Argon Gas Discharge Research Articles

Experimental study on the influence of gas flow rate on the plasma plume of N-APPJ

In order to explore the effect of the gas flow rate on the plasma plume, a quantitative study of the effect of the gas flow rate on the atmospheric pressure non-equilibrium plasma plume length was carried out using two different electrode structures. The results show that plasma plume length of up to 80.2 mm can be achieved in atmospheric condition outside the tube. The plasma plume length of the indented tube is smaller than that of the straight tube for the same argon gas flow rate, discharge voltage and axial distance between electrodes, and the effect of the argon flow rate on the plasma plume length is more obvious for the straight tube than for the indented tube. The plasma plume length of the straight-through tube tends to increase and then decrease as the argon flow rate increases, and the variation of the plasma plume length at an axial electrode distance of 0 mm is significantly greater than that of other electrode distance conditions. At the same argon flow rate, the maximum plasma plume length tends to increase and then decrease with the argon flow rate and increases with the axial distance of the electrodes.

Ultra-fast development of Ar 2p relative densities in nanosecond-pulsed barrier discharge in argon

A time-correlated single photon counting based optical emission spectroscopy technique is applied for an investigation of the nanosecond-pulsed barrier discharge in atmospheric pressure argon gas. We record the development of the light intensities originating from all ten Ar 2p (Paschen notation) radiative states with high spatio-temporal resolution. We identify different stages of the discharge development: an early rapid electron avalanching, streamer propagation phase, generation of discharge channel and surface streamer propagation over the dielectric surface. The quantified relative 2p densities for identified discharge phases enable a well-resolved insight into the ultra-fast discharge kinetics and open a possibility for the development of future detailed diagnostics of the rapidly ionized argon plasmas. Moreover, the electrical characterization of the discharge is made using the simplest equivalent circuit and it reveals new findings for the application of such an approach for similar discharges.

Control of ion flux-energy distribution at dielectric wafer surfaces by low frequency tailored voltage waveforms in capacitively coupled plasmas

Capacitively coupled plasmas are routinely used in an increasing number of technological applications, where a precise control of the flux and energy distribution of ions impacting boundary surfaces is required. In the presence of dielectric wafers and targets the accumulation of charges on these surfaces can significantly alter the time evolution of the sheath electric field that is accountable for ion acceleration from the plasma bulk to the surfaces and, thus, lead to parasitic distortions of process relevant ion flux-energy distributions. We apply particle in cell with Monte Carlo collisions simulations to provide insights into the operation, ion acceleration mechanisms, and the formation of such distributions at dielectric wafers for discharges in argon gas. The discharges are driven by a combination of a single high frequency (HF) (27.1 MHz) voltage signal and a low frequency (LF) (100 kHz) customized pulsed voltage waveform. The LF waveform includes a base square signal to realize narrow and controllable high energy peaks of the ion distribution, and steady-slope ramp voltage components. We discuss the distorting effect of dielectric surface charging on the ion flux-energy distribution and provide details about how the voltage ramps can restore its narrow peaked shape. The dependence of the surface charging properties on the LF pulse duty cycle and amplitude, as well as the HF voltage amplitude is revealed. The radial homogeneity of the ion flux is found to be maintained within % around the mean value for all quantities investigated. The radial electric field developing at the edge of the dielectric wafer with finite width has only a small influence on the overall homogeneity of the plasma across the whole surface, its effect remains localized to the outermost few mm of the wafer.

Effect of atmospheric pressure pulsed discharge spatial inhomogeneity on Ar I and H I lines: Electron number density study

AbstractThe spatial inhomogeneity of pulsed atmospheric pressure discharge in argon is investigated using the electron number density Ne diagnostics procedure applied to asymmetrically broadened Ar I lines. A dedicated fitting procedure is used for describing Ar I 703.0 nm line shape recorded from argon gas discharge and H I (at 486.13 and 656.28 nm) lines recorded from Ar‐H2 gas mixture discharge. The results revealed the change in Ne in both axial and radial directions. The additional Ar I lines at 614.5, 710.7, 731.2, and 731.6 nm, recorded from integral spatial radiation, are analysed as well to confirm the results from the plasma column region. The possibility of using AlO (B2∑+–X2∑+) and CN (B2∑+–X2∑+) molecular bands for gas temperature Tg measurements in this type of gas discharge source is demonstrated and Tg used as an input parameter for the Ne diagnostics procedure. For the proper identification of molecular band spectral lines, the Fortrat parabolas are constructed. The results obtained from Ar I 703.0 nm line indicate three different Ne values, with Ne1 ≈ 0.6 × 1016 cm−3, Ne2 ≈ 3.6 × 1016 cm−3, and Ne3 ≈ 19 × 1016 cm−3 measured from the plasma column. These Ne values increase in the cathode and anode region.

