Pulsed Plasma Jet Research Articles

Time-resolved imaging and spectroscopy of atmospheric pressure plasma bullet propagation and RONS production

An atmospheric pressure plasma jet visually appears as a continuous plasma, but is actually comprised of a series of fast moving ionization waves, commonly called plasma bullets. Plasma bullets are the visible front of ionization streamers. Studying their spatiotemporal formation and propagation can help understand the plasma dynamics. In this work, the formation and lifetime of a high voltage pulsed dc plasma jet and the subsequent bullets were observed using time-resolved synchronized measurements with an intensified charge-coupled device (ICCD) camera and an ICCD spectrometer. The operating voltage, helium flow rate, and pulse width were varied to observe changes in bullet behavior. The measured velocities of the plasma bullets largely depended on voltage but showed that flow rate can have an effect. The formation of OH and excited N2 (2+) was measured at the nanosecond timescale. It was seen that the formation of these species begins at the visible bullet, but the peak emission and decay occur ∼50–100 ns after bullet passage, indicating a finite time of reaction, excitation, and emission. Observing the temporal formation of plasma bullets and reactive species provides insight into some of the reactions occurring in the discharge and how to tailor the plasma operating conditions.

Wettability enhancement of hydrophobic artificial sandstones by using the pulsed microwave plasma jet

We report that the wettability of artificial sandstones can be significantly improved by an innovative pulsed microwave plasma jet (PMPJ). The roughness of the sandstone surface is enhanced after the PMPJ treatment, but according to the Wenzel model, it has the negative effect to make a hydrophobic surface become hydrophilic. The molecular dynamics (MD) simulation shows that the alteration of the surface chemical property has a positive effect on the hydrophilicity enhancement, whose influence can compensate for that of the roughness. It is these two factors together that make the hydrophobicity of the sandstone become weaker after the PMPJ treatment. These findings hold great potentials in petroleum engineering, which may provide some inspirations for the enhancement of oil/gas recovery by the plasma technology.

Features of treatment of metal surface layers by pulsed plasma jets formed during electrical explosion of conductors

The results analysis of the experimental studies obtained by the methods of modern physical materials science of metals and alloys surface layers after electroexplosive alloying and coating is presented.

Pulsed Jets for Dense Plasma Generation in an External Magnetic Field

In this work, results of numerical simulation of the interaction of pulsed capillary discharge plasma jets at atmospheric pressure are presented. The interaction of the pulsed plasma jets with a shock wave is considered. Modes with plasma jets created by the capillary discharge with a vaporizing wall expiring through a magnetic nozzle are simulated. Results obtained for several plasma channels are presented together with calculated plasma jets in the capillary discharge with a vaporizing wall.

Helium plasma jet interactions with water in well plates

AbstractPlasma activation of liquids or cell cultures is a method for investigating the consequences of plasma produced reactive oxygen and nitrogen species (RONS) on living systems. The reproducible transfer of RONS, ions, electrons, and photons to the liquid is critical for determining reaction mechanisms and biological outcomes, and depends strongly on system parameters. A common in vitro method of plasma treatment of cells is a plasma jet directed into a well plate filled (or partially filled) with a liquid cell growth media. This method of treatment intrinsically has several environmental and geometrical factors that could lead to variability in the activation of the media. Uncontrolled or unreported geometrical and environmental factors that affect this transfer can, therefore, influence the reproducibility of measurements. In this paper, results from a numerical modeling investigation of a pulsed helium plasma jet interacting with water in a well plate are discussed while varying the height of the well‐plate rim. The height of the rim changes gas flow patterns, the ratio of He‐to‐air, and the water vapor content in the gas layer above the liquid. With a low rim, gas flowing from the jet stagnates on‐axis and flows radially outward with few vortices that recirculate reactants. With high rims, the gas flow is dominated by vortices and recirculation. With a low rim, the ionization wave (IW) from the jet strikes the liquid and proceeds as a surface IW across the water. With higher rims, the densities of helium and water vapor are higher above the liquid, which results in a volumetric propagation of the IW, initially producing higher densities of H2, HO2, OH, and H2O2. The end result is that for otherwise identical conditions, the densities of solvated H2O2aq and select reactive nitrogen species increase with rim height due to the vortices that recirculate reactants.

