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An equivalent circuit model (ECM) is proposed for a Jerusalem cross metasurface structure loaded with plasma. Based on the microwave network theory, the electromagnetic properties of the composite structure are analyzed through this ECM. Due to the wave-absorbing effect of plasma, the parallel conductive and inductive elements are introduced to the ECM of the Jerusalem cross metasurface, forming the ECM of the composite structure. The circuit element parameters are extracted by genetic algorithm optimization. The consistency between the simulated reflection coefficient and the calculated ones by this model proves the accuracy of the proposed ECM for analyzing the electromagnetic properties of a composite structure. Moreover, the plasma collision frequency and the plasma electron density are selected within a certain frequency range to further prove the accuracy of this model. The influence of plasma parameters on the equivalent circuit element values is also analyzed. The ECM can predict the electromagnetic properties of the composite structure and provide theoretical guidance for the design. [ABSTRACT FROM AUTHOR]

Simulations on the number density and the temperature distribution of the plasma produced by the electron beam are taken by the fluid model with the lattice Boltzmann method (LBM), for which impact ionization is the major mechanism for plasma generation. The simulation results show that the electron number density of the plasma reaches the maximum value exceeding 1016 m−3 at 3-cm downstream the exit of the electron beam on the incident direction under atmospheric pressure when the electron energy is 80 keV. The gas temperature rises due to the heating effect of the electron beam, and the temperature profile is similar to a balloon. The gas flow and background pressure are two important factors that affect the plasma distribution. It is found that the plasma area will expand or compress along the background gas moving direction, and the plasma range is inversely proportional to the background gas pressure. [ABSTRACT FROM AUTHOR]

To reveal the characteristic parameters and the evolutionary rules of plasma and light flash radiation produced by aluminum powder/polytetrafluoroethylene (Al/PTFE) projectile hypervelocity impacting on 2A12 thin aluminum plate, the Al/PTFE projectile was obtained by the improved sintering process of the sample, which is based on the process of the traditional Al/PTFE (mass percentage ratio of aluminum powder and PTFE is 26.5%/73.5%). The dynamic compressive strength of the sample was characterized by the self-constructed split Hopkinson pressure bar (SHPB) system. Meanwhile, the experiments, enhanced Al/PTFE projectile (mass 0.22 g, size $5\times5$ mm) impacting on 2A12 aluminum targets with the thicknesses of 2 and 3 mm at different impact speeds (1.95–2.45 km/s), have been performed using a two-stage light gas gun loading system combining with a high-speed camera acquisition system, a transient fiber pyrometer measurement system, and a plasma characteristic parameter diagnostic system. The electron temperature, electron density of plasma, and the radiant temperature (in the range of visible light wavelength) of light flash have been experimentally studied. The results show that the dynamic compressive strength of the Al/PTFE specimen with rapid cooling was significantly improved at the strain rate of 4000 s−1 comparing with the traditional Al/PTFE projectile (the dynamic compressive strength was 32–44 MPa), which can reach more than 100 MPa. The maximum electron temperature, electron density, and visible light radiant temperature produced by the hypervelocity impact increase with an increase in impact velocities and target thicknesses, respectively. [ABSTRACT FROM AUTHOR]

Surrounding air pollution is one of the important warnings to human health. It is necessary to detect hazardous pollutant gases in the air. The gas sensor is the candidate for such detection. Progress of smart and flexible sensors has been receiving growing curiosity in recent years because of their enormous sensing applications. Such smart and flexible sensors can be manufactured by depositing conducting materials, such as conducting polymer, carbon nanotube (CNT), graphene oxide, and metallic nanoparticles, onto nonconducting polymeric flexible substrates, such as paper, plastic films, and textiles. Most of the flexible polymeric substrates, such as polyethylene, polyester, nylon, and polypropylene, have low surface energy and poor wettability, which weakens the adhesion between conducting material and flexible substrate. Plasma surface modification is a novel technique to enhance surface properties to produce stable composites. This review focuses on various types of plasmas for surface modification and their effects on the surface after plasma treatment to improve the grafting and adhesion of the sensing layer with the substrate. The aim of this article is to systematically overview the development of plasma-enhanced smart and flexible gas sensors to date and to envisage their future progress. [ABSTRACT FROM AUTHOR]

We present a numerical study disclosing non-linear effects and hysteresis loops for a swept bias Langmuir probe. A full kinetic particle in cell (PIC) model has been used to study the temporal sheath effects and the probe current. Langmuir probes are normally operated at low frequencies, since a “close to steady state” condition is required to characterize the plasma. However, during operations above frequencies normally used, capacitive and non-linear resistive effects are being unveiled. We demonstrate how ion and electron density and temperature change properties of the probe-plasma system. We also show that a swept Langmuir probe exhibits essential properties described as the “fingerprint of memristors” and how a Langmuir probe can be identified as a transversal memristor. Understanding non-linear processes might enable new ways to operate Langmuir probes with higher sampling rates and better accuracy. [ABSTRACT FROM AUTHOR]

