Search

The dynamics of the neutral atoms in Hall thrusters affects several plasma processes, from ionization to electrons' mobility. In the context of Hall thruster's particle-in-cell (PIC) modeling, the neutrals are often treated kinetically, similar to the plasma species, and their interactions with themselves and the ions are resolved using the direct-simulation Monte–Carlo (DSMC) algorithm. However, the DSMC approach is computationally resource demanding. Therefore, modeling the neutrals as a 1D fluid has been also pursued in simulations that do not involve the radial coordinate and, hence, do not resolve the neutrals' radial expansion. In this article, we present an extensive study on the sensitivity of the PIC simulations of Hall thruster discharge to the model used for the neutral dynamics. We carried out 1D axial PIC simulations with various fluid and kinetic models of the neutrals as well as self-consistent quasi-2D axial-azimuthal simulations with different neutrals' fluid descriptions. Our results show that the predictions of the simulations in either 1D or 2D configurations are highly sensitive to the neutrals' model, and that different treatments of the neutrals change the spatiotemporal evolution of the discharge. Moreover, we observed that considering the ion-neutral collisions causes a significant variation in the neutral temperature, thus requiring that the neutrals' energy equation to be included as well in their fluid system of equations. Finally, the self-consistent axial-azimuthal simulations highlighted that a neutrals' model based on the continuity conservation equation only is not an appropriate choice and leads to physically unexpected high-frequency global discharge oscillations. [ABSTRACT FROM AUTHOR]

This report describes an investigation by experimentation to elucidate atmospheric discharge plasma induced using a 50 kW millimeter-wave beam at 94 GHz. Millimeter-wave discharge plasma is useful for an ultraviolet light source, radioactive material detection, chemical decomposition, and beamed energy propulsion (BEP). The gyrotron used in this study is the "UT-94" with a frequency of 94 GHz and an output power of 100 kW, which was developed at the University of Tokyo specifically for BEP research. The 94 GHz frequency is promising for atmospheric energy beaming because of its low atmospheric attenuation, small beam divergence, and existing utilization track records in the atmosphere. This study experimentally investigated the relationship between the incident beam power density and propagation velocity of an ionization-wave front, which is particularly critical to thrust performance. In addition, the plasma structures were also clarified at 94 GHz and compared with other microwave and millimeter-wave frequencies, such as 28 GHz and those higher than 100 GHz. As a result, finer microscopic structure in the H–k plane was observed than those reported in earlier studies. Furthermore, we found a clear relation between structures and propagation velocities in terms of the electric field concentration of the incoming electromagnetic-waves. [ABSTRACT FROM AUTHOR]

In the experiment, plasma–dust clouds were obtained from the substance of the Tsarev meteorite, a simulant of lunar regolith LMS-1D and ilmenite concentrate using a microwave discharge in powder media. For each of the samples, the dynamics of the development of the discharge and the formation of a plasma–dust cloud with subsequent relaxation after the end of the microwave pulse were recorded. From the emission spectra of the plasma and the surface of a solid body, the temperatures of the gas, electrons and surface were determined. A comparison of the phase and elemental composition of the initial samples and samples after exposure to plasma showed that there is no significant change in the composition. However, scanning electron microscopy results clearly indicate spheroidization of the original angular and irregularly shaped particles. The appearance of spherical particles is also observed, the dimensions of which are larger than the linear dimensions of the particles in the original sample. The results obtained indicate the possibility of using such experiments to study chemical and plasma-chemical processes of synthesis and modification of substances under conditions of plasma–dust clouds encountered in space phenomena. [ABSTRACT FROM AUTHOR]

Using chromatography, the gas composition in a cold plasma jet, which is a flowing afterglow of a microwave glow discharge at atmospheric pressure, is analyzed. The plasma jet is formed by the interaction of the discharge plasma with atmospheric air behind the outlet of the 6-electrode plasma torch, electrical power to which is supplied from the waveguide microwave (2.45 GHz) plasmatron. An analysis of the gas samples of the jet shows that when plasma-forming argon flows through the microwave discharge, hydrogen and methane are formed behind the discharge region, and the concentration of carbon monoxide increases by 5–6 times. The reactive oxygen species in the cold plasma jet is studied using liquid chromatography of an aqueous solution of isopropyl alcohol after treatment with the plasma jet. It is found that because of plasma treatment, partial oxidation of isopropyl alcohol to acetone occurs. This makes it possible to consider acetone as an indicator of reactive oxygen species (hydroxyl radicals, atomic oxygen and ozone) in a cold plasma jet. [ABSTRACT FROM AUTHOR]

A method for activating water by plasma of an electrodeless torch discharge in a microwave electromagnetic field in argon in an environment of water vapor, at atmospheric pressure, to obtain a pure solution of hydrogen peroxide H2O2 without impurities in distilled water is proposed. It is shown that the main mechanism for the formation of atomic hydrogen H• and hydroxyl HO• radicals in the water decomposition is photolysis under the influence of excimer vacuum ultraviolet radiation of argon plasma. Hydrated electrons can be an additional source of radicals in liquid water when the plasma torch comes into contact with the water surface. Today plasma technologies are widely used to produce activated water containing hydrogen peroxide, to solve environmental problems, to increase productivity in agriculture, and for medical use. [ABSTRACT FROM AUTHOR]

