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Mark J Kushner - One of the best experts on this subject based on the ideXlab platform.

  • atmospheric pressure Plasma Jets onto a reactive water layer over tissue pulse repetition rate as a control mechanism
    Journal of Physics D, 2019
    Co-Authors: Seth Norberg, Eric Johnsen, Guy Parsey, Amanda M Lietz, Mark J Kushner
    Abstract:

    The use of Plasma Jets to treat tissue in the context of Plasma medicine often involves a thin intervening liquid layer on top of the tissue. Plasma activated species first transport through and react in the liquid layer prior to reaching the tissue. Of the many parameters that can be used to control this process, pulse repetition frequency (PRF) stands out. Results from a computational investigation of multiple pulses at varying PRF from an atmospheric pressure Plasma jet (APPJ) onto a reactive liquid layer are discussed, and three key trends are made clear. First, a high PRF (short time between pulses) enables the gaseous species produced during the previous pulse to remain in the vicinity of the Plasma at the onset of the next pulse, thereby increasing the inventory of (H)N x O y and O3 in the gas phase. These species then solvate into the liquid, water in this case, and produce higher densities of aqueous ozone, nitrate, and peroxynitrite. With a lower PRF, reactants produced on a previous pulse are convected away prior to the next discharge pulse with more spatial separation of reactants both above and within the water. As a result, more of the hydroxyl anion (), ozone anion () and nitric oxide (NOaq) reach the tissue beneath the water. The second trend is that the production of H2O2aq and its fluence to the underlying tissue are relatively independent of the PRF. The precursors for H2O2aq are primarily produced by the surface ionization wave (SIW) on the top of the liquid, which then directly solvate into the liquid. Lastly, when the Plasma plume touches the liquid, the SIW on the water layer increases the production of all aqueous species compared to configurations where the Plasma plume does not touch the liquid. These trends are true for all PRF.

  • electrode configurations in atmospheric pressure Plasma Jets production of reactive species
    Plasma Sources Science and Technology, 2018
    Co-Authors: Amanda M Lietz, Mark J Kushner
    Abstract:

    Atmospheric pressure Plasma Jets (APPJs) are a preferred Plasma source for many biomedical applications. These Jets typically consist of a rare gas flowing through a dielectric tube, possibly with an O2 or H2O admixture, and flowing into the ambient. They are typically powered by pulsed or sinusoidal voltage waveforms. However, in most other aspects APPJ designs differ greatly. In this paper, APPJ design parameters and their consequences on ionization wave (IW) propagation and reactive oxygen and nitrogen species (RONS) production are discussed using results from a two-dimensional Plasma hydrodynamics model. The base case is an APPJ with a single powered ring electrode wrapped around a dielectric tube. This configuration was varied by adding a grounded ring electrode, changing the powered and grounded electrode positions, and moving the powered electrode to the inside of the tube. Placing the powered electrode closer to the outlet of the tube increased the RONS production by increasing the energy deposition outside the tube. Adding a grounded ring increased the IW intensity inside the tube while slightly increasing the power deposition outside of the tube. An inner powered electrode increased the IW intensity and propagation velocity, and the resulting RONS production. Co-axial ground planes within 5 cm of the APPJ significantly affected the IW behavior, increasing its intensity and increasing RONS production. The consequences of voltage rise time and dielectric constant of the tube are also discussed. The systematic trends from this investigation may facilitate more informed APPJ design choices that may be tailored to the goals of a specific application.

  • molecular admixtures and impurities in atmospheric pressure Plasma Jets
    Journal of Applied Physics, 2018
    Co-Authors: Amanda M Lietz, Mark J Kushner
    Abstract:

