Low-temperature Discharge Plasma Research Articles

Dielectric barrier discharge low-temperature plasma modification of bamboo charcoal for supercapacitor applications

Biochar is commonly utilized as an electrode material in supercapacitors. However, the conventional carbonization process often results in macromolecular compounds, which obstruct the porous structure of carbon materials, thereby reducing their capacitance. Dielectric barrier discharge low-temperature plasma (DLTP) is a technology that transforms gases into highly excited states, utilizing high-energy particles for enhanced energy applications. This study investigated the effects of DLTP on the electrochemical performance of bamboo charcoal (BC), utilizing bamboo shavings (BS) as the carbon source. The results indicated that the specific capacitance of BC varied under different atmospheric conditions, input voltages, and treatment durations, thereby achieving a maximum increase of 144 F/g. Furthermore, when combined with KOH activation, DLTP modification further enhanced the specific capacitance of BC to 237 F/g. The DLTP treatment enhanced the specific surface area and the types of functional groups in BC, thereby leading to a significant enhancement of its electrochemical properties.

Advances in Particle-In-Cell Modeling of Low-Temperature Plasma Ion Sources

Ion sources that use low-temperature plasma (LTP) discharges are used in a variety of applications, including ion implantation, mass spectrometry, and plasma processing. In recent years there has been a growing interest in using particle-in-cell (PIC) modeling to improve the performance and optimization of LTP-based ion sources. PIC modeling is a powerful tool for simulating the dynamics of plasmas because it accurately models the effects of self-consistent fields, charge deposition, plasma chemistry, magnetic confinement, and accurate sheath physics. However, PIC simulations can be computationally demanding, especially for 3D systems.We present new advances in PIC modeling of LTP ion sources. We focus on two key challenges: 1. Efficient and accurate modeling of plasma chemistry: Plasma chemistry is a complex process that can have a significant impact on the performance of LTP ion sources. We demonstrate using global models to reduce the computational cost of plasma chemistry simulations, and diagnostics for understanding the physics of those reactions. 2. Energy-conserving PIC models: PIC simulations typically require a fine spatial grid in order to resolve the Debye length. This can be computationally expensive, especially for 3D systems. We present a new energy-conserving PIC model implementation that allows us to perform simulations without resolving the Debye length. We validate these methods on two different types of LTP ion sources: a Bernas source and a Penning source. Our results show that these methods can significantly improve the efficiency and accuracy of PIC simulations of LTP-based ion sources.

Analysis of Hydrogen Combustion in a Spark Ignition Research Engine with a Barrier Discharge Igniter

Hydrogen fuel is gaining particular attention in internal combustion engines. In addition to zero-carbon emissions, major advantages relate to its combustion characteristics, which allow a significant increase in thermal efficiency under ultra-lean operation and with very low NOx levels. The ignition system is one of the main technology enablers, as it determines the capability to control ultra-lean operations, avoid backfire phenomena, and/or reduce the risks of abnormal combustions. The latter results from hydrogen’s low ignition energy and it is associated with factors like high-temperature residuals, hot spots, and irregular spark plug discharge. The ACIS gen 2-Barrier Discharge Igniter excels in accelerating the initial flame growth speed by the generation of non-equilibrium low-temperature plasma, a strong ignition promoter for the combined action of kinetic and thermal effects. Moreover, its volumetric discharge facilitates combustion initiation on a wide region, in contrast to the localized ignition of traditional spark systems. In this work we present for the first time, to the best of our knowledge, experimental results showing the performance of a hydrogen engine with a low-temperature plasma discharge. Tests were conducted on a single-cylinder research engine, achieving ultra-lean conditions with cycle-to-cycle variability results below 2.5%. The analysis indicates that the H2-BDI combined solution is capable of accelerating the evolution of the flame front compared to traditional spark plugs, leading to a significant reduction in the cycle-to-cycle variability. A meticulous adjustment of the BDI control parameters further enhances igniter performance and contributes to a deeper understanding of the innovative approach proposed in this study.