A one-dimensional (1D) fluid model is developed to investigate the effect of multi-frequency excitation consisting of consecutive harmonics on the charge of a single dust grain in a weakly collisional capacitively coupled plasma discharge. The spatial distributions of the electron density, the electrons temperature, and the charged particle flux are obtained and analyzed under the effects of the number of harmonics. It is shown that the number of harmonics considerably affects the discharge properties and the sheath thickness. In order to analyze the charge of an injected dust particle under the effect of different operating parameters, the model takes into account the electron and ion currents, as well as the effect of collisions between ions and neutral atoms. The results showed that as the number of harmonics increases, the particle charge increases in the powered sheath region while it decreases in the grounded sheath due to the electrical asymmetry effect. However, the charge remains constant in the central region where the electron temperature is constant. The present study further shows that the gas pressure and the driving frequency affect the dust charge oppositely, where an increase in pressure leads to a decrease in the dust charge, especially in the sheath regions, while the particle charge negatively increases as the driving frequency increases for all excitation waveforms. [ABSTRACT FROM AUTHOR]

For atmospheric argon RF dielectric barrier discharges, a self-consistent one-dimensional fluid model based on the drift-diffusive approximations of the particles is established to investigate the role of the neutral gas temperature on the discharge process and the plasma characteristics. A finite difference method is used to solve numerically the model, and the numerical results are obtained for the cases that the neutral gas temperature varies from 300 to 600 K. It shows that an increase in the neutral gas temperature causes a decrease in the ionization rate peak and a decrease in the plasma density, but the electric field and the electron temperature do not change very much. Moreover, the discharge mode transition from α mode to α-γ mode occurs because the growing ion flux induces more secondary electron flux, even if the ions entering the sheaths decrease. In addition, the ground state ionization and the ground state excitation are the main collisions in the argon discharges. When metastable atoms are focused on, the three-body quenching is also an important collision progress. [ABSTRACT FROM AUTHOR]

Thermal stability and the kinetics of thermal decomposition of the thermally reduced graphene oxide (TRGO) treated by a pulsed high-frequency discharge in a hydrogen atmosphere have been studied. The modified Hummers method was used for obtaining the initial graphite oxide from graphite powder. Thermal exfoliation of the graphene oxide powder has been done in vacuum conditions with a heating rate of 5–7 degrees per minute to a temperature of 300 °С. TRGO has been treated by pulsed high-frequency discharge in a hydrogen atmosphere for partial graphene hydrogenation (chemical addition of atomic hydrogen) that leads to structural changes in the carbon planes and formation of C–H sp3 bonds. The thermogravimetry analysis measurements of the mass loss have been carried from room temperature to 1000 °C in a nitrogen atmosphere with a nitrogen flow rate of 20 mL/min and different heating rates: 50, 75 100, 125, 150, and 200 K/min, respectively. Kissinger's multiple heating rate method has been used to determine the activation energy for decomposing substances. Activation energies Ea1, Ea2, and Ea3 equal 28, 50, and 148 kJ/mol, respectively, have been compared with the energies of the activation of thermal defunctionalization of multiwalled carbon nanotubes (MWCNTs). The activation energy Ea3 = 148 kJ/mol is close to that of the thermal decomposition of anhydride functional groups in MWCNT. The value of Ea2 = 50 kJ/mol indicates the presence of the keto and hydroxy acid's function groups on TRGO. Activation energy Ea1 = 28 kJ/mol related with all other groups including the lighter C–H bonds that destructed due to dehydrogenation of the TRGO. Obtained experimental results are useful for further proposing the kinetic model of the mechanism of the most probable reaction of TRGO decomposition. [ABSTRACT FROM AUTHOR]

Ammonia have been attractive as one of the alternative fuels for reducing greenhouse gas (GHG) emissions. However, ammonia combustion has lower combustion performance than common hydrocarbon fuels. Furthermore, it may emit nitrous oxide (N 2 O), which is one of the GHGs. This paper presents the experimental investigations of plasma-assisted ammonia combustion (PAAC) using a rod-electrode-type microwave plasma source (MPS) at atmospheric pressure. The equivalence ratios of premixed ammonia/dry air (NH 3 /Air) gas are set below the stoichiometric combustion of NH 3 to reduce toxic NH 3 in the combustion gas. Under the condition of the equivalence ratios, the experiments are focused on reducing the unburned NH 3 and produced N 2 O concentrations in the combustion gas. In the experiments, the unburned NH 3 , nitrogen oxide (NO x) (the sum of nitric oxide (NO) and nitrogen dioxide (NO 2)), and N 2 O concentrations in the combustion gas are investigated in terms of the flow velocity of premixed NH 3 /Air gas inside the rod-electrode-type MPS and the transmission power to the rod-electrode-type MPS. In conclusion, the rod-electrode-type MPS is identified to be useful for PAAC. The NH 3 and N 2 O concentrations in the combustion gas reach approximately 25 and 4 parts per million (ppm), respectively, under the conditions of the equivalence ratio of 1.0, flow velocity of approximately 0.167 m/s, and transmission power of about 84 W. At that time, the NO x concentration is approximately 4300 ppm, and the power transmission efficiency is approximately 68 %. • Plasma-assisted ammonia combustion (PAAC) was conducted using microwave discharge. • The microwave discharge was generated using a rod-electrode-type microwave plasma source (MPS). • The experiments were conducted without a swirler and below the stoichiometric combustion. • The minimum concentrations of NH 3 and N 2 O in the combustion gas reached 25 and 4 ppm. • The rod-electrode-type MPS was identified to be useful for PAAC. [ABSTRACT FROM AUTHOR]

A pulsed microwave surfaguide-type discharge used for nitrogen fixation in N 2 –O 2 gas mixtures is characterized by optical emission spectroscopy. Results show that both rotational and vibrational temperatures are elevated in the active zone near the waveguide, decaying along the discharge tube in both upstream and downstream. The characteristic length of optical emission from NO(A - X) transition gets contracted when pressure increases, specifically at P ≥ 2 Torr. The degree of vibrational non-equilibrium (defined as the ratio between vibrational and rotational temperatures) is decreased by a factor of two when pressure changes from 0.6 to 10 Torr. Non-equilibrium likely disappears as the discharge pressure rises, resulting in a gas temperature elevation. A correlation between gas residence time, pulse duration, and characteristic times for different energy transfer channels is discussed. The rotational–vibrational dynamics differs for NO and N 2 during the pulse. Both species lose vibrational excitation at the beginning of the pulse, whereas N 2 gets re-excited again during the second half of the pulse, which may occur as a result of an efficient pumping-up effect through the vibrational–vibrational energy transfer. At the same time, vibrational relaxation of NO takes place primarily due to a strong vibrational–translational exchange via NO–O 2 and NO–O collisions. [ABSTRACT FROM AUTHOR]

