Inductive Discharge Research Articles

Superposition of low-pressure DBD and RF induction discharge for spectroscopic study of dissociative recombination in decaying plasma

The aim of the work was to find the optimal way to set up an experiment for spectroscopic study of the dissociative recombination of molecular ions with electrons in low electron density plasma at low gas pressure. In such an experiment, the influence of inelastic atom–atom collisions on the distribution of the DR flux over the excited atomic levels can be excluded. The first results of an experiment on combining a low-frequency barrier discharge (DBD) in neon at a pressure of less than 1 Torr with a pulsed radio-frequency (RF) induction discharge are presented. To create the plasma, we used DBD in a cylindrical glass tube with an inner diameter of 3.9 cm, which forms the spatial distribution of electron density with a minimum on the axis of the tube. The evolution of such a spatial distribution due to ambipolar diffusion in the initial stage of plasma decay provides an influx of charged particles to the center of the discharge tube, which increases the afterglow duration and helps to overcome the difficulties of detecting weak plasma radiation. The specific features of the DBD also appeared in the ionic composition of the plasma, which contained, in addition to Ne+ and Ne2+, the Ne++ ions, whose recombination with electrons significantly enriched the afterglow spectrum in the short-wavelength region. An RF discharge was used for pulsed heating of electrons in the afterglow. It is shown that, in accordance with the ionic composition, the radiation of a decaying plasma is presented by three groups of spectral lines with characteristic time behavior and the electron temperature dependence. The advantages of the proposed approach for studying the mechanism of dissociative recombination are discussed.

Study on Effect of Inductively Coupled Ar/O<sub>2</sub> Plasma in E- and H-Mode on Riceberry Rice by SEM/EDS

Riceberry brown rice is regarded as a source of various nutrients; often richer than white rice. Non-thermal plasma has recently been gaining a role for improving properties of cereal grains, especially brown rice. A number of methods of plasma treatment has been proposed including discharges as capacitive coupled plasma (CCP) and inductive coupled plasma (ICP). ICP has two operation modes as capacitive (E-mode) and inductive (H-mode) discharge with rather distinct characters. In this study we have focused on using ICP Ar/O2 plasma in both E-and H mode for plasma treatment on riceberry brown rice. The input power for plasma generation were set to 50 and 250 W for E-and H-mode, respectively. Plasma in H-mode was having higher plasma density than that in E-mode, as observed in the optical emission spectrum. The surface morphology of riceberry brown rice before and after Ar/O2 plasma treatment was evaluated using a scanning electron microscope without or with an energy dispersive spectroscopy (SEM and SEM/EDS). It has been found that the bran layer was richer in elemental compositions than the endosperm. The surface of rice sample was found to be etched and more porous after plasma treatment. The Ar/O2 plasma in H-mode was observed to offer higher effect. The surface contact angle was found to decrease from 120.1o ± 0.9o in untreated samples to 79.3o ± 0.6o and 99.2o ± 0.8o in plasma treated samples on E-and H-mode, respectively.

Power Losses in RF Inductor of Ferrite-Free Closed-Loop Inductively-Coupled Low Pressure Mercury Lamps

RF inductor power losses of ferrite-free electrode-less low pressure mercury inductively-coupled discharges excited in closed-loop dielectric tube were studied. The modelling was made within the framework of low pressure inductive discharge transformer model for discharge lamps with tubes of 16, 25 and 38 mm inner diam. filled with the mixture of mercury vapour (7.5×10–3 mm Hg) and argon (0.1, 0.3 and 1.0 mm Hg) at RF frequencies of 1, 7; 3.4 and 5.1 MHz and plasma power of (25–500) W. Discharges were excited with the help of the induction coil of 3, 4 and 6 turns placed along the inner perimeter of the closed-loop tube. It was found that the dependence of coil power losses, Pcoil, on the discharge plasma power, Ppl, had the minimum while Pcoil decreased with RF frequency, tube diameter and coil number of turns. The modelling results were found in good qualitative agreement with the experimental data; quantitative discrepancies are believed to be due skin-effect and RF electric field radial inhomogeneity that were not included in discharge modelling.