The effects of plasma and electrostatic field on the growth and nutrient content of Chinese cabbage have been investigated. The parameters of height, dry weight, content of vitamin C (VC), soluble sugar (SS), and total amino acids (TAAs) are used to characterize the growth speed and quality of Chinese cabbage. The results show that both plasma and electrostatic field can promote the growth, increase the dry weight, and improve the quality of Chinese cabbage. In addition, the appropriate combination of plasma and electrostatic field can produce better effects than using one of them alone. [ABSTRACT FROM AUTHOR]

The surface flashover is one of the most important factors that limit the performance of electric devices. In this article, the processes of surface flashover under different pressures are observed by a high-speed camera, and the differences between the plasma evolution processes are presented. Moreover, the simulation model of surface flashover under atmospheric conditions is established by a particle-in-cell code with direct simulation Monte Carlo (PIC-DSMC) code. Compared to the results of vacuum surface flashover, the reasons that caused the differences of the plasma evolution on surface flashover between vacuum condition and atmospheric condition are discussed. It is found that the competition between gas discharge and surface flashover would become more notable with the increase of air pressure. The results would be helpful to further understand the mechanism of the surface flashover. [ABSTRACT FROM AUTHOR]

Here, we study time- and spatially resolved heterogeneous plasma catalysis chemical looping reactions using in situ laser diagnostics in a novel parallel plate dielectric barrier discharge (DBD) plasma reactor at atmospheric pressure and temperatures: 473 and 673 K. A chemical looping material, 50:50 by mass mixture of lanthanum–nickel-based perovskite (La0.9Ce0.1NiO3) and CeO2, was placed directly in non-equilibrium DBD plasma. Optical diagnostic techniques used include high-speed imaging (i.e., ns gate width), N2 optical emission spectroscopy (OES) at 337 nm, and Rayleigh scattering (RS). During the reduction step, a mixture of CH4, CO2, and N2 flow was used, and during the oxidation step, the airflow was used. During the reduction step, the average temperatures measured at the furnace setpoint temperature of 473 and 673 K were 580 and 800 K, respectively. For the oxidation step, the average temperatures measured were 520 and 830 K, respectively. There was good agreement in average temperatures measured by RS and N2 OES. The 2-D RS imaging showed lower temperatures near the catalyst during the reduction step and higher temperatures during the oxidation step. Although corona discharges were observed over chemical looping materials in high-speed images, RS temperature measurements showed non-equilibrium plasma chemistry over the materials. [ABSTRACT FROM AUTHOR]

This study characterized the optical spectra of continuous low-pressure plasma system and evaluated its effect on milk processing. Plasma was characterized at different input power levels (24.8, 58.9, and 117.6 W which corresponds to the input voltage of 1, 1.5, and 2 kV) with a 1-cm electrode distance. Based on the characterization, the input power level 117.6 W was selected to produce maximum reactive species. The system was operated at 117.6 W to decontaminate milk flowing inside the quartz tube using three different milk flow rates 3, 6, and 9 mL/min (accounting for 5-, 2.5-, and 1-min plasma exposure time). The maximum reduction in total microbial count obtained after treatment was 1.2 log CFU/mL at an exposure time of 5 min (3-mL/min milk flow rate). Significant changes were observed in the physicochemical properties of milk after treatment. However, the only adverse effects observed were the viscosity and color of milk at 5- and 2.5-min treatment, which might be because of the use of unhomogenized milk. The continuous plasma system operated at 117.6 W reduced the microbial load in milk; further optimization of the process parameters is necessary for the complete elimination of microbial load and to increase the shelf life. [ABSTRACT FROM AUTHOR]

The sharp increase of pressure at the edge of a high confinement mode (H-mode) plasma, the pedestal, strongly impacts overall plasma performance. Predicting the pedestal is a necessity to control and optimize tokamak operations. An experimental data-driven machine learning (ML) approach is presented, which predicts the pedestal heights and widths of electron density ($n_{\mathrm {e}}$) and electron temperature ($T_{\mathrm {e}}$) profiles as well as the separatrix $n_{\mathrm {e}}$ from externally controllable parameters such as the plasma shape, heating method and power, and gas puff rate and integrated gas puff. The one modeling framework for integrated tasks (OMFIT) framework was used with DIII-D data to efficiently, robustly, and automatically build a database of pedestal parameters to train ML models. Database creation was enabled by the search engine tool for DIII-D data, TokSearch, which parallelizes data fetching, enabling fast searches through basic signals of thousands of DIII-D shots and selection of relevant time intervals. Principal component analysis (PCA) separated the database into three clusters that represent classes of plasma shapes that are regularly used in DIII-D. The most important parameters for setting the pedestal structure were plasma current ($I_{\mathrm {p}}$), toroidal magnetic field ($B_{\phi }$), neutral beam heating power ($P_{{\mathrm {NBI}}}$), and shaping quantities. The deep jointly informed neural networks (DJINNs) algorithm was applied to identify suitable neural network (NN) architectures that appropriately capture the features of the pedestal database. Separate NNs were implemented for each pedestal parameter, and ensembling methods were used to improve the prediction accuracy and allowed estimation of the prediction uncertainty. The pedestal predictions of the test dataset lie within the measurement uncertainties of the pedestal parameters. The NN outperformed simple linear regression (LR) analysis, indicating nonlinear dependencies in the pedestal structure. The presented achievements illustrate a promising path for future research, using feature extraction to infer experimental trends and thereby improve pedestal models as well as deploying NN for a fast pedestal prediction in DIII-D scenario development. [ABSTRACT FROM AUTHOR]