The dynamical behavior of the capacitively coupled Ar plasma driven by four frequencies (54, 80, 94 and 100 MHz) at fixed pressure are simulated by the particle-in-cell/Monte-Carlo collisions (PIC/MCC) model based on the electromagnetic field. The magnetic field is generated by plasma current itself. The results show that the electron density, charge density, and electron temperature increase with the frequency increase when radio frequency (RF) power is 40 W. The electron heating rate and argon ion heating rate near the sheath increase with the frequency increase. The high-energy electron density (> 3 0   eV) varies nonlinearly with the frequency increase. The high-energy electron density is highest at 80 MHz among the four frequencies. The electron density, charge density, and high-energy electron density increase with RF power (30, 45, 60, and 75 W) increase at 80 MHz. The electron temperature decreases with RF power increase at 80 MHz. The electron heating rate and argon ion heating rate near the sheath have no change with RF power increase at 80 MHz. The electron energy probability distributions (EEPF) show that the number of high-energy electrons (> 3 0   eV) is highest at 80 MHz. The reason may be the electron resonant heating that occurs in the plasma when the electron cyclotron frequency equals source frequency at 80 MHz. The electron dynamics of capacitively coupled plasma is important for microelectronics etching and membrane deposition. [ABSTRACT FROM AUTHOR]

Bands of the g 6Φ-X 4Δ, g 6Φ-A 4Π, g 6Φ-a 6Δ, and g 6Φ-b 6Π electronic transitions of iron monodeuteride (FeD) have been measured in laser excitation and in dispersed fluorescence. The molecules were produced both in a cold supersonic molecular jet source and in a chemical reaction between iron pentacarbonyl [Fe(CO5)] and a microwave discharge of argon and hydrogen gases. Dispersed fluorescence from the latter source was detected at high resolution with a Fourier transform spectrometer, yielding a large number of the transitions observed. The data reveal that FeD experiences strong interstate couplings that compromise fitting of the data with traditional Hamiltonians but that the problem is less severe than in corresponding spectra of FeH. This work greatly expands the available data on FeD, which were previously characterized only through the F 4Δ-X 4Δ spectrum and pure rotational data in the ground state. [ABSTRACT FROM AUTHOR]

• The relationship between CA3 IEDs and HFOs differs in Septal and Temporal hippocampal slices. • Most differences refer to the timing relationship of HFOs to IEDs. • A juvenile SE changes this relationship in the long term. • Juvenile SE effects differ between Septal and Temporal hippocampal slices. • The IED to HFO relationship provides insights in neuronal network activation patterns. The aim was to investigate the long-term effects of a single episode of immature Status Epilepticus (SE) on the excitability of the septal and temporal hippocampus in vitro , by studying the relationship between interictal-like epileptiform discharges (IEDs) and high-frequency oscillations (HFOs; Ripples, Rs and Fast Ripples, FRs). A pentylenetetrazol-induced Status Epilepticus-(SE)-like generalized seizure was induced at postnatal day 20 in 22 male and female juvenile rats, sacrificed >40 days later to prepare hippocampal slices. Spontaneous IEDs induced by Mg2+-free ACSF were recorded from the CA3 area of temporal (T) or septal (S) slices. Recordings were band-pass filtered off-line revealing Rs and FRs and a series of measurements were conducted, with mean values compared with those obtained from age-matched controls (CTRs). In CTR S (vs T) slices, we recorded longer R & FR durations, a longer HFO-IED temporal overlap, higher FR peak power and more frequent FR initiation preceding IEDs (% events). Post-SE, in T slices all types of events duration (IED, R, FR) and the time lag between their onsets (R-IED, FR-IED, R-FR) increased, while FR/R peak power decreased; in S slices, the IED 1st population spike and the FR amplitudes, the R and FR peak power and the (percent) events where Rs or FRs preceded IEDs all decreased. The CA3 IED-HFO relationship offers insights to the septal-to-temporal synchronization patterns; its post-juvenile-SE changes indicate permanent modifications in the septotemporal excitability gradient. Moreover, these findings are in line to region-specific regulation of various currents post-SE, as reported in literature. [ABSTRACT FROM AUTHOR]

In recent years, interest in striation phenomena in radio frequency (rf) discharges has risen due to the availability of new experimental data and the implementation of new computational models. Depending on the conditions, different mechanisms of discharge striations are realized. These are the ionization instability, the instability due to the electron attachment to electronegative gases, or the instability due to thermoelectric transport. Although the first two mechanisms were modeled quite extensively in recent years, the understanding of the influence of the Dufour effect originating from plasma density gradients on the stability of radio frequency discharges in long tubes remains poor. In this paper, the influence of this mechanism on the longitudinal striations of radio frequency discharge is presented using a one-dimensional model of argon discharge driven with rf excitation under intermediate pressure conditions of 0.5 Torr. It is found that striation formation is sensitive to the value of the thermoelectric heat transport coefficient in the low electron temperature range. The critical value of this coefficient necessary for the instability onset is derived using the linear stability analysis. [ABSTRACT FROM AUTHOR]

