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Plasma–liquid systems are involved in many fields of application. In this study, we characterize the electrical and optical properties of an ac discharge produced in the air that is in contact with water. The electrical conductivity of water is adjusted by adding KCl, H2SO4, or NaOH. The temporal evolution of voltage and current waveforms is presented, and some parameters of interest, namely, breakdown voltage, voltage drop, discharge current, and injected charge and energy, are reported under anode and cathode water polarity conditions. The optical properties of the plasma emission are also acquired, and their temporal evolution is analyzed using a photomultiplier tube (PMT) equipped with specific wavelength filters. The trends and relationships elucidated herein are highly useful in developing plasma applications, such as water processing. [ABSTRACT FROM AUTHOR]

Numerical simulation of discharge mechanism under nanosecond pulse voltage assists in the insulation performance optimization of N2-insulated switches that are widely used in the pulse power devices. This article presents a fluid dynamic model for the positive streamer propagation in N2 based on a needle-plate discharge system. The effects of the operating conditions, such as voltage amplitude, rising edge, gap width, and needle radius, are studied. Simulating results indicate that the streamer might be evoked only when the maximum electric field exceeds the critical value that is closely influenced by the needle radius and gap width, e.g., $1.3\times 10^{7}$ V/m based on a needle-to-plate electrode configuration with a 0.4-mm tip radius and 5-mm gap. The maximum electric field occurs at the head of streamer and it drops suddenly by nearly two orders of magnitude in the back of the head, which makes the streamer moves forward rapidly. Certainly, it needs a high enough voltage to ensure continuous propagation of the streamer, for example, more than 20 kV needed as the tip radius and gap set to 0.4 and 5 mm, and the electric field strength and migration speed increase with the increasing voltage amplitude. The radius of the discharge region is smaller when the rising edge time increases from 10 to 40 ns. However, if the rising edge time is too low (e.g., 2 ns), the streamer will cease before it propagates to the plate electrode and the radius of the discharge region shrink at the same time. In addition, the peak electric field and the averaged electron energy at the same position away from the needle decrease slightly with the gap width. Finally, there is an obvious decrease of the initial peak electric field as the needle radius increases. [ABSTRACT FROM AUTHOR]

The nonlinear dynamics and its wide range of applications have increased the curiosity of researchers. In short span of time, solitons have become the major interest of physicists. We investigate the nonlinear profile of plasmonic solitons with four components consisting of hot electrons, cold electrons, hot ions, and hot protons. In this framework, a couple of equations of motion are derived by invoking the reductive perturbation technique, and the resultant modified Korteweg—de Vries (m-KdV) equation is solved by the sine cosine method. Here, we analyze the effect of Sagdeev pseudopotential and the electrostatic potential with different system parameters and the characteristics of solitons are found. [ABSTRACT FROM AUTHOR]

The micro-structure miniaturization of vacuum electron devices (VEDs) in terahertz band requires the high precision description of formation and transportation for the ultrahigh density electron beams with the novelty theoretical analysis and simulation. In this article, the 3-D spatial potential of circular electron beam formation is presented by adopting differential geometry and tensor analysis theory. The specific numerical solution of the circular electron beam potential can be obtained by establishing a moving coordinate frame, carrying out numerical calculation, series expansion with adopting of Riemann method. In order to verify the complex theory, a 0.34 THz vacuum electron tube using thin circular electron beam gun and corresponding optical system are designed and analyzed. The beam voltage and current are 23.8 kV and 0.28 A respectively, with beam channel radius of 0.16 mm and magnetic field of 5250 Gs. Using 3-D simulation of CST, the ultrahigh density electron beam can transport 30 mm with good stability. The spatial potential of numerical calculation with the obtained theoretical functions and the simulation model are compared to verify our theoretical description. Both the results are with good consistent which preliminary proves the effectiveness of the theoretical function. Furthermore, we combine the theoretical function potential with the electron beam envelope under the same coordinate frame, the detailed characteristics of ultrahigh density beam formation with the potential function can be directly understood easily, which will give the deep physical mechanics vision for the development of high power and high-efficiency terahertz tube in the future. [ABSTRACT FROM AUTHOR]

Solar radiation, along with cosmic radiation, ionizes the Earth’s atmosphere and creates a dense layer known as the ionosphere. By considering weakly relativistic degenerate plasma in the planetary ionosphere, we have studied the formation and nature of the solitary structure, electrostatic double layers (DLs), and so on. As we have considered weak relativistic degeneracy, only electrons get accelerated and are the key to stationary structures. We have implemented Sagdeev’s pseudopotential method, standard Gardner equation, and accordingly identified regimes where the solitary formation and DLs may be observed. We have studied the parametric influences on solitons and DLs. Furthermore, we extended our investigation to the oscillatory Rossby solitons in the ionospheric plasma. The results may help interpret many high-energy atmospheric observations in the ionospheric plasma. [ABSTRACT FROM AUTHOR]

The formation of a nonlocal electron distribution function (EDF) in an argon dusty plasma of a dc glow discharge has been studied in a wide range of microparticle densities and their different spatial distributions inside a dusty cloud have also been explored. It is shown that the spatial profile of charges and the ambipolar potential can vary greatly, both with a change in the absolute values of the density of dust particles and the type of their spatial distribution. In turn, changes in the profiles of the ambipolar potential lead to strong differences in the nonlocal EDF at different points of the tube radius. This is most clearly seen at high densities of dust particles when nonmonotonic profiles of the potential distribution and reversal of the sign of the ambipolar field are formed. In this extreme case, great changes in the nonlocal EDF are observed not only at the discharge periphery but also inside the dust cloud. [ABSTRACT FROM AUTHOR]

A semiconductor p-n junction diode with heavy doping under consideration is kept in forward biased condition. These are oppositely propagating electron and hole currents. These two streams interact among themselves and result in recombination, which supplies additional energy to the system. Such thermal energy creates additional electrical fluctuations, which exists long after the interaction has taken place. We have carried out an analytical investigation with numerical techniques as well as carried out a simulation of the wave–wave interaction in semiconductor junction diodes. In terms of signal transmission and operation of semiconductor device, such a theoretical study is important. [ABSTRACT FROM AUTHOR]

