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Open AccessArticle

An Atmospheric Plasma Jet Generator Driven by a Current Source

by Ovidiu S. Stoican

Plasma 2026, 9(1), 6; https://doi.org/10.3390/plasma9010006 - 10 Feb 2026

Viewed by 1606

Abstract

A novel system aiming to electrically supply various cold plasma generators is proposed. It operates as a programmable linear current source which is able to maintain a dc constant discharge current at various discharge voltages required to sustain the plasma jet. Its design [...] Read more.

A novel system aiming to electrically supply various cold plasma generators is proposed. It operates as a programmable linear current source which is able to maintain a dc constant discharge current at various discharge voltages required to sustain the plasma jet. Its design is based on a specific electronic device called a switchable current regulator, which considerably simplifies the circuit topology. Experimental results carried out in real operating conditions confirm the practical purpose of the proposed solution. Full article

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

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17 pages, 488 KB

Open AccessArticle

Empirical Atomic Data for Plasma Simulations

by Stephan Fritzsche, Houke Huang and Aloka Kumar Sahoo

Plasma 2026, 9(1), 2; https://doi.org/10.3390/plasma9010002 - 29 Dec 2025

Viewed by 1396

Abstract

Recent advances in non-local thermodynamic equilibrium (non-LTE) plasma simulations, for example in modeling kilonova ejecta, have emphasized the need for consistent and reliable atomic data. Unlike LTE modeling, non-LTE calculations must include a consistent treatment of various photon-induced and collisional processes in order [...] Read more.

Recent advances in non-local thermodynamic equilibrium (non-LTE) plasma simulations, for example in modeling kilonova ejecta, have emphasized the need for consistent and reliable atomic data. Unlike LTE modeling, non-LTE calculations must include a consistent treatment of various photon-induced and collisional processes in order to describe realistic electron and photon distributions in the plasma. However, the available atomic data are often incomplete, inconsistently formatted, or even fail to indicate the main dependencies on the level structure and plasma parameters, thus limiting their practical use. To address these issues, we have extended Jac, the Jena Atomic Calculator (version v0.3.0), to provide direct access to relevant cross sections, plasma rates, and rate coefficients. Emphasis is placed on photoexcitation and ionization processes as well as their time-reversed counterparts—photo-de-excitation and photorecombination. Whereas most of these data are still based on empirical expressions, their dependence on the ionic level structure and plasma temperature is made explicit here. Moreover, the electron and photon distributions can be readily controlled and adjusted by the user. This transparent representation of atomic data for photon-mediated processes, together with a straightforward use, facilitates their integration into existing plasma codes and improves the interpretation of high-energy astrophysical phenomena. It may support also more accurate and flexible non-LTE plasma simulations. Full article

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

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24 pages, 3347 KB

Open AccessArticle

CO₂ Conversion at Reduced Pressure in a Novel Stabilized Arc Discharge for In Situ Oxygen Production on Mars

by Veselin Vasilev, Nikola Lazarov, Svetlana Lazarova, Tsvetelina Paunska and Stanimir Kolev

Plasma 2025, 8(4), 50; https://doi.org/10.3390/plasma8040050 - 10 Dec 2025

Cited by 2 | Viewed by 1822

Abstract

The aim of this work is to provide an extensive experimental study of the performance of a novel magnetically and gas-flow-stabilized arc discharge for carbon dioxide (CO₂) conversion and oxygen (O₂) production on Mars. The proposed discharge provides an [...] Read more.