Investigation into the transient flow characteristics of noble gas propellants using the pulsed inductive discharge in electric propulsion

The Pulsed Inductive Thruster (PIT) has the advantages of repeatable startup, no corruption and in-situ propellant feed. To study the flow expansion and circuit characteristics of PITs, the circuit-fluid model is developed, and the high temperature thermodynamic and transport models are combined with the circuit-fluid model to predict the critical plasma parameters. The flow fields of initial mass of 2–8 mg and charge voltages of 10–14 kV are simulated. Comparison of the flow fields of argon and helium propellants suggests that, the flow field structures are similar. Slight differences exist on the magnitude of the density and magnetic field, caused by larger velocity in lighter atom case and difference on the ionization gap between adjacent ionization levels. Analysis of the circuit characteristics by the two-dimensional results indicates that the ratio of coil inductance to circuit inductance affects both the rise rate and phase of the plasma current, the larger the ratio, the greater the rise rate and the better the following characteristic. The calculations show that the magnetic energy obtained within the decoupling distance determines the overall performance the thruster can be obtained; self-induced field maintained by the thermal motion after the main pulse leads to the long attenuation process and difference on the total impulse when the angle of conical pylon is varied under constant coil dimension.

Electrodeless UV Lamp on the Basis of Low-Pressure Mercury Discharge in a Closed Non-Ferrite Tube

Experimental study of characteristics of a nonferrite electrode-less UV lamp with a length of 500 mm and width of 130 mm in the form of a closed quartz discharge tube with an inner diameter of 25 mm was conducted. The induction discharge was excited at a frequency of 1.7 MHz within the discharge lamp power Ppl ranging between 52 and 112 W in a mixture of mercury (~10-2 mm Hg) and argon (1.0 mm Hg) vapours by means of a 3-coil inductance located along the inner perimeter of the closed tube. With Ppl increasing: a) loss power in the inductance wire first decreased from 37 down to 22 W (Ppl = 84 W) and then increased up to 44 W; 2) the UV radiant flux of the lamp in a mercury light-band of 54 nm increased from 28 to 72 W; 3) radiant efficiency of the lamp at the light-band of 254 nm first increased from 31 to 48.5 % (Ppl = 84 W) and then slightly decreased down to 46 %; 4) radiant efficiency of the discharge plasma at the wavelength of 254 nm increased from 53 % to 65 %.

Spectral characteristics of inductively coupled plasma of water vapor

The paper presents the results of experimental measurements of the emission properties of water plasma in an inductive discharge. The power of the inductive discharge was 600 W at a frequency of 27 MHz and a pressure from 0.25 to 4 mbar. Plasma temperature was estimated from the Balmer hydrogen series using relative intensities method. It is shown that in this pressure range, the plasma is not in equilibrium and the energy difference between individual excited states increased with distance from the tube axis. The plasma heating time was estimated from the dynamics of the spectral line intensities to be 200 ms.

Low temperature plasma-assisted nitriding of austenitic steel in a ferromagnetic enhanced inductive discharge

Plasma-assisted nitriding of austenitic stainless steel AISI 321 has been performed with the use of a ferromagnetic enhanced inductive discharge as the source of nitrogen ions and radicals, in the temperature range of 300–400°C, gas pressure of 50 mTorr and ion densities of about (2.5–7.7)·1010 cm−3. A significant increase in the nitriding rate was achieved, in comparison with a low temperature glow-discharge nitriding process. A possible mechanism of the nitriding rate increase is a high atomic nitrogen density achieved in the ferromagnetic enhanced inductively coupled plasma.

Investigation of electrophysical and thermophysical characteristics of a low frequency nitrogen inductive discharge

A low-frequency (100 kHz) ferromagnetic enhanced nitrogen inductive discharge has been experimentally investigated in the nitrogen pressure range of 5–55 Pa and discharge current density of 20–80 mA/cm2. Dependence of the discharge electric field strength E on the gas pressure was measured for various discharge currents. Dependence of the neutral gas temperature on the gas pressure and discharge current was determined using optical emission spectroscopy, from the measured 0–0 vibro-rotational band of the second positive system of molecular nitrogen (C3Πu–B3Πg). Based on the determined neutral gas temperatures, values of the reduced electric field strength E/N were calculated.

