Search

This paper deals with the repetitively pulsed spark discharges over the water surface by studying both the electrical and the spectroscopic aspects. Detailed discharge electrical parameters, vibrational and rotational temperatures, and electron density measurements for nine different conditions of input frequencies and voltages over the water surface have been reported. The objective of this paper was to find effective operating conditions and compile results for the future industrial applications. The spectroscopic characterizations such as temperatures and densities were gathered from the optical emission spectroscopy (OES). The N2 (C–B) second positive system (SPS) transition (370–382 nm) and the O triplet line (777 nm) obtained from plasma spectrum were analyzed by SpecAir software in order to get the vibrational/rotational temperatures and electron densities, respectively. The results of this work are concurred with our previous work on softening hard water using pulsed spark discharge, finding the most effective conditions practically. [ABSTRACT FROM AUTHOR]

This paper considers thermal neutralized charge electron flux moving through immovable static ion background. A 2-D dispersion equation is derived. The equation describes linear waves of space charge (WSC) in the flux. In the result of the dispersion equation analysis, we proved the existence of the backward and sideward WSCs. Maps on the plane $\{{k_{x}; k_{y}} \}$ were calculated and plotted for two values of the electrons drift velocity. The lines on those maps correspond to the direct, sideward, and backward WSCs. Areas of obtuse and acute drift angles are marked out. [ABSTRACT FROM AUTHOR]

This paper pays particular attention to the dynamic characteristics of dielectric barrier columnar discharge after it starts to decay based on a 2-D fluid model. Waveforms of the gas gap voltage, discharge current, and 2-D distributions of the electron density and the equipotential lines were calculated for the steady state of dielectric barrier columnar discharges in atmospheric helium. The evolution process of the discharge during its decay can be divided into four phases: phase (i), in which new discharges occur at nondischarge-column locations after the extinction of the discharge columns; phase (ii), in which the new discharges are extinguished; phase (iii), in which the axial electric field begins to reverse in the gap; and phase (iv), in which Townsend discharges occur at the discharge column locations before entering into the next columnar discharges. Via an analysis of the time evolution of the axial electron density, we show that new discharges occurred at nondischarge-column locations are Townsend discharges. An in-depth study of the reversion process of the axial electric fields at different locations shows that nonuniform accumulated surface charges play a key role in determining the spatiotemporal discharge characteristics. These results contribute toward gaining a comprehensive understanding of columnar discharges. [ABSTRACT FROM AUTHOR]

For this paper, an experiment of low-pressure Argon inductively coupled plasma (ICP) was conducted in a closed chamber. Obvious $E$ – $H$ mode transition could be observed in the experiment. To solve the problem that microwave interference diagnosis can only measure the average electron density along the transmission path of the microwave, a new microwave interference diagnosis method based on fluid dynamics modeling is put forward to gain an accurate distribution of electron density. Using this new method, the spatial resolution of electron density could be improved. Finally, the electron density of low-pressure ICP was diagnosed both with this method and the Langmuir probe. The results revealed that the electron density increased with power and the peak value reached $7.8\times 10^{17}\text{m}^{-3}$ at the radio frequency power of 700 W. The consistency in the distribution trend of electron density that resulted from two different methods illustrates that the new method can provide a relatively accurate spatial distribution detail of electron density. The electron temperature was measured via the Langmuir probe and the results show that the temperature declines with power. [ABSTRACT FROM AUTHOR]

Inductively coupled plasma sources driven by RF power at low-pressure regimes are well adopted for high-volume manufacturing of semiconductor devices. One vexing challenge to the utility of these plasma processing reactors is the existence of the E–H-mode transition. Industry notably avoids the process region associated with this transition, where plasma instabilities and bimodal power coupling prohibit reliable RF power delivery. One plasma instability detailed in this paper is associated with a hysteresis in coupled RF power (current) varying for the E-mode, or weakly capacitive coupling to the plasma, in comparison to the stronger current coupling in the H-mode, where inductive coupling is preferentially dominant. As a result, approximately two orders of magnitude of electron density is relinquished in this transition region from serving industrial manufacturing processes. We characterize the plasma parameter variation through the E-mode to H-mode with a time-resolved measurement of the electron density. Electronegative chemistries are incorporated into our experimental setup. The experimental scheme serves to evaluate RF power delivery and ameliorate its coupling through the transition region. We seek to extend this paper to adopt more efficient power coupling for toroidal plasma sources. [ABSTRACT FROM AUTHOR]

A new concept high-voltage pseudo-p-channel lateral double-diffused MOS (p-LDMOS) with multiple current paths for conduction is proposed and investigated in this paper. The proposed power device consists of two hole current paths (p-channel MOS device) and one electron current path (n-channel MOS device). The gate of the n-channel device is automatically controlled by an induced signal inside the chip, thus the proposed device can be considered as a p-LDMOS with more than 66.2% reduction of specific on-resistance in comparison with the conventional p-LDMOS device. Furthermore, the proposed device has a much better safe operation area, since the compensation of the electric flux density brought by electron and hole currents. [ABSTRACT FROM AUTHOR]

A spark discharge with variable duration has been used to ignite aluminum, aluminum–silicon alloy, and magnesium powders inside a Hartmann tube to evaluate explosion hazard. Pyrometric and spectroscopic methods have been performed to measure burning particles’ temperature and gases’ temperature, respectively. The spark discharge is also characterized to achieve a better understanding of the interaction between the metallic dust cloud and the spark during the ignition time. Since realistic experimental data are strongly in interest for computational fluid dynamics, in this paper, one provides ignition spark temperature and combustion experimental data such as ignition delay, particle temperature, gas temperature, and electron density. [ABSTRACT FROM AUTHOR]

This paper presents a glow discharge device consisting of two cathodes (with permanent magnets) and an annular plate anode operating at low pressures. In the device, the electron radiation spectrum is recorded with a linearly polarized broadband antenna. With the radiation spectra, two kinds of electron motions were studied and the electron density was estimated. [ABSTRACT FROM PUBLISHER]