The aim of this work is to provide an extensive experimental study of the performance of a novel magnetically and gas-flow-stabilized arc discharge for carbon dioxide (CO₂) conversion and oxygen (O₂) production on Mars. The proposed discharge provides an additional degree of freedom for easy scalability by adjusting its length. The discharge is examined at a pressure range of 200–612 mbar in order to optimize it for oxygen production on Mars, where low-pressure operation is preferable due to energy costs. Additionally, two quenching configurations with an actively cooled region are evaluated. They are compared to a benchmark configuration without additional cooling. Two high-voltage power supplies (PSs) are used, and the results are compared—a constant direct current (DC) and a pulsed unipolar current. The pulsed power supply offers better CO₂ conversion performance at lower pressure due to stable operation in an arc regime. The energy cost for oxygen production on Mars is also presented, including a conservative estimation of the energy needed for compressing the Martian atmosphere at ambient pressure to the discharge operational pressure. It is discussed how this affects the energy cost of oxygen production. Full article

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

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15 pages, 1536 KB

Open AccessArticle

Role of CF₄ Addition in Gas-Phase Variations in HF Plasma for Cryogenic Etching: Insights from Plasma Simulation and Experimental Correlation

by Shigeyuki Takagi, Shih-Nan Hsiao, Yusuke Imai, Makoto Sekine and Fumihiko Matsunaga

Plasma 2025, 8(4), 48; https://doi.org/10.3390/plasma8040048 - 24 Nov 2025

Cited by 1 | Viewed by 2689

Abstract

The fabrication of semiconductor devices with three-dimensional architectures imposes unprecedented demands on advanced plasma dry etching processes. These include the simultaneous requirements of high throughput, high material selectivity, and precise profile control. In conventional reactive ion etching (RIE), fluorocarbon plasma provides both accelerated [...] Read more.

The fabrication of semiconductor devices with three-dimensional architectures imposes unprecedented demands on advanced plasma dry etching processes. These include the simultaneous requirements of high throughput, high material selectivity, and precise profile control. In conventional reactive ion etching (RIE), fluorocarbon plasma provides both accelerated ion species and reactive neutrals that etch the feature front, while the CF_x radicals promote polymerization that protects sidewalls and enhance selectivity to the amorphous carbon layer (ACL) mask. In this work, we present computational results on the role of CF₄ addition to hydrogen fluoride (HF) plasma for next-generation RIE, specifically cryogenic etching. Simulations were performed by varying the CF₄ concentration in the HF plasma to evaluate its influence on ion densities, neutral species concentration, and electron density. The results show that the densities of CF_x (x = 1–3) ions and radicals increase significantly with CF₄ addition (up to 20%), while the overall plasma density and the excited HF species remain nearly unchanged. The results of plasma density and atomic fluorine density are consistent with the experimental observations of the HF/CF₄ plasma using an absorption probe and the actimetry method. It was verified that the gas-phase reaction model proposed in this study can accurately reproduce the plasma characteristics of the HF/CF₄ system. The coupling of HF-based etchants with CF_x radicals enables polymerization that preserves SiO₂ etching throughput while significantly enhancing etch selectivity against the ACL mask from 1.86 to 5.07, with only a small fraction (~10%) of fluorocarbon gas added. The plasma simulation provides new insights into enhancing the etching performance of HF-based cryogenic plasma etching by controlling the CF₂ radicals and HF reactants through the addition of fluorocarbon gases. Full article

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

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13 pages, 2651 KB

Open AccessArticle

Inactivation Effect and Influencing Factors of Cold Atmospheric Plasma Treatment with Bacteria on Food Contact Materials

by Mingyan Chen, Chenhong Wang, Tian Xie, Zheng Chen and Guimin Xu

Plasma 2025, 8(4), 46; https://doi.org/10.3390/plasma8040046 - 10 Nov 2025

Cited by 2 | Viewed by 1649

Abstract

This study investigated the inactivation effect and influencing factors of cold atmospheric plasma (CAP) treatment with Salmonella typhimurium and Staphylococcus aureus populations on three food contact materials (FCMs)—kraft paper, 304 stainless steel, and glass. The CAP was generated as an atmospheric helium plasma [...] Read more.

