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In this work, the distribution and segregation behaviors of helium (He) and the effect of yttrium (Y) on these behaviors in the symmetrical tilt tungsten (W) Σ5(310)/[001] grain boundary (GB) region were studied using first-principles calculations. The results revealed that the GB has a significant impact on the behaviors of He in W. The solution and segregation energies of He in the W Σ5(310)/[001] GB region increase with increasing the distance from He to the GB and are inversely proportional to the effective electrons of He. The density of states analysis showed that the GB can suppress partial hybridization between He and W atoms. In addition, we find that the strengthening element Y facilitates the dissolution of He in the W GB region. [ABSTRACT FROM AUTHOR]

Low-energy ion beam irradiation, combined with the introduction of impurities, presents a promising approach for nanopatterning silicon (Si) surfaces. In this research, we investigate the surface evolution of Si (100) surfaces irradiated by 75 eV helium (He) plasma, in the presence of tantalum (Ta), traditionally regarded as an impurity incapable of initiating pattern formation, as evidenced in prior studies. The Ta impurities are pre-deposited onto the Si surfaces using the magnetron sputtering method, which offers a more controlled and quantifiable approach compared with the conventional co-deposition route. After irradiation at 800 K, dense cone arrays are produced on the Si surface. The growth of the cones is explored for fluence spanning (1–10) × 1025 m−2. The cross-sectional scanning electron microscope images indicate that the cone lengths and base width are well characterized by t1/2 dependence. The kinetics of the cone growth follow Fick's law, characterized by an effective diffusive mechanism with the coefficients of diffusion: D = 6.49 ± 0.83 × 10−16 m−2 s−1. Transmission electron microscope observations reveal that the cone has distinct inner and outer parts with different microstructures and a clear interface. The growth mechanism of these cones is elucidated as a composite process involving preferential sputtering, the destabilizing influence of He bubbles, and the migration of adatoms. [ABSTRACT FROM AUTHOR]

Plasma‐facing liquids (PFLs) facilitate the storage of reactive O and N species (RONS), including H2O2 and NO2−, which remain in the PFL after plasma treatment, and they can continuously influence the target immersed in the liquid. However, their behaviors and levels of generation and extinction depend strongly on the plasma characteristics and liquid condition. Therefore, understanding the effects of the liquid type on the plasma discharge characteristics and the RONS generated via plasma discharge is necessary. We compared the RONS generation and storage trends of deionized H2O and a high‐conductivity PFL, RPMI 1640, which is a well‐known cell culture medium commonly used to culture mammalian cells. RPMI 1640 acted as an electrode and enhanced the plasma discharge power by supplying abundant radicals and RONS. The production of gaseous hydroxyl radicals and NO markedly increased, which facilitated H2O2 and NO2− production in the PFL for the first 200 s, and then the increase in the RONS concentration stagnated. With respect to storage, as the components within RMPI 1640 exhibited high reaction constants for their reactions with H2O2, H2O2 elimination was completed in <30 min. Unlike H2O2, the concentration of NO2− in the PFL was unchanged. [ABSTRACT FROM AUTHOR]

The sputtering and transport of tungsten (W) impurities in helium (He) and deuterium (D) plasma discharges are compared using the SOLPS-ITER code. To reduce the computational resources of modeling, W ions are treated using the bundled charge state model. The results show that the W erosion flux of He plasma is almost a factor of two higher than that of D plasma under the same upstream electron density and heating power due to the higher W sputtering yield in He plasma. Moreover, the W self-sputtering flux is significantly higher than the W flux sputtered by the main ions. The leakage and retention of W impurities in the divertor region is also analyzed. W ions mainly escape from the near scrape-off layer (SOL) region through the divertor entrance as the stagnation point of the average W impurity poloidal velocity is considerably closer to the target plates in the near SOL region. Furthermore, the leakage flux of W ions in He plasma is higher than that in D plasma, mainly because of the higher W sputtering level in He plasma, which results in a larger W density. W ions with low-lying charge states, mostly comprising the charge state of W10–12+, easily escape from the divertor through the near SOL flux tubes in both D and He plasmas. In addition, the effects of upstream electron density on W sputtering and retention in He and D plasma discharges are presented. [ABSTRACT FROM AUTHOR]

Summary: Salmonella contamination of fish after harvest is a significant food safety risk. To control this risk, it was aimed to reduce Salmonella Enteritidis in sea bass by helium and air plasma. Considering that preserving the fresh properties of sea bass is important for industrial applicability, determining the sensory effects of plasma treatments was also aimed. Since air plasma would provide a cheaper and easier alternative to helium plasma, their effects were compared. Additionally, the in vitro effects of these treatments on Salmonella Enteritidis were also investigated. Air and helium plasma completely inhibited the initial load of S. Enteritidis (2.79 Log CFU) inoculated on agar surface after 10 min treatment. Then, the inoculated sea bass samples were exposed to air or helium plasma for durations ranging from 1 to 15 min. Air and helium plasma treatments for 10 min provided 0.90 log cfu g−1 and 1.13 Log CFU/g reductions, respectively, but longer treatments did not lead to further significant reductions. Sensory scores were all above 7 (good) when samples were treated with air or helium plasma for 1–10 min, but longer treatments resulted in lower scores. The reduction of S. Enteritidis and changes in sensory characteristics were interpreted together and it was concluded that 10 min of air or helium plasma provided maximum reduction without causing any significant sensory changes. Overall, the current study showed that atmospheric pressure air and helium plasmas can be useful for ensuring post‐harvest safety in the fish trade. [ABSTRACT FROM AUTHOR]

Both microvoids and helium (He) impurities are widely present in tungsten (W) plasma-facing materials (PFMs), where the interaction between microvoids and He atoms has led to the intriguing development of microvoids. In this paper, we comprehensively investigated the interaction between He atoms and trivacancy (V3), a fundamental microvoid in W-PFMs, at the level of tight-binding theory. Our study showed that He atoms can catalyze the decomposition of the original V3 or facilitate its transformation into another V3 variant. We propose that a He atom near the V3 defect induces significant changes in the distribution of d-electron charges within the W atoms lining the inner wall of the V3 defect, making the W atom nearest to this He atom cationic and the other W atoms anionic. The attractive interaction between them promotes the decomposition and deformation of V3. As electronic excitation increases, the ionization of W atoms on the V3 wall gradually intensifies, thereby enhancing the cationic characteristics of the W atoms closest to the He atom. This process also prompts other W atoms to shift from anions to cations, leading to a transition in the electrostatic interactions between them from attraction to repulsion. This transformation, driven by electronic excitation, plays a significant inhibitory role in the decomposition and deformation of V3. [ABSTRACT FROM AUTHOR]