A 2-D fluid model is developed to study the pulsed discharges with pin--plane electrode in atmospheric pressure. A positive streamer forms at the pin electrode connecting to the applied voltage and then propagates toward to the ground plane electrode (cathode). Simulation results show if the streamer head is close enough to the cathode, in front of the original streamer a new streamer forms, and simultaneously a second positive current peak is observed, suggesting that the discharge mode transforms into glow mode. Otherwise, the discharge operates at corona mode. The characteristics of the two typical discharge modes are analyzed through the spatiotemporal evolution behaviors of conduction current, electron density, electric field, and electron flux. The transition between corona and glow modes depending on the discharge parameters such as applied voltage, curvature radii, and secondary electron emission coefficients are studied in this paper. It should be noted that no matter what discharge mode is, discharge with reversed direction appears at the falling edge of voltage pulse, which is caused by space charges [ABSTRACT FROM AUTHOR]

In atmospheric radio-frequency (RF) discharges, two discharge modes, namely α and y modes, have been deeply discussed by experimental measurements and computational data, and another mode, known as Ω mode, has also been reported in the electronegative gas. In this paper, we present a fluid model to investigate the formation and dynamics of Ω mode in atmospheric RF discharges but controlled by dielectric barriers with pure helium as working gas. The simulation results show that the Ω mode can be observed right after the breakdown event, and only sustained in a very narrow voltage range; then, the discharge will enter into the α mode as the applied voltage is further increased. Compared with the α mode, the numerical data reveal that in the Ω mode, a relatively larger electric fields are sustained in the bulk plasma to ensure the continuity of discharge current due to the lower electron density, consequently the Ohmic heating and ionization processes mainly take place in the central region of discharge gap. [ABSTRACT FROM PUBLISHER]

In this paper, we address the question of whether spacecraft potential depends on the ambient electron density. In Maxwellian space plasmas, the onset of spacecraft charging does not depend on the ambient electron density. The balance of electron currents causes the incoming electrons to balance with the outgoing secondary electrons. The onset is controlled by the critical or anticritical temperature of the ambient electrons, but not the electron density. Above the critical temperature, charging to negative potential occurs. If the energy of the incoming electrons increases to well beyond the second crossing point of the secondary electron yield (SEY), the value of SEY decreases to well below unity. When the secondary electron current is negligible compared with the primary electron current, the spacecraft potential is governed solely by the balance of the incoming electrons and the sum of the currents of the repelled electrons and the attracted ions. In neutral space plasma, the electron and ion charges cancel each other. But if the space plasma deviates from being neutral, then the densities can have effect on the spacecraft potential. If the ambient plasma deviates significantly from equilibrium, a non-Maxwellian electron distribution may result. For a kappa distribution, one can show that the spacecraft charging level is independent of the ambient electron density. For a double Maxwellian distribution, the spacecraft charging level depends on the electron densities. For a conducting spacecraft charging in sunlight, the charging level is low and positive. It also depends on the ambient electron density. For a dielectric spacecraft in sunlight, the high-level negative-voltage charging on the shadowed side may extend to the sunlit side and block the photoelectrons trying to escape from the sunlit side. In this case, the charging level does not depend on ambient electron density. Using coordinated environmental and spacecraft charging data obtained from the Los Alamos National Laboratory geosynchronous satellites, we showed some results confirming that spacecraft potential is indeed often independent of the ambient electron density. [ABSTRACT FROM AUTHOR]

Microwave electrothermal thruster (MET) is a type of space propulsion system that uses free floating plasma to heat the propellant gas. This paper presents a 0-D model that investigates the energy transfer from the electromagnetic wave to the propellant gas via atmospheric pressure plasma, and evaluates the steady-state plasma properties of an MET thruster. In the model, governing equations for electron particle balance, electron energy, balance and heavy particle energy balance equations are solved to obtain the plasma parameters. Electron temperatures of around 1 eV, electron number densities of 10^19~\#/\text m^3 , and heavy particle temperatures of about 3000 K are evaluated for the free floating plasma inside the MET resonant cavity for 1200-W delivered power at 2.45-GHz frequency. Obtained solutions are in good agreement with the experimental results from the literature. Along with the plasma parameters, rocket performance parameters, and specific impulse and thrust are computed. The developed model is also used to predict the plasma and performance parameters of a prototype MET system developed at the Boğaziçi University Space Technologies Laboratory. [ABSTRACT FROM PUBLISHER]

Investigation on effects of oxide activating fluxes on arc plasma was carried out in tungsten inert gas (TIG) welding on light metals, including magnesium alloy and aluminum alloy. In this paper, four oxides, i.e., ZnO, MnO2, Cr2O3, and CdO, were used to study the roles of oxide on the arc state. When the fluxes were applied, it was observed that the information of the arc (electron density and electron temperature) change obviously. Based on the results produced, the contributions of oxides were studied from two viewpoints, including the information of arc plasma and the input of energy. Under the influence of oxides, both the electron density and the arc voltage got enhanced; however, the electron temperature decreased. In addition, the phenomenon of arc constriction was not observed with the contribution of fluxes. By comparing the experimental results of single TIG welding between with and without fluxes, increase in energy was suggested as the main contribution to the augment weld morphology. [ABSTRACT FROM PUBLISHER]

In this paper, an atmospheric pressure low-temperature plasma pencil generated in helium and helium/oxygen gas mixtures was characterized in detail for its discharge characteristics, plasma power, reactive plasma species produced, plasma density, and plasma temperatures using electrical and optical emission spectroscopy (OES) diagnostics, and its efficacy for biomedical application. A visible plasma plume length of approximately 27 mm was generated using a 60-kHz ac HV power supply. The OES results showed the most intensive plasma emission lines of OH transition A^2\Sigma^+(v=0,1)\toX^2\Pi(\Delta\nu=0) at 308 nm and OH transition A^2\Sigma^+(v=0,1)\toX^2\Pi(\Delta\nu=1) at 287 nm, O I transition 3p^5P\to 3s^5S^0 at 777.41 nm, O I transition 3p^3P\to 3s^3S^0 at 844.6 nm, and N2(C\-B) second positive system with electronic transition C^3\Piu{\to}B^3\Pig in the range 300–450 nm. The effects of controlled oxygen content on the plasma pencil and on various helium plasma emissions and electrical properties are studied. A spatial distribution of reactive plasma species produced by the plasma pencil is presented. The electron density of plasma jet was estimated to be in the order of 2.1\times 10^14~cm^-3 using Stark broadening line profile of the hydrogen alpha emission. The temperatures of afterglow plasma pencil were evaluated using OH rotational temperatures, and the results demonstrate temperatures of 316 and 362 K for pure He and He/ O2 gas mixtures (0.1% O2 ), respectively. Preliminary results on inactivation of Streptococcus pneumoniae on a solid surface and in liquid suspension were carried out using the plasma pencil for biomedical applications. [ABSTRACT FROM PUBLISHER]