In this article, we investigate the influence of external discharge conditions on plasma parameters in the plasma discharge chamber of the radome configuration. We designed a conformal cavity and then used the multiphysics simulation software COMSOL to establish a 2-D axisymmetric model for discharge simulation research. In the study, we found that the changes in coil power and pressure have a noticeable effect on the distribution of plasma parameters. First, the maximum electron density, electric potential, and electron temperature are obtained by changing the power of the coil in a certain pressure argon environment. Then, under the condition of constant coil power, the discharge characteristics of plasma are studied by changing the gas pressure in the cavity. The results show that the change of coil power has a significant impact on the parameter distribution of plasma discharge. The greater the coil power, the greater the electron density, and the more concentrated the distribution. At the same time, the potential induced in the heating zone and the corresponding electron temperature decreased after the reaction stabilized. The increase of gas pressure significantly increases the peak value of electron density and changes the parameter distribution of discharge. However, when the argon pressure exceeds a certain threshold, it will no longer have a significant effect on the distribution of discharge parameters. The general conclusion is that the increase of power and argon pressure plays an essential role in improving the electron density distribution. This conclusion has guiding significance for exploring the law of plasma parameter distribution on electromagnetic scattering characteristics. [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]

We have characterized spacecraft charging events in low Earth orbit (LEO) polar regions with the Active Monitor Box of Electrostatic Risk (AMBER) instrument onboard the Joint Altimetry Satellite Oceanography Network—3 (Jason-3) ocean topography mission for the first time for this spacecraft. AMBER data, taken at an altitude of 1336 km, over the period January 2017–March 2020, with measurements recorded close to the current solar minimum have been analyzed, using systematic filtering of ions spectrograms with selected threshold energies and time windows to detect negative spacecraft charging events; 109 spacecraft charging events were found. The events are examined visually and characterized by their spatial and temporal location, duration, and intensity (e.g., spacecraft potential). At the Jason-3 altitude (1336 km), the ion signature predominately lasts under 30 s in conjunction with auroral inverted V crossings, while intense fluxes of electrons corresponding to the encounter of the discrete auroral region last between 30 s and 1 min. Most of the detected spacecraft charging events show charging levels between −30 and −1000 V. The spacecraft charging events are located in the magnetic local time (MLT) sector 17h–05h, predominately before midnight. The distribution is equal between the northern and southern hemispheres. We found a high correlation between the charging time profile and that of the auroral electron average energy and energy flux along the satellite path. Overall statistics over three years as well as different event morphologies, electron spectra, and comparisons to worst case electron flux spectral distributions are presented and discussed. [ABSTRACT FROM AUTHOR]

Plasma potential is a key parameter in plasma discharge or fusion plasma to control plasma–wall interaction or ExB drift. The magnitude of plasma potential depends on the overall energy transmitted to the plasma via direct current (dc) or radio frequency (RF) devices such as electrodes or antennas. Knowing the plasma potential from the exciting source is useful to prevent high energetic fluxes to the wall or to improve the plasma confinement or explaining shear velocity. The aim of the present model is to calculate this plasma potential with respect to a dc or RF source in a magnetized or unmagnetized plasma. This double saturated probe (DSP) model takes into account the electron saturation current and is able to derive the plasma potential as a function of the electrode/wall area ratio for a dc or RF discharge in a helium/argon plasma with or without a magnetic field. The results of the model are compared with Aanesland’s model in the case of unmagnetized capacitive sheath and particle-in-cell (PIC) simulations. The magnetized model is applied to a plasma column with a perpendicular capacitive current in an RF discharge. It appears that the plasma potential can increase to almost the RF potential value at a low wall/electrode area ratio ($A_{\text {wall}}/A_{\text {el}}$ lower than 5), while the same potential collapses as soon as the area ratio (perpendicular over the parallel current area) is higher than the electron/ion saturation current ratio. This is directly due to the saturation of electron current, preventing the plasma potential from following the imposed RF potential by the electrode, so that the maximum value can be as lower as the floating potential. The perpendicular current involved is mainly a conduction current modeled as a resistive collisional current. In fusion plasma, the maximum plasma potential can rise to higher values than in plasma discharges, but the collapse of the potential still occurs for long collisional biased flux tubes. [ABSTRACT FROM AUTHOR]

Experimental investigations of a hollow cathode discharge through the controlled variation of anode potential inside a hollow cylindrical cavity, in the absence and presence of the magnetic field, reveal the self-organization of uniform complex space charge structure formation around the spherical anode into concentrated localized anode spots. The discharge current–voltage ($I$ – $V$) characteristic along with the electrostatic floating potential and discharge current fluctuations measured during the glow discharge regime suggest that the initial stable multiple sheath formation around the anode dissociates into intermittent multiple localized anode spot formations while passing through transient states during anode potential variation. On introducing a magnetic field, the localized concentrated anode spot formations on the anode surface undergo random distribution through self-organized criticality (SOC) and pronounced low-frequency oscillations (~52.4 kHz). These oscillations gradually develop into harmonics of 100 kHz on further increasing the anode potential in the presence of the external magnetic field. Various discharge regimes are investigated through the time-resolved floating potential variation measurements using a cylindrical Langmuir probe (LP). We report on the relation between the discharge variations with the nonlinear time series analysis of the discharge current and floating potential fluctuations through the reconstructed phase space in different time domains to analyze the dynamics of complex structure formations and the existence of SOC behavior during the present hollow cathode discharge regime. The study of self-organized pattern formations and SOC behavior is vital for understanding the complex behavior of plasmas in the field of strongly coupled plasmas, plasma-based surface treatments, and thrusters for further development. [ABSTRACT FROM AUTHOR]

The article investigates the influence of electric field imperfections that manifest themselves as hexapole and octopole aberrations in a dual frequency planar Paul trap. The characteristics of the charged particle motion are analyzed by formulating equation of motion in a pseudo-potential well wherein the hexapole and octopole field effects get superimposed to yield a Duffing type of an equation. Perturbation and harmonic balance methods are applied to estimate the axial frequency shifts and the displacement of the charged particle from the axis of the trap. The axial frequency is dependent upon whereas the displacement of the charged particle from the center of the axis is independent of the variation in voltage and frequency ratio applied to the Paul trap. [ABSTRACT FROM AUTHOR]

