Plasma

125 pages, 21316 KB

Open AccessReview

Low-Current High-Voltage Vortex-Stabilized Pulsed Arc Atmospheric-Pressure Plasma Jets: Processes and Processing

by Dariusz Korzec, Florian Hoppenthaler and Simona Lerach

Plasma 2026, 9(3), 24; https://doi.org/10.3390/plasma9030024 - 1 Jul 2026

Among numerous atmospheric-pressure plasma jets (APPJs), high industrial acceptability has been reached for the ones based on high-voltage, low-current, vortex-stabilized arc, typically operated with kHz DC-pulses. This review explores the interrelations between the “process” in a chemical–physical sense and “process”, or to better [...] Read more.

Among numerous atmospheric-pressure plasma jets (APPJs), high industrial acceptability has been reached for the ones based on high-voltage, low-current, vortex-stabilized arc, typically operated with kHz DC-pulses. This review explores the interrelations between the “process” in a chemical–physical sense and “process”, or to better differentiate, “processing” in the sense of technological treatment, with respect to such APPJs. The mutual dependence of the processing requirements (e.g., high processing speed, compatibility with robotic processing, low total cost of ownership, reliability, and long service intervals) and the physical and chemical processes in the plasma jet are analyzed. The focus is on the hybrid character of the produced plasma, comprising a non-equilibrium arc and a diffuse plasma. Different operation modes of the gliding arc discharge (GAD) are discussed. The reviewed chemical processes are the generation of reactive oxygen–nitrogen species (RONS), oxidation and reduction reactions, and interactions with vapors, solids, and liquids. The considered processing examples are established applications, such as surface activation, cleaning, oxide reduction, film removal, and coating, as well as emerging applications for sterilization and plasma-activated water (PAW) production. Full article

20 pages, 13088 KB

Open AccessArticle

Formation of Electric Potential Dips and Peaks by Electron-Ion Two-Stream Instability in a Plasma Chamber with an Electron Emitter LaB₆ as the Cathode

by Lou-Chuang Lee, Kun-Han Lee, Hau-Kun Jhuang and Dong-Dong Ni

Plasma 2026, 9(3), 23; https://doi.org/10.3390/plasma9030023 - 1 Jul 2026

Abstract

This paper presents a conducting-channel model aimed at elucidating the generation of high-energy particles within a plasma chamber. Initially, the chamber is charged with neutral hydrogen gas at a density of approximately ~3.3 × 10²²/m³, equivalent to 1 torr [...] Read more.

This paper presents a conducting-channel model aimed at elucidating the generation of high-energy particles within a plasma chamber. Initially, the chamber is charged with neutral hydrogen gas at a density of approximately ~3.3 × 10²²/m³, equivalent to 1 torr at 300 K under ideal gas conditions. A Townsend discharge (dark discharge), driven by an externally imposed electric potential (500–1000 V) across the cathode and anode, is utilized to induce partial ionization of the hydrogen gas. Once a stable conducting channel with a high conductivity is established, a low electric potential (e.g., 100–500 V) is introduced to sustain the current in the conducting channel. Our investigation then delves into the impact of a high-emissivity cathode, such as lanthanum hexaboride (LaB6), on an arc discharge. We develop a theoretical model of the conducting channel that may emerge under these conditions. As the cathode surface heats, thermionic electrons form a localized layer of negative charge density outside the cathode, leading to an electric potential dip. Our multi-fluid simulations reveal the emergence of an electron-ion two-stream instability owing to the high-density electron layer, leading to the appearance of multiple potential peaks and dips, each measuring several to tens of kV. We delineate a set of conditions conducive to the formation of these potential peaks and dips within the conducting channel. Our proposed scenario furnishes a framework for elucidating electron and ion acceleration within a weakly ionized plasma chamber. Full article

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18 pages, 3192 KB

Open AccessArticle

Study on Arc Characteristics and Structural Optimization of a 550 kV Environmentally Friendly Gas Circuit Breaker

by Nian Tang, Hanyue Zhao and Dongwei Sun

Plasma 2026, 9(2), 22; https://doi.org/10.3390/plasma9020022 - 22 Jun 2026

Abstract

With increasingly stringent restrictions on SF₆ greenhouse gas emissions, C₄F₇N-based gas mixtures have attracted considerable attention as promising alternatives for high-voltage circuit breakers; however, their relatively weaker arc-quenching capability poses significant challenges for interruption chamber design at high [...] Read more.