This paper is concerned with the determination of total negative ion number density (n–) in a dc plasma discharge of N2O employing laser induced photo-detachment coupled with an electrostatic Langmuir probe. Electrons resulting from the photo-detachment are investigated and used to evaluate the negative ion number density employing the electron energy distribution function (EEDF) using the recorded $I - V$ characteristic curves. The electron temperature was found to be dependent on pressure at the lowest discharge power, while it seems to be almost independent of discharge pressure at discharge powers higher than 10 000 mW. The negative ion number density was found to increase linearly as a function of discharge power within the $10^{13}\text{m}^{\mathrm {-3}}$ scale and also increase as a function of pressure. The electro-negativity of N2O was found to be about 0.03 at the lowest pressure and the lowest discharge power. [ABSTRACT FROM AUTHOR]

High density of electron trapping in high- \kappa intergate dielectric (IGD) materials remains a major concern for planar memory cells with either poly-Si or hybrid floating gates (FGs). In this paper, for the first time, using the ultrafast I{-}V measurements, it is demonstrated that a significant portion of the P/E windows are actually contributed by electrons trapped initially in the high- \kappa$ IGD stacks during program/erase, and then discharged to FG or control gate during verification. More importantly, it is demonstrated, for the first time, that this fast charge transition can be suppressed using novel multilayer high- $\kappa$ IGD structures, and the fast window instability can be eliminated. [ABSTRACT FROM PUBLISHER]

Prediction of electron density is crucial to numerically evaluate the attenuation of electromagnetic waves in plasmas and to optimize the parameters. In this paper, a simple collisional-radiative model (CRM) to determine the electron density of Ar dielectric barrier discharge (DBD) plasmas for pressures ranging from 0.2 to 1 atm is introduced, and then, the attenuation of electromagnetic waves is analyzed. First, the radial average electron density of Ar DBD plasma is estimated by combining the measured current and a 1-D self-consist fluid numeric model. Second, based on a simple CRM, an optical emission spectroscopy method is used to determine the radial electron density distribution. Finally, according to the radial electron density distribution, the attenuation of electromagnetic waves is calculated at a frequency range from 10 MHz to 10 GHz. The result indicates that the electromagnetic waves with a relatively low frequency can be effectively attenuated by the plasma and the edge distribution of the plasma clearly affects the attenuation. [ABSTRACT FROM PUBLISHER]

In this paper, we describe ac and dc quantum Hall effect measurements at temperatures above 1.5 K, which is beyond the commonly used value for high precision measurements of the quantum Hall resistance (QHR). It is shown that GaAs devices with high electron density of about $5\times 10^{11}$ cm2 can be used as reliable dc resistance quantum standards with quantization of $R_{\mathrm {H}}$ (2) value with accuracy within a few parts in 109 even at temperatures up to 4.2 K. The devices have exhibited well-developed quantum Hall plateaus in the ac regime too, again at temperatures up to 4.2 K. The measurement system consists of a self-made cryogenic probe with TO-8 type socket together with coaxial wiring and a digitally assisted bridge suitable for ac quantum Hall effect measurements. The experiments were performed with devices placed in new double-shielded TO-8 holders. Our investigations and the evaluation of the measurement system are dedicated for the future realization of the quantum impedance standard based on ac QHR. [ABSTRACT FROM AUTHOR]

The electron density and electron temperature of the recombining argon plasma from a cascaded arc discharge source were measured by the laser Thomson scattering approach. In this paper, a small amount of nitrogen gas was introduced into the argon discharge source. The addition of the nitrogen gas was applied to investigate the change of the plasma parameters in terms of electron density and temperature. The measurements showed that the electron density dropped by 2 orders of magnitude at 10% nitrogen gas addition compared with no nitrogen addition. The dissociative recombination following the charge transfer between atomic ions and nitrogen molecules was responsible for the decrease of electron density. In addition, with the increase of nitrogen gas addition, the measurements indicated that the electron temperature first increased to a maximum and then decreased. This was due to that the superelastic collision between the electrons and the highly excited vibrational nitrogen molecules could heat the electrons leading to the increase of electron temperature while the electron-vibrational energy transfer by electron–nitrogen molecules impact excitation resulted in that electron temperature decreased due to electrons’ kinetic energy losing processes. [ABSTRACT FROM AUTHOR]

In this paper, we have employed the transfer-matrix method to study theoretically the light waves propagation in extrinsic magnetized plasma multilayer, which is composed of a bulk plasma system influenced by the presence of spatially varying external magnetic field, which leads to a photonic bandgap device. The multilayered structures are arranged in periodic, quasiperiodic (Fibonacci, Octonacci, Thue–Morse, and double period), and Gaussian random fashions. The numerical results show the emergence of two main photonic bandgaps: the first gap for low frequencies and the second one for higher frequencies. We investigate the robust nature of the higher frequencies bandgap since it shows up to be invariant to different values of applied external magnetic fields and electron density as well as changes in the position and thickness of the layers introduced by the quasiperiodic and the Gaussian random sequences, respectively. The most surprising result is that this desired robust bandgap is broadening without any intermediate resonant peaks while the randomness in the layer thickness is introduced, which had not been observed in previous works about this same system. [ABSTRACT FROM AUTHOR]