We derive some approximate expressions for the current through an electrically short dipole probe immersed in a cold magnetized plasma. The time-varying current signal due to an applied voltage input to the probe is proportional to plasma parameters such as electron density and electron neutral collision frequency in the ionosphere. By taking Laplace transformations and examining the parallel and perpendicular current contributions, we obtain an approximate theoretical expression for the impedance of the probe. We then infer an even simpler empirical expression based on the approximate theory and frequency domain data obtained from sweeping impedance probes (SIPs) flown on previous sounding rocket missions. The inverse Laplace transform of the expressions will be used to perform direct least mean squares curve fitting against measurements made by a time domain impedance probe (TDIP) flown on a CubeSat. We compare our results with previous analytical results of the impedance of an electrically short dipole in a plasma, and typical sounding rocket impedance data in the ionosphere E-layer. An expression taking into account the appearance of a sheath is also presented. In the frequency domain, our expressions are found to capture the significant features of data from sounding rocket experiments. [ABSTRACT FROM AUTHOR]

There are several configurations of a microwave chemical vapor deposition (MWCVD) reactor. The common characteristic of this reactor is the presence of waveguides. We describe a method that replaces the waveguide, responsible for conducting electromagnetic waves, with a resonant cavity (RC) coupled to a low-pressure chamber. Using RCs over waveguides can help produce dense plasma, which can be used in dissociation processes as the reagents are forced to move within a cavity until they reach the reaction chamber. Based on the excellent performance of the system, it was possible to deposit silicon oxide (SiO2), with the aid of the argon gas mixture, oxygen, and tetraethylorthosilicate (TEOS), on a silicon substrate at room temperature. The film formed was analyzed using an interferometer and FTIR, concluding on the satisfactory quality of the film. [ABSTRACT FROM AUTHOR]

Research is devoted to investigation of properties of pulsed explosive emission cathodes for X-ray tubes. Three types of annular explosive emission cathodes were studied: metal ceramic with slits (of a comb-shaped kind), ring metal ceramic, and carbon ceramic. A pulsed high-voltage generator used in experiments is characterized with the following parameters: voltage pulse full-width at half-maximum is about 20 ns, pulse voltage amplitude is up to 150 kV, and pulse repetition rate is up to 200 Hz. The installation makes it possible to study demountable models of pulsed X-ray tubes of different designs. Current and voltage waveforms corresponding to different operation modes and rates of rise of X-ray tube anode voltage were analyzed. The obtained characteristics of explosive cathodes depend on the cathode’s material, the shape, and the supply voltage of the primary energy storage. The current pulse duration for the ring carbon-ceramic cathode is considerably lower than that for the other cathodes, although it generates a higher radiation dose rate. [ABSTRACT FROM AUTHOR]

The impact of current density on the anode attachment characteristics of high current vacuum arcs was investigated using high-speed imaging techniques. The current density determines the occurrence of attachment transition into an anode spot type 2. Electrodes were made of Cu/Cr 50%/50%. In combination with the adequate amplitude of current, the anode spot type 2 was accompanied by first observed oscillating anodic plasma plumes by the higher current densities. Resulting electrode overheating processes, which depend on the instantaneous power delivered, determine the formation of a plasma region in front of the anode. Image processing indicates that this region interacts actively with the cathode, displacing the radiation intensity region, and influencing the behavior of its arc spots. In addition, increased high-frequency contents on the measured voltage signals accompanied the observed oscillations of the anodic plume. An explanation through a double-layer effect for the anode spot type 2 is proposed. [ABSTRACT FROM AUTHOR]

While the particle-in-cell (PIC) method is quite mature, verification and validation of both newly developed methods and individual codes have largely focused on an idiosyncratic choice of a few test cases. Many of these test cases involve either 1-D or 2-D simulations. This is either due to the availability of (quasi-) analytic solutions or historical reasons. In addition, tests often focus on the investigation of particular physics problems, such as particle emission or collisions, and do not necessarily study the combined impact of the suite of algorithms necessary for a full-featured PIC code. As 3-D codes become the norm, there is a lack of benchmark tests that can establish the validity of these codes; existing papers either do not delve into the details of the numerical experiment or provide other measurable numeric metrics (such as noise) that are outcomes of the simulation. This article seeks to provide several test cases that can be used for validation and bench-marking of PIC codes in 3-D. We focus on examples that are collisionless and can be run with reasonable computational resources. Three test cases are presented in significant detail; these include basic particle motion, beam expansion, and adiabatic expansion of plasma. All presented cases are compared either against existing analytical data or other codes. We anticipate that these cases should help fill the void of bench-marking and validation problems and help the development of new PIC codes. [ABSTRACT FROM AUTHOR]

