Gas Discharge Plasma Research Articles

Application of the triple-probe technique to magnetized plasmas

The triple-probe technique (TPT) is a diagnostic widely used to determine the electron temperature in various devices and plasma conditions. It was developed for measurements in low-pressure gas-discharge plasmas in the absence of a magnetic field. This paper presents a comparison of the experimental results obtained by swept Langmuir probe (LP) measurements with those obtained by the TPT in magnetized plasmas in three experimental machines with different magnetic field magnitudes (0.01–1.15 T). The reliability of the triple-probe results for the electron temperature in tokamak plasmas at higher magnetic fields is discussed. It was found that the larger the magnetic field, the more the TPT overestimates the electron temperature compared with single swept LPs. The explanation proposed in this paper is based on a shift in the floating potential towards the plasma potential in the presence of a magnetic field, yielding a more positive voltage measured by the TPT and therefore higher electron temperatures. Using the extended formula for the electron probe current in the presence of a magnetic field a correction factor is derived such that the TPT yields a temperature similar to that of the swept LP techniques.

Numerical simulation of a partially anisotropic electron distribution function in a pulsed discharge with a hollow cathode

In this paper, we propose a convenient method for calculating the electron energy distribution function (EEDF) in a gas-discharge plasma, where the presence of high-energy electrons results in the formation of a partial EEDF anisotropy. A detailed description of this method is provided. The performance of the proposed method is demonstrated to calculate the EEDF of plasma column of a high-voltage nanosecond discharge in argon with an extended hollow cathode. The applicability assessment of the proposed method calculating the EEDF in the plasma column of pulsed discharge sustained by the 50 Hz pulse and gas pressure from 5 to 40 Torr is given. It was shown that high-energy electrons were effectively formed in this type of discharge with an increase in the EEDF in the high-energy region. This technique can also be usefully employed for other types of discharges where fast electrons are formed.

Analytical Formulas for Approximating Cross Sections of Electron Collisions with Hydrogen, Noble Gases, Alkali and Other Atoms

This paper presents an analysis of data on the cross sections of elastic and inelastic collisions of electrons with noble gases, alkali and other atoms. For the selected sets of experimental and theoretical data, optimal analytical formulas are found, and approximation coefficients are calculated. The obtained semi-empirical formulas reproduce the values of the transport (diffusion), excitation and ionization cross sections for noble gases. Much attention is paid to the ionization cross sections of metal atoms, which are often present as an impurity in gas-discharge plasma. The approximation formulas reproduce the values of the ionization cross sections for hydrogen, metal and other elements in a wide range of energies with accurate orders of errors of the available theoretical and experimental data. For some elements with a two-hump plot of the dependence of the ionization cross section on the collision energy, it is proposed to use a two-term formula that takes into account ionization from both external and internal shells.

Sporicidal Action of Pulsed Radiation of Hot Plasma.

In the study, we used a Pilimin IR-10 spark discharge generator as a source of pulsed radiation of hot plasma; a corona discharge generator - as a source of cold plasma; a DKB-9 low-pressure mercury lamp - as a source of continuous radiation of UV band, wavelength of 253.7 nm. The samples were processed in Petri dishes, 40 mm in diameter, their volume being 4 and 10 cm3. The study used an L-tyrosine solution in distilled water (the concentration: 160 mg/L), a suspension of bacteria and spores of micromycetes (its concentration being ~106 cells per 1 ml). Tyrosine conversion products were identified spectrophotometrically before and after treatment. The biocidal and sporicidal effects were assessed by counting CFU (colony-forming units) after seeding incubation at 27-37°C. The oxidation of tyrosine by HO2• radicals was found to be impossible. Under 2 the action of nitrogen compounds, nitration proceeds with 3-nitrotyrosine formation. The nitration reaction is slow, taking about 100 h. A possible nitration mechanism is through the formation of the nitronium ion NO2+ in an acidic medium.The biocidal effect of hot plasma radiation turned out to be weaker than that of UV radiation of a DKB-9 lamp. This is due to the difference in their emission spectrum. The sporicidal effect of hot plasma radiation was more pronounced: a 10-fold decrease in the number of CFU was observed at radiation doses of 200-280 J. Under the action of UV radiation, at the same doses, the decrease in the number of CFU was from 3 to ~30%. The sporicidal effect of hot plasma radiation is due to the decay of a long-living …ONOOH/ONOO-… complex with the formation of a nitric oxide and a nitronium ion in an acidic medium. The study showed the viability of spores under the action of pulsed radiation of hot plasma to decrease. While the light radiation of a UV lamp, under studied conditions, slightly penetrates the protective coating of a spore. The sporicidal effect of hot plasma radiation is due to the decay of a long-living …ONOOH/ONOO-… complex with the formation of a nitric oxide and a nitronium ion in an acidic medium. Nitration plays a decisive role in the sporicidal action of the hot plasma radiation of a spark discharge. The principle of the sporicidal effect of gas-discharge plasma radiation can be used to develop disinfecting devices.