The launch of synchronous induction coilgun (SICG) is always accompanied by strong thermal and structural effects, which will cause serious damage to the structure of the armature, and multiphysics computation is an effective means to avoid this problem. Compared with the conventional circuit-based model, the finite-element analysis (FEA) is more suitable for the multiphysics computation of SICG, but it is also more time-consuming. In this article, the implicit function and level set (IFLS) method is introduced to rapidly simulate the multiphysics problem of SIGC based on FEA. The armature is modeled implicitly in the material domain and the position of it is updated through the implicit function, avoiding the moving mesh and remesh problems in the arbitrary Lagrangian–Eulerian (ALE) method, which is generally used to dealing with the dynamic mesh problem. Besides, the volume loss density and the Lorentz force per unit in the moving band are transformed back to the initial position to complete the coupling of the thermal and structural field and maintain the accuracy and continuousness of the simulation. A single-stage SICG model is established with the ALE and IFLS methods, and the results show that the computation time of the IFLS method is nearly halved. Finally, the IFLS method is applied to the simulation of multistage SICG, and the computational efficiency is greatly improved. [ABSTRACT FROM AUTHOR]

Electrospraying is a process that uses electrostatic force to break up a liquid into droplets by using a strong electric field. There are different modes of electrospraying depending on the electric field strength and the liquid flow rate for a specified liquid. The simple-jet mode is among these modes, which can produce monodisperse droplets. This article is aimed at analyzing electrospraying in simple-jet mode of a pesticide—solution issued from the nozzle of a capillary of the spray—system. The analysis includes the formation of a jet charged by conduction at low applied voltages (below corona onset) and by corona discharge at voltages higher than the corona onset value. The electric field distribution in the space between the charged jet and the target is calculated at voltages below and above the corona onset value. The disintegration of the jet into droplets is assessed to determine the jet length and radius as well as the charge and radius of droplets. The current–voltage characteristic of the spray system is calculated and checked experimentally. The agreement between the calculated and measured currents in the spray system at the same applied voltage is satisfactory. [ABSTRACT FROM AUTHOR]

High-power solar arrays are in development by the National Aeronautics and Space Administration (NASA) for near-term high-power solar electric propulsion (SEP) missions. These high-voltage (HV) solar arrays use deployable flexible blanket configurations and need to be able to operate in the plasma environment of high-power Hall thrusters operating at tens of kilowatts of power. Array voltages of 300–800 V are desired both to minimize the copper bus mass in the system and to potentially operate the SEP Hall thrusters directly at high specific impulse without an in- series power processing unit. Coupons with multiple strings of solar cells (SCs) have been tested to high positive and negative biases in a plasma environment representative of the edge of Hall thruster plumes. Proper encapsulation of the exposed metals and triple points is required to avoid excessive current collection and arc initiation. Fully encapsulated test coupons have been successfully been tested at highest anticipated thruster plume plasma densities at voltages from 600 to 1000 V, which enables both very high power arrays and direct drive configurations for SEP missions. [ABSTRACT FROM AUTHOR]

The magnetohydrodynamic (MHD) behavior and performance characteristic have been revealed by 3-D numerical simulation of the Faraday-type MHD generator. Numerical results show that the generator inlet–outlet pressure ratio (PR) will affect the plasma behaviors and generator performance in the channel. At high PR, the plasma flows at supersonic, and higher electric power [enthalpy extraction rate (EE)] can be obtained. However, at low PR, boundary layer separation occurs with deflected flow of velocity streamlines and vortex in the separated flow region, owing to the oblique shock wave. Therefore, there exists a minimum PR to maximize power generation performance. Under the strong MHD interaction, the Lorentz force causes the loss of Mach number and the increase of static pressure, but it can alleviate the effect of oblique shock for a lower PR. Furthermore, suppressing the boundary layer separation effect gradually evolves into a normal shock wave. When PR is higher, the thermoelectric conversion efficiency increases, and then a weak shock wave will be generated in the channel, which will propagate upstream and evolve into a normal shock wave. Consequently, under a higher magnetic flux density, the minimum PR can be effectively reduced, and the best generator performance can be obtained. In addition, an “ $M$ ”-shaped velocity profile will be generated due to the significantly increased MHD interaction. The results calculated in the present simulation are valuable and important for setting working gas conditions and evaluating generator performance. [ABSTRACT FROM AUTHOR]

The Langmuir probe (LP) is generally accepted as an effective and relatively simple in situ space plasma instrument (plasma density, electron temperature, and spacecraft potential). As LPs transition to small spacecraft, their implementation encounters new technical challenges. For example, a negative charge is induced on the spacecraft while positively biasing an LP due to the small surface area ratios (spacecraft surface area to probe surface area ≪ 1000). This results in a varying spacecraft potential that degrades the accuracy of electron temperature and electron density measurements, reducing the LP’s effectiveness as a diagnostic tool. To mitigate the effects of this spacecraft charging, the twin-probe method (TPM) was developed. The TPM corrects LP measurements with tracked spacecraft potentials, measured by a separate high-impedance probe. By accounting for the changes in the spacecraft potential, the LP sweeps can be reconstructed to provide more accurate measurements of the ambient plasma’s properties. Here, we detail the TPM and present laboratory experiments that study its effectiveness and summarize constraints. Through these experiments, we found that it is possible to correct for spacecraft charging effects that can cause deviations in temperature and density as large as 20% and 136%, respectively. Furthermore, we will demonstrate a clear correlation between area ratio, spacecraft charging, and the negative impact on temperature and density measurement accuracy. [ABSTRACT FROM AUTHOR]

Attaining good collector performance in terms of high collector efficiency, low backstreaming, and body interception current has been a prime motive for traveling wave tube (TWT) designers. Selection of appropriate electrode material can result in enhancement of collector performance for the same electrical design (with same electrode potentials and electrode geometry). Here, attempts have been made to quantitatively demonstrate the unexplored impact of electrode material selection on the collector performance systematically. The effect of electrode material on collector efficiency, backstreaming current, body interception current, and their fluctuations arising in a practical scenario due to the variations in input power drives and electrode potentials has been studied. This study has been extended for two different types of TWTs–one with high electronic efficiency and another with medium electronic efficiency at different operating frequencies. Five different electrode materials have been studied with precise recommendations provided for each of the two types of TWTs. [ABSTRACT FROM AUTHOR]