Analysis of the Equation of the Balance of Energy in the Field of Heating Limited to the Longitudinal Coordinate

The analysis of energy balance equation for viscous laminar flow of fluid or gas in the cylindrical channel in the area (zone) of warm up bounded along the longitudinal coordinate is made. It was found that at laminar flow of fluid or gas in a round pipe, in each warm up area bounded along the longitudinal coordinate there are the areas of direct and reverse flows separated by a plane that is a locus of points where temperature is maximal for each fixed value of radial coordinate r. The received results also explain occurrence of returnable currents in plasma of the high-frequency induction discharge of atmospheric pressure.

Electric properties of carbon films deposited by magnetron sputtering with ion assistance

The paper deals with the study of ion assistance impact on structure and electrophysical properties of the carbon films deposited by magnetron sputtering of graphite targets. The flow of assisting ions was generated in the plasma reactor based on inductive RF discharge located in the external magnetic field. The change of the ionic current density in the range from 0.5 to 1 mA/cm2 was provided. Ion energy was changed by biasing the substrate in the range from 10 to 85 V. Neon, argon and krypton were used as working gases. The electrophysical properties of carbon films are shown to depend non-monotonous on energy of the assisting ions.

Application of argon collisional-radiative model for inductive RF discharge research

The technique of optical emission spectroscopy (OES) in combination with plasma emission models for determining the parameters of a gas discharge is presented. Measurements of charge carrier concentration and electron temperature in an inductively coupled RF plasma of argon are carried out under low pressure. The concentration and temperature of electrons were determined by selecting the ratio of the intensities of the spectral lines calculated with the collision-radiative model (CRM) to the intensities of the lines obtained in the experiment. The model describes the kinetics of the first 30 excited states of argon and takes into account the following processes: direct electron impact excitation / relaxation, spontaneous emission, radiation trapping, electron impact ionization and charge loss due to diffusion on the walls. The obtained OES results were compared with the results of Langmuir probe measurements of plasma parameters.

Increasing the capillary of fiberglass under the application of a relief coating in the low-pressure radio-frequency induction discharge

the article presents the results of experimental studies of the effect of low-pressure radio-frequency induction discharge on the glassfiber capillarity indexes after the formation of a functional microrelief of SiO2 particles on the surface of fiberglass.

The phenomenon of bicyclones a high-frequency induction discharge and the related questions of flows in channels with the presence of zones of heating, bounded along the longitudinal coordinate

The phenomenon of a bicyclones in a high-frequency induction discharge is explained. It is shown that this phenomenon should be characteristic of a wider range of objects having an internal heat source, limited by the longitudinal coordinate. In the present work, this phenomenon is considered as peculiar to fairly wide class of flows in cylindrical channels if there are one or several heating zones (internal or external) inside these channels, limited by the longitudinal coordinate.

Reducing the Transition Hysteresis of Inductive Plasmas by a Microwave Ignition Aid

Inductive plasma discharge has been a part of continuous investigations since it was discovered. Especially the E- to H-mode transition and the hysteresis behavior have been topics of research in the last few decades. In this paper, we demonstrate a way to reduce the hysteresis behavior by the usage of a microwave ignition system. With this system, a significant decrease of the needed coil current for the ignition of the inductive driven plasma is realized. For the microwave generation, a magnetron as in a conventional microwave oven is used, which offers a relatively inexpensive way for microwave ignition aid. At the measured pressure of 7.5 Pa, it was possible to reduce the needed coil current for the inductive mode transition by a factor of 3.75 compared to the mode transition current without the ignition aid. This was achieved by initiating the transition by a few seconds of microwave coupling. The performed simulations suggested that the factor can be further increased at higher pressures. That is especially interesting for plasmas that are hard to ignite or for RF-sources that cannot deliver high enough currents or frequencies for the ignition.

