Plasma Jet Generator Research Articles

Generation of Large-Scale Plasma Jet with Excitation of Bipolar Nanosecond Pulse Voltage in Single-Spiral Electrode Configuration

In this study, a single-outer-spiral electrode with inductance of 20 μH is employed to couple the energy input of a bipolar nanosecond pulse for the purpose of generating a large-scale atmospheric pressure plasma jet. When the spiral electrode is wrapped around a plasma jet tube with a length of 35 cm, the electrical field can be optimized, resulting in a stable laminar flow field, and a plasma jet with a length and diameter larger than 14 cm and 1.2 cm can be generated. A comparative study of the bipolar and unipolar pulse excitation voltages is also conducted, showing that the maximum lengths of the plasma jet excited by a bipolar pulse voltage, positive pulse voltage, and negative are 14 cm, 10 cm, and 7 cm, respectively. The temporal and spatially resolved spectra of the plasma jets excited by both bipolar and unipolar pulses are investigated, respectively, and the main physiochemical processes of the active species and the plasma dynamics’ evolution are discussed.

A large-scale cold plasma jet: generation mechanism and application effect

Atmospheric pressure cold plasma jets (APCPJs) typically exhibit a slender, conical structure, which imposes limitations on their application for surface modification due to the restricted treatment area. In this paper, we introduce a novel plasma jet morphology known as the large-scale cold plasma jet (LSCPJ), characterized by the presence of both a central conical plasma jet and a peripheral trumpet-like diffuse plasma jet. The experimental investigations have identified the factors influencing the conical and the trumpet-like diffuse plasma jet, and theoretical simulations have shed light on the role of the flow field and the electric field in shaping the formation of the LSCPJ. It is proved that, under conditions of elevated helium concentration, the distributions of impurity gas particles and the electric field jointly determine the plasma jet’s morphology. High-speed ICCD camera images confirm the dynamic behavior of plasma bullets in LSCPJ, which is consistent with the theoretical analysis. Finally, it is demonstrated that when applied to the surface treatment of silicone rubber, LSCPJ can achieve a treatment area over 28 times larger than that of APCPJ under equivalent conditions. This paper uncovers the crucial role of impurity gases and electric fields in shaping plasma jet morphology and opens up the possibility of efficiently diversifying plasma jet generation effects through external electromagnetic fields. These insights hold the promise of reducing the generation cost of plasma jets and expanding their applications across various industrial sectors.

Atmospheric pressure argon plasma jets I – Measurements of spatial distribution for visible emission spectrum and vacuum ultraviolet

AbstractThis paper describes the observed position dependent emission spectrum and vacuum ultraviolet (VUV) to clarify the optical structure of argon atmospheric pressure plasma jets (APJs). Visible emission spectra of argon, nitrogen, and OH molecules were measured as a function of position from the nozzle of plasma jet generator to gas flow direction. From the results, we realized that a certain electric field is required for producing high energy excited atoms of argon in the jet from the high voltage electrode in the device to the ground positioned at downstream side. Moreover, VUV was detected along the plasma jet through the downstream direction. Thus, we could picture that the light pattern of plasma jet of which intensity weaken depend to the distance from the nozzle is sustained by the above two factors with the present steady state experiments.

Enhanced plasma jet generation through numerical integration and dielectric influence analysis

This paper reports a study on the production of plasma jets that are out of equilibrium through numerical solutions of electron energy distribution function using a self-consistent methodology. The approach includes the integration of the continuity, momentum, and Poisson equations, which allows the use of the mean electron energy to fit the transport and source coefficients. The paper concurrently presents an analysis of cold plasma generation in a tube. This investigation utilizes COMSOL Multiphysics software to simulate the electric field, potential, and electron density in space. Moreover, the study examines how the dielectric’s permittivity impacts plasma propagation. The simulated outcomes are compared with experimental and numerical results. As electron density, ionization rate and electric potential vary during plasma propagation on a dielectric surface, and the permittivity of dielectric materials increases, it promotes an increase in electron density around it. This, in turn, accelerates the ionization front, indicating efficient polarization and accumulation of electric charges, specifically electrons, near the dielectric surface.

Generation of jet-forming plasma bunch with gigagauss axial magnetic field from impact of linearly polarized laser on microtube targets

Generation of a thin plasma jet with embedded gigagauss axial magnetic fields from the frontal impact of a short linearly polarized laser pulse on an overdense microtube target is considered. It is a new scheme of axial magnetic field generation without initial laser angular momentum. Three-dimensional particle-in-cell simulations show that the space-charge field of the laser expelled tube-front electrons will pull out carbon ions to form at the tube entrance a long-living low-density plasma bunch with gigagauss magnetic fields. The front center of the plasma bunch then stretches forward to form a thin gigagauss-magnetized plasma jet, which survives for sub-picosecond after the core of the laser has passed through the tube.

