Plasma

19 pages, 1546 KiB

Open AccessArticle

Inactivation of Bioaerosol Particles in a Single-Pass Multi-Stage Non-Thermal Plasma and Ionization Air Cleaner

by Justinas Masionis, Darius Čiužas, Edvinas Krugly, Martynas Tichonovas, Tadas Prasauskas and Dainius Martuzevičius

Plasma 2025, 8(2), 22; https://doi.org/10.3390/plasma8020022 - 31 May 2025

Abstract

Bioaerosol particles contribute to the reduced indoor air quality and cause various health issues, thus their concentration must be managed. Air cleaning is one of the most viable technological options for reducing quantities of indoor air contaminants. This study assesses the effectiveness of [...] Read more.

Bioaerosol particles contribute to the reduced indoor air quality and cause various health issues, thus their concentration must be managed. Air cleaning is one of the most viable technological options for reducing quantities of indoor air contaminants. This study assesses the effectiveness of a prototype multi-stage air cleaner in reducing bioaerosol particle viability and concentrations. The single-pass type unit consisted of non-thermal plasma (NTP), ultraviolet-C (UV-C) irradiation, bipolar ionization (BI), and electrostatic precipitation (ESP) stages. The device was tested under controlled laboratory conditions using Escherichia coli (Gram-negative) and Lactobacillus casei (Gram-positive) bacteria aerosol at varying airflow rates (50–600 m³/h). The device achieved over 99% inactivation efficiency for both bacterial strains at the lowest airflow rate (50 m³/h). Efficiency declined with increasing airflow rates but remained above 94% at the highest flow rate (600 m³/h). Among the individual stages, NTP demonstrated the highest standalone inactivation efficiency, followed by UV-C and BI. The ESP stage effectively captured inactivated bioaerosol particles, preventing re-emission, while an integrated ozone decomposition unit maintained ozone concentrations below safety thresholds. These findings show the potential of multi-stage air cleaning technology for reducing bioaerosol contamination in indoor environments, with applications in healthcare, public spaces, and residential settings. Full article

(This article belongs to the Special Issue Feature Papers in Plasma Sciences 2025)

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19 pages, 4616 KiB

Open AccessArticle

Modeling Streamer Discharge in Air Using Implicit and Explicit Finite Difference Methods with Flux Correction

by Hasupama Jayasinghe, Liliana Arevalo, Richard Morrow and Vernon Cooray

Plasma 2025, 8(2), 21; https://doi.org/10.3390/plasma8020021 - 29 May 2025

Abstract

Implementing a computationally efficient numerical model for a single streamer discharge is essential to understand the complex processes such as lightning initiation and electrical discharges in high voltage systems. In this paper, we present a streamer discharge simulation in air, by solving one-dimensional [...] Read more.

Implementing a computationally efficient numerical model for a single streamer discharge is essential to understand the complex processes such as lightning initiation and electrical discharges in high voltage systems. In this paper, we present a streamer discharge simulation in air, by solving one-dimensional (1D) drift diffusion reaction (DDR) equations for charged species with the disc approximation for electric field. A recently developed fourth-order space and time-centered implicit finite difference method (FDM) with a flux-corrected transport (FCT) method is applied to solve the DDR equations, followed by a comparative simulation using the well-established explicit FDM with FCT. The results demonstrate good agreement between implicit and explicit FDMs, verifying their reliability for streamer modeling. The total electrons, total charge, streamer position, and hence the streamer bridging time obtained using the FDMs with FCT agree with the same streamer computed in the literature using different numerical methods and dimensions. The electric field is obtained with good accuracy due to the inclusion of image charges representing the electrodes in the disc method. This accuracy can be further improved by introducing more image charges. Both implicit and explicit FDMs effectively capture the key streamer behavior, including the variations in charged particle densities and electric field. However, the implicit FDM is computationally more efficient. Full article

(This article belongs to the Special Issue Recent Advances of Dielectric Barrier Discharges)

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16 pages, 66642 KiB

Open AccessArticle

Counterintuitive Particle Confinement in a Helical Force-Free Plasma

by Adam D. Light, Hariharan Srinivasulu, Christopher J. Hansen and Michael R. Brown

Plasma 2025, 8(2), 20; https://doi.org/10.3390/plasma8020020 - 26 May 2025

Abstract

The force-free magnetic field solution formed in a high-aspect ratio cylinder is a non-axisymmetric (

m = 1

), closed magnetic structure that can be produced in laboratory experiments. Force-free equilibria can have strong field gradients that break the usual adiabatic invariants associated [...] Read more.