The filamentation dynamics of a nitrogen pulsed microwave discharge generated at the antinode of a standing electromagnetic wave at a pressure of 100 torr has been numerically simulated. The results of the dynamics of the main plasma parameters, such as the concentration of charged and excited species, gas temperature, and vibrational temperature of nitrogen, are presented. [ABSTRACT FROM AUTHOR]

The paper is dedicated to the numerical study of the dependence of plasma antenna resonance wavelengths on pressure. The study was carried out by simulating a RF capacitively coupled plasma with the Comsol Multiphysics software in one- dimensional formulation. Based on the calculated electric current in the plasma, the directional pattern and axial distribution of the electromagnetic field were found by solving Maxwell's equations in a 2D formulation. The results showed that one of the advantages of plasma antennas is the transmission of waves at significantly longer wavelengths compared to metal antennas of similar geometry. [ABSTRACT FROM AUTHOR]

A microwave discharge in high-velocity (150–250 m/s) air flows induced on a half-wave vibrator is studied. A cw magnetron microwave generator with a frequency of 2.45 GHz and an output power of up to 5 kW was used for initiation of the microwave discharge. The high-speed video imaging was used for studying the discharge structure, determining the diameter and length of the plasma channel as a function of flow velocity and pressure. Electron concentration and temperature, along with characteristic gas temperature, were determined based on the optical spectra. The possibility of using this microwave discharge for ignition of hydrocarbon–air mixtures in combustion chambers of ramjet engines is proved experimentally. [ABSTRACT FROM AUTHOR]

Energy storage system play a crucial role in safeguarding the reliability and steady voltage supply within microgrids. While batteries are the prevalent choice for energy storage in such applications, their limitation in handling high‐frequency discharging and charging necessitates the incorporation of high‐energy density and high‐power density storage devices to enhance power quality, maintain power balance, and reduce fluctuations. In this study, we introduce a hybrid energy storage system (HESS) solution, combining a battery and a supercapacitor, to address intermittent power supply challenges. The effective management of this HESS is pivotal for constant DC voltage and sustaining microgrid stability. To achieve this, we propose an innovative control strategy called the Adaptive Filter‐Based Method (AFBM) for DC microgrid operation, which prioritizes stable and smooth performance while addressing safety and degradation concerns related to the storage devices. Our control strategy determines the distribution of charging and discharging currents for each storage device within the DC microgrid based on their state of charge. We conducted simulations in MATLAB/Simulink, comparing the proposed AFBM method with the conventional filter‐based approach using identical configurations, parameters, and operational modes. The results demonstrate the superior performance of our proposed system, showcasing improved voltage stability, more equitable load distribution, and efficient charging and discharging of storage devices compared to the traditional method. This research contributes to the advancement of microgrid energy storage solutions, enhancing their reliability and performance. [ABSTRACT FROM AUTHOR]

A fully kinetic 2D axisymmetric Particle-in-Cell (PIC) model is used to examine the effects of background facility pressure on the plasma transport and propulsive efficiency of magnetic nozzles. Simulations are performed for a low-power (150 W class) cathode-less radio-frequency (RF) plasma thruster, operating with xenon, between background pressures up to 1 0 − 2 Pa and average electron discharge temperatures of 4–16 eV. When the electron temperature within the near-plume region reaches 8 eV, a decisive reduction in performance occurs: at 1 0 − 2 Pa, in-plume power losses surpass 25% of the discharge energy flux. Given that the ionisation energy for Xe is 12 eV, the 8 eV threshold indicates that a consistent percentage of electrons has energy enough to trigger ionisation. On the other hand, when the temperature is below such threshold, the primary collisions are charge-exchange and inelastic ion scattering, and the power loss remains less than 10%. It is established that losses in the considered thruster are significant if the facility pressure is greater than 1 0 − 3 Pa, at absorbed powers larger than 130 W. At the nominal 150 W, this results in a 15% thrust reduction. When facility pressure is taken into consideration over ideal vacuum simulations, numerical error is reduced to < 30% when compared to experimental thrust measurements at 1 0 − 3 Pa. • Investigation of facility effects on cathode-less RF thruster performance. • Particle-in-Cell (PIC) simulation of magnetic nozzle expansion into background gas. • Up to 15% thrust reduction at 150 W beyond 1 0 − 3 Pa. • Electron inelastic collisions can cause up to 70% of total in-plume power losses. • Experimental results/setup should therefore take into account facility pressure. [ABSTRACT FROM AUTHOR]

The results of experimental studies on the formation and subsequent evolution of extended (l = 300 mm) and thin-walled (Δr ≈ 10 mm) tubular (2r ≈ 110 mm) plasma in a weak longitudinal magnetic field (B = 175 G) without the use of a thermionic cathode are presented. The cylindrical chamber in which the tubular plasma was formed was pumped with high purity argon (99.998%) at an average velocity of about 1 m/s at a pressure of P = 10–3–10–2 Torr. Two methods of creating seed electrons initiating the development of ionization avalanches were used. The difference inherent to these methods has been established in the dynamics of breakdown, completing in the formation of a tubular discharge. In the first of them, a pulsed discharge preceding the high voltage supply of the main discharge created gas preionization in a small area around the sectioned cathodes. In the second method, seed electrons were created in the entire working area of the discharge chamber by an RF discharge with a frequency of 85 kHz and duration of about 1 s. High-speed shooting with a 4-frame ICCD camera allowed us to establish the dynamics of tubular discharge formation at all its stages. Measurements of the longitudinal and radial discharge current were carried out. The results we obtained showed the possibility of spatial isolation of an extended tubular plasma from the close located metal wall of the discharge chamber by using a weak longitudinal magnetic field. [ABSTRACT FROM AUTHOR]