This study investigated the inactivation effect and influencing factors of cold atmospheric plasma (CAP) treatment with Salmonella typhimurium and Staphylococcus aureus populations on three food contact materials (FCMs)—kraft paper, 304 stainless steel, and glass. The CAP was generated as an atmospheric helium plasma jet (15 kV, 10.24 kHz, He 4 L/m), and the experimental results indicated that its inactivation effects on two bacterial species gradually increased as the plasma treatment duration increased (0, 1, 2, 3, 4, and 5 min). Three classical sterilization kinetic models (Log-linear, Weibull, and Log-linear + Shoulder + Tail) were employed to evaluate the inactivation efficiency of plasma against bacteria FCMs. Combined with the coefficient of determination (R²), accuracy factor (A_f), and bias factor (B_f), together with the root mean square error (RMSE), it can be concluded that the Log-linear + Shoulder + Tail model had the highest fitting degree among the three sterilization kinetics models. Salmonella typhimurium exhibited weaker resistance than Staphylococcus aureus to the same CAP treatment. Under the same conditions, CAP had the strongest bactericidal effect on the bacteria on the glass surface, followed by those on the 304 stainless steel, and had the weakest bactericidal effect on the bacteria on the kraft paper surface, which might be related to the surface hydrophilicity and roughness of the FCMs. The above results indicated that CAP’s inactivation effect may be influenced by the microbial species as well as the surface characteristics of FCMs. This study provides useful information for future applications of CAP in enhancing food safety. Full article

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

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29 pages, 10085 KB

Open AccessArticle

Low-Current High-Voltage Pulsed Atmospheric Arc Plasma Jet: Nanoparticle Emission from the Cathodic Spot

by Dariusz Korzec, Florian Freund, Isabelle Doelfs, Florian Zacherl, Lucas Kudala and Hans-Peter Rabl

Plasma 2025, 8(4), 44; https://doi.org/10.3390/plasma8040044 - 28 Oct 2025

Cited by 1 | Viewed by 3082

Abstract

The atmospheric pressure plasma jet (APPJ) is a popular type of cold atmospheric plasma (CAP). APPJs based on a pulsed atmospheric arc (PAA) are widely spread in industrial processing. A plasma jet of this type, PlasmaBrush PB3 (PB3), is a subject of diverse [...] Read more.

The atmospheric pressure plasma jet (APPJ) is a popular type of cold atmospheric plasma (CAP). APPJs based on a pulsed atmospheric arc (PAA) are widely spread in industrial processing. A plasma jet of this type, PlasmaBrush PB3 (PB3), is a subject of diverse research activities. The characteristic feature of PB3 is the generation of a low-current (300 mA), high-voltage (1500 V) pulsed (54 kHz) atmospheric arc. A gas flow vortex is used to stabilize the arc and to sustain the circular motion of the cathodic arc foot. During long periods of operation, nozzles acting as arc discharge cathodes erode. Part of the eroded material is emitted as nanoparticles (NPs). These NPs are not wanted in many processing applications. Knowledge of the number, type, and size distribution of emitted NPs is essential to minimize their emissions. In this study, NPs in the size range of 6 to 220 nm, emitted from four different nozzles operated with PB3, are investigated. The differences between the nozzles are in the eroded surface material (copper, tungsten, and nickel), the diameter of the nozzle orifice, the length of the discharge channel, and the position of the cathodic arc foot. Significant differences in the particle size distribution (PSD) and particle mass distribution (PMD) of emitted NPs are observed depending on the type and condition of the nozzle and their operating time. Monomodal and bimodal PMD models are used to approximate emissions from the nozzles with tungsten and copper cores, respectively. The skew-normal distribution function is deemed suitable. The results of this study can be used to control NP emissions, both to avoid them and to utilize them intentionally. Full article

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

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20 pages, 7865 KB

Open AccessArticle

Study on Development of Hydrogen Peroxide Generation Reactor with Pin-to-Water Atmospheric Discharges

by Sung-Young Yoon, Eun Jeong Hong, Junghyun Lim, Seungil Park, Sangheum Eom, Seong Bong Kim and Seungmin Ryu

Plasma 2025, 8(4), 41; https://doi.org/10.3390/plasma8040041 - 14 Oct 2025

Cited by 3 | Viewed by 2249

Abstract

We present an experimentally validated, engineering-oriented framework for the design and operation of pin-to-water (PTW) atmospheric discharges to produce hydrogen peroxide (H₂O₂) on demand. Motivated by industrial needs for safe, point-of-use oxidant supply, we combine time-resolved diagnostics (FTIR, OES), [...] Read more.