Electrode Cooling and Microwave Absorption by Phase Change Fluid Discharge Plasma

It is hard to realize the high microwave absorption property and the low operating temperature in a gas discharge plasma simultaneously, due to the electron number density, and electron neutral collision frequency physically needed for the former is a typical severe heating scenario for the latter. In this article, the phase change process is proposed to be introduced into the controlled area of the discharge plasma system to increase collision frequency and decrease the discharging electrode temperature at the same time. An ac high-voltage power-driven quasi-periodic array of the phase change fluid discharge (PCFD) device is investigated. The most apparent tendency of the PCFD plasma is the improved diffusivity and uniformity. At the same time, the temperature of the electrode and its vicinity, where the phase change material is reserved, is lower than the ambient temperature. Compared with the controlled discharge state of the low gaseous pressure dielectric barrier discharge (L-DBD) plasma without phase change process, the absorption attenuation in the <inline-formula> <tex-math notation="LaTeX">$X$ </tex-math></inline-formula>-band is enhanced in all tested polarization angles, which driving strategy could control. Analyses show that the increased microwave absorption, frequency shift, and bandwidth broadening mainly result from the phase change process and its influences on the plasma discharge.

Antibacterial effects of liquid discharge cold plasma on Enterococcus faecalis planktonic cultures and biofilms: an in vitro study of root canal treatment

Although many researchers have studied the antibacterial effects of gas discharge plasma in root canal disinfection, there are few studies on the potential of liquid discharge plasma in root canal disinfection. This study aimed to investigate the antibacterial effects of liquid discharge cold plasma (LDCP) on Enterococcus faecalis (E. faecalis) planktonic cultures and four-week-old root canal biofilms. Antibacterial efficacy was determined by the colony-forming unit method. Changes in the viability and surface morphology were studied by confocal laser scanning microscopy and scanning electron microscopy, respectively. The results showed that LDCP treatment had a significant antibacterial effect on planktonic E. faecalis, and had a better antibacterial effect on biofilms than 0.2% chlorhexidine treatment. The normal spherical structure of E. faecalis dissociated, and biofilm architectures were destroyed after LDCP treatment. This work opens doors to the potential application of using liquid discharge plasma devices for root canal treatment.

2Nd International Conference “Gas Discharge Plasma and Synthesis Of Nanostructures 2021

In the city of Kazan from December 1 to December 4, 2021 on the basis of the Kazan National Research Technical University named after V.I. A.N. Tupolev-KAI hosted the II International Conference "Gas Discharge Plasma and Synthesis of Nanostructures" was held. The main organizers of this conference are KNRTU-KAI, KFU, Academy of Science Republic of Tatarstan. This event has become a notable event for the community of scientists and researchers involved in the physics of gas discharges and the synthesis of nanostructured materials. The conference discussed issues related to fundamental, problematic issues in the physics of gas discharges, such as the theory of arc plasma, high-frequency discharges, microwave discharges, glow discharge. Nevertheless, the main attention was paid to the problems of using gas discharge plasma for the synthesis of nanostructures. It is gratifying that there are results in this direction that are ready for industrial application. This year, the topic of the conference additionally includes a section on the physics of non-ideal and dusty plasma. On this topic, several plenary reports were made at once, which were presented by leading world scientists. The conference became a platform where completely new fundamental results that are at the forefront of science were presented. The vast majority of the presented works were presented for the first time.Organizing Committee, Scientific Committee are available in the pdf