Dielectric barrier discharge (DBD) plasma has several applications in different fields. One of these fundamental applications is medical usages, where various methods are employed to improve the plasma treatment process. The combination of different gases is one of the important strategies to improve the performance of plasma in treatment. In this paper, the optimized plasma parameters for one-dimensional radiofrequency discharge produced at low pressures in a helium gas combination is studied. In this research, the optimal combination of H2O and He is identified to attain the highest amount of reactive oxygen species (ROS). Considered mixture are 5, 10, 15 and 20 precent of H2O for one dimensional helium gas discharge. The results show that the parameters of the output plasma are highly dependent on the composition of the input gases. It is found that the greatest concentrations of H+, H+, Hes (excited helium), and OH densities are observed when the H2O percentage was at 10%. Moreover, the density distributions of various species and the temperatures of electrons are numerically calculated during the electrical discharge process. These findings provide useful knowledge on how to optimize plasma parameters for biomedical applications, which may lead to improved treatment results in several therapeutic areas. [ABSTRACT FROM AUTHOR]

This paper presents a new scheme for readout of a photoionization detector (PID) that utilizes the ionization luminescence of target gases in helium plasma to generate an output signal. Our signal readout method is based on processing the recorded video and correlating the light peak intensity with the sample injection time and concentration. We successfully demonstrated the feasibility of a colorimetric readout‐based photoionization detector coupled with a gas chromatography column by detecting a mixture of non‐polar compounds (alkanes) and two polar compounds (acetone and ethanol). The detection limit for our first‐generation device was calculated to be ~118 ng for acetone and around 26 ng for ethanol. © 2024 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

We present comprehensive experimental data demonstrating that the capture process of the 1 + ions in charge breeder electron cyclotron resonance ion sources (ECRIS) is dominated by electrostatic deceleration by the ambipolar plasma potential, not by cumulative small-angle scattering of the incident ions in ion–ion collisions as postulated previously. To achieve this we varied the plasma potential of an ECRIS charge breeder by adjusting the microwave power applied to sustain the helium discharge and measured the corresponding shift in the optimum injection energy of the 1 + ions. The experiment was repeated with sodium, potassium, and cesium ions. It is shown that the optimum injection energy does not depend on the incident ion mass, which contradicts the collisional drag model. Conversely, the optimum injection energy (in eV) shifts in unison with the plasma potential (in V), which provides strong evidence for the electrostatic deceleration hypothesis. [ABSTRACT FROM AUTHOR]

The interaction between an atmospheric pressure plasma jet (APPJ) and an aqueous solution has great application prospects in biomedicine and many other fields. Reactive species adjacent to a water surface is critical to the activation of APPJ-treated water, which is affected by both the water evaporation and the admixture of ambient air. In this paper, taking He APPJ as an example, a two-dimensional (2D) cylindrically symmetric fluid model is developed to obtain the spatial distributions of gas components before discharging, and a series of global models are developed for the discharge in the boundary gas layer adjacent to the water surface. The interfacial distributions of reactive species and their fluxes onto the water surface are quantified. It is found that the electron density is 1016–1017 m−3 and it shows an annular distribution in the boundary gas layer. The density distributions of most reactive species there reveal ring-like shapes as well. The dominant cation and anion in such a boundary layer are H3O+ and OH−, respectively. The most abundant metastable is O2(a1Δ), the most abundant reactive oxygen species are H2O2 and OH, and the most abundant reactive nitrogen species are NO and HNO2. The species of H2O2, OH, HO2, and HNO2 are reportedly to have significant biological effects, and in our simulation, their fluxes onto the water surface are remarkable, higher than 1017 m−2 s−1. In addition, the effects of radial gas velocity and water evaporation on the particle flux distributions are also revealed. [ABSTRACT FROM AUTHOR]

The influence of the non‐ideality (NI) of the classical plasmas on the doubly excited singlet S states of the helium atom (He) embedded in the plasma has been investigated theoretically. A pseudopotential containing the Debye length and the non‐ideality parameter (NIP) as its characteristics is used to represent the screened interaction potentials in the plasma. Using a large wavefunction within the framework of the stabilization method, it has been possible to recognize six doubly excited singlet S states (five lying below the He+(2S) excitation threshold and one lying below the He+(3S) excitation threshold) for the plasma‐free case. The energies and the autoionization life‐times of those states are computed by fitting the density of states to the Lorentzian form. Convergence of the computed results is corroborated by increasing the number of terms in the employed wavefunction. For the plasma‐free case, these results are in excellent agreement with the established results in the literature. A comprehensive analysis has been made on changes induced on those doubly excited states by varying NI over a wide range. It has been observed that the energies of the states gradually approach the corresponding threshold energies with the increasing NI of the plasma, whereas the change in the life‐times (alternatively the widths of the states) of the states shows distinctive features depending on the angular momentum of an individual electron. [ABSTRACT FROM AUTHOR]

Conventional magnetron discharge is a widely used technology for many applications. In the last decade, the high current density sputtering regime has been an interesting alternative for tailoring thin film properties. In this paper, we focused on the electrical characterization of the helium magnetron plasma operated at average gas pressure (5 Pa) with a molybdenum target. Optical emission spectroscopy diagnostics also supports this study by providing information on electron density evolution. The analysis of the plasma–surface interaction zone on the target unveiled the physical mechanisms associated with the high current density range (6 A cm−2), corresponding to different discharge regimes. The self-sputtering yield plays a key role in high-power impulse magnetron sputtering discharge operated with helium. The electron density is highly dependent on the presence of a metal. [ABSTRACT FROM AUTHOR]

Helium plasma irradiation to various metals leads to peculiar morphology changes as forming fiberform nanostructures called fuzz when a certain set of conditions is satisfied. In this Tutorial, we overview experimental observations about the fuzz growth process, conditions, growth rate, etc. on tungsten (W), and fuzz growth observed on other various metals. The fuzz growth mechanism, open questions about fuzz growth, and current understandings on these issues are discussed based on simulation and theoretical works. Several applications (gas sensors and photocatalytic application) with fuzz are shown. We hope that this Tutorial will help new researchers in this field to perform experiments and simulations to reveal new perspectives of fuzz. [ABSTRACT FROM AUTHOR]