A cylindrically symmetric electromagnetic ion trap has been constructed that creates a potential well suitable for confining ions with the space charge of a continually resupplied electron cloud. The trap uses permanent magnets to form a linear array of magnetic field ring cusps in a cylindrical geometry and includes electrostatic plugging of the cusping magnetic fields. The ion source is electron bombardment ionization of a controlled leak of thermal molecular hydrogen directly inside the trap, and a potential well created by those selfsame electrons is the mechanism of ion confinement. The ion trap is unique in that the confinement volume has relatively minimal external static electric and magnetic field intrusion into the regions intended to confine ions and no overall axial magnetic field. Another standout feature is the inclusion of electrostatic elements in two locations inaccessible to electrons inside the trap that provide axial ion confinement in conjunction with electrons in the trap. Build-up of ions, and therefore confinement, was demonstrated via an ion signal that increased in intensity over a period of several dozen expected axial ion transit times while injecting electrons. A study has been conducted for a range of incident electron currents from the electron flood gun for several fixed partial pressures of molecular hydrogen and interpreted using a full particle-in-cell simulation of the trap. Data were acquired via a microchannel plate and phosphor screen assembly biased in a manner that could only be excited by positively charged particles exiting the trap. An order of magnitude estimate for mean lifetime is made using a combination of simulated charged particle population estimates and measured data. [ABSTRACT FROM AUTHOR]

Space plasmas, though tenuous, can lead to the development of large magnitude potentials on spacecraft surfaces relative to the ambient plasma in a process known as spacecraft charging. This effect poses a threat to spacecraft when surfaces charge differentially as it increases the risk of electrical arcing. Spacecraft engineers have primarily focused on the mitigation of charging and not its exploitation. The potentials and current collected by the spacecraft present an opportunity to harvest power from the space environment. Although the current density and floating potential due to incident charged species in the orbit-motion-limited model are identical for all spacecraft surfaces with similar geometries, material property differences between surfaces or charge control devices break the symmetry and allow for net current to flow. Differences in the secondary electron yield, in particular, produce strong differences in floating potential even when the spacecraft is eclipsed or far from the sun. This article presents a theory for computing the power available to harvest from spacecraft charging given the parameters of ambient space plasmas and surface material properties. Given a load connecting two differentially charged surfaces, optimal power is harvested by matching the load resistance to the input plasma impedance. While this holds for any model of the ambient plasma, the orbit-motion-limited theory yields closed-form solutions to the charging equations for spherical and planar surfaces. These solutions provide an upper bound on generated power that scales with the density and temperature of the cold electron population. An environment-specific optimal anode-to-cathode area ratio exists that minimizes the input impedance to the harvesting circuit. Deployable anodes are recommended to satisfy this condition and increase the amount of power harvested. Energy harvesting from spacecraft charging can be used in the Jovian magnetosphere to generate on the order of 10 mW/m2 of power. [ABSTRACT FROM AUTHOR]

The problem of dust-ion-acoustic (DIA) solitons is addressed in an electronegative collisionless dusty plasma with the presence of trapped-nonthermal electrons. To do this, we revisited the Cairns–Gurevich distribution that describes, concurrently, the evolution of the energetic electrons and those trapped in the plasma potential and analytically expressed its corresponding density. The modifications, due to the presence of this trapped nonthermal density, arising in small-amplitude DIA solitons propagation associated with both space and experimental plasmas are analyzed. In particular, we have found that, in both cases, a proportion of trapped nonthermal electrons relatively significant makes the solitary structure less spiky. Besides, we have shown that the amplitude and width of the experimental plasma soliton seem more affected due to the low ionic mass ratio. [ABSTRACT FROM AUTHOR]

Dust particles in magnetized plasma have generated considerable interest in the semiconductor industry, plasma crystals, Tokamaks, cosmological events, and so on. Upon introducing dust particles in dc glow discharge plasma, they get charged, and hence, a potential is developed surrounding the same. Coulomb potential or Yukawa potential is taken for the interaction of charged dust particles. The effect of magnetic field along the axis of the chamber and, subsequently, scattering cross section of charged dust particles due to the interaction of magnetic fields have been studied critically in this report. A generalized mathematical model is implemented, to find the scattering cross section of charged dust particles. The scattering parameter is introduced to reduce the complexity involved in the derivation of integral equations. Furthermore, to validate the mathematical model, the simulation of DC glow discharge plasma in COMSOL Multiphysics has been carried out. A rectangle chamber with charged dust particles is introduced and with varying magnetic fields, and the transport of dust particles is recorded. The scattering cross section of dust particles is determined from the velocity profile of dust particles and it has been observed that the scattering cross section decreases with the increase of the magnetic field. [ABSTRACT FROM AUTHOR]

By employing a two-fluid quantum magnetohydrodynamic (QMHD) model, linear and nonlinear aspects of magnetoacoustic wave propagation in dense magnetized electron–positron (e-p) plasma are examined in the presence of exchange-correlation potential as well. The degenerate plasma pressure and the Bohm potential effects are already taken in the model. The reductive perturbation method (RPM) is used, and the modified Korteweg–de Vries (modified KdV) equation (or KdV equation containing linear drift term) is derived for nonlinear magnetoacoustic wave propagation in degenerate pair plasma under periodic boundary conditions. The well-known Sagdeev potential approach is opted to obtain the analytical solution of magnetoacoustic cnoidal wave and soliton in dense pair plasmas. The numerical plots of magnetoacoustic cnoidal wave and soliton structures are also presented, and the condition of their formation in dense e-p plasma is discussed in detail. The parametric analysis in the absence and the presence of exchange-correlation potential effects of electrons and positrons is discussed. Moreover, the parametric analysis of the variations of plasma density and magnetic field intensity on the formation and propagation of nonlinear structures in dense e-p plasma in the presence of exchange-correlation force effects in the model is also done using the astrophysical plasma parameters mentioned in the literature for pulsars (or white dwarfs). [ABSTRACT FROM AUTHOR]