METHODS FOR CONTROL THE SELF-SUSTAINED PLASMA-BEAM DISCHARGE AT HIGH ENERGY DENSITY

Three methods for control the self-sustained plasma-beam discharge at high energy density are presented in this paper. Using a particular method, it is possible to set the location of the double layers formation in the discharge gap, as well as control its parameters at the high-current inductive discharge stage. It is shown that such methods can significantly increase the active power inputted into the discharge.

Transmission characteristics of optical nanofibers in metastable xenon.

We study the transmission characteristics of subwavelength diameter silica optical nanofibers (ONFs) surrounded with xenon plasma produced by low-pressure inductive RF discharge. In contrast with related experiments using rubidium vapor, we find essentially no degradation of optical transmission through the ONFs as a function of time. We also observe a pronounced ONF transmission modulation effect that depends on the conditions of the xenon plasma.

Simulation of an Inductive Discharge in Argon with the Gas Flow and Inhomogeneous Gas Temperature

With the purpose to create new methods for monitoring the parameters of low-temperature nonequilibrium plasma, a numerical drift-diffusion model of an inductive RF discharge in argon is developed and a study is made of ion transport onto the surface of the processed material. The model was tested against the available experimental and theoretical data. The calculations were performed for an inductive discharge in argon with parameters typical of modern plasmachemical reactors (a frequency of 13.56 MHz and a gas pressure in the chamber of 10 mTorr). The plasma density, electron temperature, and ion flux onto the processed surface are calculated; the gas temperature is found as a function of the input RF power; and the discharge parameters are determined as functions of the gas flow rate.

IR lasing on atomic xenon with pumping by longitudinal pulse inductive discharge

This article is the first report on the observation of laser IR radiation of Xe I atoms pumped by a longitudinal pulsed inductive transformer-type discharge. Both xenon and its mixtures with helium and argon were used as the active media. An emission spectrum was registered in the range of 190–1150 nm and consisted of two lines: 904.5 nm and 979.9 nm. The intensity ratios strongly depended on the composition and pressure of the active medium. Radiation energy in the first experiments did not exceed 0.1 mJ. Lasing pulse duration was 6 ± 1 ns (FWHM). Measured radiation divergence was 1 ± 0.2 mrad.

Features of the Kinetics of Bulk and Heterogeneous Processes in CHF3 + Ar and C4F8 + Ar Plasma Mixtures

We carry out a comparative study of the kinetics of plasma-chemical processes and plasma composition in CHF3 + Ar and C4F8 + Ar mixtures under the conditions of a high-frequency (13.56 MHz) induction discharge. Using diagnostic methods and plasma modeling, the general features and differences of the plasma’s electrophysical parameters in the studied systems are established together with the key bulk processes that determine the stationary concentrations of neutral particles. Тhe CHF3 + Ar system in the range 0–75% Ar is shown to be characterized by lower values of the flux densities of the fluorine atoms and polymer of the forming radicals. Model analysis of the kinetics of the heterogeneous processes (etching, polymerization, degradation of the polymer film) confirmed the advantage of the C4F8 + Ar system of silicon etching anisotropy and etching selectivity compared to the SiO2/Si system.

Measurement of the electron energy distribution in moving striations at low gas pressures

The time-resolved Electron Energy Distribution Functions (EEDFs) have been measured at different phases of moving striations in a positive column of DC discharge in argon gas. A very low gas pressure of 10 mTorr, a high energy resolution (to resolve the low energy part of the EEDF), and the dynamic range up to 3–4 orders of magnitude (to resolve the EEDF tail) with a temporal resolution of 2.5 μs distinguish our work from previous publications. The measured EEDFs reveal drastic changes in time of their low energy parts with the formation of a low energy peak. The observed EEDF dynamics is explained in the framework of nonlocal electron kinetics as electric field reversals and the trapping of low-energy electrons in potential wells propagating with striation along the discharge tube. The formation of the low energy peak in the EEDF is similar to that in rf capacitive and inductive discharges at low gas pressures where the low-energy electrons are trapped in the potential well created by the ambipolar electric field and cannot penetrate into the areas of electron heating by strong rf electric fields.