Low-temperature plasma-assisted synthesis of iron and nitrogen co-doped CoFeP-N nanowires for high-efficiency electrocatalytic water splitting

Designing efficient, stable, and low-cost non-precious metal electrocatalysts is critical for gainful utilization of renewable resources and effective water splitting. The catalytic efficiency is determined by interactions between the multiple main constituent elements and dopants. However, achieving performance-boosting synergistic interactions between different species in the catalyst is challenging. This work demonstrates such effect using low-temperature plasma-enhanced hydrothermal-phosphorization synthesis of Fe, N co-doped CoFeP-N nanowires. Nickel foam was utilized as the substrate to prepare CoFe-LDH precursor by hydrothermal method and CoFeP nanoparticles were obtained by phosphorization in a tube furnace. The N element was further doped into CoFeP using a low-temperature plasma discharge. The produced CoFeP-N nanowires exhibit far superior hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) activities in an alkaline medium compared to the original CoP due to the incorporation of Fe and N elements, with overpotentials of 64 mV and 219 mV at 10 mA cm−2 respectively, and excellent cycling stability. When CoFeP-N is used as both the cathode and anode of a two-electrode water splitting device, low voltages of only 1.516 V and 1.636 V were needed to achieve current density of 10 mA cm−2 and100 mA cm−2 respectively, which are better than that of Pt/C||RuO2 and most non-precious metal-based electrocatalysts reported to date. These experimental results provide new insights and strategies for developing efficient, stable, and low-cost bifunctional water splitting electrocatalysts.

Numerical thermalization in 2D PIC simulations: Practical estimates for low-temperature plasma simulations

The process of numerical thermalization in particle-in-cell (PIC) simulations has been studied extensively. It is analogous to Coulomb collisions in real plasmas, causing particle velocity distributions (VDFs) to evolve toward a Maxwellian as macroparticles experience polarization drag and resonantly interact with the fluctuation spectrum. This paper presents a practical tutorial on the effects of numerical thermalization in 2D PIC applications. Scenarios of interest include simulations, which must be run for many thousands of plasma periods and contain a population of cold electrons that leave the simulation space very slowly. This is particularly relevant to many low-temperature plasma discharges and materials processing applications. We present numerical drag and diffusion coefficients and their associated timescales for a variety of grid resolutions, discussing the circumstances under which the electron VDF is modified by numerical thermalization. Though the effects described here have been known for many decades, direct comparison of analytically derived, velocity-dependent numerical relaxation timescales to those of other relevant processes has not often been applied in practice due to complications that arise in calculating thermalization rates in 1D simulations. Using these comparisons, we estimate the impact of numerical thermalization in several examples of low-temperature plasma applications including capacitively coupled plasma discharges, inductively coupled plasma discharges, beam plasmas, and hollow cathode discharges. Finally, we discuss possible strategies for mitigating numerical relaxation effects in 2D PIC simulations.

In-Situ FTIR and Laser Induced Fluorescence RONS Characterization of Atmospheric Pressure Nanosecond-Pulsed Surface DBD Plasma for Indirect Treatments of E. Coli

We study the bactericidal efficacy of surface dielectric barrier discharge low-temperature plasma treatments, powered by nanosecond high voltage pulses. We achieve ∼\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim $$\\end{document}4-log reduction in Escherichia coli population, after 10 min treatments, at a distance of 1.5 cm from the plasma surface. To investigate the reactive oxygen and nitrogen species (RONS) responsible for the bactericidal effect, we employ in-situ fourier transform infrared (FTIR) spectroscopy to measure a selection of relevant species, such as O3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_3$$\\end{document}, NO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_2$$\\end{document}, N2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_2$$\\end{document}O and N2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_2$$\\end{document}O5\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_5$$\\end{document}. The measurements are taken under various relative humidity conditions to replicate the bacteria treatment environment. While RONS originating from nitrogen chemistry are detected, nitric oxide (NO), a pivotal molecule in nitrate production, is absent due to the sensitivity limitations of FTIR detection. To overcome this limitation, we employ laser induced fluorescence utilizing a picosecond-pulsed laser to measure the kinetics of NO produced by the plasma. Our results show that the NO concentration is smaller than 1 ppm and primarily localized near the plasma surface, with concentrations increasing proportionally with relative humidity. Notably, at a distance of 1.5 cm from the plasma surface, at which the E. coli is treated, the concentration of NO falls below 50 ppb. Although NO is pivotal in generating secondary reactive species within the plasma, our results suggest that it does not directly contribute to the bacteria inactivation process. Instead, other molecules, such as O3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_3$$\\end{document}, NO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_2$$\\end{document}, and N2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_2$$\\end{document}O, which are found in higher concentrations, may be responsible for the bactericidal properties observed in indirect plasma treatments.