Background: Melting corneal ulcers are a serious condition that affects a great number of animals and people around the world and it is characterised by a progressive weakening of the tissue leading to possible severe ophthalmic complications, such as visual impairment or blindness. This disease is routinely treated with medical therapy and keratoplasty, and recently also with alternative regenerative therapies, such as cross-linking, amniotic membrane transplant, and laser. Plasma medicine is another recent example of regenerative treatment that showed promising results in reducing the microbial load of corneal tissue together with maintaining its cellular vitality. Since the effect of helium plasma application on corneal mechanical viscoelasticity has not yet been investigated, the aim of this study is first to evaluate it on ex vivo porcine corneas for different exposition times and then to compare the results with previous data on cross-linking treatment. Results: 94 ex vivo porcine corneas divided into 16 populations (healthy or injured, fresh or cultured and treated or not with plasma or cross-linking) were analysed. For each population, a biomechanical analysis was performed by uniaxial stress-relaxation tests, and a statistical analysis was carried out considering the characteristic mechanical parameters. In terms of equilibrium normalised stress, no statistically significant difference resulted when the healthy corneas were compared with lesioned plasma-treated ones, independently of treatment time, contrary to what was obtained about the cross-linking treated corneas which exhibited more intense relaxation phenomena. Conclusions: In this study, the influence of the Helium plasma treatment was observed on the viscoelasticity of porcine corneas ex vivo, by restoring in lesioned tissue a degree of relaxation similar to the one of the native tissue, even after only 2 min of application. Therefore, the obtained results suggest that plasma treatment is a promising new regenerative ophthalmic therapy for melting corneal ulcers, laying the groundwork for further studies to correlate the mechanical findings with corneal histology and ultrastructural anatomy after plasma treatment. [ABSTRACT FROM AUTHOR]

Diatomic molecules He2+$$ \mathrm{H}{\mathrm{e}}_2^{+} $$, He2$$ \mathrm{H}{\mathrm{e}}_2 $$ are common compositions in plasmas using the helium as the working gas, and play key roles in quenching O2 and N2. However, the potential energy curve (PEC) of the first state He2a3Σu+$$ \mathrm{H}{\mathrm{e}}_2\left({a}^3{\Sigma}_u^{+}\right) $$ obtained at the CASSCF level of theory is not accuracy and data of higher excited states of He2+$$ \mathrm{H}{\mathrm{e}}_2^{+} $$ are lacking. Here, we calculated PECs of four excited states of He2$$ \mathrm{H}{\mathrm{e}}_2 $$ and nine lowest electronic states of He2+$$ \mathrm{H}{\mathrm{e}}_2^{+} $$ by employing CASSCF+MRCI/Aug‐cc‐pV5Z and CCSD(T)/Aug‐cc‐pV5Z level of theory with sample internuclear distance interval of 0.005 Å. PECs were extrapolated to the complete basis sets. There are double local maxima in PECs of three excited states He2+B2Σu+$$ \mathrm{H}{\mathrm{e}}_2^{+}\left({B}^2{\Sigma}_u^{+}\right) $$, He2+C2Πu$$ \mathrm{H}{\mathrm{e}}_2^{+}\left({C}^2{\Pi}_u\right) $$, He2+D2Πg$$ \mathrm{H}{\mathrm{e}}_2^{+}\left({D}^2{\Pi}_g\right) $$. The machine learning method based on the Gaussian process was used to interpolate and extrapolate the PECs, and then vibrational wave functions are solved numerically. This ab initio investigation provided rotational‐vibrational constants and new data for experimental research in the future. [ABSTRACT FROM AUTHOR]

Understanding the physical–chemical processes ruling the interaction of particles (atoms, molecules, and ions) with surfaces is fundamental in several research fields, such as heterogeneous catalysis, astrochemistry, and nuclear fusion. In particular, the interaction of hydrogen isotopes with plasma facing materials represents a high-priority research task in the fusion community. Such studies are essential to ensure the successful operation of experimental fusion reactors, such as the tokamak ITER. In this work, we present a surface science apparatus developed to study ion-surface interaction in fusion relevant systems. It combines laser-based techniques with contaminant-free ion/molecular beams, mass spectrometry, and surface science tools such as low-energy electron diffraction and Auger electron spectroscopy. It allows to cover a wide range of sample temperatures, from 130 to 2300 K, by changing the heating rate of samples from 0.1 to 135 K/s and maintaining the linearity of the heating ramps, a powerful feature to gain insight on adsorption, absorption, and desorption mechanisms. Experimental calibration and performance are presented in detail. Moreover, to provide a factual overview of the experimental capabilities, we focus on two different applications: the protocol used to clean a W(110) single crystal sample and the development of laser temperature programmed desorption to study helium retention in tungsten. [ABSTRACT FROM AUTHOR]

In this study, we investigated the effects of helium (He) plasma irradiation and thermal treatment on the morphology, the surface characteristics, and the photoelectrochemical performance of bulk iron (Fe) sheets. After processing, all samples consisted mainly of an α -Fe 2 O 3 surface. Helium plasma irradiation resulted in a cathodic shift in the onset potential of the photocurrent from 1.16 V RHE (no pretreatment) to 0.57 V RHE (plasma exposure at 660 ° C), where V RHE represents the potential versus reversible hydrogen electrode (RHE). An increase in the surface roughness and a smaller amount of hydroxyl or oxygen vacancies at the surface after photoelectrochemical measurement are related to the decrease of the onset potential. The results show that He plasma irradiation does not only modify the surface morphology, but also affects the functional properties of the materials. • The photoelectrochemical performance of α -Fe 2 O 3 is investigated. • Helium plasma irradiation resulted in a cathodic shift in the onset potential. • The onset potential shifted from 1.16 to 0.57 V RHE. • A small amount of hydroxyl or oxygen vacancies are likely to be the most influential. [ABSTRACT FROM AUTHOR]

Atmospheric pressure helium plasma jets are widely used in biomedical applications. Researchers normally introduce small amounts of nitrogen and oxygen (0.2–1.0%) into helium to enhance the electron density and electron energy, thus increasing the concentration of active species in plasma. To further explore why the combination of impurity gases N2/O2 leads to an increase in the electron density from the discharge mechanism, we used a microwave Rayleigh scattering method with excellent time-varying characteristics to monitor the temporal electron density changes when different concentrations of N2/O2 were mixed. The research revealed that even trace amounts of N2/O2 (0.2%) can increase the peak electron density, with this effect being more pronounced when N2 is added, increasing from 3.3 × 1019 to 4.6 × 1019 m−3 in pure helium. As the concentration increases, the introduction of O2 leads to a rapid decrease in the electron density. When 1.0% oxygen is mixed, the electron density decreases from 3.3 × 1019 to 2.4 × 1019 m−3. However, the situation is different when N2 is added, at 0.5% proportion of nitrogen, the electron density increases to its maximum at 6.5 × 1019 m−3. These effects are due to the electronegativity of the oxygen-containing particles or the Penning ionization related to excited nitrogen species. [ABSTRACT FROM AUTHOR]

In recent years, atmospheric-pressure plasma jets have emerged as valuable tools in many application areas, including material modification, environmental remediation and biomedicine. Understanding the discharge characteristics of these plasma jets under various operating conditions is crucial for optimizing process outcomes. This paper presents a two-dimensional fluid model for numerical simulation to study the variation in electron density within an atmospheric-pressure helium plasma jet under different operating conditions. The investigated parameters include helium gas flow rate, voltage amplitude, needle-to-ring discharge gap, and relative permittivity of the dielectric tube. The results reveal that the peak electric field and electron density initially occur at the wall of the dielectric tube and subsequently shift towards the head of the propagating jet. Gas flow rate has minimal impact on the electron density throughout the plasma jet, whereas increasing the needle-to-ring discharge gap significantly decreases the average electron density within the jet. In addition, an increase in the voltage amplitude and the relative permittivity of the dielectric tube enhances the electric field within the discharge space, thereby increasing the electron density in the plasma jet. These findings underscore the importance of understanding the correlation between electron density and operating conditions to precisely control plasma jets and enhance material treatment effectiveness for specific applications. [ABSTRACT FROM AUTHOR]