A modified expression for breakdown voltage of Townsend discharge in a non-uniform electric field and uniform axial magnetic field

Townsend breakdown mechanism for direct current discharge in argon gas by considering the effects of the non-uniformity of electric field, the loss of electrons due to radial diffusion, and the applied axial magnetic field has been discussed and an analytical expression has been derived for the breakdown voltage. It was Shown that the non-uniformity of electric field, between two parallel disc electrodes with radius R and separation of d, significantly affects the electron multiplication for d≥2.7R and that effect was disappeared for the gas pressure higher than 0.35 Torr. The loss coefficient δ was used to quantify the effects of the electron radial diffusion and axial magnetic field and the PIC-MCC numerical simulations were used to determine it. The results show that increasing the gap size above the electrode radius leads to dramatic increase of the δ coefficient while applying an axial magnetic field can effectively decrease it.

A self-consistent hybrid model of kinetic striations in low-current argon discharges

A self-consistent hybrid model of standing and moving striations was developed for low-current DC discharges in noble gases. We introduced the concept of surface diffusion in phase space (r, u) (where u denotes the electron kinetic energy) described by a tensor diffusion in the nonlocal Fokker–Planck kinetic equation for electrons in the collisional plasma. Electrons diffuse along surfaces of constant total energy ɛ = u − eφ(r) between energy jumps in inelastic collisions with atoms. Numerical solutions of the 1d1u kinetic equation for electrons were obtained by two methods and coupled to ion transport and Poisson solver. We studied the dynamics of striation formation in Townsend and glow discharges in argon gas at low discharge currents using a two-level excitation-ionization model and a ‘full-chemistry’ model, which includes stepwise and Penning ionization. Standing striations appeared in Townsend and glow discharges at low currents, and moving striations were obtained for the discharge currents exceeding a critical value. These waves originate at the anode and propagate towards the cathode. We have seen two types of moving striations with the two-level and full-chemistry models, which resemble the s and p striations previously observed in the experiments. Simulations indicate that processes in the anode region could control moving striations in the positive column plasma. The developed model helps clarify the nature of standing and moving striations in DC discharges of noble gases at low discharge currents and low gas pressures.

Fabrication of Novel Chitosan–Hydroxyapatite Nanostructured Thin Films for Biomedical Applications

In this study, we develop chitosan–hydroxyapatite (CS–HAp) composite layers that were deposited on Si substrates in radio frequency (RF) magnetron sputtering discharge in argon gas. The composition and structure of CS–HAp composite layers were investigated by analytical techniques, such as Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), metallographic microscopy (MM), and atomic force microscopy (AFM). On the other hand, in the present study the second order derivative of FT-IR–ATR spectra, for compositional analyses of CS–HAp, were used. The SEM, MM, and AFM data have shown the formation of CS–HAp composite layers. The surface of CS–HAp composite layers showed uniform growth (at an Ar gas working pressure of p = 2 × 10−3 mbar). The surface of the CS–HAp composites coatings became more nanostructured, becoming granular as the gas pressure increased from 5 × 10−3 to 1.2 × 10−2 mbar. However, our studies revealed that the surface morphology of the CS–HAp composite layers varies with the Ar gas working pressure. At the same time, optical properties are slightly influenced by Ar pressure. Their unique physicochemical properties make them suitable for various applications in the biomedical field, if we consider the already proven antimicrobial properties of chitosan. The antifungal properties and the capacity of the CS–HAp composite layers to inhibit the development of fungal biofilms were also demonstrated using the Candida albicans ATCC 10231 (C. albicans) fungal strain.