A low-energy multipole line cusp ion source with two-grid extraction system has been developed and characterized for studying the role of the charge exchange processes on ion beam extraction, transport, and neutralization. The ion source is operated for extraction of Ar+ ion beam of current 50–240 mA at energies 850–1650 eV. The characterization of the ion beam is carried out at various axial positions along a 200–815-mm beam path with a background pressure of 4– $20\times10$ −5 Torr. An 11-channel Faraday cup array is used to measure the radial profiles of ion current density and angular beam divergence at these positions. The beam divergences are found to be in the range of 6°–15° for beam perveance of 0.50– $3.75\times10$ −9 AV−3/2. The attenuation of ion beam current along the beam path is observed due to the charge exchange neutralization of the energetic ions in the presence of high background pressure. Since ion current density along the beam path can be reduced by both the charge exchange processes and beam divergence, the accounting of beam particles, i.e., energetic ions and neutrals, at larger distances is difficult by the measurements of ion current density using the Faraday cup alone. The flux of energetic particles (energetic ions and fast neutrals) is therefore obtained by a thrust measurements on a beam target fixed at a distance of 800 mm from the ion source. The neutralization of the ion beam obtained by the emission of electrons from a hot filament neutralizer is also investigated in the presence of the charge exchange processes. Space-charge neutralization is provided initially by the secondary electrons emitted from the vessel walls or by the charge exchange processes even without the neutralizer operating at the desired temperature. However, the current neutralization is achieved only by the electrons emitted from the hot filament neutralizer operating in a space-charge-limited mode. [ABSTRACT FROM AUTHOR]

In this work, numerical solution to a general electromagnetic (EM) system is studied using a formalism based on the formulas for the E–B–A– $\phi $ formulas with different gauge conditions. The finite-difference time-domain (FDTD) method is employed to discretize these formulas. In addition, the convolutional perfectly matched layer (CPML) technique is successfully applied to absorb outgoing scattered waves described by the proposed formulas. The gauge invariance of EM fields in inhomogeneous environment is demonstrated by numerical examples. Moreover, the proposed EM framework integrated with the Schrödinger equation is introduced to investigate the mesoscopic phenomenon for light–matter interaction, which is useful to design laser pulses for controlling discrete quantum states. The work offers a simple and general numerical EM framework, which is essential to bridge the classical EM and quantum mechanical systems. [ABSTRACT FROM AUTHOR]

This article presents the derivation of semianalytic solutions to a new 1-D photoelectron sheath model near the lunar surface. The plasma species include the cold solar wind protons, drifting Maxwellian solar wind electrons, and Maxwellian photoelectrons emitted from the surface. The semianalytic model is then numerically solved to obtain profiles of quantities of interest as functions of the vertical distance from the surface. A fully-kinetic 3-D finite-difference (FD) particle-in-cell (PIC) code is then utilized to simulate the 1-D photoelectron sheath and the results agree well with the numerical solution to the semianalytic model. A $\kappa $ -distribution for solar wind electrons is also implemented to the FD-PIC code to compare with the Maxwellian distribution. Results show that photoelectron sheath may reach as high as close to 100 m above the illuminated flat lunar surface near the terminator region and up to about 50 m near the equator region. Our results show that under average solar wind condition, the photoelectron sheath profiles obtained with Maxwellian and $\kappa $ -distribution (with $\kappa = 4.5$) are very close for 1-D numerical results. [ABSTRACT FROM AUTHOR]

Highly charged ion sources play an important role in the advancement of heavy-ion accelerators worldwide. Demands of highly charged heavy ions for new and existing accelerators have driven the performance of ion sources to their limits. A new high charge state ion accumulating trap concept is proposed that converts a dc ion beam from an electron cyclotron resonance (ECR) ion source into a short-pulsed ion beam with suitable compression ratios. With a simple trap composed of an electron gun, a solenoid, and a set of drift tubes (DTs), the injected ions from a dc operation ECR ion source will be trapped radially and axially. By manipulating the potential of the DT, highly charged ions can be accumulated with multiple injections and extracted with augmentation of ion intensity in pulses of tens of $\mu \text{s}$. This article presents the simulations and design features of the envisioned ion trap. [ABSTRACT FROM AUTHOR]

This article describes the performance of a multi-gap, multichannel (MGMC) spark gap switch, evaluated numerically and experimentally, to achieve multichanneling using a relatively low-magnitude trigger pulse. First, an electrostatic analysis of the switch geometry was carried out using COMSOL Multiphysics 5.5 to determine the electric field distribution during high-voltage hold-off before triggering and to determine the coupling parameters between trigger and other intermediate electrodes of the switch. Second, a circuit model was developed in PSpice Lite 16.6 for predicting the process of channel formation and its influence on adjacent channels. Based on the simulation results obtained, a six-gap, eight-channel, planar MGMC switch operating in air has been designed and developed. The developed switch was, then, incorporated into a compact experimental setup to experimentally evaluate various switch parameters such as inductance, switching delay, jitter, and closing time when triggered using a negative-polarity trigger pulse of magnitude −40 kV, generated using a compact, in-house developed trigger generator. In contrast to most of the reported MGMC switches that use complicated Marx-based generators to produce ≥120-kV trigger pulses for multichannel formation, the experimental results, thus obtained, report comparable switch performance using a low-magnitude (−40 kV) trigger pulse. In addition, framing and streak camera images taken during the current discharge indicate the presence of ~6 luminous channels. In addition, short-circuit experiments for estimating switch inductance by consecutively shorting one or more channels also indicate multichanneling in the switch using a low-magnitude trigger pulse. [ABSTRACT FROM AUTHOR]