The influence of current activation by the breakdown of the electric pulse on changes in the surface morphology and emission characteristics of a field emission (FE) cathode made based on carbon films obtained by deposition in a microwave gas discharge plasma is studied. The current activation of these films is carried out by applying microsecond voltage pulses until an electrical breakdown occurred. It is shown that during the activation, the morphology of the film surface in the breakdown region changes with the formation of a microsized emitting structure, which significantly improves the FE characteristics of the cathodes based on carbon films. [ABSTRACT FROM AUTHOR]

The effect of irradiation with a pulsed electron beam on the diffusion of titanium in the polycrystalline Zr-1 wt.% Nb alloy is studied using high-frequency glow discharge optical emission spectrometry. The depth distribution profiles of titanium concentration in the Zr-1 wt.% Nb alloy after isothermal diffusion annealing and annealing under surface irradiation with a pulsed electron beam are determined. It is shown that under simultaneous exposure to temperature and irradiation with a pulsed electron beam, an increase in the coefficient and a decrease in the activation energy of grain boundary diffusion are observed in the near-surface layer of the alloy. [ABSTRACT FROM AUTHOR]

The properties of an inductive RF discharge placed in a longitudinal external magnetic field with an induction of less than 70 G at frequencies of 2, 4, and 13.56 MHz are studied. The dependences of the region of existence of the discharge, the efficiency of the RF power input and the structure of the RF magnetic field on the external magnetic field induction are studied experimentally. The experimental results are compared with calculations based on a previously developed electromagnetic discharge model. It is shown that the local maximum of the plasma density observed at weak magnetic fields is associated with the resonant excitation of waves in the plasma source. The excited wave is close to a transverse helicon at a frequency of 2 MHz, and its properties approach the Trivelpiece–Gould wave at a frequency of 13.56 MHz,. [ABSTRACT FROM AUTHOR]

The possibilities of igniting a combustible mixture in a high-speed flow using a microwave streamer discharge are considered. The results of experimental studies of the streamer discharge structure at various pressures are presented. To quantitatively characterize the intensity of combustion of fuel ignited by a microwave discharge, pressure and temperature measurements are used in various sections of the jet in the discharge wake. The results obtained demonstrate the possibility of igniting a model combustible mixture when propane or its mixture with air is sup-plied to the discharge region. The main physical mechanisms responsible for heating the discharge plasma to the ignition temperature of the combustible mixture and their characteristic time scales are revealed. The change in the dimensions of the combustion zone with a decrease in the initial proportion of propane in the mixture is discussed. The minimum duration and minimum level of microwave radiation required to ignite a model combustible mixture under various conditions are determined. [ABSTRACT FROM AUTHOR]

Leucosapphire (c-LS) structure and transmission in visible after surface treatment in 90%H2–10%N2 RF discharge are studied. According to AFM, the number of scratches of the mechanically polished surface decreased significantly after removal of about a 300 nm layer (exposure time of 12 h) under unchanged rms of roughness. According to TEM, a two-layer structure formed in the near-surface region consists of an outer 10 nm amorphous layer followed by a crystalline layer of 40–50 nm with a high defect density. The c-LS transmission in the angle of 400–1000 nm either slightly increased or remained unchanged. The demonstrated transmission stability during exposure in 90%H2–10%N2 RF discharge allows us to consider the plasma sputtering as a promising technique for cleaning contaminated windows protecting first mirror of divertor Thomson scattering being developed for ITER divertor. [ABSTRACT FROM AUTHOR]

A new method for the synthesis and deposition of tungsten oxide nanopowders directly on the surface of a carbon-fiber-reinforced polymer composite (CFRP) is presented. The CFRP was chosen because this material has very good thermal and mechanical properties and chemical resistance. Also, CFRPs have low melting points and are transparent under ionized radiation. The synthesis is based on the direct interaction between high-power-density microwaves and metallic wires to generate a high-temperature plasma in an oxygen-containing atmosphere, which afterward condenses as metallic oxide nanoparticles on the CFRP. During microwave discharge, the value of the electronic temperature of the plasma, estimated from Boltzmann plots, reached up to 4 eV, and tungsten oxide crystals with a size between 5 nm and 100 nm were obtained. Transmission electron microscopy (TEM) analysis of the tungsten oxide nanoparticles showed they were single crystals without any extended defects. Scanning electron microscopy (SEM) analysis showed that the surface of the CFRP sample does not degrade during microwave plasma deposition. The X-ray attenuation of CFRP samples covered with tungsten oxide nanopowder layers of 2 µm and 21 µm thickness was measured. The X-ray attenuation analysis indicated that the thin film with 2 µm thickness attenuated 10% of the photon flux with 20 to 29 KeV of energy, while the sample with 21 µm thickness attenuated 60% of the photon flux. [ABSTRACT FROM AUTHOR]

Similarity laws (SLs) for low-pressure capacitive radio-frequency plasmas are generalized from one- to two-dimensional (2D) frameworks based on kinetic particle-in-cell simulations. Fundamental discharge parameters, such as the 2D distributions of electron densities and electric fields, are examined to assess the applicability of SLs to such discharges. The discharge characteristics are found to remain invariant when external control parameters are changed according to SLs. Even under conditions where nonlinear electron resonance heating caused by the self-excitation of the plasma series resonance due to the geometric reactor asymmetry plays an important role, the electron kinetics are shown to be invariant. Moreover, the validity of SLs for the ion dynamics is demonstrated. The results advance the applicability of SLs to a 2D cylindrical reactor geometry with azimuthal symmetry, indicating broad application prospects in practice. [ABSTRACT FROM AUTHOR]

Clusters of active Brownian particles in gas-discharge plasma are considered as open systems with energy exchange with the environment. The evolution of a cluster of 19 active Brownian particles with a partially absorbing metal surface (so-called Janus particles) when exposed to intense laser radiation is shown. The formation of strongly correlated clusters of charged particles with increasing laser radiation power was observed experimentally. Based on an analysis of the trajectories of particles, the region of their localization, and changes in their kinetic energy, fractal dimension, and dynamic entropy for different values of laser radiation power density, the self-organization of a cluster of strongly interacting particles in the plasma of a high-frequency glow discharge is studied. [ABSTRACT FROM AUTHOR]