In this work, we investigate the properties of the plasma induced by focusing a high-power laser beam on an aluminum target that was cooled by a helium refrigerator from room temperature down to 20 K. Fast, streak photographs of the plasma were taken at different temperatures and laser energies. From the images obtained, position-vs-time plots were made for each experiment, and from them, the speed was calculated. Additionally, narrowband interference filters were employed to image the dynamics of ions and neutrals separately. It was found that the plasma plume has two distinct speeds: that of its center and that of the outer edge. For unfiltered images, the former has values within the interval 6.2 to 9.1 km/s, while the latter can reach speeds of the order of hundreds of km/s. It was found that the plume of a target cooled to 20 K has a length that is 8%–12% less than the corresponding size at room temperature. Chilling the target did not seem to affect significantly either the plume's speed of expansion or the size of the crater produced. Lower bounds were estimated for the momentum imparted to the ejecta and the specific impulse. The latter can reach a 920-s level, nearly twice as much the amount obtained with chemical rocket fuel. [ABSTRACT FROM AUTHOR]

We present an experimental and simulation-based investigation of the temporal evolution of light emission from a thin, laser-ionized helium plasma source. We demonstrate an analytic model to calculate the approximate scaling of the time-integrated, on-axis light emission with the initial plasma density and temperature, supported by the experiment, which enhances the understanding of plasma light measurement for plasma wakefield accelerator (PWFA) plasma sources. Our model simulates the plasma density and temperature using a split-step Fourier code and a particle-in-cell code. A fluid simulation is then used to model the plasma and neutral density, and the electron temperature as a function of time and position. We then show the numerical results of the space-and-time-resolved light emission and that collisional excitation is the dominant source of light emission. We validate our model by measuring the light emitted by a laser-ionized plasma using a novel statistical method capable of resolving the nanosecond-scale temporal dynamics of the plasma light using a cost-effective camera with microsecond-scale timing jitter. This method is ideal for deployment in the high radiation environment of a particle accelerator that precludes the use of expensive nanosecond-gated cameras. Our results show that our models can effectively simulate the dynamics of a thin, laser-ionized plasma source. In addition, this work provides a detailed understanding of the plasma light measurement, which is one of the few diagnostic signals available for the direct measurement of PWFA plasma sources. [ABSTRACT FROM AUTHOR]

This study investigates the effect of a transverse magnetic field on high-voltage pulsed discharge in helium at a pressure of 30 Torr. A simple two-dimensional fluid model that describes the high-voltage pulsed discharge in helium in a transverse weak magnetic field (B  = 0.4 T) is presented, which uses an empirical relation to account for the magnetic field. The results of using the empirical relation for the effective field agree well with the experimental results. The dynamics of discharge development in the presence of the magnetic field is also investigated. The magnetic field does not significantly affect the gas-discharge development dynamics in helium at a pressure of 30 Torr. [ABSTRACT FROM AUTHOR]

Information about charged particles emitted by plasma of high-current discharges is of interest both from the point of view of understanding the fundamental processes occurring in pulsed plasma and for applied problems. Compact magnetic spectrometers based on permanent magnets make it possible to measure the flux of charged particles from a plasma under conditions of strong electromagnetic noise. Imaging plates (IP) are one of the most commonly used types of detectors for detecting charged particles in laser-plasma and electric-discharge experiments. This paper presents the results of calibration of the BAS-MS IP when detecting electrons and the BAS-TR IP when detecting helium and tungsten ions. Calibration dependences of the sensitivity of the BAS-MS IP for electrons in the energy range of 0.65–50 MeV and the sensitivity of the BAS-TR IP for tungsten ions in the energy range from 20 eV to 650 keV are obtained, taking into account the angles of incidence of particles on the detector. [ABSTRACT FROM AUTHOR]

This article describes the study of low pressure helium plasma with magnetic confinement at the experimental test setup at the Moscow Power Engineering Institute: plasma linear multicusp (PLM). This facility is intended for testing refractory materials and prototypes of elements of the first wall within the framework of development of the national fusion reactor (DEMO–FNS) and the International Thermonuclear Experimental Reactor (ITER). The facility provides the conditions of plasma impact on the surface of tested sample close to the parameters and regime of operation of tokamak divertor plates. The facility is a magnetic trap with minimum magnetic field on the axis, where the plasma is created by the flow of electrons moving from the directly heated tantalum cathode toward the anode. It is possible to create stationary helium plasma in the facility and to maintain it for several hours under constant discharge parameters: helium pressure in the chamber of 10–3–10–1 Torr, discharge current of 4–30 A, plasma column diameter of 35–40 mm, voltage drop across the discharge gap of 100–200 V. The thermal load on the surface of target introduced into the axial region of plasma column has reached 5 MW/m2. Optical emission spectroscopy is the main diagnostic tool in this work. The procedure for determining atomic concentrations from the data on the relative intensities of atomic spectral lines of metallic impurities is proposed in this work. [ABSTRACT FROM AUTHOR]

The present study investigated the production of reactive chlorine species (RCS) by Ar/O2 and He/O2 radiofrequency plasma jets in saline solution, and the sensitivity of the liver cancer cell line HepG2 to RCS and H2O2. Both plasma jets were able to produce RCS; however, at similar plasma powers, pressures, and feed gas flow rates, the He/O2 jet was more efficient for RCS production. The lower RCS yield in the case of the Ar/O2 plasma jet was mainly due to the higher RCS quenching. At a low production rate, RCS can be produced in the open air. Viability tests showed that HepG2 cells were more sensitive to H2O2 than RCS. [ABSTRACT FROM AUTHOR]

In the current study, bulk tungsten material surfaces are exposed to hydrogen, deuterium, and helium plasmas in the radiofrequency domain (13.56 MHz) at an input power of 250 W using the hollow-cathode configuration. The ejected material is collected on titanium substrates at various distances (from 6 mm up to 40 mm). Therefore, the exposed tungsten materials are investigated for surface changes (blister occurrence, dust formation, or nano-structuration), along with the crystallinity, depending on the plasma's exposure times (from 30 min up to 120 min for each plasma type). Also, the collected materials are analyzed (morphological, structural, and statistical investigations) for dust and dust film-like appearance. Plasma discharges are analyzed using two methods: optical emission spectroscopy, and single Langmuir probes, to emphasize the nature of the used plasmas (cold discharges, ~2 eV), along with the presence of tungsten emission (e.g., WI 406.31 nm, WI 421.31 nm) during the plasma lifetime. By using a dedicated protocol, a method was established for obtaining fusion-relevant tungsten surfaces in the hydrogen and deuterium plasma discharges. By using the implemented method, the current paper introduces the possibility of obtaining a new tungsten morphology, i.e., the dandelion-like shape, by using helium plasma, in which the W18O49 compound can be found. [ABSTRACT FROM AUTHOR]