Simulation study of coupled two-stream and current filamentation instability excited by accelerator electron beams in plasmas

A gas-discharge plasma device is simulated with COMSOL software, and the obtained plasma density profile is input into a two-dimensional particle-in-cell code, in which the transport of relativistic electron beams in the plasma with an actual density profile is investigated. The results show that the device can produce a wide range of high-density plasmas with the maximum density approaching 5.25×1022 m−3. With the relativistic electron beams produced from a linear electron accelerator, the gas-discharge plasma is shown to be an ideal medium for the investigation of coupled two-stream and current filamentation instability.

Deposition of metal nanofilms on cylinder-shaped items

The use of the magnetron sputtering method ensures high adhesion of the applied thin nanoscale films and allows deposition of metal coatings (Cu, Ni, Ti, Ag, Au, etc.) on various substrates. The disadvantage of planar magnetron sputtering devices is the inability to apply coatings to the inner surface of cylindrical parts (for example, silvering of the inner walls of waveguides). The formation of such films is possible with the use of a rod cathode-target and a cylindrical anode-substrate coaxially located with it. In the space between the target cathode and the anode substrate, a low-temperature gas discharge plasma is created by applying a constant electric voltage, and a magnetic induction field perpendicular to the electric field is created by permanent magnets or solenoids located outside the cylindrical anode substrate. The disadvantages of such a device include the inability to control the characteristics of the permanent magnetic induction field in the case of permanent magnets and the inhomogeneous characteristics of the magnetic induction field in the case of solenoids. A significant disadvantage is the need to rebuild the entire system of external magnets in the event of a change in the requirements for the parameters of the magnetic induction field or a change in the configuration of the substrate. Therefore, it is necessary to exclude external sources of the magnetic induction field. In the proposed device, the magnetic induction field is created due to the flow of a constant current of the required value through the cathode. The use of alternating and direct current sources and a system of capacitors and chokes allows creating a controlled magnetic field of the required configuration and implementing a discharge in the crossed fields. This makes it possible to obtain a high-quality coating with heterogeneity of about 3% throughout the product.This paper was recommended for publication by the Organizing Committee&nbsp;of the International Conference Nanophysics and Nanomaterials (24&ndash;25 November&nbsp;2021, Saint Petersburg, Mining University).

High energy electron beam generation during interaction of a laser accelerated proton beam with a gas-discharge plasma

The study of the interaction between ion beam and plasma is very important to the areas of inertial fusion energy and high energy density physics. With detailed one-dimensional electromagnetic particle-in-cell simulations, we investigate here the interaction of a laser-accelerated proton beam assuming an ideal monoenergetic beam with a gas-discharge plasma. After the saturation stage of the two-stream instability excited by the proton beam, significant high energy electrons are observed, with maximum energy approaching 2 MeV, and a new two-stream instability occurs between the high energy electrons and background electrons. The trajectories of plasma electrons are studied, showing the process of electron trapping and de-trapping from the wakefield.

Influence of Beam and Plasma Noise on the Instability of the “Fast Electron Beam–Confined Collisional Plasma” System. Kinetic Consideration

In this work the stability of the “fast electron beam–gas-discharge plasma” system was investigated within the framework of the kinetic approach and under conditions when the Knudsen number of the discharge is of the order of 1. As shown, the loss of stability of the system with respect to the beam and plasma noise occurs at the same parameters of the system. Thus, when developing the theory of the instability of the “fast electron beam–plasma” system, it is necessary to solve the problem with both initial (for plasma noise) and boundary (for beam noise) conditions. The increment of the amplification of the beam noise at frequencies close to the plasma ones is significantly higher than this value for the plasma noise. Thus, the latter have little effect on the phase focusing process at the linear stage if a plasma frequency is present in the beam noise spectrum.