Simulation of Processes on a Target Induced by a Jet System and Laser Radiation

The mathematical model and the results of computer simulation of the processes of compression, heating, and energy release in a target under the hybrid influence of a system of pulsed plasma jets and intense laser radiation in magnetic inertial thermonuclear fusion are presented. The hybrid effects of intense energy flows on a single-layer cylindrical target are compared in the experimental and simulation conditions. The main radiation magnetic and gas dynamic parameters of the compressed and heated target plasma are evaluated as well.

Application of a pulsed atmospheric arc plasma jet for low‐density polyethylene coating

AbstractThe development of a method for deposition of low‐density polyethylene (LDPE) on rotating three‐dimensional aluminum alloy substrates is presented. LDPE powder with an average diameter of 50 m is dispersed with nitrogen as a carrier gas. This suspension is injected into a plasma plume generated by a pulsed atmospheric arc plasma jet (PAA‐PJ). The optimized PAA‐PJ operating parameters are a pulse frequency of 63 kHz, a power of 1,500 W, a plasma gas (mixture of nitrogen with 3.3% hydrogen) flow of 54 SLM (standard litre per minute), a carrier gas flow of 9 SLM, and a powder rate of up to 5 g/min. The plasma head is moved at 200 mm/s, and the substrate is rotated at 10 rev/min. The net deposition rate reaches 2.5 g/min. A homogeneous, high‐quality film with 1‐mm thickness is deposited on an approximately 100 cm2 substrate surface.

Features of Pulsed Argon Plasma Jet Impinging on Grounded Target

This article describes the experimental results obtained for pulsed argon atmospheric plasma jets impinging on the grounded targets with a different conductivity. The values of the jet current and profiles of the integrated light emission of the plasma jets are presented. It was found that a propagation velocity and a length of the argon plasma jet in air depended on conductivity of the target. There were revealed differences in the jet propagating freely in air and the jet impinging on the target.

Pulsed plasma jet interaction with a metal targets

The results of experimental studies of the interaction of plasma jets, created by a pulsed capillary discharge with an evaporating wall, with metal targets are presented. It is shown that the main mechanism of targets destruction is the material melting and the subsequent removal of the melt under the dynamic pressure of the plasma jet. The main sources of energy transmitted to the target are: the high-speed flow of high-enthalpy plasma created inside the capillary, and the fluxes of charged particles accelerated in the near-electrode layers. The energy transport provided by charged particles does not exceed ∼0.1–0.2 of the total energy input onto the target. The enthalpy transport is capable to provide heat flux densities of ∼5-6 kW/mm2, an order of magnitude exceeding the values achievable in welding arcs.

Ignition of A Plasma Discharge Inside An Electrodeless Chamber: Methods and Characteristics

In this paper the generation and diagnostics of a reduced pressure (300 mTorr to 3 Torr) plasma generated inside an electrodeless containment vessel/chamber are presented. The plasma is ignited by a guided ionization wave emitted by a low temperature pulsed plasma jet. The diagnostics techniques include Intensified Charge Coupled Device (ICCD) imaging, emission spectroscopy, and Langmuir probe. The reduced-pressure discharge parameters measured are the magnitude of the electric field, the plasma electron number density and temperature, and discharge expansion speed.

Numerical Study of Jet–Target Interaction: Influence of Dielectric Permittivity on the Electric Field Experienced by the Target

This work presents a study of the influence of dielectric permittivity on the interaction between a positive pulsed He plasma jet and a 0.5 mm-thick dielectric target, using a validated two-dimensional numerical model. Six different targets are studied: five targets at floating potential with relative permittivities ϵr= 1, 4, 20, 56 and 80; and one grounded target of permittivity ϵr=56. The temporal evolution of the charging of the target and of the electric field inside the target are described, during the pulse of applied voltage and after its fall. It is found that the order of magnitude of the electric field inside the dielectric targets is the same for all floating targets with ϵr≥4. For all these targets, during the pulse of applied voltage, the electric field perpendicular to the target and averaged through the target thickness, at the point of discharge impact, is between 1 and 5 kV cm−1. For the two remaining targets (ϵr=1 and grounded target with ϵr=56), the field is significantly higher than for all the other floating targets.