Nitrogen is one of the most critical nutrients affecting algal cell biomass growth and thereby plays a crucial role in algal growth economics. Conventionally, all man-made nitrogen (N) sources are based on hydrogen derived from fossil fuels. This investigation examines the effect of a new N source, i.e., plasma-activated water (PAW), on yields of algal biomass. The N uptake rates of the algae for PAW were determined and it was compared with the conventional N sources. Four treatments of N source in duplicates were run to evaluate the potential of algae cultivation in batch microcosms (5 L). Mixotrophic algal cultures from a nearby eutrophied lake were incubated for 1 week with nitrate-N (NaNO3), nitrite-N (NaNO2), nitrate+nitrite (NaNO3+NaNO2), and PAW as sole N source in basal Bold’s media. Even though the cultures were not axenic, steady increase in chlorophyll and biomass was observed for all the cases studied. The highest biomass yield was observed in nitrate-N fed cultures, at an average of 32.5 mg/(L ⋅ day), followed by a combination of nitrate+nitrite [27.1 mg/(L ⋅ day)], PAW-N [26.6 mg/(L ⋅ day)], and nitrite-N [22.5 mg/(L ⋅ day)] fed cultures. Nitrogen uptake rates were similar in all cultures studied. The highest rates observed were in nitrite-N [4.05 mg/(L ⋅ day)], closely followed by PAW [3.56 mg/(L ⋅ day)]. The results suggest that PAW can be utilized as a N source with pre-exposed cultures. The algal biomass yields of PAW were comparable to conventional sources although cultures with PAW showed signs of better uptake of N. [ABSTRACT FROM AUTHOR]

We present a modeling technique to describe the behavior of an antenna with time-varying conductivity. The conducting channel of the antenna will consist of a series of individually-controlled plasma cells. This antenna will be fed with pulse-amplitude modulated signals. The pulses in these signals will travel down the length of the antenna but will be attenuated near the antenna tip. This time-domain matching technique allows for efficient matching at all frequencies. The time-varying antenna scheme is modeled using a modified version of Telegrapher’s equations, which includes the effects of plasma dispersion. Theoretical plasma parameters are incorporated to develop requirements for plasma density and switching speed. Simulated results suggest that the time-varying antenna scheme will radiate more efficiently at low frequencies than existing electrically short antenna designs. [ABSTRACT FROM AUTHOR]

To partially meet the communication requirements in Mars, low-frequency ground-to-ground communication is likely to be used in the future and hence, it is desirable to increase electron density in the Martian ionosphere. As a convenient means to this, we have proposed and explored the production of high electron density regions in the Martian atmosphere in daytime by suspension of low work function dust, specifically Cs-coated bronze in the atmosphere. Equations of the kinetics of the dusty air in sunlight have been introduced and a numerical estimate of the daytime electron density at 60–100 km heights has been obtained as a function of the dust parameters. Photoelectric emission from dust and accretion of electrons and ions on dust particles play the key role in getting the desired electron density at high altitudes (60–100 km). A discussion of the numerical results has been given with conclusions. [ABSTRACT FROM AUTHOR]

CO2 gas is being considered as one of the potential plasma forming gases in plasma arc material processes due to its thermophysical properties, cost, and easy availability. The understanding of the thermal behavior of CO2 plasma arc is essential for an effective utilization of it. However, the studies on CO2 arc characteristics are scanty. In this study, a 2-D axisymmetric model is built for the simulation of CO2 and Ar arcs with and without evaporation of anode. The thermal characteristics of CO2 arc are compared with those of Ar arc at different arc currents and anode materials. CO2 arc possesses higher temperature compared to Ar arc and the arc current strongly influences the temperature of CO2 arc. The anode flux in CO2 arc is higher compared to that of Ar arc and the effects of arc current and nature of the anode material on the same are stronger in CO2 arc. The arc heating efficiency in CO2 is higher than that in Ar and it reduces with increasing arc current. [ABSTRACT FROM AUTHOR]

There is a multipath effect caused by multireflections between the plasma and the vehicle surface, and there are coupling characteristics between array antennas. These two errors will seriously affect the quality of navigation signal. To solve the mutual coupling of uniform linear array (ULA) of plasma, a direction-of-arrival (DOA) estimation algorithm based on mutual coupling correction is proposed. The algorithm is based on the special structure of mutual coupling matrix (MCM) of ULA and combines spatial smoothing algorithms. It solves a quadratic optimization problem under the linear constraint and utilizes peak search technology to obtain DOA. The effectiveness of the proposed algorithm is verified by the simulation results. Numerical simulation is applied in this article to analyze the influence of array antenna from the plasma. In addition, array antenna is calibrated with the mutual coupling calibration information estimated by the algorithm. The result of antenna calibration validates the correctness of the simulation conclusion. [ABSTRACT FROM AUTHOR]

The effects of nonuniform moving plasma on the polarization properties of electromagnetic (EM) waves were theoretically studied. Taking the ${L}$ -band right-hand circularly polarized (RHCP) wave as an example, based on the nonuniform moving plasma slab moving perpendicularly to the incident wave, the relationship between the polarization properties of the transmitted wave and the normalized velocity of the nonuniform plasma slab was analyzed. The results indicate that the polarization state of the transmitted wave is closely related to the normalized velocity of the nonuniform plasma slab. When the plasma slab approaches to the incident wave, its influence on the polarization properties is greater than that away from the incident wave. In addition, when the change of the polarization state reaches the maximum, the corresponding normalized velocity is mainly determined by the incident angle and the collision frequency. Various interesting features regarding polarization properties were obtained. The results are very important for applications in space exploration. [ABSTRACT FROM AUTHOR]