Kinetic Energy of a Monolayer of Dust Particles in Gas Discharge Plasma

The phenomenon of the abnormal heating of oscillations of dust particles in a gas discharge plasma is studied. Equations of motion of of dust particles with allowance for charge fluctuations and the structural features of a near-electrode layer are formulated. Themolecular dynamics simulation of the system of dust particles is performed. The mechanism of increase of the average kinetic energy of dust particles in a gas-discharge plasma is proposed. It is shown that charge fluctuations cause forced oscillations, which tend to the warming up of vertical oscillations of dust particles. The combination of parametric and forced resonances can explain the anomalously high values of the kinetic energy of dust particles. The estimated frequency, amplitude, and kinetic energy of oscillations of dust particles are close to the experimental values.

Average Size and Density of Clusters in Dusty Plasma

As is well known, metal and metal oxide dust particles either in combustion plasmas or in low-pressure gas-discharge plasmas are able to get a positive or negative charge. When the particles are identically charged, the Debye interparticle repulsion force arises. However, due to the additional interaction of grains with plasma electrons and ions, the resultant intergrain pair potential energy becomes non-Debye. As a result, it can cause local minima by certain plasma parameters. This case develops a quasimolecular structuralization, where two equally charged grains are spaced at a finite distance in equilibrium. The same principle of grain structuralization is valid for the multibody case where grains are associated in a crystal structure or clusters. The present work is devoted to the description of the dependence of the average size and the density of clusters on the interparticle potential. The general formula for the average cluster energy via the pair potential energy is derived.

Влияние электронной температуры на распределение концентрации в поперечном сечении газоразрядной плазмы

The electron temperature and the concentration of charged particles associated with it in a gas-discharge plasma can lead to a change in the properties of the corresponding electronic devices: a change in the space charge. Even an insignificant space charge, due to the difference in the concentrations of charged particles in the plasma, can cause instabilities and lead to the formation of undamped longitudinal and transverse waves (strata) in the plasma of the positive gas discharge column. In a magnetized gas-discharge plasma, the space charge decreases due to a decrease in the parameters of motion of charged particles, and with a transverse magnetic field B = B0 = (bebp)-1/2 vanishes and the plasma becomes homogeneous. In the case when the magnetic weakly affects the plasma, it is necessary that the concentration of charge carriers be the same, i.e. the plasma is homogeneous. Therefore, it is necessary to determine the minimum value of the electron temperature at which the Maxwellian plasma is homogeneous. Goal – To estimate the effect of electron temperature on the distribution of charge carrier concentration, analyze the electron balance equation in two cases: at zero and real boundary conditions.

Influence of temporal variations in plasma conditions on the electric potential near self-organized dust chains

Self-organization of dust grains into stable filamentary dust structures (or “chains”) largely depends on dynamic interactions between individual charged dust grains and complex electric potential arising from the distribution of charges within a local plasma environment. Recent studies have shown that the positive column of the gas discharge plasma in the Plasmakristall-4 (PK-4) experiment at the International Space Station supports the presence of fast-moving ionization waves, which lead to variations of plasma parameters by up to an order of magnitude from the average background values. The highly variable environment resulting from ionization waves may have interesting implications for the dynamics and self-organization of dust particles, particularly concerning the formation and stability of dust chains. Here, we investigate the electric potential surrounding dust chains in the PK-4 experiment by employing a molecular dynamics model of the dust and ions with boundary conditions supplied by a particle-in-cell with Monte Carlo collision simulation of the ionization waves. The model is used to examine the effects of the plasma conditions within different regions of the ionization wave and compare the resulting dust structure to that obtained by employing the time-averaged plasma conditions. The comparison between simulated dust chains and experimental data from the PK-4 experiment shows that the time-averaged plasma conditions do not accurately reproduce observed results for dust behavior, indicating that more careful treatment of plasma conditions in the presence of ionization waves is required. It is further shown that commonly used analytic forms of the electric potential do not accurately describe the electric potential near charged dust grains under these plasma conditions.