In this study, the electric field distribution on the dielectric surface exposed to helium atmospheric pressure plasma jets with varying operating parameters was investigated. The study considered the effect of applied voltage (7–10 kV), pulse width (0.9–150 μs), and rate (400–2000 sccm), with the investigation based on the Pockels effect. The results suggest that the surface electric field arises from the charge transfer by ionization waves and the expansion of surface discharges. The evolution of the electric field can be segmented into three phases: establishment, maintenance, and dissipation. The gas flow rate determines the mixing "boundary" between helium and air, and consequently affects the shape of the surface electric field distribution. At 400 sccm, the field structure exhibits a solid, elongated shape. At 800–1200 sccm, the field takes on a hollow-ring appearance, and at 1600–2000 sccm, it is presented as two channels. As the applied voltage increases, the surface discharge can be extended further, even surpassing the designated boundary. At 10 kV, the maximum surface electric field and total deposited charge are 5.9 kV/cm and 4.3 nC, respectively. At a fixed frequency of 5 kHz, changing the pulse width affects charging time. The maximum value of the surface electric field and the total deposited charge exhibits an initial increase followed by a decrease. Short pulses (0.9–2 μs) result in incomplete charge transfer, while long pulses (100–150 μs) form a "dark channel" of predominantly negative charge at falling edge of the pulse, which neutralizes the positive charge in the subsequent pulse. A pulse width of 20 μs allows complete charge transfer with less influence from the dark channel. [ABSTRACT FROM AUTHOR]

Spectroscopy methods were used for studying the dynamics of neutral plasma component in current sheets formed in two-dimensional (2D) and three-dimensional (3D) magnetic configurations during discharge in helium. It has been ascertained that when the current sheet is formed in the 2D magnetic field, flows of fast suprathermal helium atoms appear in it, which are directed along the current sheet width (the largest of the sheet transverse dimensions). It is shown that helium atoms can acquire the directed energy Wx due to the resonance charge exchange of accelerated ions in the current sheet plasma. The energy of directed motion of helium atoms can reach Wx ≈ (480 ± 120) eV, which is ~20 times higher than the temperature of helium atoms Ta ≈ (20 ± 2) eV at the same times. During the current sheet formation in the 3D magnetic configuration, fast helium atoms were not observed. [ABSTRACT FROM AUTHOR]

This paper focuses on the use of an electro-optic (EO) probe for the spatially and temporally resolved characterization of the electric field (E-field) associated with guided ionization waves—or guided streamers—propagating at atmospheric pressure. An AC high-voltage power supply (6 kV at 18 kHz) is used to generate guided ionization waves in helium with a cold atmospheric pressure plasma jet device (APPJ). The capabilities of this electro-optic technique are investigated with and without the discharge. This innovative technology will use to carry out the optical polarimetric analysis of the APPJ with simultaneous real-time measurement of longitudinal and radial components of the electric field vector. Last but not least, an application-based case study of the ionization waves propagating and interacting with the EO probe—being a solid dielectric target—is also reported. The results will bring realistic information on the potential perturbation induced by the EO probe itself on the E-field characterization at the macroscopic scale. [ABSTRACT FROM AUTHOR]

Applications of plasma-induced biological effects via reactive oxygen and nitrogen species (RONS) make the non-thermal atmospheric-pressure plasma jets an appealing tool in biomedical fields. The presence of biological materials, especially as part of the electrode circuit, may change the plasma properties and impact on the production of RONS at the plasma-biomaterial interface. Effects of biomaterials on the production of hydroxyl radicals (OH) in a nanosecond pulsed, atmospheric-pressure plasma jet were investigated using a needle-to-plate electrode configuration with water, phosphate-buffered saline (PBS), or pigskin covering the ground plate. Driven by 200 ns, 7 kV pulses at 1 kHz, a helium plasma jet was generated between the hollow needle electrode and the biomaterial. Temporally resolved UV-visible imaging showed that the use of pigskin slowed down the streamer head propagation, whereas a more pronounced surface ionization wave was developed on the surface when water was used. The highest OH(A-X) emission above the biomaterial surface was observed using the PBS-covered electrode plate comparing to water or pigskin. Spatiotemporally resolved laser-induced fluorescence (LIF) showed that more OH was produced in the region near the needle electrode for both water and PBS, and the use of pigskin resulted in least OH production overall. In addition, measurements of H2O2 production in the liquid were used to determine the OH concentration in the vicinity of the biomaterial and agreed well with the relative OH-LIF measurements obtained at the gas-liquid interface for water and PBS. [ABSTRACT FROM AUTHOR]

Fiber-form nanostructured tungsten (W) formation was successfully demonstrated using a helium (He) arc discharge plasma generated at a gas pressure of 5 kPa. The W substrate was exposed to the He arc discharge plasma at a surface temperature of about 1000 °C. A bias voltage, Vb, was applied between the W substrate and the vacuum chamber to control the incident He ion energy, Ei. Scanning electron microscope (SEM) observations showed that the W surface was slightly roughened, but no fiber-form nanostructure was formed at a Vb of −22 V. On the other hand, fiber-form nanostructure growth was observed at a Vb of −112 V. Furthermore, cross-sectional SEM observations revealed the presence of He bubbles inside the W fibers and the sub-surface layer of the W substrate. As collisions between ions and neutrals in the sheath cannot be ignored at 5 kPa, a theoretical evaluation of Ei distribution was performed using the collisional sheath model. Furthermore, an experimental evaluation of Ei using the sputtering yield of carbon substrates by He arc discharge plasma irradiation was carried out, and then Ei was obtained to be 40–50 eV for Vb = −112 V. Therefore, the distribution of Ei at Vb = −112 V is considered to contain more than 20 eV, which is necessary for the growth of fiber-form nanostructured W found in conventional low-gas pressure plasma irradiation experiments. [ABSTRACT FROM AUTHOR]

