Plasma

19 pages, 7153 KiB

Open AccessArticle

A Heuristic Exploration of Zonal Flow-like Structures in the Presence of Toroidal Rotation in a Non-Inertial Frame

by Xinliang Xu, Yihang Chen, Yulin Zhou, Zhanhui Wang, Xueke Wu, Bo Li, Jiang Sun, Junzhao Zhang and Da Li

Plasma 2025, 8(3), 29; https://doi.org/10.3390/plasma8030029 - 22 Jul 2025

Abstract

The mechanisms by which rotation influences zonal flows (ZFs) in plasma are incompletely understood, presenting a significant challenge in the study of plasma dynamics. This research addresses this gap by investigating the role of non-inertial effects—specifically centrifugal and Coriolis forces—on Geodesic Acoustic Modes [...] Read more.

The mechanisms by which rotation influences zonal flows (ZFs) in plasma are incompletely understood, presenting a significant challenge in the study of plasma dynamics. This research addresses this gap by investigating the role of non-inertial effects—specifically centrifugal and Coriolis forces—on Geodesic Acoustic Modes (GAMs) and ZFs in rotating tokamak plasmas. While previous studies have linked centrifugal convection to plasma toroidal rotation, they often overlook the Coriolis effects or inconsistently incorporate non-inertial terms into magneto-hydrodynamic (MHD) equations. In this work, we derive self-consistent drift-ordered two-fluid equations from the collisional Vlasov equation in a non-inertial frame, and we modify the Hermes cold ion code to simulate the impact of rotation on GAMs and ZFs. Our simulations reveal that toroidal rotation enhances ZF amplitude and GAM frequency, with Coriolis convection playing a critical role in GAM propagation and the global structure of ZFs. Analysis of simulation outcomes indicates that centrifugal drift drives parallel velocity growth, while Coriolis drift facilitates radial propagation of GAMs. This work may provide valuable insights into momentum transport and flow shear dynamics in tokamaks, with implications for turbulence suppression and confinement optimization. Full article

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

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14 pages, 2726 KiB

Open AccessArticle

Streamer Discharge Modeling for Plasma-Assisted Combustion

by Stuart Reyes and Shirshak Kumar Dhali

Plasma 2025, 8(3), 28; https://doi.org/10.3390/plasma8030028 - 10 Jul 2025

Abstract

Some of the popular and successful atmospheric pressure fuel/air plasma-assisted combustion methods use repetitive ns pulsed discharges and dielectric-barrier discharges. The transient phase in such discharges is dominated by transport under strong space charge from ionization fronts, which is best characterized by the [...] Read more.

Some of the popular and successful atmospheric pressure fuel/air plasma-assisted combustion methods use repetitive ns pulsed discharges and dielectric-barrier discharges. The transient phase in such discharges is dominated by transport under strong space charge from ionization fronts, which is best characterized by the streamer model. The role of the nonthermal plasma in such discharges is to produce radicals, which accelerates the chemical conversion reaction leading to temperature rise and ignition. Therefore, the characterization of the streamer and its energy partitioning is essential to develop a predictive model. We examine the important characteristics of streamers that influence combustion and develop some macroscopic parameters. Our results show that the radicals’ production efficiency at an applied field is nearly independent of time and the radical density generated depends only on the electrical energy density coupled to the plasma. We compare the results of the streamer model to the zero-dimensional uniform field Townsend-like discharge, and our results show a significant difference. The results concerning the influence of energy density and repetition rate on the ignition of a hydrogen/air fuel mixture are presented. Full article

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

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28 pages, 8047 KiB

Open AccessArticle

Hybrid Dielectric Barrier Discharge Reactor: Production of Reactive Oxygen–Nitrogen Species in Humid Air

by Dariusz Korzec, Florian Freund, Christian Bäuml, Patrik Penzkofer, Oliver Beier, Andreas Pfuch, Klaus Vogelsang, Frank Froehlich and Stefan Nettesheim

Plasma 2025, 8(3), 27; https://doi.org/10.3390/plasma8030027 - 6 Jul 2025

Abstract

Reactive oxygen–nitrogen species (RONS) production in a Peltier-cooled hybrid dielectric barrier discharge (HDBD) reactor operated with humid air is characterized. Fourier-transform infrared spectroscopy (FTIR) is used to determine the RONS in the HDBD-produced gases. The presence of molecules

O_{3}

,

{NO}_{2}

[...] Read more.

