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Ute Ebert - One of the best experts on this subject based on the ideXlab platform.

  • the physics of Streamer Discharge phenomena
    Plasma Sources Science and Technology, 2020
    Co-Authors: Sander S Nijdam, Jannis Teunissen, Ute Ebert
    Abstract:

    In this review we describe a transient type of gas Discharge which is commonly called a Streamer Discharge, as well as a few related phenomena in pulsed Discharges. Streamers are propagating ionization fronts with self-organized field enhancement at their tips that can appear in gases at (or close to) atmospheric pressure. They are the precursors of other Discharges like sparks and lightning, but they also occur in for example corona reactors or plasma jets which are used for a variety of plasma chemical purposes. When enough space is available, Streamers can also form at much lower pressures, like in the case of sprite Discharges high up in the atmosphere. We explain the structure and basic underlying physics of Streamer Discharges, and how they scale with gas density. We discuss the chemistry and applications of Streamers, and describe their two main stages in detail: inception and propagation. We also look at some other topics, like interaction with flow and heat, related pulsed Discharges, and electron runaway and high energy radiation. Finally, we discuss Streamer simulations and diagnostics in quite some detail. This review is written with two purposes in mind: First, we describe recent results on the physics of Streamer Discharges, with a focus on the work performed in our groups. We also describe recent developments in diagnostics and simulations of Streamers. Second, we provide background information on the above-mentioned aspects of Streamers. This review can therefore be used as a tutorial by researchers starting to work in the field of Streamer physics.

  • electron density fluctuations accelerate the branching of positive Streamer Discharges in air
    Physical Review E, 2011
    Co-Authors: A Luque, Ute Ebert
    Abstract:

    : Branching is an essential element of Streamer Discharge dynamics. We review the current state of theoretical understanding and recall that branching requires a finite perturbation. We argue that, in current laboratory experiments in ambient or artificial air, these perturbations can only be inherited from the initial state, or they can be due to intrinsic electron-density fluctuations owing to the discreteness of electrons. We incorporate these electron-density fluctuations into fully three-dimensional simulations of a positive Streamer in air at standard temperature and pressure. We derive a quantitative estimate for the ratio of branching length to Streamer diameter that agrees within a factor of 2 with experimental measurements. As branching without this noise would occur considerably later, if at all, we conclude that the intrinsic stochastic particle noise triggers branching of positive Streamers in air at atmospheric pressure.

  • probing background ionization positive Streamers with varying pulse repetition rate and with a radioactive admixture
    arXiv: Plasma Physics, 2011
    Co-Authors: Sander S Nijdam, Ute Ebert, Gideon Wormeester, Van Em Eddie Veldhuizen
    Abstract:

    Positive Streamers need a source of free electrons ahead of them to propagate. A Streamer can supply these electrons by itself through photo-ionization, or the electrons can be present due to external background ionization. Here we investigate the effects of background ionization on Streamer propagation and morphology by changing the gas composition and the repetition rate of the voltage pulses, and by adding a small amount of radioactive Krypton 85. We find that the general morphology of a positive Streamer Discharge in high purity nitrogen depends on background ionization: at lower background ionization levels the Streamers branch more and have a more feather-like appearance. This is observed both when varying the repetition rate and when adding Krypton 85, though side branches are longer with the radioactive admixture. But velocities and minimal diameters of Streamers are virtually independent of the background ionization level. In air, the inception cloud breaks up into Streamers at a smaller radius when the repetition rate and therefore the background ionization level is higher. When measuring the effects of the pulse repetition rate and of the radioactive admixture on the Discharge morphology, we found that our estimates of background ionization levels are consistent with these observations; this gives confidence in the estimates. Streamer channels generally do not follow the paths of previous Discharge channels for repetition rates of up to 10 Hz. We estimate the effect of recombination and diffusion of ions and free electrons from the previous Discharge and conclude that the old trail has largely disappeared at the moment of the next voltage pulse; therefore the next Streamers indeed cannot follow the old trail.