Study on atomization of grounding electrodes under the influence of magnetic field for dedusting and desulfurization of negative corona discharge

Corona discharge low-temperature plasma technology has good performance in treating dust and removing gaseous pollutants. In this paper, the dust and SO2 in the flue gas are removed by using the ground electrode atomization negative corona discharge device under the action of a magnetic field, and the discharge characteristics of the device, the removal efficiency of dust and sulfur dioxide, and its influencing factors are studied. The results show that the discharge characteristics and dust removal and desulfurization efficiency of the ground electrode atomization negative corona discharge under the action of a magnetic field are superior to the traditional l corona discharge and are almost affected by the extension of the operating time. Finally, the ground electrode atomization negative corona discharge under the action of a magnetic field is analyzed. The dust removal and desulfurization mechanism of corona discharge provide a reference for the development of dust removal and integrated desulfurization equipment.

Применение обработанной плазмой воды для подготовки семян хвойных пород к посеву

The article discusses the accelerated cultivation of quality planting material using the method of seed preparation by soaking in water treated in low-temperature plasma discharge. The most promising planting material are seedlings with closed root system. They are grown from improved seed grain in optimal conditions of greenhouses. Among various methods of stimulating germination of the seed germ, it is of interest to influence it with “cold” plasma. With the help of a specially designed device, which allows to treat water with lowtemperature plasma discharge, plasma-treated water for soaking seeds was obtained. The time of water treatment varied from 1 to 4 min. Water activated by plasma had acidity indicators other than those of ordinary water. The time of acidity level restoration was from 2 to 4 days. Germination rates and germination energy were obtained for seeds of Pinus silvestrys and Picea abies soaked in water with different duration of plasma treatment. When seeds were soaked in water treated with plasma for 1, 2 and 4 min, germination energy increased by 20–31 % for pine and by 6–18 % for spruce compared to the control (soaking in distilled water). Technical germination of pine seeds increased by 11–21 %, for spruce by 3–16 %. The results of research show changes in the structure and composition of the nutrient substance of the seed, in the structure of the germ and the degree of its development. Analysis of the chemical composition of seed endosperm a day after soaking relative to dry seeds showed an increase in its carbon content by 2–3 % and a decrease in oxygen by 1 %; potassium – by 0.5 %. When seeds were soaked in distilled water, the content of phosphorus in the endosperm decreased by 0.15 %, and the content of sodium – by 0.2 %. For seeds soaked in plasma treated water, phosphorus content decreased by 0.21–0.22 % and sodium content was not observed. Soaking seeds in plasma-treated water stimulates the processes of their preparation for germination and differentiation of germ tissues (formation of seed pods), compared to seeds soaked in water. For citation: Gavrilova O.I., Gostev K.V. Use of Plasma-treated Water to Prepare Seeds of Coniferous Species for Sowing. Lesnoy Zhurnal = Russian Forestry Journal, 2023, no. 5, pp. 204–211. (In Russ.). https://doi.org/10.37482/0536-1036-2023-5-204-211

Effect of Nitrogen Arc Discharge Plasma Treatment on Physicochemical Properties and Biocompatibility of PLA-Based Scaffolds.