We present an experimentally validated, engineering-oriented framework for the design and operation of pin-to-water (PTW) atmospheric discharges to produce hydrogen peroxide (H₂O₂) on demand. Motivated by industrial needs for safe, point-of-use oxidant supply, we combine time-resolved diagnostics (FTIR, OES), liquid-phase analysis (ion chromatography, pH, conductivity), and coupled plasma-chemistry/fluid simulations to link plasma state to aqueous H₂O₂ yield. Under the tested conditions (14.3 kHz, 0.2 kW; electrode to quartz wall distance 12–14 mm; coolant setpoints 0–40 °C), H₂O₂ concentration follows a reproducible non-monotonic trajectory: rapid accumulation during the early treatment (typical peak at ~15–25 min), followed by decline with continued operation. The decline coincides with a robust vibrational-temperature (T_vib) threshold near ~4900 K measured from N₂ emission, and with concurrent NO_X accumulation and bulk acidification. Global chemistry modeling and Fluent flow fields reproduce the observed trend and show that both vibrational excitation (kinetics) and convective transport (mass/heat transfer) determine the productive time window. Based on these results, we formulate practical design rules—electrode gap (power density), discharge current control, thermal/flow management, water quality, and OES-based T_vib monitoring with an automated stop rule—that maximize H₂O₂ yield while avoiding NO_X-dominated suppression. The study provides a clear path for transforming mechanistic plasma insights into deployable, industrial H₂O₂ generator designs. Full article

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

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21 pages, 7032 KB

Open AccessArticle

Non-Thermal Plasma Treatment of Dye-Contaminated Wastewater: A Sustainable Approach for Pollutant Degradation and Enhanced Plant Growth

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

Plasma 2025, 8(4), 40; https://doi.org/10.3390/plasma8040040 - 11 Oct 2025

Cited by 3 | Viewed by 2466

Abstract

The win–win situation of dye degradation and nitrogen fixation in wastewater using non-thermal plasma (NTP) were investigated in this study. Specifically, the feasibility of utilizing plasma-treated dye-contaminated wastewater for seed germination and plant growth was explored. Crystal Violet (CV) and Rhodamine B (RhB) [...] Read more.

The win–win situation of dye degradation and nitrogen fixation in wastewater using non-thermal plasma (NTP) were investigated in this study. Specifically, the feasibility of utilizing plasma-treated dye-contaminated wastewater for seed germination and plant growth was explored. Crystal Violet (CV) and Rhodamine B (RhB) dyes were used as model pollutants, while Sorghum bicolor (great millet) seeds were used to assess germination rates and plant growth responses. In untreated wastewater containing CV and RhB, approximately 45% of seeds germinated after three days, but no significant stem or root growth was observed after 11 days. Plasma treatment significantly enhanced dye degradation, with efficiency improving as treatment time and input power increased. After 16 min of plasma treatment at 1.3 ± 0.2 W input power, about 99% degradation efficiency was achieved for both CV (0.0122 mM) and RhB (0.0104 mM). This degradation was primarily driven by reactive oxygen and nitrogen species (RONS) generated by plasma discharge. When sorghum seeds were germinated using plasma-treated wastewater, the germination rate increased to 65% after three days—20% higher than with untreated wastewater. Furthermore, after 11 days, the average stem length reached 9 cm, while the average root length extended to 7 cm. These findings highlight NTP as a promising and sustainable method for degrading textile industry pollutants while simultaneously enhancing crop productivity through the reuse of treated wastewater. Full article

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

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12 pages, 3315 KB

Open AccessArticle

Polishing Inner Surface of Dies with a Beam of Fast Argon Atoms

by Alexander S. Metel, Marina A. Volosova, Enver S. Mustafaev, Yury A. Melnik and Sergey N. Grigoriev

Plasma 2025, 8(4), 38; https://doi.org/10.3390/plasma8040038 - 28 Sep 2025

Viewed by 901

Abstract

The removal of defective surface layers can substantially improve the quality of various products. It can be carried out using beams of accelerated ions or fast argon atoms. However, it is difficult to process the inner surface of narrow channels. In the present [...] Read more.