Analysis of Tensile Strength of Inert Gas Metal Welding on Aluminum 5083 with Variations in Argon Gas Current and Discharge

In the technology industry, metal raw materials such as steel and aluminum have an important role in the production process, as so far there is no metal that cannot be joined by welding. Metal Inert Gas (MIG) welding method is a gas arc welding that uses a welding wire as well as an electrode. In the Metal Inert Gas (MIG) welding process, the heat from this welding process is generated by a welding arc formed between the wire electrode and the workpiece. The purpose of this study was to determine the tensile strength of the welding results in the connection process with Metal Inert Gas (MIG) against aluminum (Al) 5083 series 6 mm thick, the welding was carried out with various current strength treatments, namely 120 A, 130 A, 140 A. and Argon gas discharge 5 lt/minute, 10 lt/minute, 15 lt/minute in each welding process. This research is useful to know and understand about the analysis of the welding process on aluminum 5083 with a thickness of 6 mm with Metal Inert Gas (MIG) welding process using vertical (3 grove) welding techniques. The method used in this study is the analytical method, which is a method for testing by adding different treatments of current and discharge variations of Argon gas during the welding process of the specimen, so that different welding strengths will be obtained in each specimen.

Analysis of Bending Strength of Inert Gas Tungsten Welded Connections with Variations in Argon Gas Discharge and Strong Current on Aluminum 5083

The purpose of this study was to determine the bending strength of the weld in the connection process with Tungsten Inert Gas (TIG) to the 5083 series aluminum (Al) plate 6 mm thick, the welding was carried out with various current strength treatments, namely 130 A, 140 A, 150 A. and Argon gas discharge of 5 lt/minute, 10 lt/minute, 15 lt/minute in each welding process, and also to find out the defects in the weld area after the bending test was carried out. The method used in this study is the analytical method, which is the method used to test by adding different treatments of current and gas discharge variations during the specimen welding process, so that later on we will get a different welding strength difference in each specimen. From the results obtained from the research on this sample, welding using Argon gas discharge which is

Influence of cathode material type on the electrical breakdown behaviors of DC discharge

Paschen curves were studied using different cathode materials such as magnesium, zinc, and carbon graphite by discharge in argon gas of a pressure range between 0.08 and 3 Torr using a parallel plates configuration. The first and second Townsend coefficients (α and γ, respectively) and the ionization efficiency (η) of different cathode materials were deduced from Paschen curves as a function of the reduced field (E/P). The minimum breakdown voltage was found to be about 242 V for Mg material, which has the lowest work function, while carbon graphite has a higher breakdown voltage of 283 V due to its higher work function. The second coefficient γ was increased as a function of E/P and has higher values for materials of lower work functions, and a similar trend of γ is obtained as a function of the ion mean energy. On the other hand, the first coefficient α has a reverse behavior with both E/P and the work function of the cathode materials compared with the second coefficient. The ionization efficiency of the three cathode materials is identical, as η depends only on the gas properties and not the cathode material. η has a maximum value of about 0.025 V−1 for an E/P of about 185 Vcm−1Torr−1, corresponding to the maximum ionizing ability of electrons. The validation of the breakdown results has been confirmed by conferring with other published experimental measurements.

Plasma stratification in radio-frequency discharges in argon gas

We conducted experimental studies and computer simulations of standing striations in capacitive coupled plasma in agas. Standing striations were observed at frequencies 3.6, 8.4 and 19.0 MHz, in a pressure range 0.05–10 Torr, tube radius R = 1.1 cm, for a certain range of discharge currents (plasma densities). Numerical simulations revealed similar nature of standing striations in CCP and moving striations in DC discharges under similar discharge conditions. Comparisons to computer simulations with experimental observations helped clarify the nature of these striations. The non-linear dependence of the ionization rate on electron density is shown to be the main underlying mechanism of the stratification phenomena.

The Effect of Oxygen and Argon Gas Flow Rate on OH Radical Production and Dye Decolorization by Pulsed Discharge in Spray Droplet Reactor