When vehicle travels sufficiently quickly, a plasma sheath forms around the vehicle. The plasma sheath strongly affects signal detection by a receiver on the vehicle. This paper mainly investigates the effect of the plasma sheath on the detection of the single-frequency pulse signal. Using an analytical technique referred to the wave impedance calculation method, the transmission coefficient is obtained. The detection probability of transmission signal which is received by a narrowband receiver is then derived. Effects of the incident angle, signal frequency, and parameters of the plasma sheath including electron density and collision frequency on the detection probability are analyzed. Numerical results indicate that the detection probability decreases with increasing electron density and incident angle, while the detection probability first decreases and then increases with increasing collision frequency. Moreover, for high collision frequency, an interesting phenomenon that the detection probability is higher at lower signal frequency than at higher signal frequency occurs in the low-frequency signal range. This is because there is a turning point in the transmission coefficient as well as amplitude attenuation in the low-frequency range. [ABSTRACT FROM AUTHOR]

In this paper, the spatially resolved spectrum of the nitrogen second positive system ($\text{C}^{3}\Pi _{\mathrm {u}} \to \text {B}^{3}\Pi _{\mathrm {g}}$) has been measured in a nanosecond pulsed streamer corona N2 discharge with a wire-plate electrode structure. The spatial distributions of emission intensity of N2 ($\text{C}^{3}\Pi _{\mathrm {u}} \to \text {B}^{3}\Pi _{\mathrm {g}}$ , 0–0) at different pulse peak voltages, pulse repetition rates, and gas components are used to explore the distribution and variation of the high electron density (higher than 11.03 eV) with the reaction radiation rate analysis. It is found that the high electron density increases with increasing both the peak voltage and pulsed repetition rate but decreases with increasing the oxygen contents. The spatial distribution of the emission intensity of N2 ($\text{C}^{3}\Pi _{\mathrm {u}} \to \text {B}^{3}\Pi _{\mathrm {g}}$ , 0–0) is normalized to the value of the emission intensity at the wire electrode at different experimental conditions. The results show that the normalized distribution of the spatially resolved spectral intensity of N2 ($\text{C}^{3}\Pi _{\mathrm {u}} \to \text {B}^{3}\Pi _{\mathrm {g}}$ , 0–0) is independent of pulsed peak voltage, pulsed repetition rate, and gas component, which indicate that the normalized distributions of the high-energy electron density in the gap space at different experimental conditions are similar. These experimental results are significant to understand the discharge characters of pulsed streamer corona discharge and establish the molecule reaction dynamics model of pulsed streamer corona discharge. [ABSTRACT FROM AUTHOR]

The high-frequency hybrid sky-surface wave radar (HF HSSWR) has recently been used to monitor large-area sea states. However, most of the HF HSSWR detection methods are based on the assumption of a no-tilt and constant height ionospheric model, and the influences caused by uneven electron density are ignored. This paper proposes a new surface current inversion scheme for the HF distributed HSSWR system, which considers the unknown ionospheric state as a black box and extracts the key parameters to compute the surface current based on a scattering model. The computational formula of the component of the current vector is explored using spatial scattering theory instead of an approximate bistatic model. In addition, the Fourier series expansion method is applied to the HF data to extract the real first-order Bragg frequency. Subsequently, the grazing angle and the bistatic angle can be found by inversion using the first-order Bragg frequency formula after searching out the common scattering patch of two receiving stations. Simultaneously, the coordinate registration of the currents can also be determined. The feasibility and effectiveness of this new algorithm are verified with field experimental results by comparing the current vectors derived from HSSWR and traditional HF SWR. The RMS differences of the magnitude and direction of the current vectors within the core common area of the two detection systems are about 10.2 cm/s and 9.5°, respectively. [ABSTRACT FROM AUTHOR]

In this paper, an equivalent circuit model for a frequency-selective surface (FSS) embedded in a thick plasma layer is introduced. The plasma layer is a lossy and dispersive medium, and therefore, the equivalent model is not purely imaginary and consists of resistive elements as well as inductance and capacitance elements. First, a square patch FSS is simulated in a wide frequency range from 1 to 25 GHz by a full-wave electromagnetic software, and then all the circuit elements are calculated by genetic algorithm optimization to achieve reflection coefficient similar to the one obtained by simulation. It is shown that this model can mimic the simulated behavior with good approximation. Then values of different elements of the model through practical variations of cold plasma parameters are plotted, and the effects of electron density and collision frequency are investigated on circuit elements. [ABSTRACT FROM PUBLISHER]

To overcome some drawbacks of the plasma stealth technology in real-life application, a practical multilayer stealth structure composed of enclosed plasma slab and radar absorbing material (RAM) is presented in this paper. Based on a technique referred to as the transmission line analogy method, reflection coefficients of the perpendicularly polarized wave, the parallel polarized wave, and the circularly polarized wave obliquely incident upon this multilayer structure are determined, respectively. The effects of the incident angle, kinds of RAMs, and parameters of the plasma slab including electron density, collision frequency, and thickness on the stealthy effectiveness of this composite stealth structure have been studied systematically. The numerical results indicate that by a proper design, the power of reflected wave is significantly reduced over a wide frequency bandwidth, which provides some useful references to the plasma stealth technology applied to aircrafts, ships, and missiles. [ABSTRACT FROM PUBLISHER]

Mott materials have been investigated since late 1950s for their remarkably abrupt insulator to metal transition (IMT) in response to changes in temperature, strain, or electrical stimulus. Interest in these materials has been revived by recent demonstration of nanosecond-scale switching along with reproducible and fully reversible transitions in VO2-based thin film devices. These phenomena make VO2-based Mott insulator devices technologically relevant for various applications, such as memory selectors, logic switches, and building blocks for neuromorphic computing. Several groups have provisionally attributed the IMT switching to Joule heating. However, an electrothermal device simulation framework that self-consistently reproduces IMT phase transition, and in addition, explaining a variety of electrical/optical phenomena associated with IMT is still lacking. In this paper, we develop a self-consistent electrothermal device simulation framework which captures these key experimental attributes of IMT using VO2 as a model material. This framework will enable predictive modeling as well as provide insight on switching mechanisms and design of novel Mott insulator devices. [ABSTRACT FROM AUTHOR]