Effects of thermal plasma on the microstructure and mechanical behavior of alumina-mullite based oxide/oxide ceramic matrix composites

Oxide/oxide ceramic matrix composites have potential applications in thermal protection systems due to their ability to withstand very high temperatures while maintaining their load bearing capability and oxidation resistance. Under hypersonic flight conditions vehicle components may be exposed to temperatures above the melting points of alumina and mullite, as well as to chemically active ionized gases. Therefore, it is necessary to understand the response of these CMCs to not just thermal loads, but also the added challenges of plasma environments. In this study, alumina-mullite based oxide/oxide CMCs were exposed to an inductively generated plasma jet for 30 min at a heat flux of 24 W/cm2 in near vacuum conditions. Resulting microstructures were characterized with XRD and SEM/EDS. Silicon rich, sub-micron globules were observed on the surface of the impinged region. Also, the first 5 μm below the surface were enriched with silicon. The back surface showed no silicon enrichment but did have a granulated surface texture in comparison to as manufactured samples. Short beam strength tests were performed as a measure of structural performance. Differences in the overall response and short beam strength were noted between the as manufactured and plasma exposed cases.

Instant switching control between two types of plasma-driven liquid flows

Plasma-driven liquid flows that are generated in bulk liquid by plasma irradiation are one of the key factors in understanding the interaction between plasma and liquid. In this work, the direction of the plasma-driven liquid flow was successfully switched and controlled only by changing the frequency of argon plasma jet generation. The liquid flow could switch in the opposite direction within 3 s after the frequency change. Changes in the emission spectra with frequency have an important effect on the liquid flows, with results from current waveforms indicating that the frequency also changes the characteristics of the plasma jet.

Analysis of technological possibilities of N‒O‒C‒H system arc plasma in surface engineering processes

The object of this study was the substances that could be used to generate arc plasma. Conventional and promising plasma media were analyzed in order to identify the most universal one in terms of a set of properties for efficient energy transfer of material. It is shown that the mean-enthalpy media have a harmonious ratio of temperature and enthalpy and could provide a change in the energy state of the processed material with maximum efficiency. It is established that the most universal set of properties is demonstrated by the medium enthalpy plasma of the N‒O‒C‒H system. The use of mixtures of air with hydrocarbons for its generation makes it possible to reach the average mass temperature of (5...7)·103 K and change the oxidative-reducing potential of the plasma medium over a wide range. Given this, heat treatment is possible with maximum preservation of the original composition of the material. Experimental studies of plasma flows of the N‒O‒C‒H system confirmed the presence of reducing components capable of binding oxygen to air that is sucked into the jet. On rich mixtures, the oxygen content in the jet at a distance of 100 mm does not exceed 5 %. The positive effect of combined energy input into plasma-forming substance on the process of generation and formation of plasma jet has been proven. The use of energy of different physical nature makes it possible to maintain the local energy parameters of the plasma flow during material processing. This is due to the release of additional heat as a result of the interaction of plasma and plasma components with ambient air. The use of plasma of the N‒O‒C‒H system in surface engineering technologies could expand the range of processed materials and reduce the operating costs of the process

Enhancing the •OH generation of atmospheric pressure plasma jets by mixing water aerosols at downstream region

AbstractWe established a downstream plasma–aerosol mixing system to increase the generation of •OH in an atmospheric pressure plasma jet (APPJ). Four downstream plasma–aerosol mixers were designed, and flow rates of water aerosol were adjusted. Methods to increase •OH in APPJ include increasing ambient humidity, adding water to working gas, treating on wet surfaces, or using water electro‐spray, but have disadvantages. Our method can increase the reaction area between water and plasma and prevent water from quenching the plasma. The ICCD, TA test, and sterilization results revealed that mixing aerosols in the downstream region effectively increased the amount of •OH generation and enhanced sterilization effect. The cone swirl mixer and two‐way swirl mixer generated the strongest and widest •OH emission region, respectively.

