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

Partial discharge (PD) is a phenomenon often occurring in insulation system defects (cavities), which can significantly affect life and reliability. While broad knowledge on PD phenomenology of high-frequency transformers (HFT) has been achieved under ac sinusoidal voltage, much less work has been done to infer PD behavior under emerging high frequency pulsewidth modulation (PWM) operation conditions. An impediment has been the limited appropriate test equipment. A recently developed novel ±5 kV GaN-based high-frequency PWM supply with controllable dV/dt, voltage level and frequency has been developed. This article explores the application of these measurements to the testing of materials in this electrical environment. Two commonly used windings for HFT were tested under different applied voltage magnitudes, frequencies, and slew rates. According to the test results, at high frequency (up to 50 kHz) the electric field generated by space charge deposited by PD occurring during previous PWM pulses plays an important role in PD behavior. The frequency dependent permittivity of the insulation material can also affect PD measurement results. [ABSTRACT FROM AUTHOR]

Based on the plasma modified model and photoionization optimization model, this article constructs a low temperature and subatmospheric pressure air streamer discharge model. Through the model, the characteristics of streamer discharge under high-frequency square wave voltage are studied. Streamer discharge exhibits a different discharge pattern from dc voltage in the voltage drop stage and low-level stage. In addition, duty cycle and rise (fall) time have different effects on parameters, such as electron density, positive ion density, electric field, space charge density, photoionization rate, and streamer propagation velocity. [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]

In recent years, pulse-modulated radio frequency (RF) plasmas have gained considerable interest in applications due to the advantages in reducing gas temperature and power consumption. In this article, the optimizations of operation mode in atmospheric pulse modulation RF discharges are investigated by a 1-D fluid model. From simulation data, the breakdown voltage and ${{\alpha -{\gamma }}}$ mode transition voltage both decrease as the duty cycle increases; however, a minimum breakdown voltage can be observed while altering the modulation frequency at a constant duty cycle, and the transition voltage always increases with the modulation frequency. The underpinning physics of the operation regime in pulsed RF discharges is discussed in detail by investigating the effects of the duration of the power-on phase based on the computational results. Increasing the number of applied RF cycles during the power-on phase contributes greatly to the breakdown and mode transition. This study can effectively deepen the understanding of the effects of pulse modulation in RF discharges and suggest ways to further optimize the pulse-modulated RF discharges. [ABSTRACT FROM AUTHOR]

Achieving a sustainable dense plasma source has always been of broad interest. Notably, in microwave discharges, gaining dense uniform plasma has held numerous efforts. In this article, a high-efficiency dual-helical antenna for microwave plasma source to improve the performance of the Alborz Tokamak neutral beam injection (NBI) system is presented. For evaluation and analysis of the designed antenna and a conventional rod antenna, COMSOL Multiphysics software is used. Besides, by feeding the antenna using a 2.45-GHz magnetron in the 20-Pa vacuum steel enclosure and the Argon gas injection, a practical experiment has been conducted. Finally, the plasma with a density of $5.5\times 10^{17}\,\,1/\text{m}^{3}$ and the electric field intensity results show that the designed antenna is an optimal alternative in microwave plasma sources. [ABSTRACT FROM AUTHOR]

Presently, an atmospheric-pressure non-equilibrium microwave discharge plasma jet is expected to be applicable in the sterilization and disinfection equipment for dental implants. However, since the atmospheric-pressure plasma is in non-equilibrium state, there have been no simplified means established to measure basic properties of the plasma. We successfully developed a radical sensor, a simplified tool for detecting oxygen radicals released from plasma by using polyester fiber as base material, and methylene blue as dye. When this sensor detects an oxygen radical, the color of the radical sensor changes from blue, the original color, to white. In this report, we are going to explain the results of the experiments in the fabrication process to verify the behavior of this radical sensor. We combined polyester fiber, the base material of the radical sensor, and methylene blue, the dye, to prototype the radical sensor and used it in our experiments. The radical sensor features the mechanism in which the color changes from blue to white when plasma-irradiated. We used the angle meter to measure the hydrophilicity level and verified the etching effects of the oxygen radicals on the base material in order to clarify this discoloration mechanism. From this result, we found out that the hydrophilicity varied greatly as the flow rate of the oxygen gas used as plasma gas changed and that the color-changing mechanism was due to the adsorption effect of the oxygen radicals. We also used X-ray photoelectron spectroscopy (XPS) to analyze the components to further understand the adsorption effect of the oxygen radicals and clarified that the oxygen radicals accounted for the color-changing mechanism of the radical sensor. [ABSTRACT FROM AUTHOR]

