Characteristics Of Plasma Jet Research Articles

Characteristics of Ar Plasma Jet Generated by 50 Hz Alternating Current

Plasma jet generated by dielectric barrier discharge system has gain importance in surface modification processes. Characteristics of plasma of the plasma jet depend on type of gas, flow rate of gas, design of electrodes, power and frequency of the power source. In this research, the argon gas is flowed through a hollow tube is investigated. Alternating high voltage power supply connected to electrodes is operated with frequency of 50 Hz. It was found that the lengths of the plasma jet generated by this system ranges from 0.5 cm and 1 cm. The minimum and the maximum electron temperature of the plasma was 0.44 eV and 0.86 eV respectively. The electron temperature increased as the applied voltage was increased. However, the electron temperature decreased when the operating voltage was increased above 6.5 kV to 7.5 kV. It can be explained by the effect of arcing between the electrodes which causes the lost in energy. Also, increasing of the flow rate over a critical limit produces turbulence that also causes reduction in electron temperature of the plasma jet.

Inactivation of Escherichia coli using atmospheric pressure cold plasma jet with thin quartz tubes

In this study, the temporal evolution and electrical characteristics of atmospheric pressure cold plasma jet (APPJ) structures with different quartz tube wall thicknesses that used AC power were investigated via experimentation and simulation. The percentage increase of electron density based on the wall thickness was investigated. Based on the optimal electric field intensity distribution and flow field distribution, the quartz tube with the optimal wall thickness improved the electron density. We applied the optimized APPJ structures to inactivate E. coli. We demonstrated that the APPJ structures with thin-walled quartz tubes had better inactivation characteristics than those with thick-walled structures regardless of the duration of treatment. The electron density properties of APPJ structures with different quartz tube wall thicknesses have a prominent impact on the improvement in the killing rate in the sterilization processes.

In-situ heating effect of laminar plasma jet during Mo coatings deposition

Laminar plasma has the characteristics of a long plasma jet, low velocity, and high temperature, which make it able to cover and heat the substrate during the spraying process. The results show that when the standoff distance is short, the coating is strengthened by in-situ heating of the plasma jet and shows higher erosion resistance at high erosion angles and bulk-like material tendency. When the standoff distance is long, the substrate temperature is low, the coating shows higher erosion resistance at a lower erosion angle.

External axial magnetic field enhances discharge and water treatment of cold plasma jets

In this Letter, the effect of an external axial magnetic field on the propagation characteristics of a helium plasma jet and plasma-activated water was investigated. Stacked magnets surrounding the quartz tube significantly enhance the brightness and length of the ionization wave. The discharge enhancement is more pronounced at a position farther along the tube axis than near the jet nozzle. Under the action of the external magnetic field, the concentrations of aqueous reactive oxygen species, including H2O2, OH, and O2−, significantly increase with the increasing electron density, whereas the vitality of melanoma cells effectively drops. A magnetic fluid model suggests that the discharge enhancement arises mainly from the confinement of the radial motion of electrons imposed by the axial magnetic field and the radial magnetic pressure, suggesting that the external magnetic field may be beneficial in improving the effects of plasma jet applications.

Non-thermal plasma multi-jet platform based on a flexible matrix.

A new plasma source design that merges the main characteristics of capacitive dielectric barrier discharge (DBD) and cold atmospheric plasma jet (CAPJ) is discussed. The DBD system contains a flexible, porous matrix consisting of silica aerogel, which is comprised between two biased electrodes. The helium flow supply subjected to a sinusoidal voltage of around 5 kV in amplitude and 15 kHz in frequency provides a set of plasma jets that propagates more than 1cm beyond the active DBD region. The studied plasma multi-jet system consists of an array of three aligned jets that flow in the laminar regime, and it is intended for treating the surfaces of 3D objects and large areas. CAPJ performance is discussed as a hypothetical morphing source in flat and bent configurations. Electrical characterization and optical emission spectroscopy diagnostics have provided current-voltage waveforms and the composition of the CAPJ through the aerogel layer, respectively. This novel source is promising for biomedical applications that require full adaptation of plasma parameters to delicate samples, such as wound healing and treatment of surgical margins in plasma-based cancer surgery.