Numerical study of a plasma jet for plasma-assisted laser cutting

Laser fusion cutting commonly applies a high-pressurized nitrogen gas jet to blow the molten material out of the cut kerf. However, theoretical considerations suggest that the use of a plasma jet may offer some advantages over this conventional approach. In this preliminary investigation, the characteristics of a non-transferred plasma jet for the application as auxiliary gas in laser beam cutting are analyzed using numerical CFD simulation. Based on this study, a first prototype of a plasma jet generator was manufactured and used in initial cutting experiments on 6 mm thick AISI 304 stainless steel. Two different cooling concepts for the plasma torch were considered and investigated in practice. Suitable values for the nozzle exit diameter, the distance between the electrodes of the plasma torch, the auxiliary gas flow rate and the electric current were identified both model-based and experimentally. The achieved cutting performance is considered a proof-of-principle of the suggested approach of a plasma-assisted laser beam cutting process.

Microwave atmospheric pressure plasma jet generated from substrate integrated waveguide resonator

AbstractA microwave atmospheric pressure plasma jet (MW‐APPJ) generator based on a substrate‐integrated waveguide (SIW) resonator is proposed. A thin, straight plasma needle with a length of 9 cm could be obtained. Higher than 90% of microwave feeding efficiency is obtained under a wide range of gas flow rates without a microwave matching network. As the gas flow increased from 1 to 14 L/min, a transition from laminar to turbulent mode is observed in the plasma jet's morphology. Furthermore, a preliminary surface treatment was tested for the device. The polyimide film became super hydrophilic after a 5‐min treatment with the developed SIW‐based plasma generator. Generally, the SIW‐based MW‐APPJ is low‐cost, electrodeless, and low‐profile along the plasma jet length direction.

A novel method for predicting the occurrence of the large-scale shunting in the reverse-polarity plasma torch

The reverse-polarity plasma torch (RPT) is a promising high enthalpy plasma source for material processing, e.g. plasma atomization for spherical powders and plasma synthesis for the nanostructured carbon. The quality and yield of the final product highly depend on the working stability of the RPT, which may be undermined by the large-scale shunting. Large-scale shunting is an abnormal discharge phenomenon existed in the RPT, which leads to the sudden drop of the arc voltage and shrink of the generated plasma jet. Inter-electrodes between the cathode and anode are designed to limit arc fluctuations and thus large-scale shuntings. However, the construction and maintenance of the RPT with inter-electrodes are highly complex. To alleviate the large-scale shunting and retain the advantage of simple structure of the conventional RPT, a novel method for predicting the occurrence of the large-scale shunting is proposed for optimizing the RPT’s internal structure and operation condition. The method is based on the thermal non-equilibrium modelling of the RPT to calculate the thickness of the cold boundary layer (CBL) and breakdown voltage. Then, the occurrence of the large-scale shunting is predicted by comparing the breakdown voltage with the voltage drop between the electrode inner surface and arc column. Three different shapes of the front electrode (cathode) corresponding to different thicknesses of the cold boundary layer (CBL) were manufactured based on the proposed numerical method. Experimental and numerical studies on the effect of the electrode geometry, arc current and gas flow rate on the working stability of the RPT and thickness of the CBL were conducted. Results showed the quantitative correlations between operating parameters and the instability of the RPT and verified that the proposed numerical method is useful for optimizing the design and operation of the plasma torch with minimizing large-scale shunting instabilities.

Treatment of hepatocellular carcinoma with in situ generated plasma‐activated air‐driven water mist

AbstractSince the development of cold atmospheric plasma (CAP), substantial and significant usage of CAP applications was introduced in medicine. Here, we developed two combined sources of plasma to produce in situ plasma‐activated air‐driven water mist (PAAWM). The first is generated using air as a feed gas, while the second is plasma‐activated water generated by the ignition of plasma within the air‐driven water mist. Both contribute to the plasma jet generation of PAAWM. The antitumor efficacy of PAAWM was evaluated against two hepatocellular carcinoma cell lines (SNU‐449 and SNU‐475). The generated PAAWM was efficient in the treatment of both chemosensitive and chemoresistant hepatocellular carcinoma cells. These results may support using PAAWM alone or in combination with other treatment modalities.

Short-pulsed arc discharge for generation of cold plasma jet (apokamp) and prospects of its application in biomedicine

In this study, we investigated the effects of generating a cold plasma jet emanating from the surface of an arc in air at atmospheric pressure. This type of plasma was obtained relatively recently and is called apokamp. Apokamp plasmas are formed by applying short-pulsed high positive polarity voltages, which is provided when the second electrode is weakly capacitive coupled with the ground. The prospect of using apokamp plasmas in biomedical applications is also discussed.

