Plasma

31 pages, 3748 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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Graphical abstract

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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Graphical abstract

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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14 pages, 3655 KB

Open AccessArticle

Pin-Plane Electrical Discharge Driven by a MOSFET DC Current Source

by Myles Perry, Sidmar Holoman, Daniel Wozniak and Shirshak Kumar Dhali

Plasma 2026, 9(1), 5; https://doi.org/10.3390/plasma9010005 - 3 Feb 2026

Abstract

The generation of atmospheric pressure nonequilibrium plasma using electrical discharges is an active area of research due to its significance in a wide spectrum of applications including medicine, combustion, and manufacturing. In our attempt to create a helium plasma jet in a pin-plane [...] Read more.

The generation of atmospheric pressure nonequilibrium plasma using electrical discharges is an active area of research due to its significance in a wide spectrum of applications including medicine, combustion, and manufacturing. In our attempt to create a helium plasma jet in a pin-plane discharge with a constant current source, we observed self-pulsating behavior. We present the results of the electrical, optical, and spectroscopic measurements carried out to characterize the discharge. The duration of the discharge is a few tens of nanoseconds, and the repetition rate is in the few tens of kHz. The effect of the gap distance and gas flow is discussed. The effective capacitance formed by the space charge in the discharge region plays an important role in determining the pulsing frequency. The results of voltage swing, current pulse, and light emission are also discussed. Such self-pulsating discharges can be used to produce helium plasmas under ambient conditions in applications such as plasma medicine. Full article

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

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21 pages, 9238 KB

Open AccessArticle

Effect of Dielectric Thickness on Filamentary Mode Nanosecond-Pulse Dielectric Barrier Discharge at Low Pressure

by Anbang Sun, Yulin Guo, Yanru Li and Yifei Zhu

Plasma 2026, 9(1), 4; https://doi.org/10.3390/plasma9010004 - 27 Jan 2026

Cited by 1

Abstract

Filamentary mode, as a common phenomenon that appears in dielectric barrier discharge (DBD), is realized by rod-to-rod electrodes in N₂-O₂ mixtures at 80 mbar. The effects of the dielectric thickness on the characteristics of filamentary DBD are investigated through experiments [...] Read more.

Filamentary mode, as a common phenomenon that appears in dielectric barrier discharge (DBD), is realized by rod-to-rod electrodes in N₂-O₂ mixtures at 80 mbar. The effects of the dielectric thickness on the characteristics of filamentary DBD are investigated through experiments and simulations. The discharges are driven by a positive unipolar nanosecond pulse voltage with 15.8 kV amplitude, 9 ns rise time (T_r^10–90%), and 14 ns pulse width. The characteristics of filamentary DBD are recorded with an intensified charge-coupled device and a Pearson current probe in the experiment, and a 2D axisymmetric fluid mode is established to analyze the discharge. Surface discharges occur on the anode and cathode dielectric after the breakdown, and the discharge is gradually extinguished as the applied voltage decreases. A thinner total dielectric thickness (D_a + D_c) leads to larger currents, stronger discharges, and wider discharge channels. These characteristics are consistent when the total dielectric thickness is the same but anode dielectric thickness and cathode dielectric thickness are different (D_a ≠ D_c ≠ 0). If the anode is a metal electrode (D_a = 0), the current will be substantially large, and two discharge modes are observed: stable mono-filament discharge mode and random multi-filament discharge mode. It is found in simulations that the dielectric thickness changes the electric field configuration. The electric field is stronger with the decrease in dielectric thickness and leads to a more intense ionization which is responsible for most of the observed effects. Full article

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

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9 pages, 1047 KB

Open AccessArticle

Plasma-Polymerized Polystyrene Coatings for Hydrophobic and Thermally Stable Cotton Textiles

by Lian Farhadian, Samira Amiri Khoshkar Vandani and Hai-Feng Ji

Plasma 2026, 9(1), 3; https://doi.org/10.3390/plasma9010003 - 31 Dec 2025

Abstract

Dielectric barrier discharge (DBD) plasma provides a solvent-free and energy-efficient approach for the in situ polymerization of styrene on cotton textiles. Traditional methods for polystyrene (PS) coating often require elevated temperatures, chemical initiators, or organic solvents, conditions that are incompatible with porous, heat-sensitive [...] Read more.