The force-free magnetic field solution formed in a high-aspect ratio cylinder is a non-axisymmetric (

m = 1

), closed magnetic structure that can be produced in laboratory experiments. Force-free equilibria can have strong field gradients that break the usual adiabatic invariants associated with particle motion, and gyroradii at measured conditions can be large relative to the gradient scale lengths of the magnetic field. Individual particle motion is largely unexplored in force-free systems without axisymmetry, and it is unclear how the large gradients influence confinement. To understand more about how particles remain confined in these configurations, we simulate a thermal distribution of protons moving in a high-aspect-ratio force-free magnetic field using a Boris stepper. The particle loss is logarithmic in time, which suggests trapping and/or periodic orbits. Many particles do remain confined in particular regions of the field, analogous to trapped particles in other magnetic configurations. Some closed flux surfaces can be identified, but particle orbits are not necessarily described by these surfaces. We show examples of orbits that remain on well-defined surfaces and discuss the statistical properties of confined and escaping particles. Full article

(This article belongs to the Special Issue Feature Papers in Plasma Sciences 2025)

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15 pages, 4724 KiB

Open AccessArticle

Absorption of FD-150 in Brain Endothelial Cells by Cold Atmospheric Microplasma

by Md Jahangir Alam, Abubakar Hamza Sadiq, Jaroslav Kristof, Mahedi Hasan, Farhana Begum, Yamano Tomoki and Kazuo Shimizu

Plasma 2025, 8(2), 19; https://doi.org/10.3390/plasma8020019 - 12 May 2025

Abstract

The blood–brain barrier (BBB) limits drug delivery to the brain, particularly for large or hydrophilic molecules. Brain microvascular endothelial cells (bEND.3), which form part of the BBB, play a critical role in regulating drug uptake. This study investigates the use of cold atmospheric [...] Read more.

The blood–brain barrier (BBB) limits drug delivery to the brain, particularly for large or hydrophilic molecules. Brain microvascular endothelial cells (bEND.3), which form part of the BBB, play a critical role in regulating drug uptake. This study investigates the use of cold atmospheric microplasma (CAM) to enhance membrane permeability and facilitate drug delivery in bEND.3 cells. CAM generates reactive oxygen species (ROS) that modulate membrane properties. We exposed bEND.3 cells to CAM at varying voltages (3, 3.5, 4, and 4.5 kV) and measured drug uptake using the fluorescent drug FD-150, fluorescence intensity, ROS levels, membrane lipid order, and membrane potential. The results showed a significant increase in fluorescence intensity and drug concentration in the plasma-treated cells compared to controls. ROS production, measured by DCFH-DA staining, was higher in the plasma-treated cells, supporting the hypothesis that CAM enhances membrane permeability through ROS-induced changes. Membrane lipid order, assessed using the LipiORDER probe, shifted from the liquid-ordered (Lo) to liquid-disordered (Ld) phase, indicating increased membrane fluidity. Membrane depolarization was detected with DisBAC2(3) dye, showing increased fluorescence in the plasma-treated cells. Cell viability, assessed by trypan blue and LIVE/DEAD™ assays, revealed transient damage at higher voltages (≥4 kV), with recovery after 24 h. These results suggest that CAM enhances drug delivery in bEND.3 cells by modulating membrane properties via ROS production and changes in membrane potential. CAM offers a promising strategy for improving drug delivery to the brain, with potential applications in brain-targeted therapies. Full article

(This article belongs to the Special Issue Feature Papers in Plasma Sciences 2025)

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30 pages, 4647 KiB

Open AccessReview

Recent Advances in Cold Atmospheric Pressure Plasma for E. coli Decontamination in Food: A Review

by Muhammad Waqar Ahmed, Kainat Gul and Sohail Mumtaz

Plasma 2025, 8(2), 18; https://doi.org/10.3390/plasma8020018 - 7 May 2025

Abstract

Cold atmospheric plasma (CAP) acts as a powerful antibacterial tool in the food industry, effectively eliminating E. coli and a wide range of pathogens, including bacteria, viruses, fungi, spores, and biofilms in meat and vegetables. Unlike traditional bactericidal methods, CAP leverages an arsenal [...] Read more.