  • boltzmann equation analysis of electron transport in a n2 o2 Streamer Discharge
    Japanese Journal of Applied Physics, 2011
    Co-Authors: Ute Ebert, S Dujko, R D White, Zoran Lj Petrovic
    Abstract:

    A comprehensive investigation of electron transport in N2–O2 mixtures has been carried out using a multi term theory for solving the Boltzmann equation instead of conventional two term theory often employed in plasma modeling community. We focus on the way in which the transport coefficients and spatially resolved transport data are influenced by the amount of O2 in the mixture. Emphasis is placed upon the explicit and implicit effects of non-conservative collisions, ionization and attachment on various transport coefficients. In particular, the effects of three-body attachment for electrons on various transport data are considered. It is found that the differences between two sets of transport coefficients, bulk and flux, resulting from the explicit influence of non-conservative collisions is sensitive to the quantity of O2 in the mixture.

P V Bulat - One of the best experts on this subject based on the ideXlab platform.

  • ignition and combustion of air fuel mixture in a long tube induced by microwave subcritical Streamer Discharge
    Acta Astronautica, 2019
    Co-Authors: Mikhail Pavlovich Bulat, I I Esakov, Petr Denissenko, L P Grachev, K N Volkov, P V Bulat, Igor Volobuev
    Abstract:

    Abstract There have been consistent efforts in developing more efficient combustion for propulsion systems. Ignition and combustion control using cold and non-thermal plasma in microwave Discharges have become a major topic of interest. In this study, a microwave subcritical Streamer Discharge is used to initiate ignition and combustion of premixed air/fuel mixture in a long cylindrical tube. The Streamer Discharge is arising on the internal surface of the dielectric tube using a passive vibrator in a single pulse regime at atmospheric pressure and temperature. The propagation speed of the combustion front in the quartz cylindrical tube filled by the air/propane mixture is analyzed experimentally and numerically. The Streamer Discharge creating a multitude of ignition points provides practically instantaneous ignition of the mixture in the entire volume. The speed of Streamer induced combustion front has been shown to be higher compared to that initiated by a spark. Increasing the length of Streamer Discharge leads to increasing the flame propagation speed. The combustion efficiency has also been shown to be higher when using the microwave Streamer ignition.

  • ignition of premixed air fuel mixtures by microwave Streamer Discharge
    Combustion and Flame, 2019
    Co-Authors: Petr Denissenko, I I Esakov, Igor Volobuev, Mikhail Pavlovich Bulat, L P Grachev, K N Volkov, Vladimir Upyrev, P V Bulat
    Abstract:

    Abstract A variety of methods exists for fast and efficient combustion of air-fuel mixtures. In this study, a microwave subcritical Streamer Discharge is used to ignite propane-air mixtures at atmospheric pressure. The Streamer is initiated at the inner surface of a dielectric tube with the help of a passive half-wave vibrator. By creating a network of ignition lines, the Streamer Discharge forms the network of burning channels with large total surface area. This leads to the apparent speed of combustion propagation along the cylinder in excess of 100 m/s, which is more than 200 times the laminar flame propagation speed. The axial propagation of the combustion front in a cylindrical tube filled with the air/propane mixture is investigated by high speed video recording in visible light. A simple model is presented to explain observed results.

  • ignition of lean and stoichiometric air propane mixture with a subcritical microwave Streamer Discharge
    Acta Astronautica, 2017
    Co-Authors: Mikhail Pavlovich Bulat, I I Esakov, Petr Denissenko, L P Grachev, K N Volkov, P V Bulat, I A Volobuev
    Abstract:

    Abstract Pulse detonation engines are considered to be one of effective propulsion systems for future space missions. Significant efforts are being spent on acceleration of fuel combustion and rising is efficiency. Existing studies have mainly focused on optimizing fuel injection and mixing, repetitive initiation of detonation and integration of detonation tubes with fuel inlets. Understanding of Streamer propagation mechanism is of essential importance for the studies of electrical breakdown phenomena and their related applications. In this study, a subcritical microwave Streamer Discharge is used to initiate ignition of air–fuel mixtures. Ignition of lean fuel mixtures by a Streamer has been demonstrated at atmospheric pressure. The speed of Streamer-initiated combustion has been shown to be higher compared to that initiated by a spark. The combustion efficiency has also been shown to be higher when using the microwave Streamer ignition.