This paper highlights the output current saturation in a line tunneling-based tunnel FET (LT-TFET). Thereafter, a novel method to extract the onset of saturation voltage ( V\textsf {DSAT} ) for LT-TFET is proposed for the first time. A soft saturation state is attained when the electron density in the epitaxial layer over the source region saturates with the drain bias ( V\textsf {DS} ) and the conduction band energy ( E\textsf {C} ) gets pinned. In addition, at the onset of deep saturation, the electron density in the epitaxial layer over the channel region drops below its doping level and E\textsf {C} becomes invariant for any further increase in V\textsf {DS} . The difference between gate–drain bias ( V\textsf {GD} ) is found to be a constant at the onset of saturation and remains independent of the gate–source overlap lengths ( L\textsf {OV} ). A shift in V\textsf {DSAT} and V\textsf {GD} is also observed with change in the thickness and doping of the epitaxial layer. The transconductance and output resistance are reasonably good in the soft saturation regime. Furthermore, a nominal change of ~5% in the voltage gain ( A\textsf {V} ) of a common source amplifier is observed when the n-device is biased in the either soft or deep saturation regime, without any tradeoff in the bandwidth. [ABSTRACT FROM PUBLISHER]

A multi-branch pre-breakdown streamer model for natural ester-based nanofluid is established in this paper to study the influence of electrons density fluctuation on the streamer branching and propagation during the pulsed discharge. The mechanism of electron density fluctuation on the streamer branching and propagation characteristics is further studied using the finite element software. Results show that the initial streamer branched more likely near the needle tip in the nanofluids than that in the pure oils, and the branching of the initial streamers in nanofluid significantly inhibit the streamer propagation. The fluctuation of carrier density and the low charge density regions caused by adsorption of electrons with nanoparticles near the needle tip are the leading causes for the initial streamer branching in the nanofluid. The repulsion of the charge with the same polarity between the streamer branches can change the propagation pattern of the streamer, resulting in the inhibition of the streamer propagation. Results provide a novel strategy for the inhibition of streamer propagation by electron density fluctuations-induced branched initial streamer in nanofluids. [ABSTRACT FROM AUTHOR]

A new plasma-based widely tunable power limiter is introduced and experimentally investigated in this paper. The proposed limiter is composed of a high- $Q$ evanescent-mode cavity resonator loaded with a gas discharge tube in its gap area over the post. Increasing input power results in enhancing electric field over the gap, which eventually leads to microwave gas breakdown and plasma formation. The limiter loss after the breakdown depends on the electron density in the tube, which itself is a function of input power. Hence, the limiting mechanism is self-sustained. The threshold power is tunable either coarsely by selecting different tubes with various breakdown voltages or finely by dc biasing the tube. In a fabricated proof-of-concept limiter at 2.16 GHz with 22% bandwidth, preionization by an external dc bias provided 15.5 dB of limiting power tunability in the range of 370 mW–13 W, while the limiter could easily handle up to 100-W input power. The response time of this limiter is <10 ns. Thanks to the nature of capacitively coupled microwave gas discharge in the $ \alpha $ -discharge regime, the limiter performance is quite stable and no degradation was observed after a long operation under high input power. [ABSTRACT FROM PUBLISHER]

In this paper, we demonstrate an atmospheric-pressure nonequilibrium Ar microplasma array confined inside photonic crystal fiber for the first time. The diameter and the length of each microplasma plume are 3.4~\mu \textm and 2 cm, respectively. The electron density evaluated from the Stark effect of Ar spectral line is up to 8 \times 10^16 cm ^-3 . The electron temperature calculated by the Ar collisional-radiative model is 0.85 eV, while the gas temperature obtained by fitting the N2 rotational spectrum is 500 K. [ABSTRACT FROM AUTHOR]

An experimental system, SYstem for Microwave PLasma Experiments (SYMPLE), is being developed in order to investigate the physics of linear and nonlinear interaction of a high-power microwave (HPM) with an overdense plasma (plasma frequency fp \,\, > microwave frequency f\mu ) . The physics of interaction has implications in inertial fusion. The developmental task is taken up in two phases: Phase-1 using moderate microwave power ( $\sim 3$ MW), satisfying the condition \scriptstyle\raise2pt\\scriptscriptstyle1$}\mkern-4mu/\mkern-2mu{\scriptscriptstyle 2}}}\varepsilon _{\textrm {o}}\textrm {E}_{\mu }^{2}/\textrm {n}_{\textrm {e}}\, \textrm {kT}_{\textrm {e}} \sim 1 and Phase-2 involving HPM sources of much higher power. Here, E\mu is the microwave electric field, ne the plasma electron density, Te the electron temperature, m the electron mass, \varepsilon _{o} is the free space permittivity, and k is the Boltzmann constant. The Phase-1 system consists of a pulsed ( 5~\mu \texts ), S -band magnetron (3 MW, 3 GHz) coupled to a pulsed ( 100~\mu \texts ) washer-gun plasma ( ne \sim 1\times 10^{18}/\text{m}^{3}) . The tasks associated with interfacing of the magnetron and plasma have involved the indigenous design and development of different subsystems, each satisfying the specific technical requisites of the Phase-1 system. These subsystems include a washer-gun plasma ( ne \sim 1\times 10^{18}/\text{m}^{3}) driven by a pulse forming network, a line-type modulator (52-KV 120-A, 5- \mu \texts pulsewidth, $\sim 450$ -ns rise time) that drives the $S$ -band magnetron, an HPM–plasma coupling system, and an HPM TE10 – TM01 mode converter. The developmental aspects of the subsystems form the subject of this paper. [ABSTRACT FROM AUTHOR]