    A more complete understanding of reactive chemistry generated by atmospheric pressure Plasma Jets (APPJs) is critical to many emerging medical, agricultural, and water treatment applications. Adding molecular gases to the noble working gas which flows through the jet is a common method to tailor the resulting production of reactive oxygen and nitrogen species (RONS). In this paper, results are discussed from a computational investigation of the consequences of H2O and O2 admixtures on the reactive chemistry of He APPJs flowing into humid air. This investigation, performed with a 2-dimensional Plasma hydrodynamics model, addresses the RONS that are initially produced and the evolution of that chemistry on longer time scales. Without an admixture, the impurities in 99.999% pure helium are a major source of RONS. The addition of H2O decreases the production of reactive nitrogen species (RNS) and increases the production of reactive oxygen species (ROS). The addition of O2 significantly decreases the production of RNS, as well as hydrogen-containing ROS, but increases the production of ROS without hydrogen. This selectivity comes from the lower ionization energy of O2 compared to N2 and H2O, which then allows for charge exchange reactions. These charge exchange reactions change the RONS which are produced in the afterglow by dissociative recombination. The consequences of impurities were also examined. Humid air impurities as low as 10 ppm in the helium can account for 79%-98% of the production of most RONS in the absence of an intentional admixture. The degree to which the impurities affect the RONS production depends on the electrode configuration and can be reduced by molecular admixtures.A more complete understanding of reactive chemistry generated by atmospheric pressure Plasma Jets (APPJs) is critical to many emerging medical, agricultural, and water treatment applications. Adding molecular gases to the noble working gas which flows through the jet is a common method to tailor the resulting production of reactive oxygen and nitrogen species (RONS). In this paper, results are discussed from a computational investigation of the consequences of H2O and O2 admixtures on the reactive chemistry of He APPJs flowing into humid air. This investigation, performed with a 2-dimensional Plasma hydrodynamics model, addresses the RONS that are initially produced and the evolution of that chemistry on longer time scales. Without an admixture, the impurities in 99.999% pure helium are a major source of RONS. The addition of H2O decreases the production of reactive nitrogen species (RNS) and increases the production of reactive oxygen species (ROS). The addition of O2 significantly decreases the producti...

  • Plasma induced flow instabilities in atmospheric pressure Plasma Jets
    Applied Physics Letters, 2017
    Co-Authors: Amanda M Lietz, Eric Johnsen, Mark J Kushner
    Abstract:

    Pulsed Plasma excitation of rare gases flowing into air has been shown to impact the stability of the flow in non-equilibrium atmospheric pressure Plasma Jets (APPJs). In this paper, the results from a numerical modeling investigation of the stability of a round He APPJ with a powered electrode exposed to the gas flow are discussed. Localized gas heating at the powered electrode occurs on the time scale of the voltage pulse, tens to 100 ns, which is short compared to the fluid timescales. An acoustic wave propagates from this heated, expanding gas and exits the jet. The wave disturbs the shear layer between the He and surrounding humid air, exciting a shear instability which grows downstream with the flow and increases the mixing of the humid air into the He. The effects of the eddy-dominated flow on ionization wave (IW) propagation in an APPJ were investigated. The IW followed the regions of the highest helium concentration, resulting in an increased production of NO, HO2, and NO2.

  • an array of atmospheric pressure Plasma Jets from a single ionization wave
    International Conference on Plasma Science, 2016
    Co-Authors: Amanda M Lietz, Mark J Kushner
    Abstract:

    Atmospheric pressure Plasmas are being investigated for wound healing, agricultural enhancements, sterilization, and functionalization of materials. An often used configuration is the atmospheric pressure Plasma jet (APPJ). Although highly effective, the Plasma emanating from the APPJ covers a small area. In order to increase the area treated arrays of APPJs have been developed. The individual Jets in such arrays often have inter-jet interactions and may require multiple power supplies. In this paper, we discuss results from a computational investigation of an APPJ geometry which enables multiple Jets to be generated from a single ionization wave and has a minimum of jet-to-jet interactions. The configuration consists of a dielectric tube having a row of holes along its length. Helium flows through the dielectric tube and out the holes as a He plume into ambient humid air. The discharge is initiated by a powered annular electrode inside the tube and a grounded ring electrode outside of the tube which overlaps the inner electrode. An ionization wave (IW) propagates along the inside of the tube and over the holes. Depending on the size of the holes, secondary IWs are launched from the holes perpendicularly to the tube into the He plumes, thereby producing a comb of Plasma Jets. This configuration is based on the work of Robert et al.[1]

Christophe Leys - One of the best experts on this subject based on the ideXlab platform.