With increasingly stringent restrictions on SF₆ greenhouse gas emissions, C₄F₇N-based gas mixtures have attracted considerable attention as promising alternatives for high-voltage circuit breakers; however, their relatively weaker arc-quenching capability poses significant challenges for interruption chamber design at high voltage levels. In this study, a 3.5% C₄F₇N/83.5% CO₂/13% O₂ gas mixture was used as the arc-extinguishing medium in a 550 kV environmentally friendly gas circuit breaker. Based on a magnetohydrodynamic (MHD) model considering PTFE nozzle ablation effects, systematic optimization studies were conducted on key structural parameters of the puffer-type interruption chamber, including the exhaust hole diameter, nozzle throat diameter and length, arcing contact diameter, and downstream expansion angle. Simulations under arcing times of 9.9 ms and 11.4 ms were performed to evaluate chamber pressure, axial temperature, extinction peak voltage, and post-arc conductance characteristics. The results indicate that extending the nozzle throat straight section to 70 mm, enlarging the exhaust hole, and increasing the moving contact radius can effectively enhance pressure buildup, reduce arc-core temperature, and improve dielectric recovery capability. Under the 11.4 ms arcing condition, the optimized structure achieved an extinction peak voltage of 6972.4 V and a G200 value of 0.731 ms, demonstrating substantially improved interruption performance. These findings reveal the synergistic relationship between arcing time and structural parameters and provide theoretical guidance for the engineering design of environmentally friendly high-voltage gas circuit breakers. Full article

(This article belongs to the Topic Advanced Electromagnetic Modeling and Simulation for Multidisciplinary Engineering Systems)

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Graphical abstract

15 pages, 4127 KB

Open AccessArticle

Effects of Non-Thermal Electrons and Non-Extensive Positrons on Dust-Ion-Acoustic Solitary Waves in an Unmagnetized Plasma

by Satyendra Nath Barman and Kingkar Talukdar

Plasma 2026, 9(2), 21; https://doi.org/10.3390/plasma9020021 - 10 Jun 2026

Abstract

In this study, we investigated the existence and properties of solitons in an unmagnetized plasma composed of positive ions, negative ions, negatively charged dust grains, non-thermal electrons and non-extensive positrons. We have conducted our study on this complex plasma model because it moves [...] Read more.

In this study, we investigated the existence and properties of solitons in an unmagnetized plasma composed of positive ions, negative ions, negatively charged dust grains, non-thermal electrons and non-extensive positrons. We have conducted our study on this complex plasma model because it moves away from simplistic and idealized plasma models. Also, a study of solitons has not previously been conducted on this complex plasma model. Through the Sagdeev potential method, we have derived the energy integral and investigated the variation in the Sagdeev potential for different values of the parameters that are involved in our plasma model. We have found that the non-thermal parameter (β) and the non-extensive parameter (q) significantly influence the features of the solitons. The features of the solitons are also found to be influenced by the Mach number (M), the negative-ion-to-positive-ion mass ratio (

Ω

), the positron-to-positive-ion density ratio (δ_p), the electron-to-positron temperature ratio (σ_p), the dust charge density ratio (δ_d) and the negative-ion-to-positive-ion density ratio (δ_). The results from our study can be useful in investigating plasma in astrophysical environments, such as cometary tails and interstellar clouds. Full article

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23 pages, 9716 KB

Open AccessArticle

Influence of Different Catalysts on Ammonia Synthesis Performance in Coaxial DBD Plasma

by Fangcheng Qiu, Xin Zhang, Shuai Jiang, Huilin Zhou, Lin Wang, Yufeng Song, Jian Huang, Xin Zheng, Ronghai Liu and Xuekai Pei

Plasma 2026, 9(2), 20; https://doi.org/10.3390/plasma9020020 - 4 Jun 2026

Abstract

In the renewable energy-driven “green electricity–green hydrogen–green ammonia” pathway, the development of low-temperature and low-energy-consumption ammonia synthesis technologies is of great significance. In this work, a plasma-catalytic ammonia synthesis system was established using a coaxial dielectric barrier discharge (DBD) reactor. The effects of [...] Read more.