The Global Navigation Satellite System Occultation Sounder (GNOS) has been planned for the five Feng-Yun 3 series (FY3) weather satellites since 2013, the first of which, the FY3C satellite, was launched successfully at 03:07 UTC on September 23, 2013 from the Taiyuan Satellite Base, Shanxi province, China, into the orbit of 836-km altitude and 98.75° inclination. In addition to the Global Positioning System (GPS), the FY3C/GNOS is capable of tracking the occultation signal of the BeiDou Navigation Satellite System (BDS) (also called COMPASS) from space for the first time. The quality of BDS radio occultation (RO) has been verified in terms of signal-to-noise ratio. In this paper, the electron density profiles (EDPs) observed by FY3C/GNOS from both GPS RO and BDS RO, which were processed and archived in the National Satellite Meteorological Center of China Meteorological Administration, are compared with 32 globally distributed ionosonde observations, and then, we compare GPS RO EDPs with ionosonde observations at Mohe (52.0° N, 122.5° E), Beijing (40.3° N, 116.2° E), Wuhan (31.0° N, 114.5° E), and Sanya (18.3° N, 109.6° E). FY3C/GNOS EDPs show good agreement with ionosonde measurements, with larger discrepancies near the equatorial ionization anomaly region at Wuhan and Sanya. The ionospheric peak density (NmF2) and peak height (hmF2) derived from FY3C/GNOS EDPs are also compared with those obtained from the globally distributed ionosondes for the day of year 274–365 in 2013. In general, NmF2 and hmF2 have a higher correlation coefficient in the middle–high latitude than in the lower latitude region, due to the difference of ionospheric horizontal inhomogeneity. We also compared the NmF2 and hmF2 maps between FY3C/GNOS and the International Reference Ionosphere 2012 (IRI-2012) model. However, the wavenumber-4 structure, which can be indicated clearly from FY3C/GNOS observations, could not be reproduced well by IRI-2012. Further investigations show that the nighttime EDPs have obvious ionization enhancement around the ionospheric E layer over the Aurora and the South Atlantic Anomaly regions due to the energetic particle precipitation indicated by the Space Environment Monitor observations onboard FY3C. [ABSTRACT FROM AUTHOR]

A nonlinear transient time domain model is presented to reveal some detailed interplay processes between laser and its self-generated plasma in water. The laser-induced breakdown threshold and the plasma absorption coefficient calculated by this model are consistent with the experimental results quantitatively. Moreover, the distribution of free electron density, optical field, and energy losses of laser in the focusing area during whole laser pulse is predicted by the proposed model. Numerical calculation outlines that for the interaction between femtosecond laser and water, there exists a splitted Gaussian pulse along with the conical plasma. On the other hand, the plasma generated by picosecond or longer laser pulse can move in the opposite direction to laser beam propagation, and the velocity of this inverse movement linearly depends on the electric field intensity. Furthermore, the avalanche ionization is also significant for femtosecond laser interaction with water. In addition, the expansion properties of the plasma and the coupled optical field are discussed. The model proposed in this paper could be helpful to laser ophthalmological operation and laser-induced breakdown spectroscopy. [ABSTRACT FROM AUTHOR]

Objective: Dual-energy CT (DECT) strengthens the material characterization and quantification due to its capability of material discrimination. The image-domain multi-material decomposition (MMD) via matrix inversion suffers from serious degradation of the signal-to-noise ratios (SNRs) of the decomposed images, and thus the clinical application of DECT is limited. In this paper, we propose a noise suppression algorithm based on the noise propagation for image-domain MMD. Methods: The noise in the decomposed images only distributes in two perpendicular directions and is suppressed by estimating the center of mass of the same-material pixel group vertically along the principal axis where the noise disturbance is minimal. The proposed method is evaluated using the line-pair and contrast-rod slices of the Catphan©600 phantom and one patient data set. We compared the proposed method with the direct inversion and the block-matching and three-dimensional (BM3D) filtration methods. Results: The results of Catphan©600 phantom and the patient show that the proposed method successfully suppresses the noise of the basis material images by one order of magnitude and preserves the spatial resolution of the decomposed images. Compared with the BM3D filtration method, the proposed method maintains the texture distribution of the decomposed images at the same SNR and the accuracy of the electron density measurement. Conclusion: The algorithm achieves effective noise suppression compared with the BM3D filtration while maintaining the spatial distribution of the decomposed material images. It is, thus, attractive for advanced clinical applications using DECT. [ABSTRACT FROM AUTHOR]

In this paper, we present the CubeSat version of a scientific instrument called the multi-Needle Langmuir Probe (m-NLP). The m-NLP instrument measures the electron density in the ionosphere with kHz sampling rate, yielding meter scale resolution on low Earth orbit satellites. The sounding rocket version of m-NLP has flight heritage from nine sounding rockets. However, to get an in-orbit demonstration of the system a CubeSat implementation has been developed. The m-NLP measurement principle is based on several fixed bias probes, where each probe has to be biased above the spacecraft potential. To ensure that this requirement is fulfilled, the CubeSat version of the m-NLP will feature a new miniaturized thermionic electron emitter, which can actively control the potential of the satellite. The emitter is designed to accommodate the low size, weight, and power challenges of the CubeSat platform. Together with the in-flight determination of the spacecraft floating potential, it can autonomously control the potential of the spacecraft by emitting electrons. Preliminary, test results from the plasma chamber at the European Space and Technology Center in Holland are shown, verifying that a miniaturized electron emitter is able to actively control the floating potential of the spacecraft and, hence, improve the accuracy of the electron density measurements. [ABSTRACT FROM AUTHOR]

In this paper, we report measurements in Colorado and Utah of the disturbed very-low-frequency (VLF) signals from the NML Navy transmitter in North Dakota during the 2017 solar eclipse. Using an occultation mask of solar fluxes together with detailed chemistry and VLF propagation simulations, we quantify the D-region response to the eclipse, in terms of electron density variation, as well as the expected signatures of VLF transmitter signals. The VLF measurements, including an anomalous amplitude enhancement recorded in UT, can be quantitatively explained using the Wait and Spies ionospheric profile with a sharpness parameter of $\beta = 0.3$ km−1 above ~55 km and an increase in the D-region ionosphere height of $\Delta h' \simeq 8$ km. This sharpness parameter is consistent with previously reported rocket measurements and first-principles calculations. The best-fit results suggest a reduction of D-region electron density by ~90% during the eclipse in the D-region, implying an occultation of Lyman- $\alpha $ by nearly 99%. This finding agrees with detailed calculations of time-dependent obscuration factors utilizing the He 30.4-nm images from Solar Dynamics Observatory as a proxy for the distribution of Lyman- $\alpha $ across the solar disk and limb. Moreover, the present results show that subionospheric VLF propagation is sensitive to the sharpness parameter of the electron density profile in the D-region. Previously reported first-principles simulations have shown that the sharpness parameter is mostly controlled by the background concentration of minor neutral species. Thus, the VLF technique can be likely used to remotely sense these neutral species at and below the effective reflection altitudes of VLF waves. [ABSTRACT FROM AUTHOR]

