Plasma

This study proposes a self-condensing water-electrode plasma device in which ambient water vapor is condensed on a cooled needle-tip electrode within a strong electric-field region, forming continuously renewed water droplets, Taylor cones, or water-film interfaces that participate in the discharge process. The effects of ambient humidity, needle-tip temperature, and applied voltage on the self-condensation behavior were investigated. The discharge modes at different applied voltages and discharge gaps, the generation of reactive species, and the inactivation efficacy against Staphylococcus aureus were also analyzed. The results showed that increasing ambient humidity, decreasing the needle-tip temperature, and increasing the applied voltage all promoted water condensation at the needle tip. The electric field shortened the droplet formation time and reduced the droplet detachment size. As the applied voltage increased, the device sequentially underwent water condensation, electrospray, stable Taylor-cone, water-film discharge, and bare-electrode discharge stages, while the boundary voltage of each stage increased with the discharge gap. The ozone concentration remained below the instrument’s limit of detection during discharge with the self-condensing water electrode, whereas hydroxyl-radical generation was significantly enhanced. Compared with a conventional metal electrode, the self-condensing water electrode exhibited greater inactivation of S. aureus at the same applied voltage, with a more pronounced advantage under low-voltage conditions. These findings demonstrate that introducing a self-condensing water interface can regulate the local discharge morphology and reactive-species composition, providing a new strategy for developing low-temperature plasma sterilization technologies with low ozone production and high bactericidal activity.

Endogenous matrix metalloproteinases (MMPs) are activated in dentin during carious lesion progression and restorative procedures, degrading the tooth-restoration interface and contributing to restoration failure. This study investigated by means of in situ zymography whether cold atmospheric plasma activation (PA) of distilled water (DW) and phosphate-buffered saline (PBS) modulates endogenous dentinal MMP activity. A Dielectric Barrier Discharge-rod source generated PA liquids, treating DW and PBS for 22 min. Chemical characterization demonstrated that PADW yielded 9.61 mg/L H2O2, 18.3 mg/L NO2−, 375.70 mg/L NO3−, and a pH of 3.2. PAPBS yielded 9.79 mg/L H2O2, 36.01 mg/L NO2−, 505.74 mg/L NO3−, and a pH of 7.13. Both liquids served as 1 min dentin pretreatments in a simulated restorative procedure using a universal adhesive and resin composite, tested after 24 h. MMP activity was assessed via in situ zymography with fluorescein-conjugated gelatin and confocal microscopy. Data were statistically analyzed (p < 0.05). PADW increased dentinal enzymatic activity, while PAPBS reduced it (p < 0.05). Non-activated PBS elicited higher baseline MMP activity than non-activated DW. The divergent responses likely reflect differences in RONS composition, pH, and initial ionic content between the two liquids. The precise mechanism underlying PA liquid interactions with dentinal MMPs warrants further investigation.

Arbitrary-amplitude nonlinear periodic electrostatic waves and the wave-breaking limit are considered in a one-dimensional relativistic electronegative plasma consisting of positive ions, negative ions, and a relativistically degenerate electron-fluid background. A cold, inertial fluid description is adopted for the ions, while the electrons are described by a relativistic Fermi–Dirac equation of state, which provides the required restoring physics through degeneracy rather than ordinary thermal pressure. After transforming to a travelling coordinate system, we reduce the general multicomponent plasma dynamical system to a pseudopotential energy form with a constant of motion. We then determine the allowed potential range, the associated asymmetric pseudopotentials, and the wave-breaking electric field for both linear and nonlinear waves on each of the two admissible branches. We find that arbitrary-amplitude nonlinear periodic waves are intrinsically asymmetric and that the maximum field strength is set by the effective charge-density boundary of each plasma species along the field direction. Parametric analysis suggests that the critical minimum field strength required for nonlinear wave formation may be controlled by increasing either the negative-ion mass ratio, the wave propagation speed, or the negative-ion concentration; however, each of these changes produces a distinct modification of the pseudopotential geometry. This illustrates that relativistic and interspecies effects are not merely responsible for quantitative deviations from the non-relativistic and single-species cases, but instead completely reshape the nonlinear phase space governing the persistence, deformation, and breaking of periodic electrostatic waves.

We examine energetic electron distributions in the region of the diffuse aurora using a two-dimensional bi-Maxwellian model, applied to electron flux data at a single geomagnetic equator (L = 6.5). Electron flux is analyzed as a function of energy and pitch angle and transformed into velocity space to reconstruct the distribution function. An unweighted log-space least-squares fit of the bi-Maxwellian model to the reconstructed distribution yields a reduced residual measure of χ2 v = 1.000053, a mean absolute residual of |∆log10 f| = 0.0469 dex, an anisotropy factor, AT = 0.9886±0.0016, and no statistically significant bulk drift. These results show that, at this location, the bi-Maxwellian model reproduces the observed velocity-space structure with good quantitative accuracy and reveals a quasi-isotropic, near-equilibrium electron population.

The conversion of carbon dioxide (CO2) driven by microwave plasma has garnered extensive attention due to its capability to recycle carbon resources and mitigate the greenhouse effect. However, the existing microwave plasma technologies suffer from cumbersome system setups and relatively low energy efficiency. This work investigates the CO2 conversion using a portable atmospheric microwave plasma source, which requires low plasma-generating power. When the working gas is a mixture of CO2 and Ar, the minimum plasma-generating power required for the proposed portable microwave plasma source is only 50 W. A Fourier transform infrared spectrometer is used to quantify both the CO2 and CO concentrations, and the C2 Swan bands of the plasma are measured to determine the gas temperature. The maximum CO2 conversion rate is approximately 12.7%. Furthermore, the maximum energy efficiency reaches 87.9%, which exceeds that of most of the state-of-the-art atmospheric microwave plasma configurations. Owing to its simplicity of operation, portability, and high energy efficiency, this method is well-suited for distributed CO2 conversion systems.

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.

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.

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.

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.

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.

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 NHx 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.

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.

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.

Spatially resolved absolute intensities of the atomic lines Hα, Hβ, Hγ, and Hδ 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), H2, and H2+ channels. A baseline plasma chemical mechanism developed in magnetic fusion research was applied to calculate the H2+ 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 Te = 2–10 eV and electron density ∼5 × 1017 m−3. An exception is the Hα/Hγ 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 H2+ 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 Te = 1–5 eV. This experimental regime can serve as a benchmark of more sophisticated hydrogen plasma models.

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 Hα 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.

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.

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)=n01+δsin2πx/x0, where n0 is the steady electron density, x0=100m 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 fs 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.

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.

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.

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 (δp), the electron-to-positron temperature ratio (σp), the dust charge density ratio (δd) 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.