Subatmospheric Pressure Microsecond Spark Discharge Plasma Jet for Surface Decontamination

For safe handling and transport, the exterior surfaces of a container used to collect microorganisms should be disinfected. Though conventional methods are highly reliable, they could damage the container or destroy the contents, rendering the collection of microorganisms pointless. In this paper, a pulsed subatmospheric pressure microsecond spark discharge plasma jet, referred to as a pin-to-hole discharge (PHD), was used as a source of ultraviolet (UV) radiation and reactive oxygen and nitrogen species (RONS) for the sterilization of inoculated surfaces with limited thermal impact. A device was created to generate an overlapped region of treatment on a cylindrical body from an array of these PHDs. The surface was inoculated with vegetative bacteria (Escherichia coli), sporulated bacteria (Bacillus atrophaeus), or a simulated dirt and spore solution and then treated with the plasma array. Gas composition effects on the bacterial load reduction were explored, and the combination of RONS from air was found to be an improvement of the effects from pure oxygen. Increasing treatment time caused an increase in bacterial load reduction, regardless of the distance or gas composition. Treatment of simulated soil inoculation showed suppressed sterilization results which asserted the fact that addition of UV radiation from the discharges improved bacterial inactivation from PHDs. The radial array of pulsed subatmospheric pressure microsecond spark discharges was shown to reduce the bacterial load on the inoculated surface by 5-log within 20 min of treatment from a discharge in air.

Electron densities and temperatures of an atmospheric-pressure nanosecond pulsed helium plasma jet in air**{Electron properties in a nanosecond pulsed atmospheric plasma jet determined by laser Thomson scattering}.

We report temporally and spatially resolved electron property measurements of a 150 ns pulsed helium plasma jet in air operated at a low-repetition rate using Thomson laser scattering. A ring-shaped electron density distribution was revealed in the pulsed plasma jet at an axial distance of 1 mm from the electrode nozzle and started to converge after 5 mm. A peak electron density of 1 × 1020 m−3 was identified at the radius of the ring and close to the nozzle electrode. For a delay time ranging from 60 to 250 ns after the onset of the streamer, the electron temperature at the radius of the ring varied from 2.8 to 0.8 eV. Higher temperature >3.5 eV was also identified at regions with lower densities. Importantly, temporal development of the electron density and temperature of the plasma jet confirmed the strong dependence of guided streamer formation and propagation on the external pulsed electric field. The jet current measured during the rising and falling phases of the voltage pulse can be related to the peaks in the temporal development of the electron density.

Effects of pulse width on He plasma jets in contact with water evaluated by OH(A–X) emission and OHaq production

Nanosecond pulsed helium plasma jets impinging on water produce hydroxyl radicals both in gas- and liquid-phase. In this study, the effects of pulse width on a repetitively pulsed plasma jet in contact with water are evaluated via OH(A–X) emission and OHaq production in water for various pulse widths ranging from 200 to 5000 ns. The maximal energy efficiency of OH(A–X) emission is obtained for pulse widths of 600–800 ns whereas the maximal efficiency of OHaq production is at 200 ns. Temporally-resolved emission spectroscopy shows that more than 40% of OH(A–X) emission is produced during the first 200 ns of the voltage pulse regardless of the pulse width. An equivalent circuit model of the plasma jet impinging on water is compiled to understand the charge transfer process, which is important for OHaq production via charge exchange reactions.

Laser induced breakdown in pulsed helium atmospheric pressure plasma jet

This study connects two fields of research: laser induced plasmas and nonequilibrium low-temperature plasmas by studying effects of preionisation, made by a single-electrode atmospheric pressure plasma jet, on a laser induced breakdown (LIB) in helium. A laser pulse (1064 nm, 4 ns pulse width, 5 Hz repetition rate) was focused into the helium jet flowing into ambient air and synchronized with the discharge (10 kHz repetition rate). The level of preionisation in the focal volume at the moment when the laser pulse arrives was controlled by changing the time delay between voltage and laser pulse. The conditions of the discharge are strongly affecting laser induced plasma by providing initial seed of electrons and promoting the breakdown in helium. Measurements of the absorbed laser pulse energy and optical emission relative intensities were performed for different time delays between voltage and laser pulse. Study of LIB with preionisation is discussed as a potential tool for diagnostics of free plasma jets and jets interacting with various target materials.