High power radio frequency (RF) breakdown testing is a subject of great relevance in the space industry, due to the increasing need of higher transmission power and smaller devices. This work presents a novel RF breakdown detection system, which monitors the same parameters as the microwave nulling system but with several advantages. Where microwave nulling—a de facto standard in RF breakdown testing—is narrowband and requires continuous tuning to keep its sensitivity, the proposed technique is broadband and maintains its performance for any RF signal. On top of that, defining the detection threshold is cumbersome due to the lack of an international standardized criterion. Small responses may appear in the detection system during the test and, sometimes, it is not possible to determine if these are an actual RF breakdown or random noise. This new detection system uses a larger analysis bandwidth, thus reducing the cases in which a small response is difficult to be classified. The proposed detection method represents a major step forward in high power testing as it runs without human intervention, warning the operator or decreasing the RF power automatically much faster than any human operator. [ABSTRACT FROM AUTHOR]

Plasma density in a magnetized, capacitive-coupled, radio frequency (RF) discharge has been determined using the electrical impedance characteristics of the discharge. The effective impedance between the parallel plate electrodes has been treated as an equivalent electric circuit consisting of resistive and reactive components, expressed in terms of high-frequency plasma conductivity. Hence the model is used to connect the externally measured RF voltage, current, and their relative phase to plasma density. Additionally, a triple Langmuir probe (TLP) is used to substantiate the results of the electrical impedance model. The plasma density obtained using the direct probe measurement is found to be in good agreement with those determined from the passive measurements based on electrical impedance of the discharge as outlined in this article. [ABSTRACT FROM AUTHOR]

A circuit modeling approach for self-sustained capacitively coupled microwave plasmas is introduced and validated in this article. The model solves the particle balance equation using a novel circuit optimization scheme to calculate the plasma parameters like electron density, sheath thickness, and electron temperature for a given input power, operating frequency, gas type, and pressure. While the existing models capture the ohmic loss in the bulk plasma region, the proposed model also takes into account power required to sustain plasma which proves to be considerable for higher electron densities. The model is rigorously validated using experimental results from two cases—one resonant and one non-resonant—both with self-sustained microwave plasma. As the post-processing results, other discharge parameters like sheath and plasma voltages as well as plasma reduced field are calculated. The proposed modeling approach can substantially simplify design and analysis of capacitively coupled microwave plasmas. [ABSTRACT FROM AUTHOR]

Air breakdown in sub- and supersonic flows induced by the subcritical streamer discharge and the effect of the initiator shape on breakdown conditions are studied. Experiments with varying the electric field strength and air pressure show that the ability of electromagnetic vibrators to initiate air breakdown has a resonant character. Placing a small electromagnetic vibrator in a microwave beam allows one to initiate air breakdown with a field strength in the microwave beam which is significantly smaller than the critical breakdown strength. The dependencies of the critical intensity of the electric field on the pressure and location of the initiator are reported. The dependence of the field amplification coefficient at the vibrator edge on the screen dimensions is presented at different lengths and widths of the screen. [ABSTRACT FROM AUTHOR]

Turkish Accelerator Center (TAC) Proton Accelerator Facility (PAF) is a project proposal that aims to build a megawatt (MW) power proton accelerator in Turkey. The proton source of this project was chosen as a microwave discharge ion source due to its long life time, its high current, and its lower maintenance requirements when compared with other ion source types. A microwave discharge ion source test stand was built to gain experience for TAC PAF and for similar projects requiring high beam current in Turkey. A magnetron with 2.45-GHz frequency, 50-Hz repetition rate, and 150-W fixed power was used to create the hydrogen plasma. Two different electrode systems were experimented: the first design consists of 2-mm radius plasma electrode that extracts beam currents up to 0.75 mA and the second design consists of 4-mm radius plasma electrode that extracts beam currents up to 5.2 mA. [ABSTRACT FROM AUTHOR]