Ignition of combustible air/propane mixture in a high-speed flow with a microwave streamer discharge is considered. The experimental results of structure of streamer discharge and quantities at various pressures are presented. Pressure and temperature measurements in various sections of the streamer discharge in high-speed flow are analysed. The results obtained demonstrate the possibility of ignition of air/propane combustible mixture. The main physical mechanisms responsible for heating the discharge plasma to the ignition temperature of the combustible mixture and their characteristic time scales are discussed. The minimum time and minimum level of microwave radiation required to ignite a combustible mixture under various conditions are determined. • Streamer discharge structure at various pressures in high-speed flow is presented. • Streamer discharge provides reliable ignition in a high-speed flow. • Minimum time and pulse energy required to ignite a mixture are determined. [ABSTRACT FROM AUTHOR]

A linear radiofrequency plasma device is constructed, where a source operating at a frequency of 13.56 MHz and a maximum power of several kW is attached to a cylindrical vacuum chamber about 1 m in length. Seven solenoids are located around the source and the chamber, providing various magnetic field configurations by changing the solenoid currents. The plasma density of the radiofrequency linear plasma device is initially characterized in uniform and convergent magnetic field configurations. A blue mode argon plasma, being inherent to the helicon or high-density discharge, is observed in the chamber downstream of the source for both configurations, while the density near the antenna is lower than that in the chamber. Furthermore, the density for the convergent magnetic field configuration is found to be larger than that for the uniform case, providing a maximum density of about 2 × 10 19 m − 3 . Spatiotemporal measurements of the ion saturation current reveal that the density peak is formed near the rf antenna at the initial time of the discharge and the peripheral high-density region subsequently appears downstream of the antenna, implying that the rf power is efficiently coupled with the electrons downstream of the antenna once the initial plasma is created. A few ms after turning on the rf power, the density over the whole region reduces, which seems to be due to a neutral depletion. [ABSTRACT FROM AUTHOR]

A numerical simulation of the conditions for the direct initiation of detonation in the region of a combustible mixture, in which its critical energy is minimum, has been performed using a streamer microwave discharge for the source of detonation initiation. The calculations were conducted on the basis of the model of the two-dimensional detonation in a combustible mixture, flowing in a cylindrical channel, with the use of the system of gas-dynamics and chemical-kinetics equations. The process of detonation initiation was considered as applied to a stoichiometric hydrogen–air mixture flowing in a cylindrical channel at different initial pressures. The requirements for the source of initiation of detonation in a combustible mixture were investigated with respect to the attainment of its critical parameters in practice. [ABSTRACT FROM AUTHOR]

As a method to optimize the power frequency of dual-frequency plasma, we propose an optimization method that combines genetic algorithm and plasma simulation. A two-dimensional plasma simulation model of Ar plasma was constructed with a fluid model. Combining this simulation model with a genetic algorithm, 300 cases of plasma conditions with high plasma density and small variation in electron density were calculated. As a result, the optimum conditions were 175 to 210 MHz for the high-frequency generator and 1.0 to 2.5 MHz for the low-frequency generator. Furthermore, two types of single objective functions that combine the electron density and the variation rate were proposed. The single objective functions with emphasis on electron density and with emphasis on variation rate were introduced, and each objective function was optimized. [ABSTRACT FROM AUTHOR]

The contamination of Enterococcus bacterium is widely observed in the living environment and water. The decontamination of drinking water from the bacterial pollution is an important issue in water treatment. Here, the inactivation of Enterococcus bacteria is studied by placing the dielectric barrier discharge structure, with the RF discharge frequency of 13.56 MHz atmospheric pressure argon plasma jet, directly in water, whereas the water around the plasma plume was seething and the bubbles produced stirring all liquid volume. The ability to place a plasma jet nozzle directly in water for 10 min while maintaining a steady and uniform plasma plume, besides water temperature, provides the effectiveness enhancement in the inactivation of bacteria. The absorption of UV radiation in water is effective, and the role of UV radiation of plasma plume was mainly responsible for the destruction of peptidoglycan, which is the outer layer of Enterococcus. Then, the presence of electrons and plasma plume in water leads to the formation of hydroxyl, hydrogen peroxide, and other reactive radicals that are involved in chemical reactions, which lead to the inactivation of micro-organisms. The number of bacteria decreases from the initial value of 16 × 105 MPN/100 ml to less than 1.2 MPN/100 ml. The spectra of the plasma radiation, with the plume length 2 cm within the water, have been analyzed via the first nitrogen negative system N+2 (B − X). The plume temperature was calculated to be about 64 °C, which has a good agreement with water temperature measured by using a thermometer at about 67°C after 15 min at maximum 200 W input power of the plasma jet. [ABSTRACT FROM AUTHOR]

A pulsed RF discharge is considered experimentally as a working process of an RF ion source. It is shown that an increase in the ion current can be obtained in comparison with the continuous operation mode when such a discharge is operating. This increase is the greater, the greater the difference between the characteristic time of the drop of the ion current after turning off the RF power and the rise time of the ion current when the RF power is turned on. The pulsation parameters at which the ion current is maximized are estimated. It is shown that an external constant longitudinal magnetic field in the range of 0–7.2 mT nonmonotonically affects the maximum and equilibrium value of the ion current in a pulse and does not affect the decrease rate of the ion current after the RF power is turned off. [ABSTRACT FROM AUTHOR]