In the renewable energy-driven “green electricity–green hydrogen–green ammonia” pathway, the development of low-temperature and low-energy-consumption ammonia synthesis technologies is of great significance. In this work, a plasma-catalytic ammonia synthesis system was established using a coaxial dielectric barrier discharge (DBD) reactor. The effects of different catalysts, including Ag, Cu, γ-Al₂O₃, BaTiO₃ and Co/BaTiO₃, Ni/BaTiO₃ on ammonia synthesis performance were systematically investigated. The reaction process was analyzed using voltage–current waveforms, Lissajous figures, and optical emission spectroscopy (OES). The results show that different catalytic systems have a significant influence on ammonia synthesis performance, with the promotional effect ranked as follows: Ni/BaTiO₃ > Co/BaTiO₃ > BaTiO₃ > Ag > γ-Al₂O₃ > Cu. Among them, Ni/BaTiO₃ exhibited the best performance. Under the conditions of N₂:H₂ = 1:1 and a gas flow rate of 2.5 L/min, the NH₃ synthesis rate reached 259.48 μmol/min, and the maximum energy efficiency reached 1.40 g-NH₃/kWh. Catalyst characterization results indicate that the BaTiO₃ support maintained a stable crystal structure, while the loaded metal species were highly dispersed and uniformly distributed on the support surface, which is beneficial for the adsorption and conversion of reactive species on the catalyst surface. Discharge characteristic analysis shows that the introduction of BaTiO₃ enhanced the local electric field and improved the uniformity of micro-discharges, while the further incorporation of metal active components strengthened the micro-discharge behavior. OES results reveal that the intensities of characteristic emission lines, such as NH, N₂⁺, and Hα, were significantly enhanced in the Ni/BaTiO₃ system, facilitating the formation and conversion of NH_x intermediates. The superior performance of Ni/BaTiO₃ is attributed to the coupling between BaTiO₃-induced dielectric enhancement and Ni-promoted surface hydrogenation and NH₃ desorption. This work provides mechanistic insight into catalyst-dependent DBD plasma-catalytic ammonia synthesis and offers an experimental basis for the further optimization of plasma-based ammonia production. Full article

(This article belongs to the Special Issue Recent Advances of Dielectric Barrier Discharges, 2nd Edition)

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14 pages, 1606 KB

Open AccessArticle

Characteristics of Microsecond-Pulse Source for Atmospheric Pressure Helium Plasma Jet

by Chen Ma, Li Yao, Jialu Liu and Feng He

Plasma 2026, 9(2), 19; https://doi.org/10.3390/plasma9020019 - 2 Jun 2026

Abstract

In this work, based on a half-bridge circuit and pulse transformer, a miniaturized and low-cost microsecond high-voltage pulsed power supply for the atmospheric pressure plasma jet (APPJ) is designed. Because of the low bus voltage of the half-bridge circuit, low-voltage switches can be [...] Read more.

In this work, based on a half-bridge circuit and pulse transformer, a miniaturized and low-cost microsecond high-voltage pulsed power supply for the atmospheric pressure plasma jet (APPJ) is designed. Because of the low bus voltage of the half-bridge circuit, low-voltage switches can be chosen by the power supply. The characteristics of the output high voltage of the power supply are studied. The experimental results show that uni-polar and bi-polar pulses can be generated by the power supply. The high-voltage pulses have good consistency at different frequencies, and the amplitude of the high-voltage pulse varies approximately linearly with the bus voltage. A needle-ring plasma jet device was driven by the uni-polar pulse of this supply, and the single discharge current pulse can be obtained at the rising edge and falling edge of the high-voltage pulse, respectively. The effects of voltage pulse on APPJ and the characteristics of jet are also investigated. The results show that the plasma jet is only formed at the rising edge of the voltage pulse. The jet length is almost unaffected by the pulse frequency, whereas the normalized intensity of most species increases with frequency linearly. Full article

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

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11 pages, 1015 KB

Open AccessArticle

Deep Learning-Based Reconstruction of Particle Beam Energy Spectra from Attenuation Curve Data

by Vasily Kozhevnikov, Andrey Kozyrev, Dmitry Sorokin, Victor Tarasenko, Dmitry Beloplotov, Eugene Baksht and Mikhail Lomaev

Plasma 2026, 9(2), 18; https://doi.org/10.3390/plasma9020018 - 2 Jun 2026

Abstract

This paper introduces a deep learning-based methodology for reconstructing particle beam energy spectra from experimental attenuation curves. This task involves solving a classic ill-posed inverse problem for a Fredholm integral equation of the first kind. Unlike traditional Arsenin–Tikhonov regularization, the proposed framework utilizes [...] Read more.

