Spatial evolution of microscopic collision mechanisms in non-equilibrium plasmas is a key challenge in energy transfer research. This work introduces a diagnostic method: By mapping probe bias voltage, spatial position, electron energy, and collision type, we reconstruct the spatial gradient of the collision network in the negative glow region using a single Langmuir probe. Key aspects of this approach include converting voltage scans into axial movement coordinates and correlating EEDF peak energies to specific collision “fingerprints” (e.g., 9.4 eV for Penning ionization of H2S by metastable He, 19.8 eV for superelastic collisions between metastable He and fast electrons). Experiments in helium glow discharges reveal enhanced metastable helium excitation near the cathode sheath and low-energy electron de-excitation at the center, intensifying atom–atom collisions. This method allows in situ, calibration-free identification of impurities like H2S, CH4, and air components. EEDF evolution under discharge perturbations provides a comprehensive view of collision kinetics, revealing complex interactions between energy transfer, collision cross sections, and particle transport. This approach overcomes the spatial limitations of traditional point measurements, offering a high-resolution tool for plasma micro-kinetics research.

The results of a study of an abnormal glow discharge in helium initiated by direct current, a half-cycle of sinusoidal voltage, and millisecond pulses in a discharge cells with cold SiC, Mo, and Cu cathodes are presented. It is shown that under spectroscopically pure conditions, for all the experimental conditions studied, the current–voltage characteristics change from monotonically increasing to S-shaped with increasing pressure of the operating gas. It is demonstrated that under the conditions studied, the known similarity relations for the abnormal discharge U ∼ j/p2 are not fulfilled. The assessment and accounting of changes in gas concentration during its heating at constant operating gas pressure allowed to establish a similarity ratio U ∼ j/N3.2 for abnormal glow discharge under spectroscopically pure conditions, which with good accuracy does not depend on the pressure of the operating gas and is fulfilled for all studied cathode materials.

Investigation of the discontinuous change in the anode potential drop in a helium glow discharge with a cylindrical hollow cathode

Abstract Numerical analysis of an atmospheric pressure glow discharge (APGD) in helium is carried out. Numerical models are spatially one- and two-dimensional and based on drift-diffusion theory of gas discharges. On the basis of the current–voltage and current density–voltage characteristic curves, the effects of the temperature regime on the cathode surface (cooled vs uncooled), the value of the secondary electron emission coefficient, and the thermal diffusion on the discharge parameters are studied. The possible transition of the discharge to an obstructed mode with gas heating is investigated. An analysis of the formation of normal APGD was carried out, which revealed good agreement with experimental data. The spontaneous emergence of cathode spots is illustrated and discussed.

Standard end-on optical emission spectroscopy of Grimm-type glow discharges in helium shows a footprint of He forbidden lines excited in the cathode sheath electric field F and shifted proportionally to F, supporting earlier results in Ne and Ar.

Investigations of glow discharge on the Uragan-2M stellarator in helium and nitrogen atmospheres have been carried out. Studies were made in the range of discharge currents from 0.05 to 1 A and working gas pressure from 0.284 to 14.93 Pa. The current-voltage characteristics of the glow discharge were measured. The floating potential along the minor radius was measured using a single probe. In the optical emission spectrum of the plasma, spectral lines of excited He I atoms in the He atmosphere were observed. In the N2 atmosphere, spectral lines of excited molecules N2* and molecular ions N2+* were also registered.

The paper presents the results of numerical calculations to study the dynamics of the conversion of small impurities of silane SiH4 in buffer helium in a glow discharge at low pressures. It has been shown that the main products of silane conversion are atomic hydrogen, the SiH radical, and atomic silicon Si. An increase in the concentration of silane impurity leads to an increase in the concentrations of Si2H5 and Si3H8. The effect of plasma stratification in a short glow discharge (in negative glow) has been demonstrated and qualitatively described, when ion-ion plasma dominates in its central region, and electron-ion plasma dominates at the periphery near the cathode and anode layers.