Cold atmospheric plasma (CAP) acts as a powerful antibacterial tool in the food industry, effectively eliminating E. coli and a wide range of pathogens, including bacteria, viruses, fungi, spores, and biofilms in meat and vegetables. Unlike traditional bactericidal methods, CAP leverages an arsenal of reactive species, including reactive oxygen species (ROS) such as ozone (O3) and hydroxyl radicals (OH•), and reactive nitrogen species (RNS) like nitric oxide (NO•), alongside UV radiation and charged particles. These agents synergistically dismantle E. coli’s cell membranes, proteins, and DNA, achieving high degradation rates without thermal or chemical damage to processed food. This non-thermal, eco-friendly technology preserves food’s nutritional and sensory integrity, offering a transformative edge over conventional approaches. It emphasizes the critical need to optimize treatment parameters (exposure time, gas composition, power) to unlock CAP’s full potential. This review explores CAP’s effectiveness in degrading E. coli, emphasizing the optimization of treatment parameters for practical food industry applications and its potential as a scalable food safety solution. It is crucial to conduct further studies to enhance its implementation, establishing CAP as a fundamental element of advanced food processing technologies and a key measure for protecting public health. Full article

(This article belongs to the Special Issue Latest Review Papers in Plasma Science 2025)

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30 pages, 705 KiB

Open AccessArticle

Strong, Weak and Merging Lines in Atomic Spectra

by Jean-Christophe Pain

Plasma 2025, 8(2), 17; https://doi.org/10.3390/plasma8020017 - 29 Apr 2025

Abstract

We present analytical estimates for the maximum line strength in a transition array, as well as for the numbers of strong and weak lines. For that purpose, two main assumptions are used as concerns the line strength distribution. The first one, due to [...] Read more.

We present analytical estimates for the maximum line strength in a transition array, as well as for the numbers of strong and weak lines. For that purpose, two main assumptions are used as concerns the line strength distribution. The first one, due to Porter and Thomas, is more suitable for

J - J^{'}

sets, where J is the total atomic angular momentum, and the second one, based on a decreasing-exponential modeling of the line-amplitude distribution, is more relevant for an entire transition array. We also review the different approximations of overlapping and blanketing (band model), insisting on the computation and properties of the Elsasser function. We compare different approximations of the Ladenburg–Reiche function giving the equivalent width of an ensemble of lines in a frequency bin and discuss the possibility of using statistical indicators, such as the Chernoff bound or the Gini coefficient (initially introduced in economics for the measurement of income inequality), in the statistical characterization of transition arrays. Full article

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Graphical abstract

14 pages, 488 KiB

Open AccessArticle

A Theoretical Study of the Ionization States and Electrical Conductivity of Tantalum Plasma

by Shi Chen, Qishuo Zhang, Qianyi Feng, Ziyue Yu, Jingyi Mai, Hongping Zhang, Lili Huang, Chengjin Huang and Mu Li

Plasma 2025, 8(2), 16; https://doi.org/10.3390/plasma8020016 - 28 Apr 2025

Abstract

Tantalum is extensively used in inertial confinement fusion research for targets in radiation transport experiments, hohlraums in magnetized fusion experiments, and lining foams for hohlraums to suppress wall motions. To comprehend the physical processes associated with these applications, detailed information regarding the ionization [...] Read more.