This paper introduces a deep learning-based methodology for reconstructing particle beam energy spectra from experimental attenuation curves. This task involves solving a classic ill-posed inverse problem for a Fredholm integral equation of the first kind. Unlike traditional Arsenin–Tikhonov regularization, the proposed framework utilizes two coupled neural networks for spectrum approximation and adaptive kernel correction. This approach explicitly accounts for measurement uncertainties in the experimental data. As a mesh-free technique, it operates directly on raw sparse experimental datasets without preprocessing. Validation using data from subnanosecond electron beams in gas-filled and vacuum diodes demonstrates that the method successfully resolves non-trivial two-peak spectral structures. In particular, it reliably identifies populations of “anomalous” high-energy electrons that are often obscured by classical regularization artifacts. Full article

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

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15 pages, 2675 KB

Open AccessArticle

The Anti-Inflammatory Activity of No-Ozone Cold Plasma Can Be Delivered Through a Conductive Metal Needle on TNFα-Treated C2C12 Mice Muscle Cells In Vitro

by Jeong-Hae Choi, Seung-Ah Park, Hyun-Young Lee, Wonkyu Hong, Jaehong Kim, Jin-Woo Hong and Gyoo-Cheon Kim

Plasma 2026, 9(2), 17; https://doi.org/10.3390/plasma9020017 - 26 May 2026

Abstract

Recently, an anti-inflammatory effect of no-ozone cold plasma (NCP) has been reported, but the direct use of NCP for treating muscle inflammation is very difficult since NCP is a form of gas. In this study, we tested whether the anti-inflammatory effect of the [...] Read more.

Recently, an anti-inflammatory effect of no-ozone cold plasma (NCP) has been reported, but the direct use of NCP for treating muscle inflammation is very difficult since NCP is a form of gas. In this study, we tested whether the anti-inflammatory effect of the NCP could be delivered through conductive metal needles to reduce muscle inflammation. C2C12 mouse muscle cells were treated with TNFα to induce muscle inflammation and then treated with NCP and a conductive metal needle separately or in combination. The effects of NCP and a needle were monitored by performing RT-PCR and Western blot analysis. As a result, NCP effectively suppressed the TNFα-mediated expression of the TNFα, IL1β, and FasL genes, but this effect weakened as the distance between the cells and the NCP increased. On the other hand, treatment of cells with a plasma-needle (PN) had an anti-inflammatory effect regardless of distance, and the anti-inflammatory effect of the PN was maintained under conditions where the gas flow of NCP was not delivered to the cells. It is believed that the PN-mediated activation of media plays a pivotal role in the anti-inflammatory effect of the PN. Finally, this study also showed that electroacupuncture can inhibit TNFα-induced inflammatory gene expression in a manner like a PN. Taken together, the results of this study demonstrate that the anti-inflammatory effect of NCP can be delivered through metal needles, suggesting that PN may be useful for treating inflammatory muscle pain. Full article

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14 pages, 2434 KB

Open AccessArticle

Study on the Key Influence Factors of Interrupting Characteristics of C₄F₇N Gas Mixture Self-Blast Circuit Breaker

by Ke Wang, Yuying Shi, Bochen Li, Yiheng Zhang, Suoyun Yang and Xianping Zhao

Plasma 2026, 9(2), 16; https://doi.org/10.3390/plasma9020016 - 20 May 2026

Abstract

High-voltage self-blast circuit breakers feature complex gas flow field dynamics during the arc interruption process due to the multiple gas chambers and valves in the interrupter. The structure of key interrupter components and the characteristics of the operating mechanism significantly influence the gas [...] Read more.

High-voltage self-blast circuit breakers feature complex gas flow field dynamics during the arc interruption process due to the multiple gas chambers and valves in the interrupter. The structure of key interrupter components and the characteristics of the operating mechanism significantly influence the gas flow field behavior, thereby affecting the breaking performance. The C₄F₇N gas mixture is currently the most promising alternative to SF₆. However, the influence mechanisms of various factors on its breaking performance remain unclear, which limits the design of C₄F₇N-based self-blast interrupter chambers. This paper investigates the impact of nozzle throat length and mechanism stroke on the breaking performance of a 126 kV double-motion self-blast circuit breaker prototype by establishing a magnetohydrodynamic (MHD) arc model for C₄F₇N gas mixtures. The results indicate that a longer throat length can enhance the pressure-buildup capability in the expansion chamber to some extent, but its effect on short arcing times is limited, whereas it has a more pronounced influence on medium and long arcing times. However, it also impedes arc energy dissipation, potentially reducing the breaking capability for short and medium arcing times while improving performance for long arcing times. A larger mechanism stroke not only ensures a greater contact gap at current zero for long arcing times but also accelerates the gas flow velocity between the contacts, facilitating arc energy dissipation and enhancing the thermal interruption performance. Full article