The removal of defective surface layers can substantially improve the quality of various products. It can be carried out using beams of accelerated ions or fast argon atoms. However, it is difficult to process the inner surface of narrow channels. In the present work, a narrow beam of fast argon atoms is used to sputter and polish the inner surface of drawing dies with 5.7 mm wide working channels. Due to the high angle of incidence to the channel walls, sputtering with fast argon atoms decreased their roughness to Ra ~ 0.004 µm. Full article

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

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21 pages, 3298 KB

Open AccessArticle

Minimization of Chemical Kinetic Reaction Set for System-Level Study of Non-Thermal Plasma NO_x Abatement Process

by Nicolas Bente, Alfredo Cuellar Valencia and Hubert Piquet

Plasma 2025, 8(3), 36; https://doi.org/10.3390/plasma8030036 - 12 Sep 2025

Cited by 1 | Viewed by 1847

Abstract

A system-level study of a NO_x abatement process by means of non-thermal plasma (NTP) generated with dielectric barrier discharges (DBDs) is the framework of this article. With the goal of system improvement, the kinetic reaction simulation software ZdPlaskin is considered to select [...] Read more.

A system-level study of a NO_x abatement process by means of non-thermal plasma (NTP) generated with dielectric barrier discharges (DBDs) is the framework of this article. With the goal of system improvement, the kinetic reaction simulation software ZdPlaskin is considered to select the most favorable operating conditions in order to optimize NO_x abatement (deNO_x). A parametric exploration of the performance, through variations in operating conditions (temperature, power injection pattern, and input gas mixture composition), requires highly numerous simulations; thus, the shortest possible computation times with robust results are of significant interest. As such, an analysis and filtering method is proposed and detailed to build a minimized chemical kinetic reaction set, allowing us to reliably analyze the impact of the selected operating conditions for the DBD reactor on treatment performance. Full article

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

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24 pages, 6922 KB

Open AccessEditor’s ChoiceArticle

Time- and Space-Resolved Radiation from the Plasma Produced by High-Power, Sub-ns Microwave Pulse Gas Ionization

by Vladislav Maksimov, Adi Haim, Ron Grikshtas, Alexander Kostinskiy, Elhanan Magid, John G. Leopold and Yakov E. Krasik

Plasma 2025, 8(3), 35; https://doi.org/10.3390/plasma8030035 - 5 Sep 2025

Cited by 1 | Viewed by 2528

Abstract

Time- and space-resolved radiation emitted by the plasma produced by a 0.8 ns duration at full width half maximum, ~600 MW maximum power microwave (~9.6 GHz) pulse traversing a hydrogen-, helium-, or air-filled circular waveguide, is studied. Gas ionization by microwaves is an [...] Read more.