The effect of low-temperature arc discharge plasma treatment in a nitrogen atmosphere on the modification of the physicochemical properties of PLA-based scaffolds was studied. In addition, the cellular-mediated immune response when macrophages of three donors interact with the modified surfaces of PLA-based scaffolds was investigated. PLA surface carbonization, accompanied by a carbon atomic concentration increase, was revealed to occur because of plasma treatment. Nitrogen plasma significantly influenced the PLA wettability characteristics, namely, the hydrophilicity and lipophilicity were improved, as well as the surface energy being raised. The viability of cells in the presence of the plasma-modified PLA scaffolds was evaluated to be higher than that of the initial cells.

Similarity theory and scaling laws for low-temperature plasma discharges: a comprehensive review

Similarity theory and scaling laws for low-temperature plasma discharges: a comprehensive review

Design of Non-Thermal Plasma Alfalfa Seed Vigor Enhancement Device and Study of Treatment Effect

Highlights An effective seed treatment method is provided. Three generations of field growth trials were conducted. We Investigated the effects of low-temperature plasma treatment on the biological characters and yield components. Abstract. An atmospheric pressure, low-temperature dielectric barrier discharge (DBD) plasma seed treatment device was developed for plasma seed treatment. The device worked continuously on alfalfa seeds and evenly distributed the seeds in a plasma discharge range. The processing time, voltage amplitude, and frequency were adjustable. The device was used to study the effect of DBD plasma treatment at different voltages and times on alfalfa seed germination using untreated alfalfa seeds as the control (CK). The results showed that the DBD plasma treatment of alfalfa seeds promoted seed germination and seedling growth, and the optimal discharge conditions were a discharge voltage of 11 kV and a discharge time of 40 s. Compared with CK, the germination potential and germination rate increased by 12.49% and 18.08%, respectively. After treatment using the optimal discharge time, the germination potential, germination rate, dry weight, and seedling height increased by 9.9%, 16.1%, 15%, and 32.9%, respectively, compared with CK. The Scanning Electron Microscope images of the seed epidermis treated with 11 kV and 40 s plasma showed that the surface of alfalfa seeds was etched. Different doses of discharge radiation had different effects on physiological processes in seeds, and their sensitivity to plasma discharge was different. In a certain range, the germination rate, germination potential, fresh weight, dry weight, root length, and seedling height of alfalfa seeds improved to different degrees under different discharge voltages and times. Plasma has a good application prospect for improving the growth of alfalfa seeds. Keywords: Alfalfa, Dielectric barrier discharge plasma, Germination, Seed treatment device, Seedling growth.

Computational Fluid Dynamics Modeling of Low Temperature Ignition Processes From a Nanosecond Pulsed Discharge at Quiescent Conditions

Abstract Recent interest in nonequilibrium plasma discharges as sources of ignition for the automotive industry has not yet been accompanied by the availability of dedicated models to perform this task in computational fluid dynamics (CFD) engine simulations. The need for a low-temperature plasma (LTP) ignition model has motivated much work in simulating these discharges from first principles. Most ignition models assume that an equilibrium plasma comprises the bulk of discharge kernels. LTP discharges, however, exhibit highly nonequilibrium behavior. In this work, a method to determine a consistent initialization of LTP discharge kernels for use in engine CFD codes like converge is proposed. The method utilizes first principles discharge simulations. Such an LTP kernel is introduced in a flammable mixture of air and fuel, and the subsequent plasma expansion and ignition simulation is carried out using a reacting flow solver with detailed chemistry. The proposed numerical approach is shown to produce results that agree with experimental observations regarding the ignitability of methane-air and ethylene-air mixtures by LTP discharges.

Low-Temperature Barrier Discharge Plasma Modification of Scaffolds Based on Polylactic Acid.