  • influence of helium mole fraction distribution on the properties of cold atmospheric pressure helium Plasma Jets
    Journal of Applied Physics, 2012
    Co-Authors: Ranhua Xiong, Anton Nikiforov, Patrick Vanraes, Qing Xiong, Christophe Leys
    Abstract:

    The influence of helium mole fraction distribution in air on the cold atmospheric Plasma Jets excited by 1.5 kHz rectangular high voltage pulse is studied in this work. Computational fluid dynamics (CFD) with incorporation of large eddy simulation (LES) model is used to simulate the helium mole fraction distribution in air under the helium flow from laminar to turbulent regime with increasing helium outlet velocity. Numerical simulation results are combined with experimental results in order to determine the influence of helium distribution on the cold Plasma Jets. It reveals that the structure of the helium distribution caused by diffusion or by turbulent mixing in turbulent regime determines the characteristics of the cold Plasma Jets. On the other hand, the curves of Plasma jet length (L) versus helium outlet velocity (V) at different jet diameters (D) are unified in a map of jet Reynolds number (Re = ρHe·V·D/μHe, where μHe is the helium viscosity constant) versus dimensionless Plasma jet length (l = L...

  • influence of helium mole fraction distribution on the properties of cold atmospheric pressure helium Plasma Jets
    Journal of Applied Physics, 2012
    Co-Authors: Ranhua Xiong, Anton Nikiforov, Patrick Vanraes, Qing Xiong, Christophe Leys
    Abstract:

    The influence of helium mole fraction distribution in air on the cold atmospheric Plasma Jets excited by 1.5 kHz rectangular high voltage pulse is studied in this work. Computational fluid dynamics (CFD) with incorporation of large eddy simulation (LES) model is used to simulate the helium mole fraction distribution in air under the helium flow from laminar to turbulent regime with increasing helium outlet velocity. Numerical simulation results are combined with experimental results in order to determine the influence of helium distribution on the cold Plasma Jets. It reveals that the structure of the helium distribution caused by diffusion or by turbulent mixing in turbulent regime determines the characteristics of the cold Plasma Jets. On the other hand, the curves of Plasma jet length (L) versus helium outlet velocity (V) at different jet diameters (D) are unified in a map of jet Reynolds number (Re = ρHe·V·D/μHe, where μHe is the helium viscosity constant) versus dimensionless Plasma jet length (l = L...

Ranhua Xiong - One of the best experts on this subject based on the ideXlab platform.

  • influence of helium mole fraction distribution on the properties of cold atmospheric pressure helium Plasma Jets
    Journal of Applied Physics, 2012
    Co-Authors: Ranhua Xiong, Anton Nikiforov, Patrick Vanraes, Qing Xiong, Christophe Leys
    Abstract:

    The influence of helium mole fraction distribution in air on the cold atmospheric Plasma Jets excited by 1.5 kHz rectangular high voltage pulse is studied in this work. Computational fluid dynamics (CFD) with incorporation of large eddy simulation (LES) model is used to simulate the helium mole fraction distribution in air under the helium flow from laminar to turbulent regime with increasing helium outlet velocity. Numerical simulation results are combined with experimental results in order to determine the influence of helium distribution on the cold Plasma Jets. It reveals that the structure of the helium distribution caused by diffusion or by turbulent mixing in turbulent regime determines the characteristics of the cold Plasma Jets. On the other hand, the curves of Plasma jet length (L) versus helium outlet velocity (V) at different jet diameters (D) are unified in a map of jet Reynolds number (Re = ρHe·V·D/μHe, where μHe is the helium viscosity constant) versus dimensionless Plasma jet length (l = L...