Ryo Ono - One of the best experts on this subject based on the ideXlab platform.

  • effect of oxygen concentration on the postDischarge decay of hydroxyl density in humid nitrogen oxygen pulsed Streamer Discharge
    Journal of Physics D, 2020
    Co-Authors: Ryo Ono, Xiang Zhang, Atsushi Komuro
    Abstract:

    In this study, the effect of oxygen (O2) concentration in the range of 0.0001% (= 1 ppm) to 20% on the decay of OH density after pulsed Streamer Discharge is examined in a humid nitrogen-oxygen mixture under atmospheric pressure. The decay of OH density was measured using laser-induced fluorescence and compared with one-dimensional postDischarge simulations. The simulation results are consistent with the measured decay of OH density for all O2 concentrations. Essentially, the OH decay was double exponential, consisting of initial rapid decay for t 1 ms, where t represents the postDischarge time. In the slow decay phase, O2 change in the order of 10 ppm markedly affected the OH decay rate when O2 < 100 ppm. The sensitive effect of the small amount of O2 can be attributed to the reaction, H + O2 + M → HO2 + M, which converts H atoms to HO2, and the subsequent OH production via H + HO2 → OH + OH. Other production and loss processes of OH in the postDischarge phase were also examined.

  • rapid temperature increase near the anode and cathode in the afterglow of a pulsed positive Streamer Discharge
    Journal of Physics D, 2018
    Co-Authors: Ryo Ono
    Abstract:

    The spatiotemporal evolution of the temperature in the afterglow of point-to-plane, pulsed positive Streamer Discharge was measured near the anode tip and cathode surface using laser-induced predissociation fluorescence of OH radicals. The temperature exhibited a rapid increase and displayed a steep spatial gradient after a Discharge pulse. The rate of temperature rise reached 84 K μs−1 at mm, where z represents the distance from the anode tip. The temperature rise was much faster than in the middle of the gap; it was only 2.8 K μs−1 at mm. The temperature reached 1700 K near the anode tip at s and 1500 K near the cathode surface at s, where t represents the postDischarge time. The spatial gradient reached 1280 K mm−1 near the anode tip at s. The mechanism responsible for the rapid temperature increase was discussed, including rapid heating of the gas in the early postDischarge phase (s), and vibration-to-translation energy transfer in the later postDischarge phase (s). The high temperatures near the anode tip and cathode surface are particularly important for the ignition of combustible mixtures and for surface treatments, including solid-surface treatments, water treatments, and plasma medicine using pulsed Streamer Discharges.

  • two dimensional electron density measurement of pulsed positive primary Streamer Discharge in atmospheric pressure air
    Journal of Physics D, 2017
    Co-Authors: Yuki Inada, Ryo Ono, Kaiho Aono, Akiko Kumada, Kunihiko Hidaka, Mitsuaki Maeyama
    Abstract:

    Elucidating the electron density of Streamer Discharges propagating in atmospheric-pressure air is critical for achieving a systematic understanding of the production mechanisms of reactive species. Using Shack–Hartmann-type laser wavefront sensors with a temporal resolution of 2 ns, we carried out single-shot two-dimensional electron density measurements for positive primary Streamers generated in a 13 mm air gap between pin-to-plate electrodes. The electron density over the positive primary Streamers decayed from 1015 to during the propagation. The decay time constant of the electron density in the primary Streamer channels was estimated to be ~2 ns. The distribution widths of the electron density were in good agreement with those of the light emission, typically ranging from 0.8 to 1.5 mm.