In situ analysis of surfaces during high-flux plasma exposure represents a long-standing challenge in the study of plasma–material interactions. While post-mortem microscopy can provide a detailed picture of structural and compositional changes, in situ techniques can capture the dynamic evolution of the surface. In this study, we demonstrate how spectroscopic ellipsometry can be applied to the real-time characterization of W nanostructure (also known as "fuzz") growth during exposure to low temperature, high-flux He plasmas. Strikingly, over a wide range of sample temperatures and helium fluences, the measured ellipsometric parameters (Ψ , Δ) collapse onto a single curve that can be directly correlated with surface morphologies characterized by ex situ helium ion microscopy. The initial variation in the (Ψ , Δ) parameters appears to be governed by small changes in surface roughness (<50 nm) produced by helium bubble nucleation and growth, followed by the emergence of 50 nm diameter W tendrils. This basic behavior appears to be reproducible over a wide parameter space, indicating that the spectroscopic ellipsometry may be of general practical use as a diagnostic to study surface morphologies produced by high-flux He implantation in refractory metals. An advantage of the methods outlined here is that they are applicable at low incident ion energies, even below the sputtering threshold. As an example of this application, we apply in situ ellipsometry to examine how W fuzz growth is affected both by varying ion energy and the temperature of the surface. [ABSTRACT FROM AUTHOR]

A 2D axisymmetric study of the atmospheric pressure plasma jets driven by a trapezoidal pulse voltage with different polarities is performed in this work. The basic properties of the plasma jet in three stages, including the first discharge, the secondary discharge, and the afterglow of the plasma jet, are studied, with emphasis on the influence of voltage polarity on the secondary discharge and the afterglow. For the positive pulse voltage, the plasma jet propagates in the form of a bullet during the first stage. At the falling edge of the pulse, a new ionization wave resulting from the secondary discharge is formed and propagates forward along the preceding jet path in a continuous mode, resulting in a mixing jet propagation mode with the primary bullet and the luminous channel coexist. The plasma jet is finally converted to the continuous mode at the afterglow stage. Meanwhile, the first bullet almost stops propagating after the secondary discharge is ignited due to the rapid reduction of the electric field in the bullet head. In contrast, in the case of negative pulse voltage, a diffusive arrow-like plasma plume is observed during the first stage. The secondary discharge ignition does not completely change the direction of the electric field in the first ionization head and inhibits the propagation of the primary plasma jet. The dominant physics mechanisms associated with these observations are analyzed and discussed. In addition, the dependence of the reactive species on the secondary discharge under different pulse polarities is also compared. [ABSTRACT FROM AUTHOR]

A nonideal helium plasma has been compressed to a density of ρ ≈ 14 g/cm3 at a pressure of TPa (200 Mbar) in a spherical two-cascade device. The design of the device has been presented and the thermodynamic parameters of the helium plasma reached in it have been estimated. Data on the dynamics of the external and internal cascades in the device used to choose the calculation method have been obtained in a preliminary experiment with a hemispherical prototype. The experiment has been performed on the X-ray complex at the Russian Federal Nuclear Center All-Russian Research Institute of Experimental Physics, which includes BIM 234.3000 betatrons with a boundary energy of 60 MeV used in the multipulse bremsstrahlung generation regime with a multichannel optoelectronic system of recording X-ray images. A high-current linear accelerator LIU-R-T and an image detector assembly consisting of photochromic ADC screens have been used in addition to betatrons to detect the compressed shell cavity. [ABSTRACT FROM AUTHOR]

In laser-wakefield acceleration, an ultra-intense laser pulse is focused into an underdense plasma to accelerate electrons to relativistic velocities. In most cases, the pulses consist of multiple optical cycles and the interaction is well described in the framework of the ponderomotive force where only the envelope of the laser has to be considered. But when using single-cycle pulses, the ponderomotive approximation breaks down, and the actual waveform of the laser has to be taken into account. In this paper, we use near-single-cycle laser pulses to drive a laser-wakefield accelerator. We observe variations of the electron beam pointing on the order of 10 mrad in the polarization direction, as well as 30% variations of the beam charge, locked to the value of the controlled laser carrier-envelope phase, in both nitrogen and helium plasma. Those findings are explained through particle-in-cell simulations indicating that low-emittance, ultrashort electron bunches are periodically injected off-axis by the transversally oscillating bubble associated with the slipping carrier-envelope phase. [ABSTRACT FROM AUTHOR]

Low‐temperature plasma is a new transdermal drug delivery method that is different from the traditional physical and chemical methods. In this study, three touchable plasma jet devices are selected, such as direct current (DC) air plasma jet, DC helium plasma jet, and pulsed helium plasma jet. The patent blue V 1159.43 Da has been chosen for percutaneous penetration studies. The results show that 1 min DC air and helium plasma treatment significantly enhanced transdermal drug delivery by 9 and 26 times, respectively. The enhancement of pulsed plasma jet is the weakest. The skin histological analysis and reactive oxygen species (ROS) measurement shows that nonuniform distribution of ROS in DC helium and DC air plasma may cause perforation on the whole epidermis and allow more drug permeation. [ABSTRACT FROM AUTHOR]

A hyperspectral camera (HSC-type Specim IQ) has been applied at the linear plasma device PSI-2 under steady-state conditions. The camera has the capacity of hyperspectral imaging (HSI) with the dimension of a data array 512 × 512 × 204 (x, y, λ) covering the spectral span from 400 to 1000 nm with moderate average spectral resolution (FWHM ∼7 nm). After radiometric calibration and background/continuum emission subtraction, two main applications of the camera, (i) plasma diagnostics in helium (He) plasmas and (ii) plasma–material interaction studies with tungsten (W) targets in neon (Ne) plasmas, have been carried out. The measurements were complemented by a movable Langmuir double probe system (LP) measuring electron temperature (Te) and electron density (ne) in radial direction r and a fiber-coupled cross-dispersion spectrometer with high spectral resolution (Spectrelle) recording neutral He, W, and Ne emission lines over the full plasma column. (i) Two-dimensional (2D) imaging of Te and ne radial profiles in axial direction z of the He plasma column were for the first time obtained by the regression analysis of Te and ne (from LP) and six He I line ratios (from HSC). The spatially resolved plasma parameters covered in these studies range between Te ∼ 0.8–13.4 eV and ne ∼ 0.2 × 1018–3.9 × 1018 m−3 and permit a reconstruction of the plasma conditions in PSI-2 in 2D without LP perturbation. (ii) W sputtering was studied in situ in Ne plasmas exposing W target samples (negatively biased at 100 V) under perpendicular Ne plasma impact. Simultaneously, the 2D distributions of W (W I line at 429.5 nm) in front of the target and the 2D Ne plasma distribution (Ne I line at 703.2 nm) were recorded with complete spectral separation as confirmed by the Spectrelle spectrometer. This permits the simultaneous measurement of the neutral W penetration and its angular distribution induced in the sputtering process and of the impinging plasma distribution. The HSI technique offers, despite a few technical drawbacks, such as the moderate spectral resolution and poor time resolution, a new possibility to distinguish multiple emission lines from plasma and impurities and complements the portfolio of existing Optical Emission Spectroscopy techniques, providing a good compromise regarding spectral, spatial, and temporal resolution. [ABSTRACT FROM AUTHOR]