Characteristics of a kHz helium atmospheric pressure plasma jet interacting with two kinds of targets

This study investigates the influence of two types of target, skin tissue and cell culture medium, with different permittivities on a kHz helium atmospheric pressure plasma jet (APPJ) during its application for wound healing. The basic optical–electrical characteristics, the initiation and propagation and the emission spectra of the He APPJ under different working conditions are explored. The experimental results show that, compared with a jet freely expanding in air, the diameter and intensity of the plasma plume outside the nozzle increase when it interacts with the pigskin and cell culture medium targets, and the mean velocity of the plasma bullet from the tube nozzle to a distance of 15 mm is also significantly increased. There are also multiple increases in the relative intensity of OH (A2Σ → X2Π) and O (3p5S–3s5S) at a position 15 mm away from nozzle when the He APPJ interacts with cell culture medium compared with the air and pigskin targets. Taking the surface charging of the low permittivity material capacitance and the strengthened electric field intensity into account, they make the various characteristics of He APPJ interacting with two different targets together.

Multiple current pulse behavior and its dynamics of atmospheric pressure plasma jet in a needle-to-ring configuration

The characteristics of an atmospheric pressure plasma jet (APPJ) based on needle-to-ring dielectric barrier discharge (DBD) have been investigated experimentally. The plasma jet is driven by a sinusoidal voltage, and the working gas is argon. The jet length, the voltage-current waveforms, the optical emission spectra and the plasma evolution have been studied. Moreover, the transferred charges of the discharge pulse and the electron excitation temperature were investigated. These results reveal that there exist two or more current pulses per half-cycle as the applied voltage increases. In fact, the multiple current pulses correspond to multiple breakdowns between the electrodes. This phenomenon in DBD-APPJ is mainly attributed to the surface charges on the grounded ring electrode surface, which can induce a strong reverse electric field to counteract the applied electric field. In addition, the jet length is extended stepwise as the number of current pulses increases. The residual excited species or charges remaining from the previous discharge play an essential role in the formation of a stronger next discharge and are responsible mainly for a higher electron excitation temperature, which makes the jet develop farther (i.e., a longer jet). Finally, we obtain a preliminary control condition to switch a single current pulse into multiple pulses, which has a benefit for industrial applications.

Dynamics of plasma bullets by nanosecond pulsed micro-hollow cathode discharge within air

In this paper, the air plasma jet produced by micro-hollow cathode discharge (MHCD) is investigated. The discharge is powered by a positive nanosecond pulse high voltage supply. The waveforms of the discharge, the images of the jet, the evolution of the plasma bullet and the reactive species are obtained to analyze the characteristics of the MHCD plasma jet. It is found that the length of the plasma jet is almost proportional to the air flow rate of 2–6 slm. Two plasma bullets appear one after another during a single period of the voltage waveform, and both of the two plasma bullets are formed during the positive pulse voltage off. The propagation velocity of the two plasma bullets is on the order of several hundred m/s, which is approximate to that of the air flow. These results indicate that the gas flow has an important influence on the formation of this MHCD plasma jet.

Numerical Simulation of Plasma Jet Characteristics under Very Low-Pressure Plasma Spray Conditions

Plasma spray-physical vapor deposition (PS-PVD) is an emerging technology for the deposition of uniform and large area coatings. As the characteristics of plasma jet are difficult to measure in the whole chamber, computational fluid dynamics (CFD) simulations could predict the plasma jet temperature, velocity and pressure fields. However, as PS-PVD is generally operated at pressures below 500 Pa, a question rises about the validity of the CFD predictions that are based on the continuum assumption. This study dealt with CFD simulations for a PS-PVD system operated either with an argon-hydrogen plasma jet at low-power (<50 kW) or with an argon-helium plasma jet at high-power (≥50 kW). The effect of the net arc power and chamber pressure on the plasma jet characteristics and local gradient Knudsen number (Kn) was systematically investigated. The Kn was found to be lower than 0.2, except in the region corresponding to the first expansion shock wave. The peak value in this region decreased rapidly with an increase in the arc net power and the width of this region decreased with an increase in the deposition chamber pressure. Based on the results of the study, the local Knudsen number was introduced for detecting conditions where the continuum approach is valid under PS-PVD conditions for the first time and the CFD simulations could be reasonably used to determine a process parameter window under the conditions of this study.