The energy characteristics of a plasma channel (filament) are the most important for a number of applications. A numerical study of the evolution of the thin plasma channel in air in the range of discharge parameters P = 30–750 Torr and λ = 2.3–8.5 cm showed that the total absorbed energy (Joule's losses) at each time instant is close to its upper estimate, which integrally depends only on the spatial distribution of the plasma density at this instant. A simple analytical expression is obtained for estimating the fraction of the wave beam energy transferred to the channel. An express method for estimating the energy characteristics of a plasma filament is proposed. The method is based on analytical expressions and experimental data on the temporal evolution of the plasma dimensions visible in photographs. The considered example shows the possibility of fast estimation of the total absorbed energy, as well as the specific energy and gas heating in the center of the channel during a microwave pulse. [ABSTRACT FROM AUTHOR]

The electron energy probability function (EEPF) is experimentally identified in a miniature microwave discharge neutralizer over wide operating conditions. A tiny Langmuir probe coupled with the analog differentiation technique offers precise time-averaged EEPFs over about three orders of magnitude, including high-energy, low-density electrons. The non-Maxwellian, concave EEPFs are observed in all experimental conditions. They approach Maxwellian with higher gas pressure, where they deviate from Maxwellian with the absorbed microwave power. Analyzing the measured EEPFs by the generalized EEPF theory, the index that determines the shape of EEPFs (Maxwellian corresponds to 1) is found to be 0.7 ± 0.15. The ionization frequency is estimated using the measured non-Maxwellian EEPFs, and it is found that one would underestimate the ionization frequency with the Maxwellian approximation about up to ∼ 20 %, the value almost negatively correlating with the shape index. These results also suggest that the electron fluid model in microwave discharge neutralizers leads to the overestimation of the electron temperature and the Bohm velocity. [ABSTRACT FROM AUTHOR]

The radio-frequency (RF) plasma thruster has been studied to overcome the issue of a reduced lifetime of plasma thrusters due to electrode erosion, and it has been reported that a nonuniform magnetic field near the RF antenna improves the thrust performance. In this study, to obtain knowledge for optimizing the configuration of the thruster and the magnetic field, the RF discharge in a nonuniform magnetic field is numerically investigated focusing on RF power absorption and plasma generation, and the effect of the positional relation between the magnetic cusp and the RF antenna on the RF discharge is discussed. We adopt the two-fluid plasma model considering ions and electrons and confirm the qualitative validity of the simulation by comparing the simulation results with the results of a laboratory experiment. The simulation reveals that the energy transport due to the E y × B drift from the region of RF power absorption near the RF antenna determines the distributions of the plasma generation and temperature. Therefore, the plasma distribution changes depending on the RF antenna position and the phase of the RF period because the E y × B drift direction changes depending on the directions of the electric and magnetic fields. In addition, we find that it is important to place the antenna in a strong magnetic field for effective power absorption because this increases the azimuthal diamagnetic current. [ABSTRACT FROM AUTHOR]

Manganese dioxide is one of the key materials in battery, adsorption media, and catalytic materials in the environmental field because of its excellent properties. In this investigation, new synthetical technology—the microwave discharge plasma in liquid method was used directly to make manganese dioxide with potassium permanganate (KMnO4) solution. The synthesis was realized in one step by the microwave discharging plasma in potassium permanganate aqueous solution without using any dispersants or stabilizers. The reduction time was very short, it only takes 3 min to complete the reduction of the 0.2 mmol l−1 potassium permanganate solution for the formation of MnO2. The structure characteristics and adsorption-desorption curves were studied by X-ray diffractometer (XRD), transmission electron microscopy and x-ray photoelectron spectroscopy, XRD, etc. it was found that the synthesized manganese dioxide nano-sheet had a layered structure and a large specific surface area (248.89 m2 g−1). The methylene blue was used to validate the effectiveness of the prepared manganese dioxide. The results showed that the synthesized manganese dioxide had good adsorption and photocatalytic properties. In conclusion, the microwave liquid-phase discharge plasma is a very effective reduction method with potential development. [ABSTRACT FROM AUTHOR]

In this paper we developed a model of the ICRF plasma flow in a geometry of the two following regions: a plasma torch (narrow area) and a chamber (broad area). We used the numerical model developed in the COMSOL-multiphysics software with the given parameters of outlet pressure p = 133 Pa, drive power W = 1.3 kW, drive frequency f = 1.76 MHz and gas flow G = 0–0.4 g/s. We obtained the spatial dependencies of the electron density, electron temperature, pressure in the chamber, gas velocity and performed the analysis of effects in the broadening area. As a result, we noticed some features, which include an anomalous increase of the electron density in the broadening area. [ABSTRACT FROM AUTHOR]

Draix-Bléone critical zone observatory was created in 1983 to study erosion processes in a mountainous badland region of the French Southern Alps. Six catchments of varying size (0.001 to 22 km 2) and vegetation cover are equipped to measure water and sediment fluxes, both as bedload and suspended load. This paper presents the core dataset of the observatory, including rainfall and meteorology, high-frequency discharge and suspended-sediment concentration, and event-scale bedload volumes. The longest records span almost 40 years. Measurement and data-processing methods are presented, as well as data quality assessment procedures and examples of results. All the data presented in this paper are available on the open repository 10.17180/obs.draix (Draix-Bleone Observatory, 2015), and a 5-year snapshot is available for review at 10.57745/BEYQFQ (Klotz et al., 2023). [ABSTRACT FROM AUTHOR]

The results of an experimental study of the initiation, development and maintenance of a plasma surface discharge initiated by microwave (microwave) radiation of a gyrotron (75 GHz, 300 kW, 6 ms) in air under normal conditions on the surface of a quartz substrate with metal inclusions are presented. It is shown that the velocity of the propagation of the discharge ionization front reaches 40 m/s, which corresponds to the thermal conduction propagation mechanism. In this case, the maximum calculated gas temperature of the plasma reaches 5500 K, which leads to the sublimation of metal inclusions. For the first time, the plasma parameters of a surface microwave discharge on metal-dielectric targets, which have been used in various aeroplasma and plasma-chemical applications, are presented. [ABSTRACT FROM AUTHOR]