Reactive oxygen–nitrogen species (RONS) production in a Peltier-cooled hybrid dielectric barrier discharge (HDBD) reactor operated with humid air is characterized. Fourier-transform infrared spectroscopy (FTIR) is used to determine the RONS in the HDBD-produced gases. The presence of molecules

O_{3}

,

{NO}_{2}

,

N_{2}

O,

N_{2} O_{5}

, and

{HNO}_{3}

is evaluated. The influence of HDBD reactor operation parameters on the FTIR result is discussed. The strongest influence of Peltier cooling on RONS chemistry is reached at conditions related to a high specific energy input (SEI): high voltage and duty cycle of plasma width modulation (PWM), and low gas flow. Both PWM and Peltier cooling can achieve a change in the chemistry from oxygen-based to nitrogen-based.

N_{2} O_{5}

and

{HNO}_{3}

are detected at a low humidity of 7% in the reactor input air but not at humidity exceeding 90%. In addition to the FTIR analysis, the plasma-activated water (PAW) is investigated. PAW is produced by bubbling the HDBD plasma gas through 12.5 mL of distilled water in a closed-loop circulation at a high SEI. Despite the absence of

N_{2} O_{5}

and

{HNO}_{3}

in the gas phase, the acidity of the PAW is increased. The pH value decreases on average by 0.12 per minute. Full article

(This article belongs to the Special Issue Processes in Atmospheric-Pressure Plasmas—2nd Edition)

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18 pages, 995 KiB

Open AccessArticle

A Quasi-Spherical Fusion Reactor Burning Boron-11 Fuel

by Joel G. Rogers, Andrew A. Egly, Yoon S. Roh, Robert E. Terry and Frank J. Wessel

Plasma 2025, 8(3), 26; https://doi.org/10.3390/plasma8030026 - 30 Jun 2025

Abstract

In this study, particle-in-cell (PIC) simulation was used to validate a conceptual design for a quasi-spherical, net power, hydrogen-plus-boron-11-fueled fusion reactor incorporating high-temperature superconducting (HTS) magnets. By burning a fully thermalized plasma, our proposed MET6 reactor uses the principles of the 1980 magneto-electrostatic [...] Read more.

In this study, particle-in-cell (PIC) simulation was used to validate a conceptual design for a quasi-spherical, net power, hydrogen-plus-boron-11-fueled fusion reactor incorporating high-temperature superconducting (HTS) magnets. By burning a fully thermalized plasma, our proposed MET6 reactor uses the principles of the 1980 magneto-electrostatic trap design of Yushmanov to improve the classic Polywell design. Because the input power consumed by the reactor will barely balance the waste bremsstrahlung radiation, future research must focus on reducing the bremsstrahlung losses to reach practical net power levels. The first step to reducing bremsstrahlung, explored in this paper, is to tune the reactor parameters to reduce the energies of trapped electrons. We assume the quality factor Q can be approximated as the ratio of fusion power output divided by bremsstrahlung power loss. Thus, assuming the particles’ power loss is negligible compared to bremsstrahlung power loss, the resulting quality factor is estimated to be Q ≈ 1.3. Full article

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

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16 pages, 4367 KiB

Open AccessArticle

Non-Thermal Plasma-Assisted Synthesis of ZnO for Enhanced Photocatalytic Performance

by Harshini Mohan, Subash Mohandoss, Natarajan Balasubramaniyan and Sivachandiran Loganathan

Plasma 2025, 8(2), 25; https://doi.org/10.3390/plasma8020025 - 18 Jun 2025

Abstract

Non-thermal plasma (NTP)-assisted material synthesis and surface modification provide a promising approach in various applications, particularly in wastewater treatment. In this study, we reported the synthesis of photocatalytic zinc oxide (ZnO) from zinc hydroxide (Zn(OH)₂) utilizing NTP discharge generated by dielectric [...] Read more.

Non-thermal plasma (NTP)-assisted material synthesis and surface modification provide a promising approach in various applications, particularly in wastewater treatment. In this study, we reported the synthesis of photocatalytic zinc oxide (ZnO) from zinc hydroxide (Zn(OH)₂) utilizing NTP discharge generated by dielectric barrier discharge (DBD). The results demonstrated that the 40 min plasma treatment at 200 °C (ZnO-P) with a voltage of 20 kV significantly improved the material’s physicochemical properties compared to conventional calcination at 600 °C (ZnO-600). ZnO-P exhibited better crystallinity, a significantly reduced particle size of 41 nm, and a narrower band gap of 3.1 eV compared to ZnO-600. Photocatalytic performance was evaluated through crystal violet degradation, where ZnO-P achieved an 60% degradation rate after 90 min of UV exposure, whereas ZnO-600 exhibited only a 50% degradation rate under identical conditions. These findings underscore the effectiveness of NTP synthesis in enhancing the surface properties of ZnO, leading to superior photocatalytic performance. Full article

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

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15 pages, 399 KiB

Open AccessArticle

Ionospheric Electron Density and Temperature Profiles Using Ionosonde-like Data and Machine Learning

by Jean de Dieu Nibigira and Richard Marchand

Plasma 2025, 8(2), 24; https://doi.org/10.3390/plasma8020024 - 16 Jun 2025

Abstract

Predicting the behaviour of the Earth’s ionosphere is crucial for the ground-based and spaceborne technologies that rely on it. This paper presents a novel way of inferring ionospheric electron density profiles and electron temperature profiles using machine learning. The analysis is based on [...] Read more.