We have explored the effect of low-temperature barrier discharge plasma treatment in oxygen, nitrogen, and argon on modification of the physicochemical properties of polylactic acid (PLA)-based scaffolds. The cellular-mediated immune response to the interaction of macrophages of three donors with the modified surface of PLA-based scaffolds was also investigated. Carbonization of the PLA surface accompanied by a carbon atomic concentration increase is shown to occur following plasma treatment. Argon plasma significantly affects the wettability characteristics of PLA; the hydrophilicity and lipophilicity are improved, and the surface energy is increased. The viability of cells in the presence of plasma-modified PLA scaffolds is lower than that for unmodified PLA but remains greater than that for the negative control. We find that PLA scaffolds do not cause increased expression of the proinflammatory (TNFα, IL-6, IL-1β) cytokines after 6 days of cell cultivation. At the same time, PLA scaffolds do not affect the increased production of anti-inflammatory cytokines (IL-10).

A Device for Activating Repair Processes Using Low-Temperature Plasma Discharges in Patients with Bedsores: Optimization of Parameters and Assessment of Efficacy

A Device for Activating Repair Processes Using Low-Temperature Plasma Discharges in Patients with Bedsores: Optimization of Parameters and Assessment of Efficacy

A spectral element method for modelling streamer discharges in low-temperature atmospheric-pressure plasmas

Streamers are ionization fronts that occur in gases at atmospheric and sub-atmospheric pressures. Numerical studies of streamers are important for practical applications but are challenging due to the multiscale nature of this discharge type. This paper introduces a spectral element method for modelling streamer discharges. The method is developed for Cartesian grids but can be extended to be used on unstructured meshes. The streamer model is based on the Poisson equation for the electric potential and the electron continuity equation. The Poisson equation is discretized via a spectral method based on the integral representation of the solution. The hierarchical Poincaré-Steklov (HPS) scheme is used to solve the resulting set of equations. The electron continuity equation is solved by means of the discontinuous Galerkin spectral element method (DGSEM). The DGSEM is extended by an alternative definition of the diffusion flux. A subcell finite volume method is used to stabilize the DGSEM scheme, if required. The entire simulation scheme is validated by solving a number of test problems and reproducing the results of previous studies. Adaptive mesh refinement is used to reduce the number of unknowns. The proposed method is found to be sufficiently fast for being used in practical applications. The flexibility of the method provides an interesting opportunity to broaden the range of problems that can be addressed in numerical studies of low-temperature plasma discharges.

Application of Polyethylene Terephthalate Films Containing Small-Volume Fluorine-Based Additives for Creating Electrets

A complex of methods, including atomic force microscopy and X-ray photoelectron spectroscopy, is used to study treated by low-temperature corona discharge plasma polyethylene terephthalate films containing small volume amounts of fluorine-based additives. It is determined that small amount of fluorine-containing additives presence leads to the improvement of the electret stability than in films without additives. The enhancement of electret state changes in chemical composition, and the structure of the polymer surface is caused by the migration of additives toward the film surface.

Kinetics of Low-Temperature Plasma-Assisted Ignition of Ethanol-Gasoline Surrogate under Gasoline Engine like Conditions

ABSTRACT The plasma-assisted reaction kinetic mechanism for high-voltage nanosecond discharge at high pressure was developed for lean and stoichiometric ethanol-gasoline surrogate/O2/N2/AR mixture. The numerical results show that plasma-assisted ignition of ethanol-gasoline surrogate is mainly associated with the electron impact dissociation of O2, nC7H16, iC8H18 and C2H5OH molecules and excited O2* produced from electron impact during discharge phase. The generation of H and O atoms, radicals and O2* facilitates plasma-assisted ignition (PAI). The formation of C2H5OH+, C8H18 + and O− increases ignition delay time. PAI improves the ignition stability of lean mixture mainly by increasing the reaction rate in reaction iC8H18+ HO2⇋C8H17+ H2O2. The reaction CH3+ HO2⇋CH4+ O2 promotes auto-ignition. But it delays the plasma-assisted ignition of stoichiometric mixture while it facilitates plasma-assisted ignition in lean mixture. The ignition delay time in lean-burn conditions can be shortened only by a proper timing of low-temperature plasma discharge at low temperature.