We present the results of experiments, analytical modeling, and numerical particle-in-cell (PIC) simulations for the propagation of a high-power, sub-nanosecond microwave pulse through a plasma-filled cylindrical waveguide in a parameter regime not studied before. Depending on the experimental conditions, the non-linear interaction of the high-power microwave (HPM) pulse with the plasma results in self-channeling through it or causes the formation of a wakefield. To study this phenomenon, two backward wave oscillators (BWOs), operating in the super-radiant mode at frequencies of 9.6 and 28.6 GHz, were designed and tested. These BWOs were driven by an electron beam (~280 keV, ~1.5 kA, ~5 ns) generated in a magnetically insulated foil-less diode, from which it propagates through a slow wave structure guided by an external axial magnetic field. Microwave pulses of ~0.4-ns width, up to ~500-MW peak power at 9.6 GHz, and up to ~1.2 GW at 28.6 GHz were obtained. These powerful subnanosecond timescale microwave beam pulses were injected into the neutral gas, plasma, or their mixture in various configurations. [ABSTRACT FROM AUTHOR]

Results of numerical experiments on ignition of pulverized coal in a plasma-fuel system (PFS) are presented. PFS is designed for fuel oil-free startup of the boilers and stabilization of pulverized coal flame and represents a pulverized coal burner equipped with plasma torch. The calculations were carried out using the PlasmaKinTherm program. It combines kinetic and thermodynamic methods for calculating the processes of motion, heating, thermochemical transformations, and ignition of the fuel mixture in the volume of the PFS. The ignition conditions of the fuel mixture had previously been determined for two operating parameters of the PFS: the electric power of the plasma torch and the ash content of coal. Also, one of the main regime parameters of the PFS providing ignition of the fuel is the concentration of coal dust in the fuel mixture. It can vary within a wide range. Therefore, conditions for fuel mixture ignition in the PFS have been investigated, depending on the concentration of coal in the fuel mixture in the range from 0.4 to 1.8 kg of coal per 1 kg of air. Calculations were performed for cylindrical PFS of 0.2 m diameter and 3 m of length at fixed consumption of coal (1000 kg/h), the plasma torch power (60 kW), and three values of coal ash content (20%, 40%, and 70%). Nontrivial regularities of the process of plasma thermochemical preparation of fuel for burning were revealed. [ABSTRACT FROM AUTHOR]

Non-thermal plasma technology has great potential for the removal of the emission of volatile organic compounds (VOCs). However, the plasma-alone process may produce various undesired by-products that cause secondary pollutions. Here, a coaxial dielectric barrier discharge (DBD) reactor has been developed for the removal of xylene over an Al2O3-based catalyst (Mn/Al2O3, Co/Al2O3, Ce/Al2O3) at low temperatures. Compared with the plasma-alone process and other plasma-catalytic combined process, the combination of plasma and the Mn/Al2O3 catalyst obviously enhanced xylene conversion and substantially restrained the formation of by-product organic aerosol (up to 100%), and what is more is that our setup was more efficient than those in other studies. In the meantime, ozone could be effectively converted by the Mn/Al2O3 catalyst; as the main active group with a long period of existence during discharge, ozone adsorbed onto the surface of the catalyst under the action of Mn/Al2O3 and participated in the oxidation of xylene. Mn4+ and the high lattice oxygen content were the reasons for the highest efficiency of 1% Mn. [ABSTRACT FROM AUTHOR]

Spark discharge under flow conditions in different gas media is compared. The gases include nitrogen, pure methane, and methane–air mixtures with different volume ratios. The self-illuminated spark plasma photos, and the discharge current and voltage waveforms are recorded. [ABSTRACT FROM AUTHOR]

A comparative study of capacitively coupled radio frequency discharges was conducted using 2-D particle-in-cell simulation (PIC) and 2-D fluid plasma simulation. The selected scenario was a planar discharge with a 3-cm gap operated in helium, at a gas pressure of 400 Pa, with a driving voltage between 120 and 400 V at 3.2 MHz. The solvers were adapted to a 1-D problem by using periodic boundary conditions perpendicular to the gap, and the models included ion impact-induced secondary electron emission from the electrodes. A good agreement was obtained between the results of both solvers, with less than 23% deviation in the peak plasma density. For the studied range of secondary emission coefficients, $0.08 < \gamma _{\mathrm {se}} < 0.378$ , it was found that a common transition point between “alpha” and “gamma” modes occurs at $V_{\mathbf {rf}} \sim 250$ V. Since the simulation results were shown to be less sensitive to the secondary emission coefficient below this transition voltage, these results can serve as a standard benchmark for plasma codes. [ABSTRACT FROM AUTHOR]