Dielectric barrier discharge (DBD) plasma provides a solvent-free and energy-efficient approach for the in situ polymerization of styrene on cotton textiles. Traditional methods for polystyrene (PS) coating often require elevated temperatures, chemical initiators, or organic solvents, conditions that are incompatible with porous, heat-sensitive substrates such as cotton. In this work, we demonstrate that DBD plasma can initiate and sustain styrene polymerization directly on cotton fibers under ambient conditions. FT-IR spectroscopy confirms the consumption of the vinyl C=C bond and the formation of atactic, amorphous polystyrene. Thermogravimetric analysis indicates that the cotton coated with DBD polymerized PS exhibits enhanced thermal stability compared to cotton coated with commercial PS. Additionally, UV aging tests confirm that the plasma-deposited coating maintains its hydrophobicity after exposure to light. Together, these findings highlight DBD plasma as a sustainable and effective approach for producing hydrophobic, thermally robust, and UV-stable textile coatings without the need for solvents, initiators, or harsh processing conditions. Full article

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

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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

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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19 pages, 777 KB

Open AccessArticle

Enhanced Quantum Dot Emission in Fibonacci Photonic Crystal Cavities Optimized for PECVD-Compatible Porous Silicon: A Computational Study

by J. E. Mastache-Mastache, M. C. González, H. Martínez and B. Reyes-Ramírez

Plasma 2026, 9(1), 1; https://doi.org/10.3390/plasma9010001 - 26 Dec 2025

Abstract

This computational study investigates the optical properties of a sixth-order Fibonacci quasi-periodic photonic crystal cavity designed for the infiltration of near-infrared colloidal quantum dots (QDs, e.g., InAs/ZnSe or PbS) and fully compatible with plasma-enhanced chemical vapor deposition (PECVD) using porous silicon layers. Using [...] Read more.

This computational study investigates the optical properties of a sixth-order Fibonacci quasi-periodic photonic crystal cavity designed for the infiltration of near-infrared colloidal quantum dots (QDs, e.g., InAs/ZnSe or PbS) and fully compatible with plasma-enhanced chemical vapor deposition (PECVD) using porous silicon layers. Using the transfer matrix method (TMM), we simulate transmission (T), reflection, absorption, electric field distributions and Purcell factors (F) for both TE and TM polarizations, incorporating the wavelength-dependent absorption of porous silicon. A multi-objective figure-of-merit is defined to simultaneously maximize transmission (

T > 95 %

at 800 nm) and the one-dimensional Purcell factor. The optimized structure (

P_{H} = 0416

) yields a quality factor

Q \approx 4300

, a 1D Purcell factor

F_{1 D} \approx 3.6

and a realistic 3D Purcell enhancement estimated between 4 and 8 (under lateral confinement assumptions). This conservative estimate, derived via the effective index method to account for 3D effects, aligns with the detailed discussion within the article and is lower than the ideal upper bound of the 1D model. The integrated emission enhancement is approximately 3.0-fold. Monte Carlo simulations demonstrate remarkable robustness to fabrication tolerances (

\pm 10

nm thickness variations result in a <5% reduction in transmission), highlighting the structure’s scalability for PECVD-based processing. Comparison with periodic Bragg structures reveals superior angular stability and disorder tolerance in the Fibonacci design, positioning it as a promising platform for robust QD-based light sources and integrated refractive index sensors. Full article

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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

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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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

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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14 pages, 2582 KB

Open AccessArticle

The Effect of the Axial Plasma Electron Density Distribution on the Effective Length and Radiation Pattern of a Plasma Antenna

by Nikolai N. Bogachev, Vyacheslav P. Stepin, Vsevolod I. Zhukov, Sergey E. Andreev, Dmitry M. Karfidov, Maksim S. Usachonak, Evgeny M. Konchekov and Namik G. Gusein-zade

Plasma 2025, 8(4), 49; https://doi.org/10.3390/plasma8040049 - 28 Nov 2025

Abstract

This study investigates the axial electron density distribution in two plasma antenna configurations excited by a surface wave microwave discharge and its influence on the radiation pattern of antennas. The axial plasma electron density profiles were characterized using two non-invasive diagnostic techniques: the [...] Read more.

This study investigates the axial electron density distribution in two plasma antenna configurations excited by a surface wave microwave discharge and its influence on the radiation pattern of antennas. The axial plasma electron density profiles were characterized using two non-invasive diagnostic techniques: the resonant cavity measurements in the TM₁₁₀ mode and the waveguide transmission analysis. A linear decrease in the plasma electron density along the antenna was observed. The effective electrical length of the plasma antennas, accounting for this density distribution, is found to be approximately half the physical plasma column length. Numerical simulations employing COMSOL Multiphysics based on the Drude model revealed that a realistic nonuniform axial plasma electron density distribution markedly modifies the antenna radiation characteristics. For the wave-type plasma monopole antenna, this results in a shift in the emission maximum, a reduction in the main lobe amplitude, a nearly twofold broadening of the main lobe, and the disappearance of the side lobe. For the quarter-wave-type plasma asymmetric dipole antenna, there is a reduction in the main lobe amplitude without a shift in the maximum and a broadening of the main lobe due to an increase in the side-lobe level and its merging with the main lobe. Full article

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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

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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