Nonequilibrium plasma is an effective and one of versatile advanced oxidation process due to the formation of reactive species such as hydroxyl radicals, oxygen atom, and hydroperoxyl radicals. In pulsed discharge, free electrons gain energy from an imposed electric field and lose this energy through collisions with neutral gas/liquid molecules. The transfer of energy to the molecules leads to the formation of a variety of new species including atoms, free radicals, and ions. These products are all active chemically, and in our case, we measure the amount of hydroxyl radicals generated in the reactor and also the amount of escaped ozone generated in the reactor and decolorized indigo reagent in a graduated cylinder (GC). In this paper, we used oxygen and argon gases in various flow rate and mixed ratios to feed a gaseous phase in a water spraying droplet reactor. The experimental results indicated that the oxygen and O2/Ar mixture flow rates in spraying reactor have an effect on both hydroxyl radical generation and decolorization of indigo reagent solution. Argon gas discharge has less effect on hydroxyl radical production compared to the oxygen gas discharge with the same flow rates and no effect on the decolorization of indigo reagent solution in GC. We obtained remarkable results on both hydroxyl radical generation rate and decolorization efficiency of indigo reagent solution when we discharged with the mixture of O2/Ar “especially when the ratio has more oxygen than argon gas.” Hence, the presence of oxygen in the water spray plasma discharge is very important as it influence the generation of reactive species such as O atoms and ozone in the gas and liquid phase, which can react directly with organic contaminants and also contribute to more production of hydroxyl radicals in the aqueous phase.

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.

Jitter mitigation in low density discharge plasma cells for wakefield accelerators

In the field of beam driven acceleration of particles in plasma wakefields (PWFA), the source of the plasma medium is a crucial part of the accelerator setup. Gas discharges have proven to be a reliable and simple type of a plasma source in past experiments. Nevertheless, especially in plasma cells that aim for peak density in the range of 1015 cm−3, physical apertures around 10 mm, and lengths of up to several meters, the stability of the discharge ignition and the pulse current waveform is limiting the applicability. We show successful mitigation of these jitters in a 0.1 m argon gas discharge cell, operating at maximum densities of ≤1016 cm−3 by optimisation of the cell design and the discharge current pulse circuit.

Pulsed-DC Discharge for Plasma CVD of Carbon Thin Films

A pulsed-dc discharge method for plasma chemical vapor deposition (CVD) was developed using a constructed versatile pulsed-dc generator and a vacuum discharge chamber. Argon (Ar) gas discharge experiments were performed under a variety of discharge conditions, and plasma conditions were evaluated using optical emission spectroscopy. The developed system can perform glow discharge by employing nearly rectangular, unipolar, and high-voltage negative pulses with a wide variation of voltage amplitudes and a set discharge current, pulse repetition rate, and duty cycle. Plasma conditions could also be tuned by varying the pulse parameters. A preliminary test of the deposition of diamond-like carbon (DLC) films on silicon (Si) substrates and ultrathin pyrolytic carbon (PyC) films on nanothickness metal-catalyzed glass substrates was performed with acetylene (C 2 H 2 ) by selecting some typical deposition conditions based on the gas discharge experiments. The deposited films were characterized via Raman spectroscopy. The characteristic properties of DLC and PyC films were achieved. The DLC films demonstrated conventional hard insulating properties while the ultrathin PyC films exhibited conductive and semitransparent properties. These results revealed that the developed pulsed-dc discharge system for plasma CVD is applicable for the synthesis of insulating hard as well as soft conducting carbon thin films.

The influence of magnetic field and cathode dimensions on plasma characteristics in hollow cathode system

Experimental study on the effect of cylindrical hollow cathode, working pressure and magnetic field on spatial glow distribution and the characteristics of plasma produced by dc discharge in Argon gas, were investigated by image analyses for the plume within the plasma. It was found that the emission intensity appears as a periodic structure with many peaks appeared between the electrodes. Increasing the pressure leads to increase the number of intensity peaks finally converted to continuous form at high pressure, especially with applied of magnetic field, i.e. the plasma is more stable with the presence of magnetic field. The emission intensity study of plasma showed that the intensity has a maximum value at 1.07 mbar pressure and decrease with more pressure.

Closing the gap between Aboriginal and non-Aboriginal health workers through story telling