  • anti tumor immune response induced by nanosecond pulsed Streamer Discharge in mice
    Journal of Physics D, 2017
    Co-Authors: Kazue Mizuno, Kenta Yonetamari, Yuki Shirakawa, Taketoshi Akiyama, Ryo Ono
    Abstract:

    Plasma is known to activate immune cells in vitro; however, its effect on cancer immunotherapy is not well understood in vivo. In this study, we report B16–F10 tumor growth suppression at a non-irradiated site on a mouse leg after a nanosecond pulsed Streamer Discharge was applied to the tumor on the other leg. The tumor growth suppression at non-irradiated remote sites was observed from the day next to that of plasma irradiation: the rapid abscopal effect suggests innate immune response activation. Additionally, the production of inflammatory cytokines from splenocytes was enhanced after plasma irradiation. This suggests the activation of adaptive immune response specific to B16–F10 melanoma by plasma irradiation.

  • measurement of oh o and no densities and their correlations with mouse melanoma cell death rate treated by a nanosecond pulsed Streamer Discharge
    Journal of Physics D, 2015
    Co-Authors: Ippei Yagi, Ryo Ono, Kazue Mizuno, Yuki Shirakawa, Taketoshi Akiyama, Kenta Hirakata, Seiya Yonemori, Tetsuji Oda
    Abstract:

    Mouse melanoma cells in a culture medium are treated using a nanosecond pulsed Streamer Discharge plasma and the correlations between the rate of cell death and the densities of reactive species (OH, O, and NO) in the plasma are measured. The plasma is irradiated onto the culture medium surface with a vertical gas flow of an O2/N2 mixture from a glass tube at various gas flow rates and O2 concentrations. The densities of the reactive species are measured very close to the culture medium surface, where the reactive species interact with the culture medium, using laser-induced fluorescence. In the case of the N2 Discharge (O2 = 0%), an increase in gas flow rate decreases OH density because it lowers the water vapor concentration by diluting the vapor, which is required for OH production. The increase in gas flow rate also leads to a decreased cell death rate. In the case of the O2/N2 Discharge, on the other hand, an increase in O2 concentration at a fixed flow rate does not affect the rate of cell death, although it considerably changes the O and NO densities. These findings indicate that some reactive species derived from water vapor such as OH are responsible for the melanoma cell death, whereas those from O2, such as O and NO, are less likely responsible. They also indicate the importance of water evaporation from the culture medium surface in cell treatment.

Tetsuji Oda - One of the best experts on this subject based on the ideXlab platform.

  • measurement of oh o and no densities and their correlations with mouse melanoma cell death rate treated by a nanosecond pulsed Streamer Discharge
    Journal of Physics D, 2015
    Co-Authors: Ippei Yagi, Ryo Ono, Kazue Mizuno, Yuki Shirakawa, Taketoshi Akiyama, Kenta Hirakata, Seiya Yonemori, Tetsuji Oda
    Abstract:

    Mouse melanoma cells in a culture medium are treated using a nanosecond pulsed Streamer Discharge plasma and the correlations between the rate of cell death and the densities of reactive species (OH, O, and NO) in the plasma are measured. The plasma is irradiated onto the culture medium surface with a vertical gas flow of an O2/N2 mixture from a glass tube at various gas flow rates and O2 concentrations. The densities of the reactive species are measured very close to the culture medium surface, where the reactive species interact with the culture medium, using laser-induced fluorescence. In the case of the N2 Discharge (O2 = 0%), an increase in gas flow rate decreases OH density because it lowers the water vapor concentration by diluting the vapor, which is required for OH production. The increase in gas flow rate also leads to a decreased cell death rate. In the case of the O2/N2 Discharge, on the other hand, an increase in O2 concentration at a fixed flow rate does not affect the rate of cell death, although it considerably changes the O and NO densities. These findings indicate that some reactive species derived from water vapor such as OH are responsible for the melanoma cell death, whereas those from O2, such as O and NO, are less likely responsible. They also indicate the importance of water evaporation from the culture medium surface in cell treatment.