We present observations and modeling of argon gas at pressures of a few Torr that have been excited with high-voltage pulses (hundreds of volts) on the order of nanoseconds in duration. These tests are motivated by an effort to determine the feasibility of utilizing pulsed argon plasma as a conducting media in a novel antenna configuration. A vacuum chamber is constructed with plate electrodes inserted. An optical observation system is constructed to observe the temporal response. The rise time and fall time of the plasma’s optical emissions, taken as a proxy of the electron density, are measured as a function of pulse voltage and pressure using the captured optical light curve. In addition, spectroscopy measurements are made on a longer time scale. The maximum electron density of the plasma is then inferred through the use of PrismSPECT, a commercially available collisional radiative model, via the line ratio method. Measured pulsed plasmas reached their maximum ionization in as low as 5 ns and recombine in as low as 140 ns. Spectral measurements show that a 1-Torr plasma ionized with 5-ns long pulses had a maximum electron density of $5.2\times10\,\,^{\mathrm{ 20}}$ /m3 and maximum electron temperature of 1.28 eV. [ABSTRACT FROM AUTHOR]

Research of ionospheric electric current density is generally based on some theoretical formulas and empirical models. The electrodynamic process of charged particles in plasma with a magnetic field can help analyze the formation mechanism of ionospheric electric field and current so that the ionospheric electric field intensity and current density can be simulated and studied. Furthermore, by establishing partial differential equations in magnetic dipole coordinates, electric current density in mid- and low-latitude ionosphere can be calculated by means of a series of more reasonable boundary conditions in this article. Besides, the wind drag and particles diffusion are taken into account to make the results more accurate. The electric field value fitted by the empirical model is used to verify the rationality of current density calculated indirectly. Through this theoretical model, the distribution of electric fields and currents in ionosphere has been carefully studied. In addition, several physical elements influencing the current value and direction are also studied, including external environmental factors, such as solar activity and geomagnetic index, as well as the internal factors, such as electrons and ions temperature. These works will be a great help in the future for the precise determination of ionospheric currents. [ABSTRACT FROM AUTHOR]

The proper orthogonal decomposition technique is applied to a finite-element time-domain particle-in-cell (PIC) algorithm for the simulation of kinetic plasmas, resulting in a reduced-order system. The reduced model is tested with representative examples involving an accelerated electron beam and a plasma ball expansion and compared with full-order simulations. The strengths and weakness of this type of model order reduction when applied to PIC algorithms are discussed through the analysis of the results. In particular, the method allows for a major reduction in the field degrees of freedom necessary to capture the relevant physics, but it can also lead to spurious results if proper care is not taken when assembling the reduced-order system. [ABSTRACT FROM AUTHOR]

There are a number of applications for artificial conducting regions at a convenient ionospheric height and electron density. As a convenient means to this end, we have proposed and explored the production of high-electron-density regions in the atmosphere in daytime by suspension of low work function dust, specifically Cs-coated bronze in the atmosphere. Accretion of electrons and ions on dust particles and photoelectric emission from dust play the key role in getting a steady state dusty plasma with desired electron density at high altitudes (30-60 km). The basic equations of kinetics of dusty air in sunlight have been introduced and a numerical estimate of the day time electron density at 30- and 60-km altitudes (mid-latitudes) as a function of dust parameters has been obtained. A discussion of the numerical results is provided in this article. The present method offers the additional advantage of flexibility in height and the corresponding electron density. [ABSTRACT FROM AUTHOR]

The formation condition of the virtual cathode (VC) formed by a self-focusing relativistic electron beam in plasma is studied theoretically and numerically. Together with the threshold function of the VC formation and the self-focusing condition, the parametric regions of forming the VC are found. Then the theoretical result is verified by the particle-in-cell (PIC) simulation, which further shows the phase-space characteristics of the VC formation. This study not only provides a theoretical basis for creating VC with a self-focusing relativistic electron beam in plasma but also helps in parameter selections for the related beam-plasma experiments and simulations. [ABSTRACT FROM AUTHOR]

A parametric investigation of plasma wake geometry is conducted to determine the applicability of Coulomb actuation to resident space objects (RSOs) in low earth orbit (LEO). The use of Coulomb forces could provide a touchless means to achieve the relative position and attitude adjustments between close-proximity objects on orbit. Theoretical models developed for techniques in the geosynchronous earth orbit (GEO) regime indicate that Coulomb actuation could facilitate on-orbit proximity operations in a highly fuel- and power-efficient manner. In LEO, however, only the plasma parameters in the wakes behind orbiting objects are a promising region for Coulomb actuation applications. These physical phenomena investigated by the charging hazards and wake studies (CHAWS), space experiments with particle accelerators (SEPAC), and other on-orbit experiments exhibit substantially decreased plasma density relative to the surroundings. This investigation considers the wake which forms behind objects of various potentials and cross-sectional areas, particularly focusing on methods of enhancing the wake with negligible changes in the objects’ area, and therefore their mass. Experimental results are presented and compared with previous theoretical, numerical, and experimental works. The size of a wake formed by an uncharged object is shown to depend on its cross-sectional area. However, the same object charged to a positive potential generates a substantially larger wake. Additional experimental results indicate that a positively charged, sparse structure with similar dimensions, but significantly less cross-sectional area forms a wake similar to the previous, solid object charged to the same level. This indicates that a large wake can be generated without significantly increasing the mass or area-dependent perturbations such as the drag and the solar radiation pressure. These results increase the applicability of Coulomb actuation in LEO by enhancing the region in which the technique is feasible. [ABSTRACT FROM AUTHOR]