Plasma focus devices generate discharges with dense hot plasma (HP) flows and fast ion streams (FIS) with energies up to several MeV, enabling their use to test materials for nuclear fusion applications. Tungsten plates were exposed to deuterium and to mixed deuterium-helium plasmas at distinct power flux densities at the large PF-1000U device. Elemental modifications as the induced deuterium retention and co-deposition of impurities at the target surfaces were studied by scanning electron microscopy and, particularly, by ion beam analysis (IBA). The results evidence that typically, deuterium retention is enhanced during the first discharges and may decreases afterwards due to surface erosion. Additionally, by adding helium to the working gas to generate the plasmas, deuterium retention increase. Similar results may be achieved by decreasing incident flux densities. The experiment highlights the role of the use of IBA to quantify elemental modifications imposed by irradiation of materials in plasma focus facilities. [ABSTRACT FROM AUTHOR]

Determination of the key chemical reaction pathways in cold atmospheric plasmas (CAPs) is of great importance not only for understanding the spatiotemporal evolutions of the key plasma parameters during discharges but also for improving the plasma materials processing qualities. In this paper, a novel chemical reaction reduction method (CRRM) is proposed by using the global fluid model coupled with the genetic algorithm and the dynamic programming technique. With the aid of this newly developed CRRM, the key chemical reaction pathways can be automatically screened with a high computational efficiency under a pre-set critical calculation accuracy for the atmospheric pure helium and helium–nitrogen glow discharge plasmas. By comparing the calculated key plasma parameters, e.g., the species number densities, electron temperatures, voltage–current characteristics, based on the simplified models and their corresponding full models with those of the experimentally measured data, the reliability of the CRRM itself and the established key chemical reaction database for the atmospheric pure helium and helium–nitrogen CAPs are validated. This research also provides a general method for screening the key chemical reaction pathways for various low-temperature plasma sources. [ABSTRACT FROM AUTHOR]

The propensity for nano-tendril bundle (NTB) vs widespread nano-tendril growth (i.e., fuzz) on polycrystalline W under varying ion energy modulation conditions, from DC to peak-to-peak energy modulation of 42 eV at 13.56 MHz, is correlated with the crystal orientation of the underlying grains. Grains that are vicinal to crystal orientations with high surface diffusivity (e.g., {101} for a body centered cubic crystal structure) exhibit NTB growth at lower ion energy modulation amplitude than grains that are vicinal to low surface diffusivity orientations, such as {100}. Adatom mobility considerations are presented to describe the experimental observations. These results support that surface diffusion or W adatom mobility enhanced by ion bombardment plays a key role in the surface morphology evolution of W under He irradiation. [ABSTRACT FROM AUTHOR]

This paper presents the experimental and numerical results about the influence of nitrogen (N2) and oxygen (O2) admixture on the development of a helium (He) atmospheric-pressure plasma jet (APPJ) in a long dielectric tube. The results revealed that the jet length and the propagation velocity are strongly affected by introducing N2 or O2 into the He flow. Specifically, it was observed that a higher N2/O2 admixture led to the decrease in the density of both energetic and relative low-energy electrons outside the grounded electrode, which corresponds to the shortening of the jet length. In the He/O2 mixture, the electrons are easily captured by O2/O in the region of the plasma bulk. In the He/N2 mixture, the jet propagation characteristics will change since N2 has many low-level excitation states that consumed a large number of energetic electrons. The simulation shows that the magnitude of the axial electric field in the jet head depends strongly on the amount of N2 and/or O2 in the gas flow. In both cases, the peak electric field is on the order of 5 kV/cm, which is significantly higher than that in pure helium of 3 kV/cm even if the admixture is low (less than 4% N2 or 2% O2 in this work). Positive charges of higher density in the jet head are needed to induce a stronger electric field for the jet propagating in N2(x%)/He and O2(x%)/He mixtures compared with that in pure He. [ABSTRACT FROM AUTHOR]

Lentil seeds have been packed in a dielectric barrier device and exposed for several minutes to a cold atmospheric plasma generated in helium with/without a reactive gas (nitrogen or oxygen). While no impact is evidenced on germination rates (caping nearly at 100% with/without plasma exposure), seeds' vigor is clearly improved with a median germination time decreasing from 1850 min (31 h) to 1500 min (26 h), hence representing a time saving of at least 5 h. We show that the admixture of nitrogen to helium can further increase this time saving up to 8 h. Contrarily, we demonstrate that the addition of molecular oxygen to the helium discharge does not promote seeds' vigor. Whatever the plasma chemistry utilized, these biological effects are accompanied with strong hydrophilization of the seed coating (with a decrease in contact angles from 118° to 25°) as well as increased water absorption (water uptakes measured 8 h after imbibition are close to 50% for plasma-treated seeds instead of 37% for seeds from the control group). A follow-up of the seeds over a 45-days aging period shows the sustainability of the plasma-triggered biological effects: whatever the plasma treatment, seeds' vigor remains stable and much higher than for seeds unexposed to plasma. For these reasons, the seed-packed dielectric barrier device supplied with a He–N2 gas mixture can be considered as a relevant dry atmospheric priming plasma in the same way as those used in routine by seed companies. [ABSTRACT FROM AUTHOR]

Partial arbitrary electron energy distribution function (EEDF) results for cold atmospheric-pressure plasma are reported. The EEDF is obtained using the visible bremsstrahlung inversion (VBI) method. This machine learning method requires only optical emission spectroscopy (OES) measurement and a momentum transfer cross section to determine a partial EEDF. Numerical EEDF of a pure-argon dielectric barrier discharge dataset with changing peak-to-peak voltage and a helium–argon discharge with changing mixture ratio are reported. Resemblance between the numerical EEDF and a two-temperature Maxwell distribution is observed and a simplified three-point numerical EEDF is obtained. The electron temperature and relative electron number density for the bulk and high-energy electron populations are measured. The bulk electron temperature was consistently 0.3 eV. For pure argon, the high-energy electron temperature decreased exponentially from 3 to 2.2 eV with increasing peak-to-peak voltage from 3.6 to 6.3 kV. For the helium–argon dataset, the high-energy electron temperature decreased linearly from 4.2 to 2.2 eV with increasing argon fraction 25%–100%. From an OES measurement, the arbitrary EEDF can be observed by utilization of the VBI method. Based on this numerical EEDF, appropriate assumptions can be applied to simplify the quantification of electron diagnostics. [ABSTRACT FROM AUTHOR]

This paper presents the results of the experimental studies of the helium plasma interaction with a surface carbide layer of tungsten. The experiments were carried out on a plasma beam installation (PBI) at a constant energy of incoming ions of 2 keV and at a surface temperature of the tungsten carbide layer of ~905 and ~1750 °C. The local parameters (Te, n0) of the helium plasma were evaluated using the probe method and spectrometric analysis of the plasma composition. The helium plasma irradiated two types of the carbide layer on the tungsten surface, WC and W2C. The mechanisms of changing the tungsten surface morphology in the result of the plasma irradiation have been described. The study of the surface structure of the tungsten samples with a carbide layer of two types (WC, W2C) after the exposure to the helium plasma has revealed two different types of the formation of helium bubbles and changes in the surface morphology. The physical mechanism of the formation of helium bubbles consists in the capture of helium atoms by the thermal vacancies generated at high temperature by the material surface. However, with a significant increase in temperature to 1750 °C, the formation of the bubbles was no longer observed and the sample surface had a developed corallike structure with crystallographically oriented grains. [ABSTRACT FROM AUTHOR]