Global model of miniature electron cyclotron resonance ion source

Miniature electron cyclotron resonance (ECR) ion sources are widely used in compact ion implanters, miniature neutron tubes, and miniature ion thrusters. To understand the mechanism of miniature ECR ion source, a miniature deuterium ion source developed by Peking University is taken as the research object. In this work, a global model based on particle balance equations is developed for studying the hydrogen plasma and the deuterium plasma inside the miniature ECR source. The research results show that both the hydrogen discharge process and the deuterium discharge process of the ion source are strongly dependent on the gas pressure and microwave power. The calculated results show that high power is beneficial to increasing the proportion of H&lt;sup&gt;+&lt;/sup&gt;(D&lt;sup&gt;+&lt;/sup&gt;) ions, low pressure is helpful in augmenting the ratio of &lt;inline-formula&gt;&lt;tex-math id="M3"&gt;\begin{document}$ {\text{H}}_2^ + $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20212250_M3.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20212250_M3.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;(&lt;inline-formula&gt;&lt;tex-math id="M4"&gt;\begin{document}$ {\text{D}}_2^ + $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20212250_M4.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20212250_M4.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;) ions, high pressure and low power are beneficial to enhancing the proportion of &lt;inline-formula&gt;&lt;tex-math id="M5"&gt;\begin{document}$ {\text{H}}_3^ + $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20212250_M5.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20212250_M5.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;(&lt;inline-formula&gt;&lt;tex-math id="M6"&gt;\begin{document}$ {\text{D}}_3^ + $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20212250_M6.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20212250_M6.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;) ions. In addition, there is a large difference in ion proportion between hydrogen discharge and deuterium discharge. Under the same operating parameters, the proportion of D&lt;sup&gt;+&lt;/sup&gt; ions is 10%–25% higher than the proportion of H&lt;sup&gt;+&lt;/sup&gt; ions since the plasma density of deuterium discharge is higher than that of hydrogen plasma. Therefore, during the operation of miniature source, H&lt;sub&gt;2&lt;/sub&gt; gas, instead of D&lt;sub&gt;2&lt;/sub&gt; gas, can be used in experiment, and the proportion of D&lt;sup&gt;+&lt;/sup&gt; ions under the corresponding operating parameters can be estimated based on the proportion of H&lt;sup&gt;+&lt;/sup&gt; ions. Finally, the calculated results show that high microwave power is a prerequisite for achieving the high proportion of H&lt;sup&gt;+&lt;/sup&gt; (D&lt;sup&gt;+&lt;/sup&gt;) ions. However, owing to the limitation of microwave coupling efficiency, the miniature ECR ion source cannot work when the microwave power is greater than 150 W, so that the H&lt;sup&gt;+&lt;/sup&gt; (D&lt;sup&gt;+&lt;/sup&gt;) proportion cannot be further increased, thereby limiting its further applications in neutron sources, implanters, etc. Therefore, how to improve the microwave coupling efficiency has become one of the key research contents of the miniature ECR ion source. The global model proposed in this paper is helpful in understanding the physical process of the miniature ECR ion source, but there are also some shortcomings. Firstly, the effect of the secondary electron emission coefficient is not considered in the model, so it is impossible to study the influence of wall materials on ion proportion in detail. Secondly, the dissociation degree depends on the plasma measurements, and the error of plasma measurements in turn affect the accuracy of the model to a certain extent. In addition, only the hydrogen plasma model and deuterium plasma model are established in this work, based on which it is impossible to study the processes of other gas discharge plasmas. In the future, the above factors will be considered and the model will be further improved to establish a complete and self-consistent global model of the miniature ECR ion source.