The presence of impurities in a high-temperature plasma is one of the major challenges in an inertial fusion reactor. In addition to radiation losses, the impurities affect the ignition parameters of the fusion plasma in the reactor. In this article, the effect of the arbitrary concentration of impurity nuclei carbon, beryllium, and lithium on the ignition properties of the p6Li fusion plasma is investigated. The results show that by increasing the concentration of impurities, the reaction rate decreases and the rate of energy loss self-radiation increases in the p6Li plasma. This effect is considerably stronger than the weak positive effect of reducing the energy lost for matter acceleration and electron heat conduction. With 20% impurity concentration of carbon, beryllium, and lithium, the reaction rate decreases 3.4, 2.7, and 2.2 times, respectively, and the radiation loss rate increases 6.7, 3.5, and 2.4 times, respectively, by more than a factor in comparison to pure p6Li plasma. The factors of energy losses related to material acceleration and electron heat conduction reduce only to 1.1–1.2 in comparison to pure p6Li plasma. The ignition is impossible at any values of the ignition parameter, areal density. The results show that the minimum ignition temperature from 800 keV increases to 1250, 950, and 840 keV with 20% impurity concentration of carbon, beryllium, and lithium, respectively. Also, both areal density and ignition energy parameters increase by increasing the concentration of these impurities. The conclusions show gain decreases in the p6Li plasma due to a decrease in the fusion reaction rate. [ABSTRACT FROM AUTHOR]

A wideband circularly polarized (CP) multi-turns plasma helical antenna (HA) with reconfigurable bandwidth is investigated for wireless communications in the $x$ -band. The proposed plasma-based HA is suitable for integration with electronic circuit components used in system-on-chip applications. A parametric study on the effect of different design parameters on the antenna radiation characteristics is introduced. The antenna dimensions are optimized for wideband CP endfire radiation. The proposed antenna has an impedance matching bandwidth of 48%, a maximum gain of 8.5 dBi, and a wideband CP of 31%. The variation in the number of helix turns improves the antenna gain and bandwidth by changing the plasma frequency. An improvement in antenna gain and radiation efficiency is achieved by loading the antenna with shaped dielectric lenses with a different cross section. The endfire directional gain is improved to 11.5 dBi for hemispherical-shaped lens and 10.5 dBi for a quarter spherical lens with half-power beamwidth (HPBW) of 40°. The finite integration technique (FIT) is used to simulate and analyze the proposed structures. [ABSTRACT FROM AUTHOR]

The sweeping Langmuir probe (SLP) instrument is a payload of the European Space Agency’s (ESA) in-orbit demonstrator PicoSatellite for Atmospheric and Space Science Observations (PICASSO) cubesat, measuring the plasma environment in a high-inclination low earth orbit (LEO) orbit. Because of the small size of the spacecraft (0.3 m $\times \,\,0.1$ m $\times \,\,0.1$ m), the spacecraft floating potential can significantly drift when sweeping the probe bias voltage, affecting the current–voltage characteristic from which plasma parameters are retrieved. In LEO, the spacecraft generally encounters a high-density, cold (less than 1 eV) plasma environment, but due to the high orbital inclination, PICASSO passes the auroral regions exposing the spacecraft to precipitating fluxes of hot (several kiloelectron volts) electrons with potentially harmful, high-level spacecraft charging as a result. To investigate the spacecraft charging and the in-orbit operation of the Langmuir probes in both of these regimes, simulations of PICASSO were carried out in Spacecraft Plasma Interaction System (SPIS). The conditions of the LEO plasma and the constraints imposed by the particle-in-cell (PIC) models on the mesh size make this type of plasma simulations a very challenging task. [ABSTRACT FROM AUTHOR]

We have explored the generation of high-charge-state ion beams by a vacuum arc ion source. A pulsed vacuum arc with current up to several kiloamperes and pulse duration about $1~\mu \text{s}$ was used. In a vacuum arc ion source with bismuth cathode and at a background pressure of about $40~\mu $ Pa, a bismuth ion beam was formed with a maximum charge state Bi19+. For an ion accelerating voltage of 60 kV, this corresponds to a maximum bismuth ion energy of over 1 MeV. [ABSTRACT FROM AUTHOR]

In this paper, we characterize a Transparent Cathode Discharge (TCD), a type of Inertial Electrostatic Confinement (IEC) plasma, operated in helium and argon in the pressure range of 1–100 Pa. The discharge was investigated using a combination of electrical and optical diagnostic techniques. The imaging of the discharge indicated distinct operating regimes related to the background gas pressure, with each mode being characterized by different patterns of optical emission. The spectroscopic analysis of the optical emission showed that this mode structure represented an electron-driven discharge at higher pressures, and a discharge sustained by the activity of energetic heavy particles at lower pressures. The high-pressure discharge is shown to be assisted by the hollow cathode effect toward its low-pressure limit, and the visible color of emission from the discharge in helium is found to provide a convenient diagnosis of active species. The identification of a stable discharge mode in which energetic heavy particles are responsible for collisional processes has the potential to lead to new industrial applications based on this novel heavy particle-driven reactive plasma source. [ABSTRACT FROM AUTHOR]