The characteristics of dust coagulation process in gravitational direction are investigated in an ethylene RF (radio frequency) discharge plasma system. The experiment shows that dust particles can aggregate into the huge fractal structure (centimeter scale). The coagulation process is mainly characterized by the scattering laser intensity, the distribution of dust clouds, and the fractal dimension. In this experiment, the rotational characteristics of the huge fractal structure can be observed and investigated by the oscillation of the scattering spectrum. These results provide an experimental basis for the investigation of dust coagulations. [ABSTRACT FROM AUTHOR]

The impedance characteristics of radio frequency (RF) (13.56 and 27.12 MHz) and very high-frequency (60 MHz) magnetron discharges were investigated by the voltage–current probe technology. The discharge impedances $Z$ were found to decrease with the increase of discharge current at the frequency of 13.56 MHz, then change from a decreasing trend to an increasing trend at the frequency of 27.12 MHz, and further increase at the frequency of 60 MHz. This evolution was mainly related to the transition of the imaginary part $X$ from the capacitance to the reactance. Because of the low-electron density at the frequencies of 27.12 and 60 MHz and the enhanced electron Lorentz gyration at high voltages in the magnetron discharge, the electron inertia effect was enhanced. As a result, the plasma body reactance increased. The compensation of the plasma reactance to the sheath capacitance led to the transition of impedance $Z$. Therefore, for the 27.12- and 60-MHz magnetron discharges, the electron inertia had a significant influence on the discharge impedance. [ABSTRACT FROM AUTHOR]

Although plasmas commonly present as electrical neutrality, for plasma jet plume at atmospheric gas pressure, it might appear nonneutral polarity due to plasma bullet being consisted of a large amount of electron avalanches. In this paper, the polarity transition and the ionization enhancement of atmospheric argon plasma jet plumes generated by the repetitive microwave pulses are studied. Three interesting phenomena have been found despite of discharges either with or without the hairpin metal wire, including: 1) a potential voltage pulse with positive polarity invariably arises steeply at each moment of power on; 2) high-speed photograph images show that there are ionization enhancements happened twice in each pulsed periods; and 3) ahead of the confluence point, the polarity transits from negative to positive while behind of this point, its positive polarity changes into the negative one. Moreover, the experiment results and electromagnetic simulations suggest that the theories of guided negative ionization wave and microwave resonant discharge excited by surface plasma polaritons should be used to interpret the spatial–temporal discharge process of the proposed microwave plasma jets. [ABSTRACT FROM AUTHOR]

We found that steady-state paired-particle motion was often observed in a fine-particle cloud in the argon plasma produced by a 100-kHz high-frequency discharge. Monodispersed spherical silica particles with a diameter of $5.0~\mu \text{m}$ were trapped in the plasma. The 2-D motion of these charged particles was carefully recorded using a microscope camera, and their orbits and perturbation frequencies were analyzed. The loci and fast Fourier transform spectra of many paired particles were obtained. By moving the camera horizontally, 3-D images of the particles were recorded, and a 3-D map of the positions of charged particles was obtained. It is considered that the forces inducing the paired-particle motion were generated by the Debye shielding and the electric field surrounding the paired particles. [ABSTRACT FROM AUTHOR]

Analysis of the laminar flame propagation in the methane–air mixture seeded by sodium with microwave energy coupling to the flame front was presented. Calculation results showed that a flame suppression effect caused by sodium could be reduced by the microwave discharge, but an increase in the sodium concentration up to 0.5% leads to overheating of combustion products and flame extinguishment. Thermal effect of the microwave discharge influence on the laminar flame speed prevails, but additional slight increase in a flame speed is caused by the formation of excited oxygen species. [ABSTRACT FROM AUTHOR]

A subcritical microwave streamer discharge is used to initiate ignition of premixed air/fuel mixture. The streamer is arising on the internal surface of the dielectric tube using a passive vibrator in a single-pulse regime at atmospheric pressure and temperature. The propagation speed of the combustion front in the quartz cylindrical tube filled by the air/propane mixture is analyzed numerically. The performed studies showed that the streamer discharge, which creates a multitude of ignition points, provides practically instantaneous ignition of the mixture in the entire volume of the tube, where the streamers reach. The results of numerical simulation are compared with the experimental data. Increasing the length of streamer discharge leads to increasing the flame propagation speed. [ABSTRACT FROM AUTHOR]