Tantalum is extensively used in inertial confinement fusion research for targets in radiation transport experiments, hohlraums in magnetized fusion experiments, and lining foams for hohlraums to suppress wall motions. To comprehend the physical processes associated with these applications, detailed information regarding the ionization composition and electrical conductivity of tantalum plasma across a wide range of densities and temperatures is essential. In this study, we calculate the densities of ionization species and the electrical conductivity of partially ionized, nonideal tantalum plasma based on a simplified theoretical model that accounts for high ionization states up to the atomic number of the element and the lowering of ionization energies. A comparison of the ionization compositions between tantalum and copper plasmas highlights the significant role of ionization energies in determining species populations. Additionally, the average electron–neutral momentum transfer cross-section significantly influences the electrical conductivity calculations, and calibration with experimental measurements offers a method for estimating this atomic parameter. The impact of electrical conductivity in the intermediate-density range on the laser absorption coefficient is discussed using the Drude model. Full article

(This article belongs to the Special Issue Feature Papers in Plasma Sciences 2025)

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15 pages, 4340 KiB

Open AccessArticle

Voltage Dependent Effect of Spiral Wound Plasma Discharge on DBC1.2 Cellular Integrity

by Abubakar Hamza Sadiq, Md Jahangir Alam, Mahedi Hasan, Farhana Begum, Tomoki Yamano, Jaroslav Kristof and Kazuo Shimizu

Plasma 2025, 8(2), 15; https://doi.org/10.3390/plasma8020015 - 12 Apr 2025

Abstract

Low temperature plasmas (LTPs) generated at atmospheric pressure and room temperature have gained increasing attention in biomedical research due to their ability to control cellular behavior through the production of reactive oxygen and nitrogen species (RONS), electric fields, and UV radiation. Among several [...] Read more.

Low temperature plasmas (LTPs) generated at atmospheric pressure and room temperature have gained increasing attention in biomedical research due to their ability to control cellular behavior through the production of reactive oxygen and nitrogen species (RONS), electric fields, and UV radiation. Among several LTP configurations, dielectric barrier discharge (DBD) plasma has been extensively studied for its ability to stimulate controlled biological effects while maintaining low gas temperature, making it suitable for cell-based applications. This study designed a novel spiral-wound DBD plasma device to investigate the voltage-dependent effects of plasma discharge on DBC1.2 epithelial cells. Plasma was applied at 2 kV_p-p, 3 kV_p-p, and 4 kV_p-p to evaluate its effect on cellular permeability, mitochondrial activity, viability, and apoptosis. FITC-dextran-70 (FD-70, MW: 70 kDa) was used as a model permeation marker to assess cellular uptake. The results showed a voltage-dependent increase in FD-70 uptake, suggesting improved plasma-assisted drug delivery. The cell mitochondrial activity, evaluated with a MT-1 MitoMP detection kit, revealed that plasma exposure at 2 kV_p-p and 3 kV_p-p slightly enhanced mitochondrial membrane potential (MMP), signifying increased metabolic and mitochondrial activity, whereas exposure at 4 kV_p-p led to a reduction in MMP, suggesting oxidative stress and early apoptosis. Early and late apoptosis was further assessed using FITC Annexin-V and propidium iodide (PI). The results showed enhanced cell viability and a reduced apoptotic cell at 2 kV_p-p and 3 kV_p-p plasma exposure when compared to the control. However, at 4 kV, there was a decline in cell viability and an increase in apoptosis, suggesting a shift towards plasma-induced cytotoxicity. This study established a safe plasma exposure threshold for DBC1.2 cells and explored the potential use of a spiral-wound DBD plasma device for biomedical applications, particularly in drug delivery and cell modulation. Full article

(This article belongs to the Special Issue Recent Advances of Dielectric Barrier Discharges)

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15 pages, 3975 KiB

Open AccessArticle

Decomposition Mechanisms of Lignin-Related Aromatic Monomers in Solution Plasma

by Takaki Miyamoto, Jeanielle Amurao, Eiji Minami and Haruo Kawamoto

Plasma 2025, 8(2), 14; https://doi.org/10.3390/plasma8020014 - 10 Apr 2025

Abstract

Lignin is a natural aromatic macromolecule present in wood and an abundant resource on Earth, yet it is hardly used. In this study, an aqueous solution plasma treatment was investigated for the catalyst-free production of valuable chemicals from lignin. To elucidate the decomposition [...] Read more.