Study of the influence of discharge loop parameters on anode side on generation characteristics of metal plasma jet in a pulsed vacuum discharge

In a pulsed vacuum discharge, the ejection performance of a metal plasma jet can be effectively improved by preventing charged particles from moving to the anode. In this paper, the effects of resistance and capacitance on the anode side on the discharge characteristics and the generation characteristics of plasma jet are investigated. Results show that the existence of a resistor on the anode side can increase the anode potential, thereby preventing charged particles from entering the anode and promoting the ejection of charged particles along the axis of the insulating sleeve nozzle. The application of a capacitor on the anode side can not only absorb electrons at the initial stage of discharge, increasing the peak value of the cathode hump potential, but also prevent charged particles from moving to the anode, thereby improving the ejection performance of the plasma jet. In addition, the use of a larger resistance and a smaller capacitance can improve the blocking effect on charged particles and further improve the ejection performance of the plasma jet. Results of this study will provide a reference for the improvement of the ejection performance of plasma jets and their applications.

Study on the characteristics of helium plasma jet by pulsed micro-hollow cathode discharge

In this paper, the helium plasma jet generated by micro-hollow cathode discharge (MHCD) was studied. The MHCD was driven by a square-wave pulsed power source, and the characteristics of discharge and plasma jet were measured experimentally. The influences of the gas flow rate on the MHCD and the plasma jet were investigated. And the propagation mechanisms of the plasma jet were analyzed. The results show that within 100–1000 sccm of the gas flow rate, the breakdown delay time of the MHCD increases with the helium flow increasing. It is considered that the gas flow affects the density of seed electrons and thus the breakdown delay time. With the helium flow rate increasing, the whole plasma jet length increases firstly and then decreases. A detailed investigation shows that during one discharge pulse, two distinguishable propagation processes of the plasma jet are observed. It is found that the jet of the first stage is formed during the rising edge of the current pulse, while the other is generated after the discharge current becomes stable. The propagation velocity of jet in the first stage is on the order of several km s−1, which is similar to that of the discharge evolution obtained by simulation. And the propagation speed of the jet in the second stage is on the order of several hundred m s−1, which is close to the velocity of gas flow. The spatial–temporal distributions of light emission show that high-energy electrons can only be observed during the jet propagation in the first stage, and low-energy electrons can be detected in both the first and second stages. The results show that the electric field plays an important role on the jet propagation in the first stage, and the jet propagation during the second stage is mainly promoted by the thermal gas expansion.

The influence of gas humidity on the discharge properties of a microwave atmospheric-pressure coaxial plasma jet

This paper investigated the influence of gas humidity (1%, 3%, 8%, 10%, and 12%) on the characteristics of a microwave-induced atmospheric plasma jet. The plasma discharge was generated by a microwave solid-state source with a H2O–Ar mixture gas flow of 8.1 L/min. The variation in energy efficiency, O and OH concentrations, rotational temperature of heavy species, shapes of plasma plumes with different humidities, and microwave input powers were recorded and analyzed. The results showed that the concentrations of O and OH increase monotonously with gas humidity at higher input powers while they fluctuate with gas humidity at lower input powers. With an increase in the H2O/Ar ratio from 1% to 12%, the energy efficiency of the plasma generator decreases, and the plasma plumes become shorter and thinner. The rotational temperature of plasma at the nozzle also showed positive correlation with increasing humidity. Adding more input power would make all the values of these parameters increase. This paper is supposed to be helpful for the research of the interaction mechanism of mix gas plasma and microwave power and for improving the effect of plasma treating biomedical materials.