Development of liquid atomization technology with low-temperature plasma discharge

Non-thermal equilibrium plasma is a fundamental technology that supports the state-of-the-art plasma science and is applied in various industrial fields. In particular, surface modification by plasma has caused technological innovation in the biomedical field because it can improve the biocompatibility of medical devices composed of heat-sensitive materials. In recent years, many studies focusing on the interaction between plasma and liquids have been undertaken, and industrial applications, including in the medical field, are progressing. In this study, we developed a method to generate the nano-sized mist by passing a solution through the dielectric barrier discharge. With this method, the majority of the generated mist produced was found to be less than 400 nm in size. This method is also applicable to both water-based and oil-based solutions in the nano-sized mist generation. The newly developed method is expected to become a technology that can be applied to various industrial fields.

Electrode Design for Thermal and Nonthermal Plasma Discharge Inside a Constant Volume Combustion Chamber

Abstract Previous methods of achieving ignition in the Plasma, Combustion and Fluid imaging (PCFi) Laboratory’s Constant Volume Combustion Chamber (CVCC) utilizes either a standard or modified spark plug. The standard spark plug achieves a representation of side wall ignition (similar to a combustion engine), while the modified spark plug has an extended electrode to allow for a center camber ignition used for laminar burning speed (LBS) measurements. The creation of the modified spark plug required welding a stainless-steel (SS) wire to the electrode of the plug. This process is time consuming and requires a large quantity to effectively test a wide range of parameters such as gap size or electrode geometry. Two custom-design electrodes are presented in this paper which extend the experimental range of the PCFi’s CVCC system. Electrode Design A, gives the ability to test thin wire electrode with adjustability of gap size and different diameters through use of a compression fitting. This electrode design (i.e., tip-to-tip) is utilized with a traditional style of automotive ignition system (i.e., capacitive discharge) to study ignition process (i.e., thermal plasma) and spherical flame propagation. Electrode Design B, adds the ability to change tip geometry (i.e., plate-to-plate, tip-to-plate, tip-to-sphere, plate-to-sphere, etc.). In this paper, the plate-to-plate configuration is demonstrated to study uniform low-temperature nanosecond plasma discharge. Both electrode designs reduce structural weakness by removing the welded joint and allow for linear gap size adjustment. The electrode utilizes high-temperature epoxy, ceramic, and grafoil seals to make parameter adjustments easy and precise. The design was analyzed, prior to building and testing, based on the stress induced from the sealant, the total rated voltage, the rated temperature, and the fracture stress of the ceramic material. The stress induced in the electrodes was analyzed with finite element analysis (FEA) and the results were found to be within the limits of the material in terms of the compressive and fracture strengths. The maximum voltage was found to be around 30 kV. Design A is presented with three different electrode diameters of 1.3, 1, and 0.5 mm and Design B which utilizes a threaded connection for adjustable tip geometry. A sample of data, visual and electrical, is presented for the newly created electrode with a 0.5 mm diameter as well as combustion images for up to 10 atm of initial pressure for methane-air mixture. The new electrode design was able to survive several months of experimental use with few issues compared with the previous welded design.

Landau damping of electrons with bouncing motion in a radio-frequency plasma* *Project supported by the National Key Research and Development Program of China (Grant No. 2017YFE0300406) and the National Natural Science Foundation of China (Grant Nos. 11975272, 12075276, 11805133, 11705236, and 11375234).

One-dimensional particle simulations have been conducted to study the interaction between a radio-frequency electrostatic wave and electrons with bouncing motion. It is shown that bounce resonance heating can occur at the first few harmonics of the bounce frequency (nω b,n = 1,2,3,…). In the parameter regimes in which bounce resonance overlaps with Landau resonance, the higher harmonic bounce resonance may accelerate electrons at the velocity much lower than the wave phase velocity to Landau resonance region, enhancing Landau damping of the wave. Meanwhile, Landau resonance can increase the number of electrons in the lower harmonic bounce resonance region. Thus electrons can be efficiently heated. The result might be applicable for collisionless electron heating in low-temperature plasma discharges.