Pulsed electric fields (PEFs) had the potential to be a new pasteurization technology due to its advantages of energy-saving, high efficiency, and less influence on food quality based on the electroporation effect of PEF on microorganisms. At the same time, temperature played a significant role in the electroporation process. We established a two-membrane dielectric model that coupled temperature and PEF to study the influence of temperature on the dynamic process of electroporation. In this model, we considered both the effect of Joule heat on temperature generated by PEF and the effect of temperature on the conductivity of suspension, cytoplasm, nucleus, the characteristic voltage of electroporation, and molecules transport. The simulation results showed that under the higher ambient temperature, the transmembrane voltage of the cell membrane after electroporation could be stabilized at a higher value, the maximum value of membrane conductivity and pore density on the cell membrane was higher. The relationship between pore radius and temperature was simulated. What is more, temperature facilitated molecules transport, which intensified the destruction of cell homeostasis. [ABSTRACT FROM AUTHOR]

This article studies the features and patterns of the formation of high-intensity beams of metal and gaseous ions of low and ultralow energy from dc vacuum arc and gas-discharge plasma. It presents the results of repetitively pulsed plasma immersion extraction of aluminum, titanium, and nitrogen ions from the plasma followed by the formation and transport of ion beam under conditions of its ballistic focusing. This article presents the experimental data on the influence of the grid focusing electrode cell sizes of 150 and $500~\mu \text{m}$ , the bias potential amplitude from 0.1 to 2 kV, the conditions for neutralizing the space charge of the beam during preliminary plasma injection into drift space and when using an additional thermoelectron source on the transport and focusing of ion beams. Here, it discusses the effect of the characteristic dimensions of the fine-structured grid and plasma parameters at ultralow bias potential amplitudes and the presence of significant initial energy in ions on the ion beam focusing. It was found that at bias potential amplitudes of 0.6 kV, it is possible to form repetitively pulsed ion beams with high current density reaching 170 mA/cm2. The obtaining of such beams opens up the possibility of implementing the method of high-intensity ion implantation under conditions of multiple decreases in the irradiated surface sputtering. [ABSTRACT FROM AUTHOR]

We present a model of the space charge limited (SCL) electron injection into a gap combined with trap-filled dielectric solid and vacuum or a gap combined with two different trap-filled dielectric solid. An optimized calculation method is proposed to calculate the SCL current density $J$ inside the gap under different gap voltages $V_{g}$. The $n$ scaling of $J$ – $V_{g}^{n}$ varies in a different range of $V_{g}$ , which is described as the Ohm regime, trap-limited regime, and SCL regime. It is found that the $n$ scaling is dependent on electron mobility and relative length scale between two media, which indicates that traps in the dielectric have a profound impact on SCL electron transport properties. [ABSTRACT FROM AUTHOR]

We used the tone burst floating probe method to measure plasma parameters in a hollow cathode discharge. In this method, the electron temperature is directly calculated from a shift in the floating potential of the burst interval when a tone burst signal is applied to a probe through an intermediary blocking capacitor. The tone burst signal is a signal that applies an ac signal for a fixed time and turns off the remaining time of the cycle. It was possible to measure the same electron temperature as in the floating probe method that we previously reported. In the tone burst floating probe method, it is possible to measure the ion current by a shift in the floating potential from the time constant of the burst interval. This is a new measurement method that can measure the plasma density from the ion current and the electron temperature during the tone burst signal input. [ABSTRACT FROM AUTHOR]

Prior experiments have demonstrated that the pole in a magnetically shielded Hall thruster sputters and erodes visibly, in contrast with that in an unshielded thruster. To determine the reason for this, a particle-in-cell simulation was conducted, and the difference between shielded and unshielded thrusters in terms of plasma behavior near the exit plane was studied. The results show that in the case of the magnetically shielded thruster, the ion flux peak is on the magnetic pole face with higher ion energy, indicating severer erosion at the pole. By contrast, the flux peak of the unshielded thruster is on the head face of the channel wall, indicating severer bombardment at the wall and milder erosion at the pole. Therefore, pole erosion occurs in the magnetically shielded thruster, and channel head face erosion can be observed in the unshielded thruster. In addition, the simulation results indicate that the greater the outward shift of the magnetic field, the severer the pole erosion. [ABSTRACT FROM AUTHOR]

The article is the continuation of the work devoted to the numerical study of processes in the single-phase ac plasma torch operating at low current (up to 10A RMS). The main attention is paid to the analysis of the flow pattern and the behavior of gasdynamic parameters. The effects of flow acceleration and rarefaction of near axial arc core are shown. The effects of the transformation of gasdynamic structures typical for cold flow (e.g., vortex behind the back step), as well as the appearance of new structures (e.g., vortexes in the jet periphery), are demonstrated and discussed. An explanation is given for the effect of the increase of the arc voltage drop with the increase of the flow rate of supplied air, associated with the increase of the medium electric resistance. The presented results are in accordance with the experimental data on the voltage drop in a conventional ac plasma torch. [ABSTRACT FROM AUTHOR]

This study investigates different geometry configurations for obtaining photoplasma in a gas cell of Na–Ar mixture. For this purpose, 2-D simulations with the fluid model of plasma have been conducted for single-chamber and two-chamber cells. For the studied range of pressure, the drift-diffusion approximation has been used. The simulation model is based on solving the continuity, momentum balance for charged particles, coupled with electron energy balance equation and the Poisson equation. Detailed plasma chemistry has been considered, and plasma parameters have been obtained, such as electron density and temperature, and the electric potential of the plasma. The obtained results show the effectiveness of the two-chamber cell configuration over the single-chamber one in generating a notable electromotive force (EMF). [ABSTRACT FROM AUTHOR]

Capacitively coupled plasmas (CCPs) are widely used for material processing, for example, for the manufacturing of semiconductors textile and modified surface. The ever-increasing requirements that companies face with respect to the quality, efficiency, and environmental friendliness of their manufacturing processes demand continuous progress. One simple and significant path to gain insight is the global model. Global models, which are, in engineering, called the lumped element model, allow for a complete and transparent mathematical analysis. Therefore, this work will study three models, the example of the exact model, and its verification using the step model to find the analytical relation between the sheath charge and the overall voltage drop across it. This formula is the missing factor in the global model that establishes the aim of the research. In addition, an effective lumped element model was studied, which allows describing the sheath dynamics in simple, though nonlinear engineering terms, such as resistance, capacitance, and inductance. The study achieves more detailed dynamics, such as the time-varying charge, voltage distribution, charge–voltage distribution Vsh(Q) that controls the nonlinear sheath dynamics, current distributions, and the equation of the sheath distance for dc and ac sheaths. The results obtained at low computational complexity provide satisfactory calculations for nonlinear dynamics of collision sheath behavior. [ABSTRACT FROM AUTHOR]