Time- and space-resolved radiation emitted by the plasma produced by a 0.8 ns duration at full width half maximum, ~600 MW maximum power microwave (~9.6 GHz) pulse traversing a hydrogen-, helium-, or air-filled circular waveguide, is studied. Gas ionization by microwaves is an old subject but the regime investigated in the present experimental research, of very high-power microwaves and very short pulses using modern diagnostic tools, is new and follows a series of new studies performed so far only in our laboratory, revealing non-linear phenomena never observed before. In the present research, plasma radiation is observed along a slit made in a circular waveguide wall by either an intensified fast frame camera or a streak camera. Using calibrated input and output couplers, the transmission and reflection coefficients of the high-power microwaves were determined over a broad range of gas pressures, 0.1 kPa < P < 90 kPa. It was found that the intensity of the plasma light emission increases significantly after the high-power microwave pulse has left the waveguide. Depending on pressure, the radiation is either uniform along the slit, while the front of the emitted light follows the microwave pulse at a velocity close to its group velocity, or it remains in the vicinity of the input window, indicating that the plasma density is above critical density. It was also found that the radial distribution of radiation depends on pressure. At pressures <10 kPa, when the electron oscillatory energy reaches 20 keV close to the waveguide axis, light emission forms faster near the waveguide walls, where the ionization rate is maximal. Otherwise, when pressure is >80 kPa, light emission is most intense on the axis where the electron oscillatory energy is ~100 eV and the ionization rate is maximal. We also studied the UV radiation from the plasma, the duration of which was found to be longer than the duration of visible light emission. This indicates the existence of energetic electrons for tens of ns after the high-power microwave pulse has left the observation region. Considering that the emitted light intensity depends on the plasma density and temperature, the observed data may be used for a comparison with the results of collisional radiative models if the electron time and spatial energy distribution is known. Full article

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

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14 pages, 1657 KB

Open AccessArticle

Fluorine Plasma Functionalization of Borophene Nanoflakes

by Juan Casanova-Chafer, Pedro Atienzar and Carla Bittencourt

Plasma 2025, 8(3), 33; https://doi.org/10.3390/plasma8030033 - 22 Aug 2025

Cited by 1 | Viewed by 2407

Abstract

Theoretical studies have indicated that borophene is a promising two-dimensional material characterized by remarkable chemical, mechanical, and electrical properties. Nonetheless, its practical applications in areas such as catalysis and gas sensing are hindered by the limited density of reactive sites in its pristine [...] Read more.

Theoretical studies have indicated that borophene is a promising two-dimensional material characterized by remarkable chemical, mechanical, and electrical properties. Nonetheless, its practical applications in areas such as catalysis and gas sensing are hindered by the limited density of reactive sites in its pristine form. To address this limitation, the present study explores the controlled fluorination of borophene nanoflakes as a strategy to modify their surface chemistry and enhance the availability of active sites. Furthermore, it is anticipated that surface fluorination will improve hydrophobicity, which is crucial for reducing humidity-related interference in sensing applications. In this study, we report the successful functionalization of borophene nanoflakes with fluorine using a plasma arc discharge technique for the first time. Borophene nanolayers were synthesized via a sonochemical-assisted exfoliation method, yielding nanosheets with an average lateral dimension of approximately 100 nm. The fluorinated samples were characterized using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and high-resolution transmission electron microscopy (HRTEM). A systematic investigation of plasma exposure durations demonstrated that fluorine was effectively introduced as a dopant while maintaining the crystallinity of the borophene lattice. Full article

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

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13 pages, 3312 KB

Open AccessArticle

MMMnet: A Neural Network Surrogate for Real-Time Transport Prediction Based on the Updated Multi-Mode Model

by Khadija Shabbir, Brian Leard, Zibo Wang, Sai Tej Paruchuri, Tariq Rafiq and Eugenio Schuster

Plasma 2025, 8(3), 32; https://doi.org/10.3390/plasma8030032 - 22 Aug 2025

Cited by 2 | Viewed by 2342

Abstract

The Multi-Mode Model (MMM) is a physics-based anomalous transport model integrated into TRANSP for predicting electron and ion thermal transport, electron and impurity particle transport, and toroidal and poloidal momentum transport. While MMM provides valuable predictive capabilities, its computational cost, although manageable for [...] Read more.