The paper described further development of a gas-jet method of synthesizing diamond coatings with the use of a high-velocity jet for transporting the gas mixture (hydrogen, methane, and argon) activated in a microwave discharge to a silicon substrate. A substrate holder is developed, which ensures substrate integrity under thermal loading under conditions of chemical vapor deposition. The diamond synthesis rate in the present experiments is higher than that obtained previously in microwave plasma-assisted chemical vapor deposition experiments without addition of argon. [ABSTRACT FROM AUTHOR]

A new form of microwave discharge with a filament inside plasma volume was investigated in a microwave plasma‐assisted chemical vapor deposition (CVD) reactor. The threshold values of methane content in a hydrogen–methane gas mixture, gas pressure, and microwave power for discharge transition to the new form were found. The parameters' range of existence of the new form of discharge was investigated in three types of CVD reactors. Measurements of the electron density, gas temperature, and spatial distributions of the plasma optical emission lines intensity were carried out for both forms of the discharge. The reasons for the transition of the discharge to a new form and the possibility of using the new discharge form in the microwave plasma‐assisted (MPA) CVD reactor are discussed. [ABSTRACT FROM AUTHOR]

Capacitive equipment refers to its insulation design using the principle of capacitance of electrical equipment, mainly by a variety of different capacitive components in series. Most of the equipment in the substation is capacitive equipment. Once an insulation failure occurs, it will lead to extremely serious consequences. Monitoring grid overvoltage and insulation degradation of capacitive equipment is an effective means to ensure the stable operation of the power system. Therefore, in order to enhance the health management of capacitive equipment, including transformers, bushings, and current transformers, and to mitigate the risk of severe failures, it is imperative to conduct broad-spectrum frequency-domain online monitoring of overvoltages, dielectric losses, and partial discharge. However, the current monitoring work requires the utilization of multiple detection apparatuses. Aiming at the disadvantage that the existing inspection is not well integrated and requires a combination of multiple devices. This paper proposes a smart grid overvoltage identification system that utilizes partial discharge (PD) signals in correlation with dielectric loss detection. The system achieves synchronous detection of dielectric loss and high-frequency partial discharge by synchronously and in real-time acquiring four current signals from the power grid, enhancing the integration level of the hardware system. [ABSTRACT FROM AUTHOR]

We investigate the discharge characteristics of a low-pressure geometrically asymmetric cylindrical capacitively coupled plasma discharge with an axisymmetric magnetic field generating an E × B drift in the azimuthal direction. Vital discharge parameters, including electron density, electron temperature, DC self-bias, and electron energy probability function (EEPF), are studied experimentally for different magnetic field strength (B) values. A transition in the plasma parameters is observed for a specific range of magnetic fields where the discharge is highly efficient with lower electron temperature. Outside this range of magnetic field, the plasma density drops, followed by an increase in the electron temperature. The observed behavior is attributed to the transition from geometrical asymmetry to magnetic field-associated symmetry due to reduced radial losses and plasma confinement in the peripheral region. The DC self-bias increases almost linearly from a large negative value to nearly zero, i.e., it turns into a symmetric discharge. The EEPF undergoes a transition from bi-Maxwellian for unmagnetized to Maxwellian at intermediate B and finally becomes a weakly bi-Maxwellian at higher values of B. The above transitions present a novel way to independently control the ion energy and ion flux in a cylindrical capacitively coupled plasma system using an axisymmetric magnetic field with an enhanced plasma density and lower electron temperature that is beneficial for plasma processing applications. [ABSTRACT FROM AUTHOR]

We demonstrate similarity-based scaling networks for capacitive radio frequency (RF) plasmas, which extensively correlate discharge characteristics under varied conditions, incorporating the transition from original to similarity states. Based on fully kinetic particle-in-cell simulations, similar RF discharges in argon are demonstrated with three external control parameters (gas pressure, gap distance, and driving frequency) simultaneously tuned. A complete set of scaling pathways regarding fundamental discharge parameters is obtained, from which each plasma state finds its neighboring node with only one control parameter tuned. The results from this study provide a promising strategy for plasma multi-parameter mapping, enabling effective cross-comparisons, prediction, and manipulation of RF discharge plasmas. [ABSTRACT FROM AUTHOR]

High-resolution far-ultraviolet broadband Fourier-transform photoabsorption spectra of 32S16O, 33S16O, 34S16O, and 36S16O are recorded in a microwave discharge seeded with SO2. The B 3 Σ − (v = 4 − 30) ← X 3 Σ − (v = 0) and C 3 Π (v = 0 − 7) ← X 3 Σ − (v = 0) bands are observed or inferred in the 43,000 –51,000 cm−1 (196 to 233 nm) spectral range. This is the first experimental detection of a C 3 Π (v > 2) level and of any of these observed bands in an S-substituted isotopologue. Additional measurements of A 3 Π (v = 1 − 3) ← X 3 Σ − (v = 0) provide a calibration of the SO column density. Measured band profiles are fitted to an effective-Hamiltonian model of coupled excited B 3Σ− and C 3Π states along with their predissociation linewidths and absorption band strengths. Electronic-state potential-energy curves and transition moments are deduced. The end result is a list of line frequencies, f-values, and dissociation widths describing the far-ultraviolet photodissociation spectrum of SO that is accurate enough for computing atmospheric photolytic isotope-fractionation. Linelists, and photoabsorption and photodissociation cross sections are available as supplementary data. [ABSTRACT FROM AUTHOR]