Abstract This work deals with the numerical study of spontaneous temporal oscillations in an atmospheric pressure glow discharge (APGD) in helium. The transition of helium APGD from stationary to periodic oscillatory state through the Hopf bifurcation, and further from periodic to chaotic oscillations through period-doubling bifurcations is explored. The choice of the discharge and external electric circuits parameters is guided by the relevant experiments. The ballast resistance and supply voltage of the external circuit play the role of control parameters. The method is based on the stability analysis of stationary states of the discharge. 

The stability diagram predicting parameter regimes at which stable and oscillatory states of the APGD can be expected is obtained. The effects of the discharge parameters (such as the gas gap, secondary electron emission coefficients, and capacitance in the external electric circuit) on the bifurcation curves are identified. 

The Lorenz map and corresponding period-doubling bifurcation diagram characterizing transition to chaotic oscillations in helium APGD with an increase in the control parameter are derived. The value of the capacitance in the external circuit plays a critical role in the dynamical behavior of the discharge. Decreasing its value contributes to the dissipation/damping of the system, whereas increasing it enhances the irregular behavior of the system.

In the Large Helical Device (LHD), diborane (B2H6) is used as a standard boron source for boronization, which is assisted by helium glow discharges. In 2019, a new Impurity Powder Dropper (IPD) system was installed and is under evaluation as a real-time wall conditioning technique. In the LHD, which is a large-sized heliotron device, an additional helium (He) glow discharge cleaning (GDC) after boronization was operated for a reduction in hydrogen recycling from the coated boron layers. This operational time of 3 h was determined by spectroscopic data during glow discharges. A flat hydrogen profile is obtained on the top surface of the coated boron on the specimen exposed to boronization. The results suggest a reduction in hydrogen at the top surface by He-GDC. Trapped oxygen in coated boron was obtained by boronization, and the coated boron, which has boron-oxide, on the first wall by B-IPD was also shown. Considering the difference in coating areas between B2H6 boronization and B-IPD operation, it would be most effective to use the IPD and B2H6 boronization coating together for optimized wall conditioning.

Combined experimental and numerical studies reveal a significant effect of the cathode temperature on the basic parameters (such as the electric field profile, thickness of the cathode fall layer, current density, and gas temperature) of the cathode fall of the self-sustained normal direct current atmospheric pressure glow discharge (APGD) in helium. Numerical models are spatially one- and two-dimensional and based on drift-diffusion theory of gas discharges. It was observed that heating of the cathode, resulting from a flow of the discharge current in APGD with a constricted positive column, leads to an increase of the interelectrode voltage if the cathode is not cooled and its temperature increases. With additional heating of the cathode by an external heat source, the interelectrode voltage tends to decrease. Radially inhomogeneous profiles of the reduced electric field on the uncooled cathode surface were measured. Simulation results exhibit reasonably good agreement with experiment for APGDs with cooled and uncooled cathodes.

In this paper, the effect of pre-ionization on the small-gap and large-gap direct-current glow discharge at atmospheric pressure are investigated based on a two-dimensional self-consistent fluid model. For both the discharges, the results show that with the enhancement of pre-ionization, the charged particle distribution gradually shifts toward the cathode along the discharge direction, making the cathode fall zone shrink continuously. The width of the positive column region, negative glow space, and cathode fall zone continuously extend along the vertical discharge direction, and the distribution of electron density and ion density are more uniform. For the electric field, with the enhancement of pre-ionization, the longitudinalal component distribution of the electric field in the cathode fall zone gradually contracts toward the cathode, and the overall electric field near the cathode decreases and becomes more uniformly distributed. The transverse component distribution of the electric field gradually decreases and shrinks toward the wall. The overall electron temperature in the discharge space decreases with the enhancement of the pre-ionization level, and the electron temperature distribution in the cathode fall zone gradually shrinks toward the cathode. In addition, the overall potential of the discharge space also decreases. The introduction of pre-ionization significantly reduces the maintaining voltage and discharge power of the direct-current glow discharge. Furthermore, the potential drop in the small-gap discharge is always concentrated in the cathode fall zone as the pre-ionization increases, while the potential drop in the large-gap discharge is gradually shifted from the cathode fall zone to the positive column region. This simulation shows that the pre-ionization not only effectively enhances the discharge uniformity, but also largely reduces the maintaining voltage and energy consumption of the direct-current glow discharge. This work is an important guideline for further optimizing the electrode configuration and the operating parameters of the plasma source.