Non-thermal plasma has been used in many medical applications, including treatment of living cells, blood coagulation, wound healing, and sterilization. The process uses an environmentally friendly gas (e.g., argon, helium, oxygen, nitrogen, or hydrogen) to destroy bacteria cells with no serious adverse effect on humans or animals. However, information on the effect of argon plasma on blow fly eggs is lacking. In this study, we explored the ability of cold argon plasma to destroy the eggs of the Australian sheep blow fly, Lucilia cuprina (Wiedemann, 1830); its larvae are a myiasis-producing agent in both human and animals. We tested the effect of cold argon plasma exposure for 1, 2, 3 and 5 min on L. cuprina eggs. Since the temperature of cold Ar plasma is around 30 °C, to clarify the effect of temperature on the fly eggs, hot air from an electric dryer was tested for comparison. Cold argon plasma exposure in eggs significantly reduced the survival rates of second instar larvae at all exposures tested; the effects were time dependent, with a stronger effect at longer exposure (32% survival rate after a 1-min treatment; 20%, 2 min; 20%, 3 min; and 6%, 5 min), compared to the control (86%). No significant differences were observed in larval survival rates from eggs treated with hot air (80-84%, after 1- to 5-min treatments) versus the control (86%). These results were supported by observing the treated eggshells under a scanning electron microscope (SEM), we found noticeable aberrations only in the plasma treated groups. The emission spectrum of the argon gas discharge revealed emission lines of hydroxyl radicals at 309.1 nm; these may cause the deterioration of the treated L. cuprina eggs. Our results have shown the possibility of using cold argon plasma in medical applications, in particular treating myiasis wounds.

Effect of cold argon plasma on eggs of the blow fly, Lucilia cuprina (Diptera: Calliphoridae)

Non-thermal plasma has been used in many medical applications, including treatment of living cells, blood coagulation, wound healing, and sterilization. The process uses an environmentally friendly gas (e.g., argon, helium, oxygen, nitrogen, or hydrogen) to destroy bacteria cells with no serious adverse effect on humans or animals. However, information on the effect of argon plasma on blow fly eggs is lacking. In this study, we explored the ability of cold argon plasma to destroy the eggs of the Australian sheep blow fly, Lucilia cuprina (Wiedemann, 1830); its larvae are a myiasis-producing agent in both human and animals. We tested the effect of cold argon plasma exposure for 1, 2, 3 and 5min on L. cuprina eggs. Since the temperature of cold Ar plasma is around 30°C, to clarify the effect of temperature on the fly eggs, hot air from an electric dryer was tested for comparison. Cold argon plasma exposure in eggs significantly reduced the survival rates of second instar larvae at all exposures tested; the effects were time dependent, with a stronger effect at longer exposure (32% survival rate after a 1-min treatment; 20%, 2min; 20%, 3min; and 6%, 5min), compared to the control (86%). No significant differences were observed in larval survival rates from eggs treated with hot air (80-84%, after 1- to 5-min treatments) versus the control (86%). These results were supported by observing the treated eggshells under a scanning electron microscope (SEM), we found noticeable aberrations only in the plasma treated groups. The emission spectrum of the argon gas discharge revealed emission lines of hydroxyl radicals at 309.1nm; these may cause the deterioration of the treated L. cuprina eggs. Our results have shown the possibility of using cold argon plasma in medical applications, in particular treating myiasis wounds.

Rotation of a single vortex in dusty plasma**Project supported by the National Natural Science Foundation of China (Grant Nos. 11205044 and 11405042), the Program for Young Principal Investigators of Hebei Province, China, the Natural Science Foundation of Hebei University, China (Grant No. 2011JQ04), the NaturalScience Fund for Excellent Young Scholars of Hebei Province, China(Grant No. A2017201099), and the Midwest Universities

A single vortex is obtained in radio-frequency capacitive discharge in argon gas. The dust subsystem is confined in the horizontal plane with an asymmetrical saw structure placed on the lower electrode. The vortex rotates as a whole along the long side of the saw-teeth. Asymmetry of the saw structure plays an important role in the rotation of the vortex. Nonzero curl of the total force resulting from the local ion flow and the electric field in the plasma sheath could be attributed to the persistent rotation of vortex.

Current self-limitation of the nanosecond hollow cathode discharge

The nanosecond hollow cathode discharge in argon gas at the pressure of 1–10 Torr is studied using 2D particle-in-cell Monte Carlo collisions model. We obtain that at the low gas pressure discharge operates in the plane-to-plane mode. This mode allows the generation of energetic electrons (>1 keV) in the gap between the cathode and the anode. However, these electrons do not form the focused beam. At higher pressures, the rather dense plasma penetrates inside the cathode which allows the generation of energetic electrons inside the cathode. However, since the energy relaxation length of 1 keV electrons is shorter than the cathode–anode gap, these electrons dissipate almost all their energy in collisions with neutrals during their propagation toward the anode. Additionally, the optimal conditions necessary for the generation of high-energy electrons are discussed.