  • influence of helium mole fraction distribution on the properties of cold atmospheric pressure helium Plasma Jets
    Journal of Applied Physics, 2012
    Co-Authors: Ranhua Xiong, Anton Nikiforov, Patrick Vanraes, Qing Xiong, Christophe Leys
    Abstract:

    The influence of helium mole fraction distribution in air on the cold atmospheric Plasma Jets excited by 1.5 kHz rectangular high voltage pulse is studied in this work. Computational fluid dynamics (CFD) with incorporation of large eddy simulation (LES) model is used to simulate the helium mole fraction distribution in air under the helium flow from laminar to turbulent regime with increasing helium outlet velocity. Numerical simulation results are combined with experimental results in order to determine the influence of helium distribution on the cold Plasma Jets. It reveals that the structure of the helium distribution caused by diffusion or by turbulent mixing in turbulent regime determines the characteristics of the cold Plasma Jets. On the other hand, the curves of Plasma jet length (L) versus helium outlet velocity (V) at different jet diameters (D) are unified in a map of jet Reynolds number (Re = ρHe·V·D/μHe, where μHe is the helium viscosity constant) versus dimensionless Plasma jet length (l = L...

Wenhong Zhang - One of the best experts on this subject based on the ideXlab platform.

  • generation of long laminar Plasma Jets at atmospheric pressure and effects of flow turbulence
    Plasma Chemistry and Plasma Processing, 2001
    Co-Authors: Wenhua Zhang, Wenhong Zhang, Chengkang Wu
    Abstract:

    Long, laminar Plasma Jets at atmospheric pressure of pure argon and a mixture of argon and nitrogen with jet length up to 45 times its diameter could be generated with a DC arc torch by restricting the movement of arc root in the torch channel. Effects of torch structure, gas feeding, and characteristics of power supply on the length of Plasma Jets were experimentally examined. Plasma Jets of considerable length and excellent stability could be obtained by regulating the generating parameters, including arc channel geometry, gas flow rate, and feeding methods, etc. Influence of flow turbulence at the torch nozzle exit on the temperature distribution of Plasma Jets was numerically simulated. The analysis indicated that laminar flow Plasma with very low initial turbulent kinetic energy will produce a long jet with low axial temperature gradient. This kind of long laminar Plasma jet could greatly improve the controllability for materials processing, compared with a short turbulent arc jet.

  • generation of long laminar Plasma Jets at atmospheric pressure and effects of flow turbulence
    Plasma Chemistry and Plasma Processing, 2001
    Co-Authors: Wenxia Pan, Wenhua Zhang, Wenhong Zhang
    Abstract:

    Long, laminar Plasma Jets at atmospheric pressure of pure argon and a mixture of argon and nitrogen with jet length up to 45 fi,Hes its diameter could be generated with a DC are torch by! restricting the movement of arc root in the torch channel. Effects of torch structure, gas feeding, and characteristics of power supply on the length of Plasma Jets were experimentally examined. Plasma Jets of considerable length and excellent stability could be obtained by regulating the generating parameters, including are channel geometry gas flow I ate, and feeding methods, etc. Influence of flow turbulence at the torch,nozzle exit on the temperature distribution of Plasma Jets was numerically simulated. The analysis indicated that laminar flow Plasma with very low initial turbulent kinetic energy will produce a long jet, with low axial temperature gradient. This kind of long laminar Plasma jet could greatly improve the controllability for materials processing, compared with a short turbulent are let.

Michael G. Kong - One of the best experts on this subject based on the ideXlab platform.

  • investigation on the rons and bactericidal effects induced by he o2 cold Plasma Jets in open air and in an airtight chamber
    Physics of Plasmas, 2018
    Co-Authors: Han Xu, Michael G. Kong, Weitao Wang, Mingzhe Rong
    Abstract:

    He + O2 Plasma Jets in open air and in an airtight chamber are comparatively studied, with respect to their production of gaseous/aqueous reactive species and their antibacterial effects. Under the same discharge power, the Plasma jet in open air has higher densities of gaseous reactive species and a higher concentration of aqueous H2O2 but lower concentrations of aqueous OH and O2-. In addition, the increase in the O2 ratio in He in both Plasma Jets causes a linear decrease in the population of gaseous reactive species, except for O(3p5P) when a small amount of O2 is added to the working gas. The concentrations of aqueous reactive species for OH and H2O2 also drop monotonically with the increase in additive O2, while the aqueous O2- first increases and then decreases. Moreover, it is interesting that the bactericidal inactivation in the airtight chamber condition is much greater than that in the open air condition regardless of the presence or absence of additive O2 in the He Plasma jet. The concentration trends of O2- for both the Plasma Jets are similar to their antibacterial effects, and little antibacterial effect is achieved when a scavenger of O2- is used, indicating that O2- should be a main antibacterial agent. Moreover, it should not be O2- alone to achieve the antibacterial effect, and some reactive nitrogen species such as ONOO- and O2NOO- might also play an important role.He + O2 Plasma Jets in open air and in an airtight chamber are comparatively studied, with respect to their production of gaseous/aqueous reactive species and their antibacterial effects. Under the same discharge power, the Plasma jet in open air has higher densities of gaseous reactive species and a higher concentration of aqueous H2O2 but lower concentrations of aqueous OH and O2-. In addition, the increase in the O2 ratio in He in both Plasma Jets causes a linear decrease in the population of gaseous reactive species, except for O(3p5P) when a small amount of O2 is added to the working gas. The concentrations of aqueous reactive species for OH and H2O2 also drop monotonically with the increase in additive O2, while the aqueous O2- first increases and then decreases. Moreover, it is interesting that the bactericidal inactivation in the airtight chamber condition is much greater than that in the open air condition regardless of the presence or absence of additive O2 in the He Plasma jet. The concentratio...

  • production of simplex rns and ros by nanosecond pulse n2 o2 Plasma Jets with homogeneous shielding gas for inducing myeloma cell apoptosis
    Journal of Physics D, 2017
    Co-Authors: Zhijie Liu, Michael G. Kong, Dingxin Liu, Qingjie Cui, Haifeng Cai, Hailan Chen
    Abstract:

    In this paper, atmospheric pressure N2/O2 Plasma Jets with homogeneous shielding gas excited by nanosecond pulse are obtained to generate simplex reactive nitrogen species (RNS) and reactive oxygen species (ROS), respectively, for the purpose of studying the simplex RNS and ROS to induce the myeloma cell apoptosis with the same discharge power. The results reveal that the cell death rate by the N2 Plasma jet with N2 shielding gas is about two times that of the O2 Plasma jet with O2 shielding gas for the equivalent treatment time. By diagnosing the reactive species of ONOO−, H2O2, OH and in medium, our findings suggest the cell death rate after Plasma Jets treatment has a positive correlation with the concentration of ONOO−. Therefore, the ONOO− in medium is thought to play an important role in the process of inducing myeloma cell apoptosis.

  • Contrasting characteristics of linear-field and cross-field atmospheric Plasma Jets
    Applied Physics Letters, 2008
    Co-Authors: James L. Walsh, Michael G. Kong
    Abstract:

    This letter reports an experimental study of two types of atmospheric pressure Plasma Jets in terms of their fundamental properties and their efficiency in etching polymeric materials. The first Plasma jet has a cross-field configuration with its electric field perpendicular to its gas flow field, whereas the second is a linear-field device having parallel electric and flow fields. The linear-field jet is shown to drive electron transportation to the downstream application region, thus facilitating more active Plasma chemistry there. This is responsible for its etching rate of polyamide films being 13-fold that of its cross-field counterpart.

  • contrasting characteristics of pulsed and sinusoidal cold atmospheric Plasma Jets
    Applied Physics Letters, 2006
    Co-Authors: James L. Walsh, J J Shi, Michael G. Kong
    Abstract:

    Pulsed excitation of cold atmospheric Plasmas is commonly believed to offer valuable benefits compared to the mainstream sinusoidal excitation. However, direct comparison of pulsed and sinusoidal atmospheric Plasmas remains few, if any, thus casting an uncertainty of whether pulsed excitation facilitates any significant advantage. In this letter, we report a comparison study of pulsed and sinusoidal cold atmospheric Plasma Jets through electrical characterization, gas temperature measurement, and optical detection of reactive Plasma species. An example of pulsed excitation is shown to reduce the electrical energy consumption by a factor of 12 for producing the same amount of oxygen atoms.