  • two dimensional lif measurements of humidity and oh density resulting from evaporated water from a wet surface in plasma for medical use
    Plasma Sources Science and Technology, 2014
    Co-Authors: Ippei Yagi, Ryo Ono, Tetsuji Oda, Koichi Takaki
    Abstract:

    In plasma medicine, plasma is applied to a wet surface and is often accompanied by dry-gas flow. The dry-gas flow affects water evaporation from the wet surface and influences production of reactive species derived from water vapor, such as OH radicals. In this study, the effect of the dry-gas flow on two-dimensional distributions of humidity and OH radical density are examined by measuring them using laser-induced fluorescence (LIF). First, humidity is measured when nitrogen flows from a quartz tube of 4 mm inner diameter onto distilled water and agar media from 5 mm distance. NO gas is added to the nitrogen as a tracer and humidity is obtained from the quenching rate of NO molecules measured using LIF. This measurement has a spatial resolution of 0.2 mm3 and a temporal resolution of less than 220 ns. The two-dimensional humidity distribution shows that the dry-gas flow pushes away water vapor evaporating from the wet surface. As a result, a low-humidity region is formed near the quartz tube nozzle and a high-humidity region is formed near the wet surface. The thickness of the low-humidity region reduces with increasing gas flow rate. It is 0.1–0.5 mm for the flow rate of higher than 0.3 l min−1. Next, the OH density is measured when a nanosecond pulsed Streamer Discharge is applied to a distilled water surface with dry-air flow. The OH density decreases with increasing gas flow rate due to decreased humidity. When the flow rate is lower than 0.1 l min−1, the OH distribution is approximately uniform in the plasma region, while the humidity distribution shows a large gradient. The importance of the thin high-humidity region on the flux of reactive species onto the wet surface is discussed.

  • effects of pulse voltage rise rate on velocity diameter and radical production of an atmospheric pressure Streamer Discharge
    Plasma Sources Science and Technology, 2013
    Co-Authors: Atsushi Komuro, Ryo Ono, Tetsuji Oda
    Abstract:

    The effect of pulse rise rate on a Streamer Discharge is investigated through both experiments and simulations. Pulsed voltages with a pulse rise rate of 0.11–0.52 kV ns−1 are applied to point-to-plane electrode configurations, and the effects are observed from ICCD photographs. The Streamer emission of light is simulated by a previously developed two-dimensional Streamer simulation model, and the simulation results are compared with experimental results. The results show that as the pulse rise rate is decreased, there is a decrease in the Discharge current, velocity of the primary Streamer, diameter of the Streamer channel and emission length of the secondary Streamer. The simulated reduced electric field of the primary Streamer head remains constant and does not depend on the pulse rise rate. The simulated temporal variations of O and OH radical production show that almost the same number of the radicals are produced in the primary Streamer, regardless of the pulse rise rate. However, the radical production in the secondary Streamer decreases as the pulse rise rate decreases. Therefore, the pulse rise rate affects the ratio of radical production in the primary Streamer to that in the secondary Streamer.

  • behaviour of oh radicals in an atmospheric pressure Streamer Discharge studied by two dimensional numerical simulation
    Journal of Physics D, 2013
    Co-Authors: Atsushi Komuro, Ryo Ono, Tetsuji Oda
    Abstract:

    The production process of OH radicals in an atmospheric-pressure Streamer Discharge is studied. A Streamer Discharge model is developed to analyse the characteristics of a pulsed positive Streamer Discharge in point-to-plane electrodes filled with humid air at atmospheric pressure. The results indicate that the behaviour of OH radicals in and after the Discharge pulse is characterized by three reaction processes: ‘OH-production’, ‘OH-cycle’ and ‘OH-recombination’. The first process of OH-production includes dissociation reactions of H2O with O(1D) and N2 , which are the main production processes of OH in the Discharge. Immediately after the OH-production process, the OH radicals are destroyed by a reaction with O(3P) to form O2 and H. Then the subsequent reactions produce OH again through the reaction of H + HO2, which is the OH-cycle process. Finally, the OH radicals are consumed by the OH-recombination process.