Low-temperature argon plasma jet with cascading electrode technique for biological applications

In this study, the design, performance, and characteristics of a low-temperature argon plasma jet with cascading electrode technique (APJCE) are presented. APJCE is designed based on a tip-ring structure with a cascading ring. The effect of plasma jet driven by repetitive high-voltage microsecond pulses in APJCE structure was measured qualitatively in local surface temperature detection system. Then, by applying the generated plasma jet to biological surface and measuring and characterizing the electrical parameters, we obtained a plasma jet, which is electrically and thermally in the cold plasma regime. Simulation of the electric field distribution in the nozzle also yielded similar results to the experimental results. Finally, by cascading electrodes, we guided the plasma column to the nozzle output so that the plasma temperature within four centimeters of the nozzle output is 37 °C. The resulting plasma jets were studied by atomic emission spectroscopy and the intensity of the spectral lines of the atmospheric argon plasma jet spectra was obtained as a final experimental result at the output.

Atmospheric micro-sized cold plasma jet created by a long and ultra-flexible generator with sputtered gold thin film electrode

Atmospheric cold plasma jets with various configurations have drawn intense interests in diverse applications, such as surface modification and endoscopic applications. In this paper, a long and ultra-flexible micro-sized cold plasma jet generator is presented and its characteristics are analyzed. The generator mainly consists of two concentric silicone tubes with the inner one acting as the gas channel and the outer one acting as insulating layer of heat and high voltage. Gold thin film was sputtered on the circular surface of inner tube to work as the electrode as well as separation layer of ultraviolet radiation. Electrical, optical and thermal characteristics of this generator were investigated. Cold microplasma jet can be generated and ejected to the ambient air with the length varied from 0.1 m to 2.5 m, and it can impact on the finger without electric and heat sensation. Optical emission spectra analysis indicated that reactive species like OH and O atoms were generated in the plasma. This device exhibits ultra-flexible property which can be arbitrarily bent and plugged into complex and deep environment. Localized internal surface modification of polyvinyl chloride tube using this microplasma jet was also demonstrated and the result showed that surface wettability can be greatly improved after plasma treatment. This generator shows great potential for internal surface processing, plasma endoscopic and maskless lithography applications.

A poly‐diagnostic study of the shield gas‐assisted atmospheric pressure plasma jet propagation upon a dielectric surface

AbstractThe significance of shield gases on atmospheric pressure plasma jet (APPJ) propagation over a horizontal dielectric surface using various diagnostic methods has been investigated. The obtained results imply that adding nitrogen as a shield gas only has an impact on the N2 reactive species generation, mainly close to the plasma effluent while argon shield gas can boost the optical emission intensity of all excited species, especially at distances further away from the plasma jet, which is in agreement with the observed length of the plasma propagation all over the surface. On the basis of the obtained results, the employment of a shield gas can improve the plasma jet efficiency to achieve the desired treatment effect on a flat surface.

Downstream high-speed plasma jet generation as a direct consequence of shock reformation

Shocks are one of nature’s most powerful particle accelerators and have been connected to relativistic electron acceleration and cosmic rays. Upstream shock observations include wave generation, wave-particle interactions and magnetic compressive structures, while at the shock and downstream, particle acceleration, magnetic reconnection and plasma jets can be observed. Here, using Magnetospheric Multiscale (MMS) we show in-situ evidence of high-speed downstream flows (jets) generated at the Earth’s bow shock as a direct consequence of shock reformation. Jets are observed downstream due to a combined effect of upstream plasma wave evolution and an ongoing reformation cycle of the bow shock. This generation process can also be applicable to planetary and astrophysical plasmas where collisionless shocks are commonly found.

Peculiarities of pulsed plasma jet initiation

The generation of a cold plasma jet of atmospheric pressure in helium by unipolar positive pulses excitation at a voltage of 2-6 kV and the impact on a dielectric target made of aluminum oxide has been studied. It is shown that the main parameter influencing the regular nature of the streamer breakdown is the pulse duration, and the achievable parameters of cold plasma impact on the target identical to those for sinusoidal excitation. Keywords: plasma jet of atmospheric pressure, pulse excitation.

Особенности импульсного инициирования плазменной струи

The generation of a cold plasma jet of atmospheric pressure in helium by unipolar positive pulses excitation at a voltage of 2–6 kV and the impact on a dielectric target made of aluminum oxide has been studied. It is shown that the main parameter influencing the regular nature of the streamer breakdown is the pulse duration, and the achievable parameters of cold plasma impact on the target identical to those for sinusoidal excitation.