Lignin is a natural aromatic macromolecule present in wood and an abundant resource on Earth, yet it is hardly used. In this study, an aqueous solution plasma treatment was investigated for the catalyst-free production of valuable chemicals from lignin. To elucidate the decomposition mechanism, the aqueous solution plasma treatment was applied to the fundamental lignin aromatic model compounds—phenol, guaiacol, and syringol. The results showed that the decomposition rate followed the order syringol > guaiacol > phenol, indicating that electron-donating methoxy groups enhance reactivity. These aromatic model compounds underwent hydroxylation at the ortho and para positions, oxidative ring cleavage, and fragmentation, leading to the formation of various dicarboxylic acids, primarily oxalic acid. All these reactions were promoted by hydroxyl radicals generated from water. Ultimately, decarbonylation and decarboxylation of carboxyl groups resulted in gasification, mainly producing H₂, CO, and CO₂. These results provide fundamental insights into lignin decomposition and demonstrate that aqueous solution plasma is a promising method for producing dicarboxylic acids from lignin under mild conditions without catalysts. Full article

(This article belongs to the Special Issue Feature Papers in Plasma Sciences 2025)

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17 pages, 3091 KiB

Open AccessReview

A Tutorial on One-Dimensional Numerical Simulation of Virtual Cathode Oscillation

by Weihua Jiang

Plasma 2025, 8(2), 13; https://doi.org/10.3390/plasma8020013 - 1 Apr 2025

Abstract

This review article is the continuation of a previous publication, by the same author, on one dimensional theory of space charge effect and virtual cathode. The virtual cathode is known to be unstable. However, the process of virtual cathode oscillation is very complicated [...] Read more.

This review article is the continuation of a previous publication, by the same author, on one dimensional theory of space charge effect and virtual cathode. The virtual cathode is known to be unstable. However, the process of virtual cathode oscillation is very complicated both physically and mathematically. No satisfactory theoretical model exists that can fully describe the oscillatory behavior of the virtual cathode. On the other hand, computer simulations allow us to numerically observe this phenomenon and establish certain relations between the electron beam parameters and the virtual cathode characteristics. This article explains the detailed procedure of numerical modeling by dealing with the one-dimensional case as an example. A sample code written in the C language is attached at the end following the main text. This article is expected to serve as a reference for young researchers and students who are interested in computer simulations of intense particle beams and high-power microwave generation. Full article

(This article belongs to the Special Issue Latest Review Papers in Plasma Science 2025)

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20 pages, 5520 KiB

Open AccessReview

Runaway Electrons in Gas Discharges: Insights from the Numerical Modeling

by Dmitry Levko

Plasma 2025, 8(1), 12; https://doi.org/10.3390/plasma8010012 - 20 Mar 2025

Abstract

This paper reviews the state of the art of our understanding of the mechanisms of runaway electron generation in pressurized gases from the numerical modeling perspective. Since the energy relaxation length of these electrons is comparable to the interelectrode spacing, these electrons can [...] Read more.

This paper reviews the state of the art of our understanding of the mechanisms of runaway electron generation in pressurized gases from the numerical modeling perspective. Since the energy relaxation length of these electrons is comparable to the interelectrode spacing, these electrons can be captured only using the kinetic approach. Therefore, only the results from kinetic models are discussed here. Special attention is given to pulsed discharges, which play an important role in modern industry. It is concluded that the mechanisms of runaway electron generation are defined by the gap overvoltage and the discharge gap geometry. For small and moderate overvoltages, runaway electrons are primarily generated at the heads of fast ionization waves or streamers. Due to their long energy relaxation length, these electrons can pre-ionize the discharge gap far from their origin, accelerating ionization and starting new avalanches. At high overvoltages, cathode surface irregularities enhance the local electric field, leading to electron emission into the interelectrode space. These electrons, injected into the strong electric field, gain high energy and reach discharge walls with extremely high energies measuring tens and hundreds of electron volts. These electrons not only pre-ionize the gas but also stimulate the emission of high-energy photons, which can further contribute to the pre-ionization of the discharge gap. Full article

(This article belongs to the Special Issue New Insights into Plasma Theory, Modeling and Predictive Simulations)

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19 pages, 6382 KiB

Open AccessArticle

Quantifying Plasma Dose for Barley Seed Treatment by Volume Dielectric Barrier Discharges in Atmospheric-Pressure Synthetic Air

by Jiří Fujera, Petr Hoffer, Václav Prukner and Milan Šimek

Plasma 2025, 8(1), 11; https://doi.org/10.3390/plasma8010011 - 17 Mar 2025

Abstract

Plasma-assisted treatment is a potentially interesting technology for advanced seed processing. In this work, we address the issue of defining and quantifying the plasma dose during the exposure of seeds to microdischarges formed in a barrier discharge configuration fed with synthetic air at [...] Read more.