In this work, we developed a highly sensitive, fast and convenient procedure for the determination of mercury in flue gas based on GA-APGD-AES.

In recent years, the artificial intelligence computing paradigm represented by physics-informed neural networks (PINNs) has received great attention in the field of plasma numerical simulation. However, the plasma chemical system considered in related research is relatively simplified, and the research on solving the more complex multi-particle low-temperature fluid model based on PINNs is still blank. In more complex chemical systems, the coupling relationship between particle densities and between particle densities and mean electron energy become more intricate. Therefore, the applicability of PINNs in dealing with sophisticated reaction systems needs further exploring and improving. In this work, we propose a general PINN framework (source term decoupled PINNs, Std-PINNs) for solving multi-particle low-temperature plasma fluid model. By introducing equivalent positive ions and replacing each particle transport equation with the current continuity equation as a physical constraint, Std-PINN splits the entire solution process into the training processes of two neural networks, realizing the decoupling of the source term of the heavy particle transport equation from the electron density and mean electron energy, which greatly reduces the complexity of neural network training. In this work, the application of Std-PINNs to solving multi-particle low-temperature plasma fluid models is demonstrated through two classic discharge cases with different complexity of reaction systems (low-pressure argon glow discharge and atmospheric-pressure helium glow discharge) and the performance of Std-PINN is compared with that of conventional PINN and finite element method (FEM). The results show that the training results output from the traditional PINN are completely incorrect due to the strong coupling correlation of each physical variable through the source terms of each particle transport equation, while the <i>L</i><sub>2</sub> relative error between Std-PINN and FEM results can reach up to ~10<sup>–2</sup> , thus verifying the feasibility of Std-PINN in simulating multi-particle plasma fluid model. Std-PINN expands the application of deep learning method to modeling complex physical systems and provides new ideas for conducting low-temperature plasma simulations. In addition, this study provides novel insights into the field of artificial intelligence scientific computing: the mathematical form that describes the state of a physical system is not unique. By introducing equivalent physical variables, equations suitable for neural network solutions can be derived and combined with observable data to simplify problems.

Abstract A negative DC high voltage is used to generate plasma at ambient condition. Self‐organized patterns (SOPs) are formed on the surfaces of the liquid anodes. With increased current or gap distance or reduced gas flow rate, the diameters of SOPs increase and SOPs become more complex, coinciding along with an increases of gas temperature and plasma radius and a decrease of electron density. Both plasma expansion and liquid evaporation in terms of gas temperature, lead to a drop of electron density and pattern formation. Our research elucidates the correlation between SOPs evolution and plasma properties and clarifies the physical process of SOPs formation based on the interaction between atmospheric pressure plasma and liquid anodes.

One-dimensional numerical models of a direct current atmospheric pressure glow discharge in helium are developed and examined. The models use a fluid description of charged and neutral particles and a drift-diffusion approximation for particle fluxes. The effects of plasma-chemical models, the form of the electron energy distribution function (Maxwellian vs non-Maxwellian), the energy loss due to gas heating and the width of the gas gap on the discharge characteristics are analyzed. The performance of different modeling approaches is examined by superimposing computed current–voltage characteristic (CVC) curves with each other and with measured and computed CVCs available in the literature.