As a microwave plasma excitation structure, the tapered waveguide is mostly used in some industrial applications. A novel ridged waveguide is proposed in this paper. The fluid approximation method is applied here to simulate the excitation of argon plasma within 1 s at atmospheric pressure. Some physical parameters, such as the electron density, electron temperature, gas temperature, and scattering parameter S11 , are obtained. When the input power is set to 1500 W, and the steady state is achieved, the electron density reaches 3.05\times 10^20~\textm^-3 , the electron temperature gets to 282 15 K, and the gas temperature is 5590 K. Remarkably, at the same power, the energy coupling efficiency from microwave to plasma is 17.3% higher than that in the tapered waveguide, and the electron density and gas temperature also increase by 4.5\times 10^19~\textm^-3 and 346 K, respectively. [ABSTRACT FROM PUBLISHER]

This paper investigates the dynamic effects of the reentry plasma sheath on electromagnetic wave propagation from the viewpoint of communication. Both the spatial turbulence and the temporal variation of the plasma electron density are included in our model, and the transmission matrix method is employed to investigate the interactions between the plasma and the electromagnetic wave. The simulation results indicated that because of the nonlinear property of plasma, the amplitude variation caused by the plasma sheath has a lognormal distribution, while the phase fluctuation is Rayleigh distributed. Moreover, with a higher relative variation intensity, the probability density function curves become more decentralized, indicating larger channel dynamics of both amplitude variation and phase fluctuation. The power spectrum broadening phenomena caused by the plasma sheath are also investigated and discussed. [ABSTRACT FROM AUTHOR]

The desire for continuously gaining new knowledge in fusion reactor technology has pushed the frontier of engineering methods to deliver highly stable ion source for 14-MeV neutron generators. The diagnostic of the ion source of 14-MeV neutron generator is one of the prime concerns for future fusion reactor technology. An accelerator-based 14-MeV neutron generator is developed at Fusion Neutronics Laboratory of Institute for Plasma Research, Gandhinagar, India. The ion source of this 14-MeV neutron generator is diagnosed via the optical emission spectroscopy technique. In order to achieve optimum electron temperature and electron density for stable operation of ion source, the controlling parameters, namely, deuterium ambient gas pressure, ambient gas flow rate, and microwave power coupled to the deuterium plasma, are varied systematically. An investigation on the effect of microwave power coupled with deuterium plasma on the overall electron temperature as well as electron density is investigated in this paper. Prominent Balmer emission lines of deuterium \alpha , \beta , and \gamma ( , \text{D}_{\beta } , and \text{D}_{\gamma })$ are observed in the deuterium plasma generated by electron cyclotron resonance. The overall electron temperature of deuterium plasma is measured by Boltzmann plot at various microwave power, 100–400 W, whereas the electron density is measured by Stark broadening. [ABSTRACT FROM PUBLISHER]

Synthesizing the compressible turbulent flow theory and plasma electromagnetic (EM) theory together, a novel method connecting pressure variation and relative permittivity of re-entry plasma sheath is developed. Using this method and transmission line analogy, effects of pressure variation on polarization properties of obliquely incident EM waves at GPS frequency and Ka frequency is studied. Numerical results indicate that effects in different conditions are various. When electron density is lower than 10^18~\textm^\mathrm -3 , influences of pressure variation are obvious at GPS frequency, while Ka frequency is feeble. For GPS frequency, effects enlarge with the increase in incident angle, but reduce with the increase in collision frequency and electron density. Ka frequency has more advantages on mitigating the disturbances of pressure variations in this situation. While in the opposite situation, influences are more remarkable at Ka frequency. Considering that GPS wave rapidly attenuates in the sheath when electron density is higher than 10^18~\textm^\mathrm -3 and Ka wave does not, Ka frequency is an effective way to mitigate the blackout during the re-entry process after its shortcomings on polarization alteration have been carefully considered. [ABSTRACT FROM PUBLISHER]

A novel multifrequency method is introduced in this paper for measuring the plasma produced by a \Phi 800 -mm shock tube. The core of the measured object is a volume of relatively uniform plasma contained by the rectangular test section, and the dual-frequency or multifrequency configuration of the measuring system enables the coherent cancellation of measurement deviations. Based on the Lorentz model of plasma, the obvious correspondence exists between the plasma parameters and the transmittance variation with different frequencies of the electromagnetic wave; hence, the electron density N_{e} and the collision frequency \nu $ of the plasma could be retrieved according to the measured transmittance. A dual-frequency system is established as the verification of the proposed method. The measured values of the electron density by the proposed method are compared with those obtained by other means, and the results are in good agreement. [ABSTRACT FROM PUBLISHER]

The kinetic model simulating plasma chemistry induced by Transient Spark (TS) discharge in air is presented in this paper. TS is a dc-driven self-pulsing discharge of streamer-to-spark transition type. The presented kinetic model defines the temporal evolution of reduced electric field strength $E/N$ , gas temperature, and density of neutrals $N$ during the evolution of TS discharge, so that calculated electron density is in agreement with experimental results. We studied the mechanism of the streamer-to-spark transition and breakdown in TS using this model. We assume that the breakdown mechanism in TS is based on the gas density decrease and can be summarized as follows: heating of the channel $\rightarrow $ increase in the pressure $\rightarrow $ hydrodynamic expansion $\rightarrow $ decrease in $N$ in the core of the channel $\rightarrow $ increase in $E/N~\rightarrow $ acceleration of ionization processes. However, this mechanism is influenced by species accumulated due to previous TS pulses at higher TS repetition frequencies. Sensitivity analysis focused on major electron loss and production processes indicates an important role of the amount of O2 dissociated by the previous pulses. A lower density of O2 means a lower rate of electron attachment, while accumulated atomic oxygen atoms lead to acceleration of electron detachment processes. [ABSTRACT FROM PUBLISHER]