Plasma-assisted treatment is a potentially interesting technology for advanced seed processing. In this work, we address the issue of defining and quantifying the plasma dose during the exposure of seeds to microdischarges formed in a barrier discharge configuration fed with synthetic air at atmospheric pressure. Using advanced imaging and other optoelectrical diagnostics, we identify suitable conditions for the formation of microdischarges developing exclusively between the powered electrode and the seed coat, which allows for the relatively accurate quantification of the plasma dose for an individual barley seed. In addition to determining the microdischarge energy/power consumed to treat a single seed during controlled exposure, we also provide an estimate of the electric field and gas temperature, which are key parameters that can affect seed viability. In this way, each individually exposed seed can be linked to the exact exposure time, total number, energy, and temperature of the microdischarges that came into contact with it. This is fundamentally different from conventional “averaging” approaches based on the simultaneous exposure of many seeds, which makes it virtually impossible to correlate the responses of individual seeds with the corresponding individual plasma dose. Finally, we propose a minimal treatment protocol that could allow for the more direct interpretation of the results of subsequent biological tests to reveal seed responses to specific plasma–chemical stimuli during germination and seedling growth. Full article

(This article belongs to the Special Issue Processes in Atmospheric Pressure Plasmas)

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11 pages, 1336 KiB

Open AccessArticle

Network Analysis as a Method for Identifying Operational Modes of Cold Atmospheric Plasma Jets

by Blake Haist and Richard E. Wirz

Plasma 2025, 8(1), 10; https://doi.org/10.3390/plasma8010010 - 10 Mar 2025

Abstract

Network analysis is a convenient method for analyzing cold atmospheric plasma (CAP) devices across a wide range of operating conditions. By using frequency and voltage as nodes in the network, edges are formed between nodes when the combination of voltage and frequency results [...] Read more.

Network analysis is a convenient method for analyzing cold atmospheric plasma (CAP) devices across a wide range of operating conditions. By using frequency and voltage as nodes in the network, edges are formed between nodes when the combination of voltage and frequency results in an ignited plasma jet. Singular value decomposition is used to identify modalities in the network that are representative of operational modes in the plasma jet. An analysis of the spectra produced by the jet provides validation of the operational modes and shows that voltage and frequency predominately affect the operation of the jet with remarkable independence. Full article

(This article belongs to the Special Issue Processes in Atmospheric Pressure Plasmas)

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17 pages, 13969 KiB

Open AccessArticle

Combined Plasma and Laser Heating of Graphite

by Aleksey Chaplygin, Mikhail Yakimov, Sergey Vasil’evskii, Mikhail Kotov, Ilya Lukomskii, Semen Galkin, Andrey Shemyakin, Nikolay Solovyov and Anatoly Kolesnikov

Plasma 2025, 8(1), 9; https://doi.org/10.3390/plasma8010009 - 4 Mar 2025

Abstract

This paper investigates a novel combined laser and plasma heating test technique. Integrating the 1.5 kW Raycus RFL-C1500 laser source into the VGU-4 Inductively Coupled Plasma Facility (IPMech RAS) allowed the study of fine-grain MPG-7 graphite ablation in the high-temperature range from 2920 [...] Read more.

This paper investigates a novel combined laser and plasma heating test technique. Integrating the 1.5 kW Raycus RFL-C1500 laser source into the VGU-4 Inductively Coupled Plasma Facility (IPMech RAS) allowed the study of fine-grain MPG-7 graphite ablation in the high-temperature range from 2920 to 3865 K under exposure to subsonic nitrogen plasma flow and combined exposure to nitrogen plasma flow and laser irradiation. Graphite nitridation and sublimation were observed. The subsonic nitrogen plasma flow was characterized by numerical modeling, probes, and spectral measurements. The proposed experimental approach is promising for simulating the entry conditions of planetary mission vehicles into different atmospheres. Full article