This paper presents an optimal design approach for a dual-active-bridge series resonant converter (DABSRC) based on frequency domain analysis. The proposed design technique ensures efficient performance of DABSRC over a wide range of voltage gain and load variations. The operating principle of the converter is detailed to illustrate both zero voltage switching (ZVS) and zero current switching operations during bidirectional power transfer. Modeling the current-dependent power loss components as an equivalent series resistance, the converter is analyzed in frequency domain to derive amplitude and phase of the state variables accurately. Performing the power loss analysis in a normalized form, the characteristic equations for bidirectional power transfer, tank current, converter efficiency, and ZVS criteria are derived. Using these characteristics, the design of DABSRC is formulated as an efficiency optimization problem. Particle swarm optimization technique is adopted to determine the optimal tank parameters and transformer turns-ratio. Converter performance is evaluated on a 120-W lab-prototype, and peak efficiency of 95.2% and California energy commission efficiency of 92.1% are achieved. Close agreement among analytical predictions, numerical simulation, and experimental results validate the proposed design technique. [ABSTRACT FROM PUBLISHER]

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]

The design of a dual gas magnetron system for ion sputtering of two source materials with an activation of a reactive gas in the remote microwave (MW) discharge for the deposition of multinanolayered coatings is presented. The design of the reactive gas activator with the electron cyclotron resonance was realized on the basis of the analysis of possible schemes for the formation of MW gas discharge plasma systems. The vacuum electron magnetron is used as a MW generator (2.45 GHz and $\sim 800$ W). Geometry of the electrodynamic part of the activator was selected by means of simulation with Comsol Multiphysics. The practical examination of the dual sputtering system was carried out by sputtering of Ti and B4C targets, while nitrogen was used as the reactive gas. The characteristics of the multinanolayered Ti-B-C-N coatings were studied and it was determined that the deposited coatings had the nc-TiNx/(a-BN+a-C) structure. The Knoop hardness of the coatings was found to be $\sim 45$ GPa, while the nanohardness was lower than Knoop ones by $\sim 20$ %–30%. The presented sputtering system could be recommended for deposition of wear-resistant and protective coatings. [ABSTRACT FROM AUTHOR]

Microwave plasma was generated on top of the electrode by applying microwave radiation of 2.45 GHz in water. The light-emitting region and radicals formed by microwave discharge were investigated. The experimental results showed that the light-emitting region of microwave plasma in water increased with increasing microwave power, and conversely, decreased with increasing pressure; bubble around the plasma also became small when pressure was enhanced. OH radicals, H atoms, and O atoms were identified using optical emission spectroscopic analysis. The emission intensity of these radicals and atoms increased with increasing microwave power and decreased with increasing internal pressure of reactor vessel. Moreover, the electron excitation temperature of the plasma increased with electric power from 3300 to 4100 K and decreased with pressure from 4300 to 4100 K in comparison with the intensities of \textH\alpha and \textH\beta . [ABSTRACT FROM PUBLISHER]

Locating corona discharges is essential for the safe operation and the reliability of smart grid. This paper proposed a novel method for corona discharge location based on tunneling magnetoresistive (TMR) sensors. A dual-axial TMR sensor device was designed to measure the vector magnetic field. The sensor’s responses to the corona discharge magnetic field have been compared with the results of standard probes and proved to be practicable. The location algorithm based on the vector magnetic field measurement results of sensor array indicated a relative error of approximately 10%, which was reasonable for the practical application. This method fully utilizes the merits of the sensors and provides a promising solution for corona discharge location. [ABSTRACT FROM PUBLISHER]

The vertical shrinkage of the advanced CMOS processes thicknesses makes electrostatic discharge (ESD) issues become more significant. RF and millimeter-wave (mm-wave) circuits are very sensitive to the ESD components’ capacitive parasitic effect. Surface area is a key factor as well in an ESD protection circuit for mm-wave applications. This paper presents silicon-verified ESD solutions, which fulfill physical dimensions, ESD robustness, and broadband frequencies requirements. [ABSTRACT FROM PUBLISHER]

Partial discharge (PD) measurement is a widely extended technique for the diagnosis of electrical machines and power cables. Since PD and noise recognition is really important in industrial environments, the authors proposed the use of the spectral Power Ratios (PR) of the detected high-frequency (HF) signals, which show promising results. However, the frequency bands selected for their calculation have a clear influence on the position of the clusters in the classification maps. Following this research trend, a new algorithm for the automatic selection of the frequency bands which gives a proper separation between the clusters, has been proposed in part I of this paper. The first results presented in this paper revealed a good behavior of the technique for PD and noise separation in simple test objects. In this second part of the paper, more results from the application of this system to PD source recognition in simple test objects and also in real equipment are developed. [ABSTRACT FROM PUBLISHER]