Semiconductor industry is experiencing a rising demand for environmentally friendly processes with the emphasis on green policies and worldwide environmental sustainability. Nitrogen trifluoride (NF3), the most common plasma chamber cleaning agent gas, poses a significant concern as a potent greenhouse gas since it has global warming potential (GWP), 740 times and 6 times higher than that CO2 and N2O. This study investigated the exhaust gas using quadrupole mass spectroscopy (QMS) and analyzed the change in cleaning speed and the type of exhaust gas through plasma monitoring using optical mass spectroscopy (OES). The objective is to lower the use of the amount of NF3 gas in chamber cleaning process to partially contribute the environmental sustainability in the point of semiconductor manufacturing. When a small amount of N2 was added to NF3 whose ratio of 7:23, the cleaning efficiency reached to 90% compared to NF3 gas alone. Addition of N2 positively affected electron density and temperature to increase the F-radical in remote plasma system. In conclusion, 18% of NF3 usage amount was reduced during the Sio2 deposition chamber cleaning process. [ABSTRACT FROM AUTHOR]

In this paper, the dynamic characteristics of type-I edge-localized modes (ELM) time series from the JET tokamak, the world’s largest magnetic confinement plasma physics experiment, have been investigated through recurrence plots (RPs). The analysis has been focused on RPs of pedestal temperature, line averaged electron density, and outer divertor $D_{ {\alpha }}$ time series during experiments with a carbon wall. The analysis of RPS shows the patterns similar to those characteristics of signals exhibiting type-2 intermittency, in particular, a characteristic kite-like shape; this gives useful hints to model the temperature signal as well as the $D_{ {\alpha }}$ radiation time series, with simple nonlinear maps capturing the nearly periodic behavior of type-I ELMs. [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]

A novel Abel inversion method has been employed to obtain the precise electron density profile from chordal interferometric measurements on J-TEXT tokamak, in which the Gauss–Legendre integration method and dynamic boundary are introduced. To demonstrate the feasibility of this novel method, a hypothetical function \(I({x})\) is established, which resulted in a valid local value. Numerical results under different conditions are presented in the paper. [ABSTRACT FROM PUBLISHER]

In this paper, a global ionospheric data assimilation model is constructed based on the empirical international-reference-ionosphere model and the Kalman filter. A sparse matrix method is used to militate the huge computation and storage problems. A series of observing system simulation experiments has been performed based on the existing global ground-based global navigation satellite system (GNSS) network, the planned Constellation Observing System for Meteorology, Ionosphere, and Climate #2/Formosa Satellite Mission #7 (COSMIC-2/FORMOSAT-7) orbits, and the real global position system and GLObal NAvigation Satellite System (GLONASS) orbits. Specifically, the COSMIC-2 will have six 24° inclination satellites in 500-km altitude and six 72° inclination satellites in 800-km altitude. The slant total electron content of ground-based GNSS, radio occultation and ocean reflection (OR) of 12 low-Earth-orbit satellites, and cross-link between COSMIC-2 low and high inclination satellites are simulated by the NeQuick model. The ORs show great impacts in specifying the ionosphere except over the inland area. It complements the existing ground-based GNSS network, which mainly observes the ionosphere over the land area. The 24° and 72° satellites can complement each other to optimize the global ionospheric specification. The COSMIC-2 mission is expected to contribute significantly to the accurate ionospheric nowcast. Its potential ability in ionospheric short-term forecast is also discussed. [ABSTRACT FROM PUBLISHER]

This paper reviews the recent activities for normally-off GaN-based gate injection transistors (GITs) on Si substrates and their application to inverters. Epitaxial growth of the AlGaN/GaN heterostructures with good crystallinity over 200-mm Si substrates with eliminated bowing enables low-cost fabrication of GaN devices with high breakdown voltages. A novel normally-off GaN transistor called as GIT is proposed in which hole injection from the p-type AlGaN gate increases the drain current with low on-state resistance by conductivity modulation. The low on-state resistance in GaN-based devices greatly helps to increase the efficiency of power switching systems. A GaN-based three-phase inverter successfully drives a motor with high efficiency of 99.3% at a high output power of 1500 W. The presented GaN-based devices are expected to greatly help saving energy in the future as an indispensable power switching system. [ABSTRACT FROM AUTHOR]

The deuterium plasma parameters of a miniature Penning discharge ion source have been measured by a single probe. Electron temperature and electron density can be acquired from the $I$ – $V$ curves. The results show that electron temperature increases and electron density decreases with the probe tip departing from the centre of plasma area. Meanwhile, both electron temperature and electron density increase with increase in discharge current. Electron temperature is about 1.8 ~ 7.1 eV and electron density is about $2.7 \times 10^{14} \sim 3.7 \times 10^{15}\,\,\text{m}^{-3}$ , when the distance between the probe tip and the centre of plasma area varies from 1 to 6 mm. Electron temperature is about 5.7 ~ 12.5 eV and electron density is about $6.7 \times 10^{14}\sim \,\,2.2 \times 10^{15}\,\,\text{m}^{-3}$ , when discharge current varies from 50 to 200 $\mu \text{A}$. The results can provide useful information for the design and operation of Penning ion sources. [ABSTRACT FROM AUTHOR]

During reentry, plasma sheath is affected by many flight factors, such as trajectory, velocity, angle of attack, and fluid turbulence. As a result, the plasma parameters are time-varied and nonstationary. The nonstationary effects of reentry plasma sheath on electromagnetic (EM) wave propagation are investigated in this paper. First, the factors that affect the plasma sheath are analyzed, and the plasma sheath variation is divided into three scales. A multiscale reentry plasma sheath electron density model is established. A compatible modeling method is proposed, and this method is proven effective. Finally, we analyze the effects of plasma sheath on EM wave at 1.57542, 2.2, and 5 GHz, which are generally used in GPS and telemetry, tracking, and command systems. Results show that the statistical parameters of complex transmission coefficients are time-varied and nonstationary. [ABSTRACT FROM PUBLISHER]