The Titan haze simulation experiment: Investigating Titan’s low-temperature atmospheric chemistry in a pulsed plasma jet expansion

AbstractThe Titan Haze Simulation (THS) experiment is a unique experimental platform that allows to simulate Titan’s complex atmospheric chemistry at low Titan-like temperature by generating a plasma discharge in the stream of a plasma jet expansion. Both gas and solid phase products are generated and can be analyzed using different in-situ and ex-situ diagnostics. Here, we present an overall description of the work accomplished with the THS in the last 10 years, our current research efforts, and the important implications for the analysis of Cassini’s returned data and preparation for future Titan missions.

Decay of the electron density and the electron collision frequency between successive discharges of a pulsed plasma jet in N2

The decay of the electron density and electron collision frequency between successive discharges in a pulsed plasma jet in N2 feed gas has been investigated using microwave cavity resonance spectroscopy. The method and analysis were adapted to be able to apply this diagnostic to a pulsed plasma jet at atmospheric pressure. The results are compared to a global model. It is shown that the electron density and effective collision frequency can be measured using this technique from about 1 up to approximately 60 after the discharge, where the former time scale is limited by the response time of the cavity and the latter by the detection limit of the setup. Although the data analysis requires an estimation of the plasma volume, which limits the absolute accuracy of the electron density to its order of magnitude, the measured electron densities are in the same range as those predicted by the global model. Additionally, there is a good qualitative agreement in the electron density decay rate between the measurements and the model. Furthermore, it is inferred from the model that the minimum seed electron density required for repeatable guided streamer discharges in a pulsed plasma jet in N2 feed gas is of the order of 1015 .

Using RF inductive rings to improve the efficiency of a designed pulsed plasma jet

In this work, the radiofrequency inductive rings are placed on a pulsed plasma jet plume to improve its efficiency and capability. The optical emission spectroscopy method is used to examine the physical and technical features of the improved pulsed plasma jet. The influences of applied impulse voltage and frequency on the pulsed plasma jet along with the inductive rings diameter and its turns and applied RF voltage amplitude on its performance are studied. It is seen that, at the higher applied voltages and frequencies on the pulsed plasma jet, while the plasma density is increased, the plasma electron excitation and rotational temperatures will decrease. Furthermore, the inductive RF voltage application on the rings enhances the ionization rate and plasma density of the jet, and consequently, the excitation and rotational temperatures of plasma electrons are reduced. Increasing of the applied inductive RF voltage amplitudes on the ring will result in the higher electrons density and reduction in the excitation and rotational temperatures. It is shown that, at the higher inductive ring diameters and its turns, the excitation temperature of plasma electrons is reduced.

Plasma Dynamics Modeling of the Interaction of Pulsed Plasma Jets

The basic properties of the plasma of capillary discharges are discussed. A mathematical simulation of the interaction of pulsed plasma jets generated by a capillary discharge at atmospheric pressure is presented.

Effect of oxygen as additive on an atmospheric nanosecond pulsed helium plasma jet impinging on a dielectric surface

Based on a 2D axisymmetric plasma fluid model, the effect of the levels of O2 admixtures on the plasma dynamics of an atmospheric pressure He plasma jet incident on a dielectric surface situated normal to the jet axis has been studied. The introduction of O2 admixture in the feedstock gas changes the shape of the discharge ionization rate that approaches the target surface from a ring to a solid disk. As the streamer extinguishes radial propagation along the dielectric surface, comparatively larger plasma-surface contact areas were obtained for O2 additions to the He plasma of less than 0.5% relative to that for the discharge in pure He, while in the case of 2% O2, the radial propagation distance dropped off significantly. The propagation of an ionization wave peaked in the range 0.2%–1% for the O2 admixture. The enhanced ionization reactions are considered to predominate for small concentrations of O2 as additive, and the negative role played by the excitation energy loss and the attachment of electrons to O2 is more important with the addition of 2% O2. There was a remarkable incremental gain in the flux intensity of O on the surface center, while the flux of N was mainly concentrated on the streamer head. The magnitude of the O flux on the surface showed a peak at the 0.5% O2 admixture level, and the flux of O3 on the surface was directly proportional to the O2 concentration.