The Multi-Mode Model (MMM) is a physics-based anomalous transport model integrated into TRANSP for predicting electron and ion thermal transport, electron and impurity particle transport, and toroidal and poloidal momentum transport. While MMM provides valuable predictive capabilities, its computational cost, although manageable for standard simulations, is too high for real-time control applications. MMMnet, a neural network-based surrogate model, is developed to address this challenge by significantly reducing computation time while maintaining high accuracy. Trained on TRANSP simulations of DIII-D discharges, MMMnet incorporates an updated version of MMM (9.0.10) with enhanced physics, including isotopic effects, plasma shaping via effective magnetic shear, unified correlation lengths for ion-scale modes, and a new physics-based model for the electromagnetic electron temperature gradient mode. A key advancement is MMMnet’s ability to predict all six transport coefficients, providing a comprehensive representation of plasma transport dynamics. MMMnet achieves a two-order-of-magnitude speed improvement while maintaining strong correlation with MMM diffusivities, making it well-suited for real-time tokamak control and scenario optimization. Full article

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

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24 pages, 8575 KB

Open AccessEditor’s ChoiceArticle

Space Charge Structures on Spherical Hollow Electrodes

by Florin Enescu, Codrina Ionita, Dan Gheorghe Dimitriu and Roman Schrittwieser

Plasma 2025, 8(3), 30; https://doi.org/10.3390/plasma8030030 - 25 Jul 2025

Viewed by 1805

Abstract

In this article, we present an overview of our investigations on the formation and behavior of space charge structures in an argon discharge plasma on gridded and smooth spherical hollow electrodes with and without orifices. Four experiments are described, in which we have [...] Read more.

In this article, we present an overview of our investigations on the formation and behavior of space charge structures in an argon discharge plasma on gridded and smooth spherical hollow electrodes with and without orifices. Four experiments are described, in which we have used the following: (1) one spherical gridded sphere with one orifice, (2) one hollow smooth stainless steel sphere with two opposing orifices, (3) two smooth polished stainless steel spherical electrodes without orifices, (4) two smooth polished stainless steel spherical electrodes with opposing orifices. The experiments were conducted at the University of Innsbruck in a stainless steel cylindrical chamber (the former Innsbruck DP machine—IDP), and at the Alexandru Ioan Cuza University of Iaşi (Romania) in a Pyrex Vacuum Chamber (PCH). As diagnostics, we have used mainly optical emission spectroscopy to determine electron temperature and density. Full article

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

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18 pages, 995 KB

Open AccessEditor’s ChoiceArticle

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

Cited by 2 | Viewed by 2974

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 KB

Open AccessEditor’s ChoiceArticle

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

Cited by 7 | Viewed by 2955

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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19 pages, 1546 KB

Open AccessEditor’s ChoiceArticle

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

Cited by 2 | Viewed by 3461

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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16 pages, 66642 KB

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 | Viewed by 2278

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 KB

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

Cited by 2 | Viewed by 2237

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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14 pages, 488 KB

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

Viewed by 1972

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, 3975 KB

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

Cited by 4 | Viewed by 2197

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, 13969 KB

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

Cited by 4 | Viewed by 3763

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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15 pages, 2986 KB

Open AccessReview

A Tutorial on the Mechanism of Beam-Field Interactions in Virtual Cathode Oscillators

by Weihua Jiang

Plasma 2025, 8(4), 51; https://doi.org/10.3390/plasma8040051 - 13 Dec 2025

Viewed by 1269

Abstract

This review article is the third of a three-article introductory series on virtual cathode oscillators. The first article has laid the theoretical ground for understanding the physical properties of the virtual cathode, and the second article has provided a numerical tool for studying [...] Read more.

This review article is the third of a three-article introductory series on virtual cathode oscillators. The first article has laid the theoretical ground for understanding the physical properties of the virtual cathode, and the second article has provided a numerical tool for studying virtual cathode oscillation. This third article focuses on the interaction between the electron beam and electromagnetic field. The virtual cathode oscillator has been studied for decades with the aim of developing it as high-power microwave source. The beam-field interaction has been one of the core issues that always perplexes both experimentalists and theorists. Using the physical model established in the first article and the numerical method described in the second article, this article is an attempt to answer some of the key questions based on a more comprehensive description of the device and its interaction process. This article is expected to serve as a reference for young researchers and students working on high-power microwaves and pulsed particle beams. Full article

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

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