinetic Boltzmann equation for the electron energy distribution function, drift-diffusion equations for ions and dust particles, the Poisson equation for electric field were calculated self-consistently for different discharge conditions. The radial distributions of the discharge plasma and the dust particles parameters were obtained for different discharge gases. The influence of the buffer gas sort is revealed and discussed.

Spatial and temporal formation dynamics of glow discharge constriction and stratification

In the present work, we experimentally study the formation dynamics of positive column constriction in neon glow discharge at intermediate pressures () with the simultaneous development of longitudinal instabilities in the form of moving striations. Discharge current, which exceeded the critical value for the transition to the constricted regime, was modulated by short rectangular pulses in order to avoid the inhomogeneous heating of the gas. During the pulse, the ionization balance was establishing and then discharge was switching to the constricted regime. The temperature field of neutral atoms was determined using interferometric methods based on a scheme of the Michelson interferometer. The heat equation was solved for the stationary and pulsed regimes. It is shown that under the described discharge conditions, in spite of the absence of inhomogeneous gas heating, discharge switches to the constricted regime with the appearance of moving striations. On the basis of the performed experiments, it can be concluded that inhomogeneous gas heating in neon is not the main cause of discharge constriction. A nonlinear dependence of the ionization rate on the electron density related to the Maxwellization of the electron energy distribution function should be considered as the basic mechanism of constriction.

The role of molecular ions in cryogenic dusty plasmas of dc discharge in neon

The diffusion-drift model of positive column of glow discharge in neon have been used to study the effect of molecular ions in the interaction of plasma with dust particles of micron size. Simulations have been carried out at a pressure of 20 – 100 Pa and gas temperature of 77 K. The electric field of the discharge, the concentrations of discharge components, including metastable atoms and molecular ions, and the charge of dust particles have been simulated.

Spectral Study of Glow Discharge With Dusty Structures

We present the results of the experimental study of the influence of dusty structures on plasma. We have studied glow discharges in neon and argon with $\text{Al}_2 \text{O}_3$ polydisperse particles and melamine-formaldehyde monodisperse particles with the diameter of $\text{4.83} \; \mu m$. We used optical emission spectroscopy and laser-induced fluorescence methods to measure shift of excited atoms populations, which led to similar results. In most cases, the population change was negligible as compared to the inaccuracy. $\text{Al}_2 \text{O}_3$ particles in argon formed large structures which caused dramatic redistribution of radiation. In this case, spectral lines and fluorescence became 9-50% weaker at the tube center after dusty structure formation. It might be accounted for by a decrease of electron density due to recombination on the surfaces of the particles. Near the tube wall, the radiation became brighter due to an electron temperature increase. Photographs of the discharge allowed us to calculate the radial distribution of the population shift.

Surface Modification of Melamine-Formaldehyde (MF-R) Macroparticles in Complex Plasma

The surface modification of melamine-formaldehyde (MF-R) macroparticles (4.12 ± 0.09 μm in diameter) in dc glow discharges in neon, argon, and an argon–oxygen mixture (90% Ar, 10% O2) was studied experimentally. The macroparticles were treated in the discharge plasma for 10, 20, 40, and 60 min. The macroparticles were placed in ordered plasma–dust structures and then extracted from them. The results of atomic force microscopy of the surface profile are presented. Quantitative data on destruction of the surface layer and aspects of its modification are discussed. The amount of substance removed from the particle surface for the exposure time was calculated using the fractal analysis method.

Transition rate diagrams and excitation of titanium in a glow discharge in argon and neon

Emission spectra of titanium in a Grimm-type glow discharge in argon and neon were studied using the formalism of transition rate diagrams. Ti I spectra in argon and neon discharges are similar, without signs of selective excitation, and populations of Ti I levels exhibit a decreasing trend as function of energy, except for some scatter. A major excitation process of Ti II in argon discharge is charge transfer from argon ions to neutral titanium. In neon discharge, a strong selective excitation was observed of Ti II levels at ≈13.3–13.4 eV relative to the Ti I ground state. It was attributed to charge transfer from doubly charged titanium ions to neutral titanium, while the Ti++ ions are produced by charge transfer and ionization of neutral titanium by neon ions. Cascade excitation is important for Ti II levels up to an energy of ≈13 eV relative to the Ti I ground state, both in argon and neon discharges.