A simple sensor is described to measure satellite potentials. The proposed instrument consists of two small spherical Langmuir probes biased to different fixed voltages, from which currents are measured. A predictive model is constructed for spacecraft floating potentials by combining the orbital motion limited (OML) approximation for spherical probes, and a multivariate regression algorithm. Construction of the model is based on a training data set obtained from 3-D simulation results, covering a range of plasma parameters of relevance to satellites in low earth orbit (LEO) at midlatitudes. The model skill is then assessed by comparing predictions with potentials in a distinct validation data set. Owing to large satellite orbital speeds, fixed bias probes would provide measurements with higher temporal and spatial resolution than possible with sweep voltage probes. [ABSTRACT FROM AUTHOR]

Langmuir probe (LP) diagnostics is performed on an inductively coupled plasma (ICP) generated using a flat spiral antenna. The current–voltage (I - V) characteristics are measured using a radio frequency (RF) compensated LP to mitigate the effect of RF distortion in I - V measurements. All-important plasma parameters such as electron density (ne), electron temperature (Te), plasma potential (Vp), and electron energy distribution function (EEDF) are measured in a cylindrical-shaped ICP. The plasma is generated by feeding RF (13.56 MHz) current in the planer multiple spiral antennas. It is seen that the plasma is uniform over an area with 200 mm diameter, with an electron number density in the range from ~ 1011 to 1012 cm−3. Typically for plasma processing of materials, the required density fall in that region. Variation of plasma parameters is investigated as a function of applied RF power and operating pressure and the observed results are discussed. [ABSTRACT FROM AUTHOR]

Employing the Sagdeev pseudopotential technique, we have investigated ion-acoustic double layers (IADLs) in multicomponent plasma comprising adiabatic ions (positive and negative) with Maxwellian electron distribution. We have numerically calculated the occurrence range of IADLs in negative ion plasmas and studied the influence of various parameters on Mach number ($M$). The existence of large-amplitude IADLs and corresponding phase portrait is investigated analytically. Our system also supports the coexistence of compressive and rarefactive DLs for certain set of parameters. This present model is applied to study the large-amplitude IADLs in the plasmas containing (Xe $^{+}$ , $\text{F}^{-}$), (CS $^{+}$ , Cl $^{-}$), (Ar $^{+}$ , $\text{F}^{-}$), and ($\text{H}^{+}\,\,\text{H}^{-}$) ion species. Our theoretical predications are found to be a good agreement with the experimental observations of large-amplitude IADLs in (Ar $^{+}$ , SF $_{6}^{-}$) negative ion plasma. Present investigations may be helpful to understand the DLs in laboratory and space plasma, where negative ions are present with Maxwellian electrons. [ABSTRACT FROM AUTHOR]

The collective dynamics of a collision-less nonneutral plasma is analyzed in the presence of stray electric field inside a Paul trap. Experiments in Paul traps have indicated the presence of power tail distribution functions. Therefore, a Tsallis distribution function represents the initial distribution of charged particles inside the trap. The stroboscopic map in phase space reveals a closed curve, indicating that a carefully chosen initial distribution function will yield a time-periodic distribution function. The time-averaged distribution function is doubled humped indicating instabilities. The position of the double hump and the asymmetry in the spatial variation of temperature inside the trap depends on the magnitude and the orientation of the stray electric field inside the trap. [ABSTRACT FROM AUTHOR]

In this article, an investigation has been performed to analyze the role of hollow cathode aperture wall profile on pseudospark (PS) discharge-based single gap sheet electron beam source. A simulation study using COMSOL Multiphysics has been carried out for different hollow cathode aperture wall profile parameters, such as thickness and radius of curvature of aperture wall. The role of hollow cathode aperture wall thickness “ $t$ ” and the radius of curvature of aperture wall “ $R$ ” for different gas pressures, 16–20 Pa, and the corresponding applied gap voltage 16–20 kV have been studied. The hollow cathode aperture wall thickness has been analyzed for the range of ~1–3 mm, keeping the constant aspect ratio 12:1, while the radius of curvature of aperture wall has been analyzed for the range of 0–3 mm for different wall thicknesses. Experimental studies have also been performed to analyze the role of the thickness of the aperture wall on PS discharge. A good correlation has been obtained between the simulation and experimental studies. [ABSTRACT FROM AUTHOR]

The exhaust ion stream from an electron cyclotron resonance (ECR) plasma source is investigated in detail. Two sets of coils allow for different shapes of the external field under which the plasma is created. Parameters in the form of electron density $n_{e}$ , electron temperature $T_{e}$ , and ion energy distribution function (IEDF) are evaluated using Langmuir probes and retarding field energy analyzers (RFEAs). Parameters are evaluated under 10 and 20 W of microwave energy at pressures in argon between $1\times 10^{-3}$ and $2\times 10^{-3}$ mbar. In the middle of the plasma, we see electron temperatures in the range of 4–5 eV for most measurements and electron densities of up to $5\times 10^{16}/\text{m}^{3}$ in agreement with particle and power balance models. For a purely expanding magnetic field, the detailed IEDFs indicate a directed ion speed within the plasma column of up to $3.1\times 10^{3}$ m/s with respect to the low-energy background. With increasing downstream magnetic field, the low-energy part of the IEDFs vanishes downstream of the magnetic mirror. Structures with energies increasing in the radial direction appear as radial confinement improves. [ABSTRACT FROM AUTHOR]