(This article belongs to the Topic Advanced Electromagnetic Modeling and Simulation for Multidisciplinary Engineering Systems)

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31 pages, 3749 KB

Open AccessReview

Design Considerations for Low-Temperature Plasma Production in Air Using Pulsed Dielectric Barrier Discharges: A Review

by Luutzen Franciscus Ate Wymenga, Jan van Turnhout, Mohamad Ghaffarian Niasar, Henk van Zeijl, Willem Dirk van Driel and Guoqi Zhang

Plasma 2026, 9(2), 15; https://doi.org/10.3390/plasma9020015 - 14 May 2026

Abstract

Low-temperature atmospheric plasma (LTP) is widely used in industrial processes, such as disinfection, surface modification and wastewater treatment. The dielectric barrier discharge (DBD) is regarded as one of the most robust and reliable methods for generating LTP in ambient air. Compared to conventional [...] Read more.

Low-temperature atmospheric plasma (LTP) is widely used in industrial processes, such as disinfection, surface modification and wastewater treatment. The dielectric barrier discharge (DBD) is regarded as one of the most robust and reliable methods for generating LTP in ambient air. Compared to conventional AC excitation, pulsed powering offers several advantages (i.e., lower energy use and heat production). The present trend is to use short and fast pulses (in the nano- and picosecond range). In this review, the key design parameters of a DBD (barrier thickness, relative permittivity and gap distance) are discussed. Material-specific phenomena like surface charging and degradation are analyzed. The complex interactions between the pulse source and DBD are examined. By mapping the interdependencies, this review aims to support the rational design and optimization of pulsed DBD systems, and to facilitate their broader industrial use. Full article

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24 pages, 4051 KB

Open AccessArticle

Magnetic Confinement Effects in a Hybrid DC–RF Internal-Antenna Inductively Coupled Plasma: Spatial Diagnostics and Semi-Empirical Modelling

by Mahmood Nasser

Plasma 2026, 9(2), 14; https://doi.org/10.3390/plasma9020014 - 8 May 2026

Abstract

A hybrid DC–RF inductively coupled plasma (ICP) driven by a single-turn internal antenna was experimentally investigated to quantify magnetic confinement effects in low-pressure argon discharges. Superposition of a dc current on the RF antenna generated an azimuthal magnetic field that modified electron transport [...] Read more.

A hybrid DC–RF inductively coupled plasma (ICP) driven by a single-turn internal antenna was experimentally investigated to quantify magnetic confinement effects in low-pressure argon discharges. Superposition of a dc current on the RF antenna generated an azimuthal magnetic field that modified electron transport and reduced cross-field diffusion in the near-antenna region. Spatially resolved measurements of plasma density, electron temperature, plasma potential, and magnetic-field components were obtained using Langmuir, emissive, and B-dot probes. Increasing the dc current enhanced electron confinement and increased the plasma density by up to an order of magnitude at low RF power, together with improved radial and axial uniformity. A semi-empirical diffusion model incorporating electron-temperature-dependent ambipolar transport reproduced the measured ion-density distributions, ni(R,Z), within ±15%. The results support the interpretation that the discharge behaviour is governed by the coupled effects of localized magnetic confinement and inductive power deposition, and show that hybrid DC–RF excitation provides an effective route to denser and more spatially extended plasmas under low-pressure conditions. Full article

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15 pages, 6137 KB

Open AccessArticle

Experimental Investigation of Arc Characteristics Between Piezoelectrically Actuated Contacts in Air, Vacuum, and Nitrogen

by Mohmmad Al-Dweikat, Moath Bani Fayyad, Hana Rababah and Qirong Wu

Plasma 2026, 9(2), 13; https://doi.org/10.3390/plasma9020013 - 8 May 2026

Abstract

Piezoelectric actuators enable ultra-fast switching due to their microsecond-scale response and high acceleration capability. This study experimentally investigates arc behavior in air, vacuum, and nitrogen using round and flat contacts driven by an amplified piezoelectric actuator. Unlike prior work focused mainly on actuation [...] Read more.