Структура и свойства покрытия системы SnO2-In2O3-Ag-N, сформированного на меди комплексным методом

The aim of this work is to analyze the structure and properties of coating of the SnO2-In2O3-Ag-N composition formed on copper by a complex method combining electroexplosive spraying, irradiation with a pulsed electron beam, and subsequent nitriding in the plasma of a low-pressure gas discharge. It is shown that the thickness of the coating is ≈ 100 μm. The wear resistance of a coated copper specimen exceeds the wear resistance of uncoated copper by a factor of 2.8. The friction coefficient of coated specimens μ = 0.479 is less than the coefficient of friction of copper without coating μ = 0.679 ± 0.048 by a factor of 1.4. It was found that the hardness of the coating increases as it approaches the substrate and reaches a maximum value of ≈ 1400 ± 98 MPa (the hardness of the substrate is 1270 MPa). Micro X-ray spectral analysis showed that the main chemical element of the coating is silver; copper, tin, indium, oxygen and nitrogen are present in much smaller amounts. It was established by X-ray phase analysis that the main phases of the coating are solid solutions based on copper and silver.

Слаботочный разряд в потоке аргона при атмосферном давлении в условиях образования атомов металлов: электрические и оптические характеристики

The paper presents the results of a study of the current-voltage characteristics and optical emission spectra of plasma of a atmospheric pressure pulsed discharge plasma at a frequency of several tens of kilohertz and a pulse duration of up to 10 μs, in the mode of generation of plasma flows containing metal particles. The features of the plasma generator conclude in combination of the design of electrodes, as well as the modes of electric and gas supply of the discharge system. The cathode is a crucible containing a melting insert which allows the discharge operation in a low-current form with a current of 40 mA to 1 A, at a sufficiently high voltage of 150 to 200 V, without transition to arc discharge mode. Such parameters make it possible to generate atomic flows of a melting cathode insert, which are blown out by a jet of working argon gas, pumped at a flow rate of 1 l/min, outside the discharge system. The entry of a metal component into a gas-discharge plasma affects the parameters of the discharge operation, as well as the properties of its optical emission. In the context of this phenomenon, the spectral distributions of the intensity of optical radiation corresponding to the lines of magnesium, indium, and zinc were investigated, as well as their time dependence during the current pulse period operation, in relation to the identification of physical features leading to stable generation of flows of metal atoms at atmospheric pressure.

Impact of the plasma flow of a low-pressure high-frequency capacitive discharge on the adhesive and physical and mechanical characteristics of aramid and carbon fibers

The changes in the adhesive and physico-mechanical characteristics of aramid and carbon fibers treated with plasma of a highfrequency capacitive gas discharge of reduced pressure are considered. An increase of ~ 30% in the wettability of the surface of aramid and carbon fibers is shown. It was found that the strength of plastics made on the basis of aramid and carbon fibers treated with a plasma flow increases by ~ 26%.

Plasma methods for preparation of the substrate and fixing the nanoparticles in the obtaining of disposable antibacterial synthetic materials

The presented work is devoted to the study of the use of a gas-discharge plasma of a low-pressure radio-frequency discharge in the processes of preparing substrates and fixing silver nanoparticles in the preparation of antibacterial synthetic non-woven materials for disposable use. The results of the study of antibacterial activity to assess the inhibition of colony formation of E. coli culture on polypropylene non-woven materials for disposable surgical, medical clothing and underwear, as well as personal protective equipment are presented. To assess the antibacterial activity, fluorescent staining of the samples was carried out. The study of the surface of the samples was carried out using a scanning electron microscope. The materials were treated with preparations based on silver nanoparticles; to ensure the uniformity of properties and fixation of the preparations, treatment in radio-frequency gas-discharge plasma was used. The use of radio-frequency gas-discharge plasma treatment in the processes of modification of polypropylene fibers with antibacterial preparations based on silver nanoparticles makes it possible to obtain antibacterial materials with bacteriostatic and/or antibacterial activity over their entire surface area.