Iron nanopowders (Fe-NPs) were extracted and downsized by evaporating the iron powders in an atmospheric microwave plasma flame. The microwave plasma, which was generated by a mixture of nitrogen and argon swirl gases, evaporated the iron powders, immediately downsizing them to Fe-NPs. Subsequently, the Fe-NPs samples were collected by using bar magnets inside the collecting chamber. The Fe-NPs were analyzed by X-ray diffraction, Raman spectroscopy, optical emission spectroscopy, and a scanning electron microscopy. The Fe-NPs consisted of only iron phase and no Fe2O3 or Fe3O4 phases were formed during synthesis. The average sizes of the raw iron powders and the Fe-NPs were approximately $20~\mu \text{m}$ and 20 nm, respectively. The proposed method is simple and easily scalable. Thus, it is suitable for the mass production of Fe-NPs, overcoming the limitations of other catalyst-based synthesis methods. This paper provides a potential method for large-scale production of metal nanopowders which have potential applications in various fields owing to their unique properties at the nanoscale. [ABSTRACT FROM AUTHOR]

In this paper, we propose an innovative method for synthesizing copper nanoparticles (Cu-NPs) using underwater plasma. The proposed method using underwater plasma has advantages such as one-pot synthesis, fast reaction time, and high throughput. We obtained yields as high as 15 g of Cu-NPs powder from 25 g of copper hydroxide, for 10-min a reaction time. In addition, we confirmed that the Cu-NPs produced are spherical and range in size between 40 and 80 nm. We also verified that the synthesized Cu-NPs are almost pure Cu powder, close to 100 %, through high-resolution transmission electron microscopy and X-ray diffraction analysis. [ABSTRACT FROM AUTHOR]

A new time-domain impedance probe is presented in this paper. The new instrument is able to make measurements of absolute electron density and electron-neutral collision frequency in the ionosphere at temporal and spatial resolutions not previously attained. A single measurement is made in $100~\mu \text{s}$ , which yields an instantaneous spatial resolution of 0.1 m for sounding rocket experiments. A prototype of this instrument was integrated into the payload of a NASA Undergraduate Student Instrument Program sounding rocket launched out of Wallops Island on March 1, 2016. Here, we describe the instrument, and present the data obtained from the sounding rocket experiment. A 6-V amplitude Gaussian derivative excitation was applied to a dipole probe structure, and the current through the probe terminals measured with a balanced active bridge circuit. The time-domain current response was sampled at 5 MS/s, at 12-bit resolution. In the course of the flight, the instrument measured a highly nonlinear response of the plasma because of the large input voltage signal applied. The linear theory cannot explain this response, which obscured interpretation of the data. As a result, we used time- and frequency-domain trend analysis to obtain the variation of electron density over the upleg and downleg of the rocket trajectory. The obtained time and fast Fourier transform trends showed enhanced electron densities in the F layer, which confirmed that the instrument was able to measure the density variations during a significant portion of the flight. [ABSTRACT FROM AUTHOR]

The electrical characteristics of single Si-fin n-type fin field-effect transistors at the threshold voltage (${V} _{\mathbf {T}}$) implantation energy 6 and 10 keV in the experimental work were practically extracted and analyzed. In general, the electrical performance of the tested devices at the lower implantation energy shows a better performance than the other group such as in drive current, subthreshold swing, punchthrough voltage, and drain-induced barrier lowering, especially as the feature size of these devices gets smaller up to 17 nm of channel width. However, the channel mobility in transconductance view at the higher implantation energy is better due to the smaller channel scattering. [ABSTRACT FROM AUTHOR]

To realize the broadest potential of nonthermal atmospheric-pressure plasma (APP) technology, there is a need to develop low-cost, compact devices that can be used for portable applications. One of the greatest impediments to this is the power supplies and/or electronics needed to generate breakdown at atmospheric pressure. Piezoelectric transformers (PTs) are solid-state transformers that can produce large gains in voltage, which along with their modest size, makes them attractive candidates for use in plasma production. In this paper, we use a low-voltage power supply in line with a PT to produce an APP jet (APPJ). While operating at the resonance frequency of the PT (88 kHz), plasma jets were generated with input voltages as low as 10 V. The electrical and optical characteristics of the piezoelectric-driven jet were compared to an APPJ produced with a high-voltage sine wave of comparable operating frequency. Both APPJs were examined in helium and argon for a variety of different flow rates and operating voltages. In argon, the length of the jets was nearly identical for all operating parameters but produced different discharge currents. In helium, the discharge currents were similar but the lengths of the jet differed. Optical emission spectroscopy showed similar chemical composition between the two jets for both feed gases. Together, the results suggest that the piezoelectric material has an influence beyond simply amplifying voltage but can be successfully integrated to meet the requirements needed for plasma production. [ABSTRACT FROM AUTHOR]

The results of direct observation of the initial phase of explosive electron emission using high-resolution X-ray radiography in X-pinch radiation are reported. The confirmation of common “Ecton” theory was not found within achieved temporal and spatial resolutions. A mechanism involving the surface breakdown of whiskers that leads to plasma development is proposed. [ABSTRACT FROM AUTHOR]