Piezoelectric actuators enable ultra-fast switching due to their microsecond-scale response and high acceleration capability. This study experimentally investigates arc behavior in air, vacuum, and nitrogen using round and flat contacts driven by an amplified piezoelectric actuator. Unlike prior work focused mainly on actuation dynamics, this study provides a multi-medium comparison and investigates the coupled effects of drive operating time and contact geometry on arc characteristics. Arc tests were conducted using a capacitor discharge platform, with synchronized electrical measurements and high-speed imaging. In air (140 V, 350 A), arc voltage increased with rise time, reaching 800 V, 840 V, and 1080 V at 0.5 ms, 1 ms, and 2 ms, respectively, while shorter rise times reduced arc duration but promoted reignition. In vacuum (140–200 V), arc voltage stabilized at 80–90 V, with longer rise times extending arc duration; round contacts exhibited faster voltage rise and higher peaks. In nitrogen (140–200 V), higher voltages were obtained at shorter rise times, reaching 2680 V, 2600 V, and 2320 V at 0.5 ms, 1 ms, and 2 ms, respectively, with reduced arc duration. Across all media, round contacts consistently produced higher arc voltages than flat contacts. These results demonstrate that drive dynamics and contact geometry critically influence arc voltage and duration, providing practical guidelines for the design of high-speed piezoelectric-based switching devices. Full article

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20 pages, 6703 KB

Open AccessArticle

Laser Wakefield Electron Acceleration in a Periodically Modulated Plasma Density Profile

by Rareș Iovănescu, Radu P. Daia, Anana C. Gîrlea, Emil I. Slușanschi and Cătălin M. Ticoș

Plasma 2026, 9(2), 12; https://doi.org/10.3390/plasma9020012 - 29 Apr 2026

Abstract

We investigate laser wakefield electron acceleration in a periodic plasma density profile using 2D PIC simulations with the EPOCH code. The profile of the electron density has the form [...] Read more.

We investigate laser wakefield electron acceleration in a periodic plasma density profile using 2D PIC simulations with the EPOCH code. The profile of the electron density has the form

n (x) = n_{0} (1 + δ sin 2 π x / x_{0})

, where

n_{0}

is the steady electron density,

x_{0} = 100 m

is the spatial periodicity in the laser propagation direction and

δ

, taking the values 0,

0.1

,

0.3

,

0.5

and

0.7

, is the modulation parameter. The bubble size varies with the modulated plasma density, thereby influencing the electron acceleration, which occurs within a continuously changing bubble structure. We propose an analytical model to estimate the energies of the accelerated electrons, and evaluate the maximum electron energies at

500 f s

intervals for the five modulated density profiles. We then calculate the dephasing and depletion lengths for these modulated plasma profiles and examine their dependence on

δ

. The results show a growth in both lengths with

δ

, with depletion being the main limitation in these cases. Additionally, we compute and compare the transverse emittance of the self-injected electron bunches corresponding to the various density profiles at the same simulation time, and other characteristics, like the center energy and energy spread. Emittance is observed to experience a decrease with the increase in the modulation parameter. Full article

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26 pages, 22809 KB

Open AccessArticle

Measurements and Modeling of the Hydrogen Balmer Radiation Intensities in the Linear Plasma Device PSI-2

by Vladislav Kotov, Marc Sackers, Oleksandr Marchuk, Michael Reinhart, Gennady Sergienko, Arkadi Kreter, Mauricio Gago, Bernhard Unterberg and Sebastijan Brezinsek

Plasma 2026, 9(2), 11; https://doi.org/10.3390/plasma9020011 - 1 Apr 2026

Abstract

Spatially resolved absolute intensities of the atomic lines

H_{α}

,

H_{β}

,

H_{γ}

, and

H_{δ}

have been measured and analyzed in pure hydrogen plasma in the linear plasma device PSI-2. Two regimes have been investigated, with nominal (0.04 [...] Read more.