Predicting the behaviour of the Earth’s ionosphere is crucial for the ground-based and spaceborne technologies that rely on it. This paper presents a novel way of inferring ionospheric electron density profiles and electron temperature profiles using machine learning. The analysis is based on the Nearest Neighbour (NNB) and Radial Basis Function (RBF) regression models. Synthetic data sets used to train and validate these two inference models are constructed using the International Reference Ionosphere (IRI 2020) model with randomly chosen years (1987–2022), months (1–12), days (1–31), latitudes (−60 to 60°), longitudes (0, 360°), and times (0–23 h), at altitudes ranging from 95 to 600 km. The NNB and RBF models use the constructed ionosonde-like profiles to infer complete ISR-like profiles. The results show that the inference of ionospheric electron density profiles is better with the NNB model than with the RBF model, while the RBF model is better at inferring the electron temperature profiles. A major and unexpected finding of this research is the ability of the two models to infer full electron temperature profiles that are not provided by ionosondes using the same truncated electron density data set used to infer electron density profiles. NNB and RBF models generally over- or underestimate the inferred electron density and electron temperature values, especially at higher altitudes, but they tend to produce good matches at lower altitudes. Additionally, maximum absolute relative errors for electron density and temperature inferences are found at higher altitudes for both NNB and RBF models. Full article

(This article belongs to the Special Issue Application of Neural Networks to Plasma Data Analysis)

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23 pages, 9331 KiB

Open AccessArticle

Non-Ideal Hall MHD Rayleigh–Taylor Instability in Plasma Induced by Nanosecond and Intense Femtosecond Laser Pulses

by Roman S. Zemskov, Maxim V. Barkov, Evgeniy S. Blinov, Konstantin F. Burdonov, Vladislav N. Ginzburg, Anton A. Kochetkov, Aleksandr V. Kotov, Alexey A. Kuzmin, Sergey E. Perevalov, Il’ya A. Shaikin, Sergey E. Stukachev, Ivan V. Yakovlev, Alexander A. Soloviev, Andrey A. Shaykin, Efim A. Khazanov, Julien Fuchs and Mikhail V. Starodubtsev

Plasma 2025, 8(2), 23; https://doi.org/10.3390/plasma8020023 - 10 Jun 2025

Abstract

A pioneering detailed comparative study of the dynamics of plasma flows generated by high-power nanosecond and high-intensity femtosecond laser pulses with similar fluences of up to

3 \times 10^{4}

J/cm² is presented. The experiments were conducted on the petawatt laser facility [...] Read more.

A pioneering detailed comparative study of the dynamics of plasma flows generated by high-power nanosecond and high-intensity femtosecond laser pulses with similar fluences of up to

3 \times 10^{4}

J/cm² is presented. The experiments were conducted on the petawatt laser facility PEARL using two types of high-power laser radiation: femtosecond pulses with energy exceeding 10 J and a duration less than 60 fs, and nanosecond pulses with energy exceeding 10 J and a duration on the order of 1 ns. In the experiments, high-velocity (>100 km/s) flows of «femtosecond» (created by femtosecond laser pulses) and «nanosecond» plasmas propagated in a vacuum across a uniform magnetic field with a strength over 14 T. A significant difference in the dynamics of «femtosecond» and «nanosecond» plasma flows was observed: (i) The «femtosecond» plasma initially propagated in a vacuum (no B-field) as a collimated flow, while the «nanosecond» flow diverged. (ii) The «nanosecond» plasma interacting with external magnetic field formed a quasi-spherical cavity with Rayleigh–Taylor instability flutes. In the case of «femtosecond» plasma, such flutes were not observed, and the flow was immediately redirected into a narrow plasma sheet (or «tongue») propagating across the magnetic field at an approximately constant velocity. (iii) Elongated «nanosecond» and «femtosecond» plasma slabs interacting with a transverse magnetic field broke up into Rayleigh–Taylor «tongues». (iv) The ends of these «tongues» in the femtosecond case twisted into vortex structures aligned with the ion motion in the external magnetic field, whereas the «tongues» in the nanosecond case were randomly oriented. It was suggested that the twisting of femtosecond «tongues» is related to Hall effects. The experimental results are complemented by and consistent with numerical 3D magnetohydrodynamic simulations. The potential applications of these findings for astrophysical objects, such as short bursts in active galactic nuclei, are discussed. Full article

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

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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

Cited by 1

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

Cited by 3

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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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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