A motor-driven, high-current switch is being designed by Stäubli Electrical Connectors in collaboration with Princeton Plasma Physics Laboratory to reverse the DIII-D Toroidal field coil current. The existing field reversing procedure requires approximately 4 h of labor performed between run days to reconfigure the bus work, thus requiring a separate run day to complete experimental scans with both field directions. This typically results in different wall conditions which complicate the results or make them invalid. The proposed switch will complete the reversal process in approximately 4–5 min, between shots, so that wall conditions are not a factor, and easily fits within the 10–12 min DIII-D shot cycle. The switch is a compact design fitting into a $157.5\times41$ cm envelope. The switch uses two copper pins that slide between Stäubli MULTILAM contacts. The switch is rated for total current of 180-kA dc for 10 s with a 12-min repetition rate; the maximum operating coil current is 124-kA dc. The switch diagnostics include: voltage drop, current monitor, thermal monitors, position sensors, and motor torque. The switch is rated for 300 cycles per year, and 3000 cycles overall before contact replacement, with contact inspection yearly. The design details and operation of the switch are covered in this article. [ABSTRACT FROM AUTHOR]

A theoretical investigation is carried out for understanding the properties of three-dimensional degenerate pressure-driven (DPD) gravitoelectrostatic solitary waves (SWs) in a general (but realistic) self-gravitating degenerate quantum plasma (SGDQP) medium whose constituents are noninertial degenerate electron and inertial degenerate heavy and light ions/nuclei/elements. The formation of solitary electrostatic and self-gravitational potential structures in such an SGDQP system is examined. The standard reductive perturbation method is employed to derive the (3+1)-D cylindrical Korteweg–de Vries equation (also known as cylindrical Kadomtsev–Petviashvili equation). The parametric regimes for the existence of solitary electrostatic and self-gravitational potential structures are found. It is shown that the present plasma model supports the DPD SWs with positive and negative electrostatic potentials as well as self-gravitational potentials. The effects of the degenerate plasma particles are found to significantly modify the basic properties (viz., the amplitude, width, and speed) of the electrostatic and self-gravitational SWs. The present investigation can be of relevance to the electrostatic and self-gravitational solitary pulses observed in various plasma space environments (viz., white dwarfs, neutron stars, and so on). [ABSTRACT FROM AUTHOR]

A self-consistent model of steady-state electron flow in a planar crossed-field diode with a thermionic cathode is presented. Our formulation is a generalization of the classic work of Fry and Langmuir, to include a constant magnetic field B of arbitrary strength parallel to the electrode surfaces. Some effects of the magnetic field on the electron flow are illustrated in an example. [ABSTRACT FROM AUTHOR]

A novel numerical method has been developed that incorporates electrically conducting objects into particle-in-cell simulations of electrostatic plasma. The method allows multiple objects connected by voltage and current sources in an arbitrary circuit topology. Moreover, by means of an unstructured mesh, the objects can have arbitrary shapes. The electric potential of the objects is solved self-consistently by incorporating charge constraints into the finite element discretization of the Poisson equation. This method has been implemented in a new code, Particles-in-Unstructured-Cells (PUNC), suitable for rapid prototyping. The flexibility of this code has proven convenient to survey various methods, and an issue of reduced convergence rate of today’s unstructured plasma–object interaction codes is highlighted. The results for a conducting sphere immersed in the Maxwellian plasma are in good agreement with previous studies. [ABSTRACT FROM AUTHOR]

A W-band folded waveguide traveling wave tube (FWTWT) with lowered 19.4-kV operation voltage and improved gain flatness was investigated and developed. In this article, design methodology, fabrication, and test results were presented and discussed. Two kinds of slow-wave circuits with the positive and negative period stepping were chosen to carry out the contrastive study. A folded waveguide automatic measurement code was independently developed, and the FWTWT was fabricated by LIGA method. The test results showed that a saturated output power was greater than 87 W in the frequency range of 93–100 GHz and greater than 102 W in the frequency range of 95–98.3 GHz with the maximum output power of 123 W at 96.9 GHz. Within the frequency range of 93–100 GHz, saturated gains were higher than 30.05 dB, and gain fluctuation was 3.47 dB with the maximum gain of 33.52 dB at 96.9 GHz. The maximum electronic efficiency of 7.04% and the maximum total efficiency of 13.52% were obtained. [ABSTRACT FROM AUTHOR]

A novel concept of the mass ratio of negative to positive ions has been introduced to explore its effect on the sheath structure in three electronegative cold plasmas, namely, CF4, O2, and C60 plasmas, for spherical geometry with different probe radii. The magnitudes of velocity of positive ions and potential at the sheath edge are found to modify with the mass ratio, electronegativity, and probe radius. The modification in positive ions’ velocity is designated as modified Bohm criterion. Expression is obtained for the sheath thickness, which is found to increase with the higher mass ratios, whereas it reduces with the enhancement in electronegativity and probe radius. No oscillatory structure is observed for the potential profile when the negative ions are described by their fluid equations (as that of the positive ions), instead of their Boltzmann distribution assumed by the other workers. Positive ions’ density as a function of distance from the probe for the different mass ratios is also examined. [ABSTRACT FROM AUTHOR]

This article presents a systematic investigation on the frequency dependence of the discharge current $J_{g}$ versus the gap voltage $V_{g}$ in the atmospheric-pressure helium dielectric barrier discharges (DBDs) by means of numerical simulation based on a 1-D fluid model. The DBDs are excited by a sinusoidal voltage with frequencies from several tens of kHz to MHz. This article concludes the following. There is a characteristic frequency $f_{c}$ located in a range, smaller than the lower limit of which the $J_{g}$ – $V_{g}$ curve universally behaves as a pinched hysteresis loop, and higher than the upper limit of which it changes to a nonpinched one, and an estimation of $f_{c}$ has been given. Smaller than the lower limit of $f_{c}$ , in spite of its $J_{g}$ – $V_{g}$ pinched hysteresis loop, the discharge plasma part in the DBD cannot be described as a memristor, but exhibits a memory effect. With the increase in frequency, the $J_{g}$ – $V_{g}$ curves display two typical shapes similar to a hockey stick and a quasi-triangle, corresponding to a Townsend discharge and a glow discharge, respectively. Higher than the upper limit of $f_{c}$ , the $J_{g}$ – $V_{g}$ curve is no longer a pinched hysteresis loop, and its evolution with frequency is in a change between symmetry and asymmetry. These evolution behaviors of the $J_{g}$ – $V_{g}$ curves are mainly due to the charges remained in the gap when the frequency is higher. [ABSTRACT FROM AUTHOR]