How Hydrogen Admixture Changes Plasma Jet Characteristics in Spray Processes at Low Pressure

In plasma spraying, hydrogen is widely used as a secondary working gas besides argon. In particular under low pressure, there are strong effects on the plasma jet characteristics even by small hydrogen percentages. Under such conditions, fundamental mechanisms like diffusion and recombination are affected while this is less relevant under atmospheric conditions. This was investigated for argon–hydrogen mixtures by optical emission spectroscopy (OES). The small electron densities under the investigated low pressure conditions implied specific difficulties in the application of several OES-based methods which are discussed in detail. Adding hydrogen to the plasma gas effected an increased plasma enthalpy. Moreover, the jet expanded radially as the reactive part of the thermal conductivity was enhanced by recombination of atomic hydrogen so that the shock waves were less reflected at the cold jet rims. In the jet cores, the lowest temperatures were found for the highest hydrogen admixture because the energy consumption due to the dissociation of molecular hydrogen outbalanced the increase of the plasma enthalpy. Variations in the radial temperature profiles were related to the jet structure and radial thermal conductivity. The local hydrogen–argon concentration ratios revealed an accumulation of hydrogen atoms at the jet rims. Clear indications were found, that higher hydrogen contents promoted the fast recombination of electrons and ions. However, it is assumed that the transport properties of the plasma were hardly affected by this, since the electron densities and thus the ionization degrees were generally small due to the low pressure conditions.

Estimation of gas-dynamic characteristics of supersonic plasma jets based on spectroscopy results

A method for estimating the gas-dynamic characteristics of supersonic plasma jets based on the minimum number of plasma parameters (electron number density and temperature) that are easily measured by spectral diagnostic methods is considered. The course of the most important parameters characterizing the gas dynamics of the nonequilibrium plasma flow in the shock-wave region of a supersonic plasma jet created by a pulsed capillary discharge is revealed, and their values are estimated. A significant difference between the electron and gas temperatures was found in the vicinity of the central shock wave.

Optical diagnostics of the characteristics of a square unipolar nanosecond pulse-driven atmospheric pressure helium plasma jet

Compared with the traditional sinusoidal voltage source, a short rising nanosecond voltage source can generate a high electron current for a short rising time. This paper investigates how the nanopulse parameters such as the voltage amplitude, pulse duration, and repetition frequency affect the radical generation and the plasma bullet propagation in an atmospheric pressure helium plasma jet. An intensified charge-coupled device was used to observe the bullet propagation in the nanosecond gate mode. The plasma bullet’s propagation speed is mainly affected by the applied voltage and externally biased electrodes rather than the pulse duration or the driving frequency. In contrast, optical emission spectroscopy diagnostics estimate that the radical density inside the atmospheric pressure plasma jet mainly increases with the repetition frequency. At the same time, the population of high-energy electrons can be controlled with the unipolar voltage amplitude. Thus, unipolar nanosecond pulses make it possible to control the emitting charges and the generated radicals independently.

Numerical simulation of an atmospheric pressure plasma jet with coaxial shielding gas

A two-dimensional (r, z) numerical simulation of the discharge characteristics of an atmospheric pressure plasma jet (APPJ), with coaxial shielding gas, was performed. The helium working gas flowed in a central capillary tube, engulfing a needle electrode powered by 13.7 MHz radio frequency sinusoidal voltage. The N2 shielding gas flowed in the annular space of a coaxial tube. These gases emerged, in laminar flow, in a 78%N2-21%O2-1%Ar dry air ambient. The characteristics of the APPJ with shielding gas were compared to those of the APPJ without shielding gas. The nitrogen shielding gas hindered the diffusion of oxygen and argon from the ambient air into the helium jet. With the shielding gas present, more nitrogen penetrated into the helium core, causing a shorter plasma ‘plume’. The flow rates of the working and shielding gas, critically affected the gas temperature, and in turn the discharge characteristics. For a He flow of 2 standard liters per minute (slm), switching on the nitrogen shielding gas flow (at 4.5 slm) reduced the on-axis O2 and Ar mole fractions from to and from to , respectively, at an axial distance of 3 mm downstream of the nozzle. The radial profiles of the mole fractions of the ambient gases were monotonically and strongly decreasing towards the system axis, for short axial distances from the nozzle (∼1 mm), but became progressively flatter at longer distances from the nozzle (3 mm and 5 mm). Simulation predictions captured the salient features of experimental data of ambient species mole fractions in the plasma jet, and the 706 nm optical emission intensity profiles of the He 33S excited state.