Spatially resolved absolute intensities of the atomic lines

H_{α}

,

H_{β}

,

H_{γ}

, and

H_{δ}

have been measured and analyzed in pure hydrogen plasma in the linear plasma device PSI-2. Two regimes have been investigated, with nominal (0.04 Pa) and elevated (0.5 Pa) gas pressure in the sample chamber. The measurements have been compared with local 0D calculations taking into account radiation from

H (n = 1)

,

H_{2}

, and

H_{2}^{+}

channels. A baseline plasma chemical mechanism developed in magnetic fusion research was applied to calculate the

H_{2}^{+}

density. Both the plasma chemical mechanism and the population factors applied are based on Sawada–Fujimoto collision-radiative model of atomic and molecular hydrogen. The calculations were found to reproduce both the absolute radiation and the line radiation intensity ratios measured in the 0.04 Pa experiment with electron temperature

T_{e}

= 2–10 eV and electron density ∼5 × 10¹⁷ m⁻³. An exception is the

H_{α} / H_{γ}

intensity ratio, which tends to be overestimated by the model. The calculations suggest that the majority of the observed Balmer radiation in this regime is due to the

H_{2}^{+}

channel. At the same time, both the applied simplified approach without detailed transport modeling and the baseline mechanism were found to be inappropriate for the 0.5 Pa experiment with reduced

T_{e}

= 1–5 eV. This experimental regime can serve as a benchmark of more sophisticated hydrogen plasma models. Full article

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23 pages, 2425 KB

Open AccessArticle

Spatially Resolved Inactivation of Escherichia coli in a RF (13.56 MHz) Capacitively Coupled Air Plasma at 4.0 mbar

by Mahmood Nasser, Layla Nasser, Fatima Makhlooq, Batool Abulwahab and Elias Naser

Plasma 2026, 9(2), 10; https://doi.org/10.3390/plasma9020010 - 31 Mar 2026

Abstract

A spatially resolved investigation of bacterial inactivation using a radiofrequency (13.56 MHz) capacitively coupled plasma (RF CCP) discharge operating in ambient air at 4.0 mbar is presented. The plasma was generated in a parallel-plate reactor without external gas precursors and characterized using Langmuir [...] Read more.

A spatially resolved investigation of bacterial inactivation using a radiofrequency (13.56 MHz) capacitively coupled plasma (RF CCP) discharge operating in ambient air at 4.0 mbar is presented. The plasma was generated in a parallel-plate reactor without external gas precursors and characterized using Langmuir probe diagnostics and optical emission spectroscopy (OES). Electron densities on the order of 109 cm³ were measured near the powered electrode, exhibiting pronounced axial and radial gradients across the discharge volume. OES revealed strong excitation of oxygen- and nitrogen-containing emitters, including O I (777 nm), N₂ s positive system (337–380 nm), and N₂⁺ first negative system features, with emission intensities increasing monotonically with applied RF power. The bactericidal performance was evaluated using Escherichia coli American Type Culture Collection (ATCC) 11775 exposed at different axial and radial positions within the reactor. At a fixed exposure time of 60 s, the log₁₀ reduction increased nonlinearly with RF power, rising from 0.29 at 20 W to 0.81 at 40 W, followed by a sharp transition to the assay reporting ceiling (≥2.95-log₁₀ under the adopted half-count correction) at 50 W and above. Time-resolved measurements at 50 W demonstrated rapid inactivation kinetics, with measurable reductions occurring within 5–10 s and reaching the reporting ceiling within 60 s. In contrast, samples positioned at the chamber periphery or approximately 20 cm from the discharge center exhibited negligible inactivation, confirming strong spatial localization of the biocidal effect. These results identify a threshold-like operating regime in which increased discharge intensity produces rapid inactivation in the plasma core while remaining strongly position dependent. The findings establish medium pressure, air-based RF CCP as an efficient, gas-free, and spatially controllable platform for localized surface decontamination under non-thermal conditions. Full article

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18 pages, 2222 KB

Open AccessArticle

Unsupervised Anomaly Detection of Internal Reconnection Events in the VEST Spherical Tokamak

by Dae-Won Ok, Dae-Yeol Pyo, Hong-Sik Yun, Yong-Seok Hwang and Yong-Su Na

Plasma 2026, 9(2), 9; https://doi.org/10.3390/plasma9020009 - 29 Mar 2026

Abstract

Internal reconnection events (IREs) are rapid magnetohydrodynamic phenomena that play an important role in the confinement and stability of spherical tokamak plasmas. Reliable identification of IREs in experimental data is challenging due to short discharge durations, ambiguous event boundaries, and the limited availability [...] Read more.