(This article belongs to the Special Issue Feature Papers in Plasma Sciences 2025)

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13 pages, 4074 KiB

Open AccessArticle

Characterization of Tungsten Sputtering Processes in a Capacitively Coupled Argon Plasma

by Espedito Vassallo, Miriam Saleh, Matteo Pedroni, Anna Cremona and Dario Ripamonti

Plasma 2025, 8(1), 8; https://doi.org/10.3390/plasma8010008 - 28 Feb 2025

Abstract

A capacitively coupled radio-frequency argon plasma, used for tungsten sputtering deposition, is characterized using Langmuir probe measurements. Druyvesteyn’s method is used to evaluate plasma parameters through the integral of the Electron Energy Distribution Function (EEDF). In the pressure range analyzed (0.6–10 Pa), the [...] Read more.

A capacitively coupled radio-frequency argon plasma, used for tungsten sputtering deposition, is characterized using Langmuir probe measurements. Druyvesteyn’s method is used to evaluate plasma parameters through the integral of the Electron Energy Distribution Function (EEDF). In the pressure range analyzed (0.6–10 Pa), the obtained distributions are not Maxwellian, which suggests some depletion of electrons with higher energies. The obtained plasma parameters are compared with those derived from the graphical method. The electron temperature obtained via the graphical method is always lower than the effective temperatures derived from EEDFs, and vice versa, the electron density is overestimated by the graphical method. Optical Emission Spectroscopy is used to monitor the atoms sputtered in the plasma process. The behavior of excited species correlates with the plasma parameters. Full article

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8 pages, 1370 KiB

Open AccessArticle

An Implicit Flux-Corrected Transport Algorithm Used for Gas Discharge Calculations

by Richard Morrow

Plasma 2025, 8(1), 7; https://doi.org/10.3390/plasma8010007 - 28 Feb 2025

Abstract

An implicit flux-corrected transport (FCT) and diffusion algorithm was developed and used in many gas discharge calculations. Such calculations require the use of a fine mesh where the electric field changes rapidly; that is, near electrodes or in a streamer front. If diffusion [...] Read more.

An implicit flux-corrected transport (FCT) and diffusion algorithm was developed and used in many gas discharge calculations. Such calculations require the use of a fine mesh where the electric field changes rapidly; that is, near electrodes or in a streamer front. If diffusion is included using an explicit method, then the von Neumann stability condition severely limits the time-step that can be used; however, this limitation does not apply to implicit methods. Further, for gas discharge calculations including space-charge effects, it is necessary to solve the continuity equations with no negative number densities nor point-by-point oscillation in the number density. This is because the electron number densities are finely balanced with the ion number densities to determine the space-charge distribution and hence the electric field which drives the motion of the particles. An efficient way to solve the particle transport equation, with the required properties, is to use FCT. The most accurate form of FCT developed by the author is implicit fourth-order FCT; hence, the method presented incorporates implicit diffusion into the implicit fourth-order FCT scheme to produce a robust algorithm that has been successfully used in many calculations. Full article

(This article belongs to the Special Issue Recent Advances of Dielectric Barrier Discharges)

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18 pages, 1488 KiB

Open AccessArticle

Plasma-Induced Abatement of Tar from Syngas Produced in Municipal Waste Gasification: Thermodynamic Modeling with Experimental Validation

by Mobish A. Shaji, Francis Eboh, Alexander Rabinovich, Liran Dor and Alexander Fridman

Plasma 2025, 8(1), 6; https://doi.org/10.3390/plasma8010006 - 16 Feb 2025

Abstract

Municipal waste gasification presents a promising avenue to extract useful energy from waste through syngas. This technology’s application is limited by tar formation (long-chain hydrocarbons), which can decrease energy conversion efficiency and applications of raw syngas. Non-thermal plasma-based tar degradation is a simple [...] Read more.