Study on generation characteristics of plasma jets of multi-electrode in a pulse vacuum discharge

In order to increase the production of plasma jets in a pulse vacuum discharge, based on the insulated anode electrode structure (IAES), discharge experiments by using multiple electrodes under one power supply are performed in this paper. During experiments, discharge currents flowing through multiple cathode sides (cathode currents) were measured by identical Rogowski coils at the same time. The plasma density and propagation velocity of plasma jets were measured by the self-designed ‘+’ type probes. Firstly, the differences in discharge characteristics and generation characteristics of plasma jets between the single-electrode and the double-electrode discharge were compared and analyzed. Secondly, the effects that the electrode spacing (D) and the capacitor capacity had on the discharge characteristics and generation characteristics of plasma jets of the multi-electrode were analyzed. Results show that because the discharge voltage of the IAES is dropped to the arc voltage after a long duration, the simultaneous discharge of multiple electrodes in a single pulse can be realized. Compared with the single-electrode discharge, using multiple electrodes to discharge simultaneously in a single pulse can decrease the initial discharge voltage, increase the peak of cathode current and increase the amount of plasma production. In addition, there is interaction between plasma jets of the multi-electrode, and the spatial electric field generated by the first ejected plasma jet will hinder the generation of plasma jets of subsequent electrodes. Only by keeping a certain electrode spacing (D) between the electrodes, can multiple electrodes be all discharged and plasma jets of the same length be produced. Increasing capacitor capacity can increase the plasma density, propagation velocity, length of plasma jets of the multi-electrode, and realize the simultaneous discharge of more electrodes in a single pulse.

Influence of a nearby conductor on shape and length of a microwave plasma jet.

This Rapid Communication reports on the observation of an interesting phenomenon: the shape, especially the length, of a microwave plasma jet (MPJ) can be clearly influenced by simply placing a conductor near the plasma source, particularly when the nearby conductor is in contact with the external conductor of the coaxial microwave plasma generator, accompanied by a significant change in microwave reflection power from the terminal. To further investigate this discovery, the relationships between the length of the plume and some important factors, such as the conductivity and length of the nearby conductor, microwave input power, and gas flow velocity, are analyzed, and we find nonlinear rules of influence of these factors on the jet. Measurements of the electric potential around the jet reveal the nonuniform and non-neutral charge distribution inside the visible plasma plume, which plays a vital role in uncovering the mechanism underlying this phenomenon. The results are helpful for providing a deeper understanding of microwave plasma jet characteristics. More importantly, it provides guidelines to control the MPJ using simple structures.

Study of large-area atmospheric pressure plasma jet based on coplanar dielectric barrier discharge

<p indent="0mm">In order to obtain a uniform large-area plasma jet at the atmospheric pressure, a new structure of coplanar dielectric barrier discharge (DBD) is proposed in this paper. The structure used in large-area DBD plasma jet consists of two coaxial annular dielectric tubes, and an alternating current electric field is applied by metal film electrodes outside the tubes to form dielectric barrier discharge in the air gap. Based on this configuration, a uniform annular jet is achieved, with diameter of <sc>12 mm</sc> and thickness of <sc>2–3 mm.</sc> The discharge characteristics of the proposed structure and the development process of plasma jet are studied. The spectra of the discharge, the electron temperature, the electron density, and the discharge waveforms are diagnosed. The results show that the physical characteristics of the large-area jet obtained in this work are basically the same as that of the traditional small-diameter DBD jet. It is considered that the physical mechanism of the large-area jet propagation is the mutual coupling propulsion process of a large number of positive corona discharges. The influence of electrode structure and air gap structure on the characteristics of the large-area DBD plasma jet is further studied by experiments, and the optimization principle of the large-area DBD plasma jet is proposed.

Application of Similarity Theory to the Characteristics of Laminar Plasma Torch With Pure Nitrogen

Because of the complex generation process, the jet characteristics of laminar plasma torch were always studied by experiments at present. In order to reduce the experimental costs and the workloads, the similarity theory is a good method to study the characteristics of the laminar plasma jet. Thus, with some experimental results under specified conditions, the relationships between the characteristics and the working parameters have been obtained to predict the characteristics with other specified working parameters. Compared with the experimental results, the theoretical arc voltage characteristics, thermal efficiency characteristics, and jet lengths characteristics coincided with the experimental ones with a difference lower than 2%, 2.5%, and 8%, respectively.