The medical capillary catheters occupy a high proportion of medical diagnosis, monitoring and treatment devices, and will cause serious cross-infection without being disinfected adequately. This paper presents a new plasma structure for efficient inactivation of harmful microorganisms in medical capillaries. An innovative coaxial-dual-gap dielectric barrier discharge (CDG-DBD) reactor powered by nanosecond-pulsed power supply was designed for disinfection of Escherichia Coli (E. coli) inside and outside medical capillary catheters in this work. Atmospheric helium plasma (AHP) and atmospheric air plasma (AAP) were successfully obtained inside and outside capillary (0.6mm inner diameter and 1.0mm outer diameter), respectively. The electrical and optical characteristics of AHP and AAP were investigated. As the threshold of applied voltage amplitude (Uamp) was below 7.0kV, only one helium glow discharge was generated inside the capillary at the rising and falling stages of pulse voltage. As the Uamp exceeded the threshold, two helium glow discharges were generated that further caused generation of air discharge. Under the Uamp of 9.0kV, the production of AHP lowered the breakdown voltage in air gap, resulting in the formation of high-volume and uniform AAP, which was conducive to the realization of full inactivation. The inactivation rates of E. coli reached 98.13% and 99.99% by 2min AHP and 0.5min AAP treatment, respectively. The electrical stress of AHP and the reactive oxygen and nitrogen species (RONS) produced by AAP were contributed to the inactivation of E. coli. The results of SEM show that plasma treatment can destroy the cellular structure of E.coli.

Results of numerical investigation of kinetics of fast electrons and parameters of negative-glow plasma in low-pressure glow discharge in helium are presented. It is demonstrated that electron temperature in the negative-glow region is low and equals to a few tenths of an electronvolt. Numerical simulation revealed the formation of narrow peaks in the electron distribution function and the dependence of the differential flux on energy that are related to fast electrons formed in the reactions of Penning ionization. The results of numerical simulation are corroborated by the results of probe diagnostics of plasma. The possibility of determining concentration of excited helium atoms in negative-glow plasma by detection of fast electrons created as a result of reactions of Penning ionization is demonstrated.

A one-dimensional self-consistent fluid model was employed to comparatively investigate the influence of pre-ionization on the helium direct-current glow discharge in the large gap and the small gap at atmospheric pressure. For the large-gap and small-gap discharges, the negative glow space and the cathode fall layer are both offset to the cathode with the increase in pre-ionization, which is mainly ascribed to the decrease in charged particle density in the original negative glow space as a result of the increased probability of collision and recombination between ions and electrons, and the new balance between the positive and negative charges established at the distance closer to the cathode. The electron density tends to grow in the negative glow space due to the elevated pre-ionization, while the ion density exhibits an overall downward tendency in the cathode fall layer because the increase in secondary electrons produces more newly born electrons that neutralize more ions via the recombination reaction. Thanks to the pre-ionization, a significant reduction of sustaining voltage and discharge power is obtained in both the large-gap and small-gap discharges. A remarkable characteristic is that the absent positive column in the small-gap discharge comes into being again due to the pre-ionization. Moreover, with the increase in the pre-ionization level, the potential fall shifts from the cathode fall layer to the positive column in the large-gap discharge, while it is always concentrated in the cathode fall layer in the small-gap discharge.

Cold plasma studies on the influence of surface microstructured thickness in the secondary electron emission from tungsten coatings

Self-organization at the plasma–liquid anode interface is a commonly observed phenomenon for atmospheric pressure glow plasmas, resulting in patterns with distinctive shapes such as circular ring, star-shaped, and gear-like structures, depending primarily on the discharge current and solution conductivity. Recent studies have shown that the electrode gap distance, solute used for liquid anode solution, and gas composition can also significantly impact pattern formation. Nonetheless, an overarching model or explanation of the key underlying mechanisms consistent with all experimentally observed trends is not yet reported. We propose a key underlying mechanism enabling pattern formation motivated by a detailed parametric study of pattern formation complemented by the temporal development of patterns and consistent with all observed trends. Pattern formation was observed to be on a time scale of 100 μs, similar to the time scales of gas heating and evaporation. It was found that a minimum water evaporation rate of (3.5 ± 0.5) × 10−6 kg s−1 and reduced electric field in the positive column of 16.6 ± 0.4 Td is required for pattern formation in the investigated cases irrespective of solution conductivity and gas composition for NaCl solutions. Nonetheless, the presence of cations for which the corresponding metal atom has a low ionization energy was identified as a necessary condition for pattern formation. The reported results suggest that the presence of a small amount of metal atoms in the gas phase with low ionization energy enhances the overall ionization rate in the near anode region which triggers pattern formation.