Excitation of microwave discharges by pulsed microwave radiation (≤2 MW, 1.95 GHz, 1–10 \mu \texts ) on dielectric surfaces in vacuum ( 10^-6 torr) was studied experimentally. Different stages of a surface microwave discharge were observed: secondary-electron-emission microwave discharge (multipactor), surface microwave breakdown (filamentary microwave discharge), and plasma-flare microwave discharge. It is found that, in the stage of microwave breakdown (which lasts for \sim 0.1~\mu \texts ), ≥70% of the incident microwave power is absorbed by a dense plasma filament with a diameter of \sim 100~\mu \textm , an electron density of up to 2 \times 10^18 cm ^-3 , and an electron temperature of about 2 eV. Strong interaction of the dense plasma of the filamentary microwave discharge with the dielectric leads to local destruction of the dielectric surface in the form of a long thin erosion track ( $l \approx 6$ cm, d \sim 100~\mu \text{m} ). The coefficient of microwave power absorption by a plasma filament in a rectangular waveguide is calculated using an electrodynamic model that does not involve expansion in the waveguide modes and takes into account reflections of the scattered wave from the waveguide walls by introducing an array of filament mirror images. It is shown that the coefficient of microwave power absorption by the filamentary discharge plasma can reach 70% and more, which agrees well with the experimental data. [ABSTRACT FROM PUBLISHER]

To understand the essentiality of the electron energy distribution function in a low-pressure discharge plasma, an experimental study is carried out on the diagnostics of microwave discharge hydrogen plasma with its discharge pressure $\sim 1$ torr in a cylindrical quartz tube. The electron kinetic temperature and density are measured by a Langmuir double probe. Number densities of electronically excited states of hydrogen atoms are experimentally examined by an optical emission spectroscopic (OES) measurement of line intensities of the Balmer series. The rotational and vibrational temperatures are observed for the Fulcher- $\alpha $ band spectrum of hydrogen molecule to understand the approximate value to the neutral gas temperature. The number density of the ground state of hydrogen atom is also experimentally estimated from the actinometry measurement. The electron energy probabilistic function (EEPF) is numerically calculated as a solution to the Boltzmann equation. Number densities of excited hydrogen atoms are calculated with the collisional–radiative (CR) model with experimentally measured data as input parameters. It is found that the population densities of excited states of hydrogen atoms become about one order or much larger than those determined by OES measurement if we assume Maxwellian EEPF. The CR model with the EEPF as a solution to the Boltzmann equation theoretically reproduce the experimentally measured values very well. [ABSTRACT FROM PUBLISHER]

Computer investigations devoted to hot filaments of streamer microwave (MW) discharge features and to shock wave (SW) ( $M\approx 1.5$ ) propagation through the MW filaments area have been made. Analysis of SW propagation through the hot filaments showed that there is a strong influence on SW, which leads to SW destruction at some filament forms and displacement. This shows a possibility of MW discharge hot filament applicability for technologies. [ABSTRACT FROM PUBLISHER]

In this paper, the merits of a high-frequency resonant converter for supplying dielectric barrier discharges (DBD) devices are established. It is shown that, thanks to its high-frequency operating condition, such a converter allows to supply DBD devices with short discharge current pulses, a high repetition rate, and to control the injected power. In addition, such a topology eliminates the matter of connecting a high-voltage transformer directly across the DBD device and avoids the issues related to the parasitic capacitances of the latter which disturbs the control the power transfer to the plasma. The design issues of the converter, including the inverter and its switches, the resonant inductor, and the parameter drift compensation are studied. An experimental validation is performed: a mega Hertz resonant converter using GaN FET switches has been manufactured and tested with an excimer lamp. [ABSTRACT FROM AUTHOR]

We study the plasma discharge initiated by microwave radiation with stochastically jumping phase (MWRSJP) in a coaxial waveguide at the optimal mode of the beam-plasma generator. Present results continue the line of the previous research. In this paper, the conditions of a microwave discharge ignition, its stable maintenance in air by MWRSJP, and the pressure range at which required power is minimal are found. We also experimentally examine optical characteristics of the discharge plasma in a wide range of air pressure. In general, the research aims to develop a new type of sources of optical radiation. [ABSTRACT FROM PUBLISHER]