Internal reconnection events (IREs) are rapid magnetohydrodynamic phenomena that play an important role in the confinement and stability of spherical tokamak plasmas. Reliable identification of IREs in experimental data is challenging due to short discharge durations, ambiguous event boundaries, and the limited availability of labeled data. In this study, we propose an unsupervised, event-level IRE detection framework based on anomaly detection techniques and apply it to experimental data from the VEST spherical tokamak. The proposed framework combines a two-stage detection strategy using plasma current and

H_{α}

emission signals with sliding-window segmentation and event-level evaluation, enabling physically meaningful IRE identification without labeled training data. Three unsupervised models—K-Nearest Neighbors (KNN), One-Class Support Vector Machine (OCSVM), and an autoencoder (AE)—are evaluated within a unified framework. All models achieve stable detection performance, with precision exceeding 80% and recall above 70% under a precision-oriented operating point. To enhance detection robustness, a KNN-based cleaning procedure is introduced during training to remove noise-driven, locally isolated windows, significantly reducing spurious detections while preserving physically meaningful IRE signatures. Event-level analysis indicates that missed detections under this operating regime predominantly correspond to weak events with limited impact on global plasma behavior. The proposed framework is fully unsupervised, computationally efficient, and readily extensible to other spherical tokamak devices, providing a flexible foundation for incorporating additional diagnostics, such as Mirnov coil signals, toward precursor-aware detection and future predictive modeling of IRE activity. Full article

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15 pages, 3448 KB

Open AccessArticle

Deposition Behavior in Atmospheric-Pressure Plasma CVD Evaluated by a Quartz Crystal Microbalance

by Kenichi Yamazaki, Hiroyuki Yasui, Tsuyoshi Noguchi, Yuuma Suenaga and Akitoshi Okino

Plasma 2026, 9(1), 8; https://doi.org/10.3390/plasma9010008 - 17 Mar 2026

Abstract

Atmospheric-pressure plasma-enhanced chemical vapor deposition (AP-PECVD) enables low-temperature coating in open air, yet the interplay between precursor activation and ambient-derived species remains unclear. Here, thin films from an amine precursor are deposited using a helium plasma and characterized by gas chromatography–mass spectrometry (GC-MS), [...] Read more.

Atmospheric-pressure plasma-enhanced chemical vapor deposition (AP-PECVD) enables low-temperature coating in open air, yet the interplay between precursor activation and ambient-derived species remains unclear. Here, thin films from an amine precursor are deposited using a helium plasma and characterized by gas chromatography–mass spectrometry (GC-MS), a quartz crystal microbalance (QCM), and X-ray photoelectron spectroscopy (XPS). GC-MS indicates partial precursor conversion and formation of oxygen- and nitrogen-containing products, consistent with participation of ambient air and moisture. QCM identifies a limited precursor-concentration window in which mass increases monotonically during plasma exposure and remains constant after shutdown; outside this window, post-discharge mass loss occurs, indicating desorption of weakly bound species. XPS confirms carbon-rich films incorporating oxygen- and nitrogen-containing functionalities and complete substrate coverage at higher precursor concentrations. Full article

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

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15 pages, 4301 KB

Open AccessArticle

Underwater Electrical Explosions of Different Metal Wires on the Microsecond Timescale

by Ron Grikshtas, Sergey Efimov, Nikita Asmedianov and Yakov E. Krasik

Plasma 2026, 9(1), 7; https://doi.org/10.3390/plasma9010007 - 11 Feb 2026

Abstract

Underwater electrical explosions of single metallic wires driven by microsecond current pulses are investigated and compared with previously reported sub-microsecond experiments. Current and voltage waveforms, streak camera shadow imaging, and one-dimensional hydrodynamic simulations are employed to characterize how the energy density, energy density [...] Read more.

Underwater electrical explosions of single metallic wires driven by microsecond current pulses are investigated and compared with previously reported sub-microsecond experiments. Current and voltage waveforms, streak camera shadow imaging, and one-dimensional hydrodynamic simulations are employed to characterize how the energy density, energy density deposition rate, and the generated shock waves in water depend on the wire parameters. It was found that, similar to the sub-microsecond timescale, the solid–liquid phase transition occurs later than thermodynamic calculations predicted, while the liquid–vapor phase transition happens sooner than expected, leading to a two-phase coexistence. Additionally, most materials show a notable resistance peak (Ti, Fe, Ni, Zn, Ag, Sn, Ta, Au) compared to a quasi-plateau for Cu and Mo or a continuous increase for Al and Pt. Moreover, the specific action integral values are significantly smaller than those observed in wire explosion experiments in vacuum. Finally, the plasma formed at peak resistive voltage is non-ideal but exhibits lower electron density, ionization degree, and temperature compared to the sub-microsecond case. Full article

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9 pages, 1392 KB

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

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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