  • numerical simulation for production of o and n radicals in an atmospheric pressure Streamer Discharge
    Journal of Physics D, 2012
    Co-Authors: Atsushi Komuro, Ryo Ono, Tetsuji Oda
    Abstract:

    A Streamer Discharge model is developed to analyse the characteristics of a pulsed positive Streamer Discharge in point-to-plane electrodes filled with oxygen–nitrogen mixed gas at room temperature and atmospheric pressure. In this paper we study the mechanisms of O and N radical production in an atmospheric-pressure Streamer Discharge. To confirm the validity of the simulation model, the Discharge emission of light and the Discharge current are compared with experimental data at several voltages in gas mixtures with 2–20% oxygen concentrations. The calculated streak picture and the axial distribution of Streamer luminous intensity are in good agreement with our previous experimental results. After demonstrating the reliability of the model, we performed a numerical study on radical production by the Streamer Discharge. The experimentally obtained axial distributions of oxygen radical production in O2(20%)/N2 and nitrogen radical production in O2(2%)/N2 are successfully reproduced in our simulation. For the production of nitrogen radicals, two-step dissociation through the vibrationally excited states is predominant.

Alexander Lindsay - One of the best experts on this subject based on the ideXlab platform.

  • Momentum, Heat, and Neutral Mass Transport in Convective Atmospheric Pressure Plasma-Liquid Systems and Implications for Aqueous Targets
    Journal of Physics D: Applied Physics, 2015
    Co-Authors: Alexander Lindsay, Carly Anderson, Elmar Slikboer, Steven Shannon, David B. Graves
    Abstract:

    There is a growing interest in the study of plasma-liquid interactions with application to biomedicine, chemical disinfection, agriculture, and other fields. This work models the momentum, heat, and neutral species mass transfer between gas and aqueous phases in the context of a Streamer Discharge; the qualitative conclusions are generally applicable to plasma-liquid systems. The problem domain is discretized using the finite element method. The most interesting and relevant model result for application purposes is the steep gradients in reactive species at the interface. At the center of where the reactive gas stream impinges on the water surface, the aqueous concentrations of OH and ONOOH decrease by roughly 9 and 4 orders of magnitude respectively within 50 m of the interface. Recognizing the limited penetration of reactive plasma species into the aqueous phase is critical to discussions about the therapeutic mechanisms for direct plasma treatment of biological solutions. Other interesting results from this study include the presence of a 10 K temperature drop in the gas boundary layer adjacent to the interface that arises from convective cooling. Though the temperature magnitudes may vary among atmospheric Discharge types (different amounts of plasma-gas heating), this relative difference between gas and liquid bulk temperatures is expected to be present for any system in which convection is significant. Accounting for the resulting difference between gas and liquid bulk temperatures has a significant impact on reaction kinetics; factor of two changes in terminal aqueous species concentrations like H2O2, NO, and NO are observed in this study if the effect of evaporative cooling is not included.

  • Momentum, heat, and neutral mass transport in convective atmospheric pressure plasma-liquid systems and implications for aqueous targets
    Journal of Physics D: Applied Physics, 2015
    Co-Authors: Alexander Lindsay, Carly Anderson, Elmar Slikboer, Steven Shannon, David Graves
    Abstract:

    There is a growing interest in the study of plasma-liquid interactions with application to biomedicine, chemical disinfection, agriculture, and other fields. This work models the momentum, heat, and neutral species mass transfer between gas and aqueous phases in the context of a Streamer Discharge; the qualitative conclusions are generally applicable to plasma-liquid systems. The problem domain is discretized using the finite element method. The most interesting and relevant model result for application purposes is the steep gradients in reactive species at the interface. At the center of where the reactive gas stream impinges on the water surface, the aqueous concentrations of OH and ONOOH decrease by roughly 9 and 4 orders of magnitude respectively within 50 $\mu$m of the interface. Recognizing the limited penetration of reactive plasma species into the aqueous phase is critical to discussions about the therapeutic mechanisms for direct plasma treatment of biological solutions. Other interesting results from this study include the presence of a 10 K temperature drop in the gas boundary layer adjacent to the interface that arises from convective cooling and water evaporation. Accounting for the resulting difference between gas and liquid bulk temperatures has a significant impact on reaction kinetics; factor of two changes in terminal aqueous species concentrations like H$_2$O$_2$, NO$_2^-$, and NO$_3^-$ are observed if the effect of evaporative cooling is not included.