The possibility of mode switching from one pulse to another in a 6-cavity gigawatt magnetron with axial extraction of radiation through a horn antenna (such a magnetron is known as the MDO, i.e., magnetron with diffraction output) using a weak (200–300 kW), short (15-ns), and single-frequency RF signal was demonstrated using particle-in-cell simulations in our earlier work. This mode switching exploits the symmetric nature of the MDO that facilitates the use of any eigenmode as the operating mode. All scenarios of mode switching were considered using common properties of dynamical systems with two stable states separated by an unstable saddle point. In this paper, we continue to study the problem of mode switching, but this time for a 12-cavity MDO, for which we found splitting of the radiation frequency for each eigenmode owing to its different longitudinal distributions. Since splitting manifests as a bifurcation of frequency for definite values of the applied axial magnetic field, scenarios of frequency switching for this 12-cavity magnetron are considered. [ABSTRACT FROM PUBLISHER]

In high-frequency (HF) ionospheric communications, the dynamic nature of the high-latitude ionosphere creates small-scale ionospheric irregularities capable of scattering HF radio waves. In addition, there are large-scale irregularities which may be identified using some specific methods. However, small-scale irregularities cannot be easily identified and characterized. The aim of this paper is to introduce a new wavelet-based multifractal dimension mapping approach for the identification and the quantification of the small-scale irregularities. Numerical results show the improvement of the proposed methods compared to those obtained by the classical Legendre multifractal analysis. In our analysis, we have used the scattering function as a tool for the HF channel characterization. Our analysis deals with experimental scattering functions measured during the solar eclipse on August 11, 1999. [ABSTRACT FROM AUTHOR]

Within the framework of a project sponsored by the European Space Agency (ESA), we have developed a software tool to predict the occurrence of multipactor discharge in a simple radio frequency (RF) device modeled as parallel plates. The tool uses a micro-level explicit representation of the electrons (i.e., each electron in the system is modeled separately), and includes a detailed Monte Carlo model of the secondary electron emission process in the plates. Materials secondary emission yield (SEY) is described using either the usual parameter set (E1, E2, and σmax), or a more detailed model, where the contributions due to true secondary, backscattered or elastically reflected electrons are given their own sets of parameters, together with additional parameters for the angle dependence. The simulator has been validated using experimental data gathered at ESA and the Universidad Auto´noma de Madrid, Madrid, Spain. The simulator helped in the selection of material coatings for the mitigation of Multipactor effect in RF transmission lines on-board satellite payloads. [ABSTRACT FROM PUBLISHER]

The concept of effective diffusion length, as a means to characterize diffusion losses in calculations of microwave breakdown in radio frequency (RF) devices with inhomogeneous electric fields, is discussed in detail with emphasis on geometrical situations where the inhomogeneity of the microwave electric field plays an important role for the breakdown threshold. In particular, good analytical approximations are found for the microwave breakdown threshold field, in a number of different geometrical situations. Finally, an explicit experimental example demonstrates how the effective diffusion length in a coaxial resonant filter structure can be inferred from a set of breakdown threshold data obtained for different pressures. [ABSTRACT FROM PUBLISHER]

Results from diagnostics of diffusion-controlled stationary gas discharges maintained in the field of propagating surface waves are presented in this study. The set of the plasma parameters obtained includes: 1) the plasma density n¯, averaged over the discharge cross section; and its axial profile n¯(z);. 2) the electron-neutral elastic collision frequency ν; 3) the parameter μ, which describes the radial profile of the plasma density; 4) the parameter Θ, the power absorbed on average by an electron, and its axial variation Θ (z); 5) the electron temperature Te (z); and 6) the gas temperature Tg. The mechanisms of electron heating and discharge self-consistency are discussed [ABSTRACT FROM PUBLISHER]

A regime of discharge maintenance with a net dc current flowing through the plasma is established in the gas-pressure range that is usually governed by ambipolar diffusion. The conclusion is based on results from a 2-D fluid-plasma model developed for describing discharge maintenance in a two-chamber plasma source with metal walls. [ABSTRACT FROM AUTHOR]