In this study, by injecting cold plasma into the silk fibroin (SF) solution, and adding poly (3,4‐ethylenedioxythiophene): polystyrene sulfonic acid (PEDOT:PSS) into the SF solution, the conductive SF‐PEDOT:PSS hydrogel modified by plasma was successfully prepared. The changes of the electrochemical parameters and structure of SF‐PEDOT:PSS hydrogels after plasma modification were observed with plasma discharge time (60, 120, 180 s) and the type of working gas (Ar, air, He) as variables. The results of electrochemical impedance spectroscopy show that both argon plasma and helium plasma can reduce the impedance of SF‐PEDOT:PSS hydrogel in the extremely low‐frequency range (10−2–10° Hz), and a longer discharge time shrinks the impedance, while the impact of air plasma on the impedance of hydrogel is not obvious. The capacitance results show that both argon and helium plasma can make the capacitance of hydrogel larger, and the longer discharge time leads to the larger capacitance. While air plasma can reduce the capacitance of hydrogel. The results of Fourier infrared absorption spectroscopy and X‐ray diffraction spectrum show that the secondary structure of SF is mainly β‐fold. The results of Raman show that PEDOT:PSS is successfully incorporated into hydrogel, and there exists random coil conformation of SF in hydrogel. The results of X‐ray photoelectron spectroscopy show that the SF‐PEDOT:PSS hydrogel mainly contains C, O, and N elements. [ABSTRACT FROM AUTHOR]

Surface micro-discharge (SMD) has received growing interest for its great prospect in various emerging applications spanning the fields of biomedicine, manufacturing, and agriculture. Discharge properties and the nature of the chemical species are heavily dependent on the electrode configuration. However, insight into the effect of electrode configuration on SMD remains scarce. This paper reports on the effect of the geometry of the powered planar electrode on the dynamic evolution of plasma in a helium SMD array at atmospheric pressure. The observed symmetric and asymmetric luminous patterns correspond to odd and even numbered current pulses in negative half-cycle, respectively. When the powered electrode is not covering the full area of the mesh unit of the grounded electrode, the luminous pattern dominated by the negative pattern consists of three parts: the distinct luminous channel, the flabelliform luminous area, and the discontinuous cambered channels under the incomplete powered electrode condition. The distinct luminous channel is ascribed to the propagation of the bullet-like plasma volume originated at the middle part of the mesh side before merging with other plasmas. The merging plasma forms a cambered front and continuous to propagate, leading to the formation of a flabelliform area. The discontinuous cambered channels result from the propagation of bullets ignited at the mesh corners, especially the slide of luminous area with maximum emission intensity along the streamer. Moreover, the mesh element without a powered electrode can also initiate breakdown due to the sufficiently high voltage and the propagation of surface charges, suggesting that the grounded mesh electrode should be extended to avoid redundant discharges. [ABSTRACT FROM AUTHOR]

The surface treatment of ultra-high-molecular-weight polyethylene (UHMWPE) in helium plasma at a pressure of 0.133 mbar has been studied by IR spectroscopy, X-ray photoelectron spectroscopy, and atomic force microscopy. It has been shown that the helium plasma treatment leads to the formation of double bonds in the UHMWPE surface layer and the associated formation of intermolecular crosslinks. The crosslinking of the surface layer is accompanied by a decrease in the nanowear of the UHMWPE surface by more than three orders of magnitude, which is confirmed by measurements using an atomic force microscope in the contact mode. [ABSTRACT FROM AUTHOR]

The expectation values of radial and angular geometric quantities ⟨ r ⟩ , ⟨ r - 1 ⟩ , ⟨ r 2 ⟩ , ⟨ r 12 ⟩ , ⟨ r 12 - 1 ⟩ , ⟨ r 12 2 ⟩ , ⟨ r < ⟩ , ⟨ r > ⟩ , ⟨ cos (θ 12) ⟩ , and ⟨ θ 12 ⟩ for the ground states of the hydrogen negative ion and helium atom embedded in dense quantum plasmas are calculated using the Hylleraas configuration-interaction wave functions. The exponential cosine screened Coulomb potential is employed to model the effective interaction between charged particles in the dense quantum plasmas. The present calculations for free atoms show good agreement with other state-of-the-art predictions. In the plasma screening environments, our results improve previous estimations especially at large screening parameters. The radial expectation values ⟨ r < ⟩ and ⟨ r > ⟩ and the interelectronic angle ⟨ θ 12 ⟩ for the plasma-screened hydrogen negative ion and helium atom are reported for the first time, and we show that the combination of them provides a fairly good description of the geometric structure of two-electron atoms in different screening conditions. We finally analyze the asymptotic behavior of ground-state energies and radial quantities for two-electron systems nearing the bound-continuum limit, and provide strong evidence that the two-electron critical screening parameters are in coincidence with those for one-electron atoms. [ABSTRACT FROM AUTHOR]

A non-uniform distribution of the electric field along an atmospheric pressure helium plasma jet has been determined using the Stark spectroscopy technique at the stepwise propagation of a guided streamer in a free plasma jet and in the jet interacting with a grounded dielectric target. The plasma jet with guided streamers in the stepwise propagation mode is generated by tailoring applied voltage bunches consisting of a superposition of microsecond bipolar square pulses and damped oscillations. The guided streamer head stops at the oscillating voltage falling slope and then propagates further on the next raising voltage front. The electric field distribution along the jet reflects the dynamics of streamer propagation. The electric field strength decreases at a streamer propagation stagnation phase. The field strengthening at the subsequent raising voltage front accelerates the guided streamer at the second propagation step. [ABSTRACT FROM AUTHOR]

Low-temperature plasma jets at atmospheric pressure generated by sinusoidal and positive pulsed voltages interact differently with the treated surface. In the experiment and in numerical simulations, we compare the operating modes of helium plasma jets for these types of operating voltages. The discharge current on the treated surface over time and the surface heating are studied for different discharge parameters acceptable for anticancer therapy. The intensity of the emission spectrum is analyzed to improve the effectiveness of the plasma jet. Surface heating is controlled in order to meet the safety conditions of plasma exposure to biological objects. For the case of pulsed voltage the effect of voltage pulse duration on the intensity of plasma-surface interaction is discussed. The results on cancer cells A549 and MCF-7 demonstrate the high efficiency of the cold plasma jet generated at found optimal modes. [ABSTRACT FROM AUTHOR]