Municipal waste gasification presents a promising avenue to extract useful energy from waste through syngas. This technology’s application is limited by tar formation (long-chain hydrocarbons), which can decrease energy conversion efficiency and applications of raw syngas. Non-thermal plasma-based tar degradation is a simple and cost-effective alternative to existing thermal and catalytic tar mitigation methods. While plasma stimulates tar reformation reactions like steam reformation, there are thermodynamic energy requirements associated with these endothermic processes. Determining thermodynamic energy requirements and the equilibrium composition of products during tar reformation can aid with the proper optimization of the treatment process. In the present study, thermodynamic modeling and experimental validation are conducted to study energy requirements and product formation during the plasma-assisted steam reformation of tar present in raw syngas with an inlet temperature of 300 °C and 30% moisture content. The thermodynamic study evaluated the effect of adding air into the system (to increase the temperature by oxidizing a portion of raw syngas). Results show that up to 75% of energy requirement can be brought down by adding up to 30% air; experimental validation using gliding arc discharge with 30% air addition agrees with the thermodynamic model finding. The thermodynamic model predicted an increase in H₂ and CO concentration with the degradation of tar, but experimental validation reported a reduction in H₂ and CO concentration with the degradation of tar, as syngas was consumed to increase the temperature to support oxidation, owing to the low temperature (300 °C) and significant moisture presence (~30%) of raw syngas analyzed in this study. Full article

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25 pages, 7953 KiB

Open AccessArticle

A Study of Particle Heating and Oxidation Protection in a Modified Internally Injected Ar–H₂ Atmospheric Plasma Spraying Torch

by Mahrukh Mahrukh, Sen-Hui Liu, Li Zhang, Sohail Husnain, Cheng-Chung Yang, Xiao-Tao Luo and Chang-Jiu Li

Plasma 2025, 8(1), 5; https://doi.org/10.3390/plasma8010005 - 13 Feb 2025

Cited by 2

Abstract

This study employs computational fluid dynamics (CFD) to analyze the in-flight dynamics of particles in an Ar–H₂ atmospheric plasma spray (APS) torch with a modified diverging-type nozzle. The focus is on optimizing injection parameters—plasma gas flow rates, input power, and carrier gas [...] Read more.

This study employs computational fluid dynamics (CFD) to analyze the in-flight dynamics of particles in an Ar–H₂ atmospheric plasma spray (APS) torch with a modified diverging-type nozzle. The focus is on optimizing injection parameters—plasma gas flow rates, input power, and carrier gas flow rates—to enhance coating microstructure and deposition efficiency by achieving superheated molten metal droplets. Using a discrete phase model, the heat and momentum transfer of Ni/Al/C (2 wt.% diamond) composite powders (30–110 µm) within the plasma jet were simulated. Results show that particle characteristics, such as temperature and oxidation, can be controlled by adjusting plasma jet temperature (T∞) and velocity (U∞). Smaller particles heat faster, reaching higher temperatures with increased evaporation and oxidation rates. The modified nozzle enables Ni-based alloy particles to reach ~2500 °C, reducing oxygen inclusion in the plasma jet core. This setup allows for the control of the onset of carbon and oxygen reactions, wherein carbon serves as a sacrificial element, protecting the base alloy elements (such as aluminum) from excessive oxidation. Full article

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13 pages, 1929 KiB

Open AccessArticle

An Approach to Nuclear Fusion Utilizing the Dynamics of High-Density Electrons and Neutrals, Part I

by Alfred YiuFai Wong and Chun-Ching Shih

Plasma 2025, 8(1), 4; https://doi.org/10.3390/plasma8010004 - 31 Jan 2025

Abstract

An approach to achieve nuclear fusion utilizing the formation of high densities of electrons and neutrals is described. The abundance of low energy free electrons produces intense electric fields that reduce the Coulomb barrier in nuclear fusion. Meanwhile, high-density rotating neutrals provide high [...] Read more.

An approach to achieve nuclear fusion utilizing the formation of high densities of electrons and neutrals is described. The abundance of low energy free electrons produces intense electric fields that reduce the Coulomb barrier in nuclear fusion. Meanwhile, high-density rotating neutrals provide high centrifugal forces to achieve the extreme pressure gradients of electrons and consequent negative electric fields to reduce the ion repulsive Coulombic fields. These high-density neutrals also provide better stability and higher reaction rates. Ion–neutral coupling is responsible for the control of neutral dynamics. Since high-frequency excitations favor the generation of free electrons, pulsed operations are recommended to achieve fusion with higher gains. Full article

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