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The temperature spike or sparking is vital to the catalytic effect with metallic powders in microwaves, but the mechanism is still unclear. In this article, the local field enhancement (LFE) of periodical metallic powders in microwaves is studied. It shows that microwaves can get through the separations among metallic powders with the LFE, which provides a preliminary understanding of the temperature spike or sparking among metallic powders. First, for simplicity, metallic powders are simplified to 2-D periodical metallic bars, which can be analyzed by the transmission line model and full-wave simulations. When the incident electric field is perpendicular to the separations among metallic bars, the electric field can be compressed. Specifically, even with the volume fraction of 99% metals, microwaves can pass through the separations well with intensive LFEs. Then, metallic powders are simplified to 3-D periodical spherical metallic powders. In this case, microwaves propagate at the slow wave mode with the LFE. Finally, the proposed models are validated by measuring reflectivity and observing the discharge in neon (Ne) gas at atmosphere in a rectangular waveguide at the TE10 mode. This work provides a way of controlling LFEs for enhancing reaction reactivity and creating plasma. [ABSTRACT FROM AUTHOR]

A novel transverse-mode overlapping technology is proposed to enable significant advancement in the development of wideband extended interaction klystrons (EIKs). To obtain the individual beams with comparatively low perveance and low current density, the double sheet beams are used to drive the circuit. For the purpose of allowing the circuit to operate in the fundamental mode, two innovative extended structures, ridge-loaded barbell structure (RLBS) and ridge-loaded ladder structure (RLLS), are proposed. It is found that both the two structures are capable of transverse-mode overlapping (superposition of TM11 mode and TM21 mode) by adjusting the dimensions of the ridges. On the basis of such ideas, a wideband six-cavity circuit at 0.22 THz is designed. The input and output cavities are with the RLBS, while the idler cavities are with the RLLS. The bandwidth of the output cavity and the frequency tuning of cavities are carefully considered to preserve good gain uniformity across the continuous frequency band. The particle-in-cell (PIC) simulation results show that the maximum output power reaches 138 W with the operating voltage of 15.8 kV and each beam current of 0.3 A, and the corresponding gain is 34.3 dB. The 1-dB bandwidth is 1.95 GHz, approximately 1% of the operating frequency. The relatively small in-band ripple indicates the excellent bandwidth characteristics of the circuit. [ABSTRACT FROM AUTHOR]

The plasma limiter (PL) is a suitable method to protect electronic devices from high-power electromagnetic pulses. The $S$ -band PL has target specifications of 100 kW of power handling capability, < 100 ns of response time, and < 0.5 dB of insertion loss. Carbon nanotube (CNT) can be used to reduce power losses and instrument corrosion under frequent electromagnetic attacks. This article used CNT-coated copper needles in a PL to increase the electric field for the rapid breakdown process. Furthermore, the impact of dimensional parameters (needle’s length, needle’s radius, and axial displacement of the needles) were investigated. The experiment was conducted at 1800 W of peak power and 25 ns of the $S$ -band (2.45 GHz) microwave duration. In this case, the height of 19 mm and diameter of 1 mm were found to be the optimal needle parameters, in which the fastest breakdown of the electric field is available. The finite-element method was used by CST software to verify the experiment results. The transmission losses were < 5% in the normal state. The breakdown electric field threshold was ~431 kV/m near the atmospheric pressures. There was an error of < 1.28 in the case with the lowest compatibility. [ABSTRACT FROM AUTHOR]

In this article, the power- and spatial-dependent macroscopic electrical transmission and reflection properties of an argon microwave plasma are analyzed. A custom two-port coaxial prototype is built with a variable spatial gap between two electrodes. All measurements are based on the extension of the large-signal scattering parameter (Hot-S) measuring environment and are proof-of-concept for the determination of plasma properties without an external probe. The coaxial topology of the prototype has a fixed reference impedance so that the reference planes can be located at the tip of both electrodes. An equivalent lumped element circuit valid over a wide bandwidth is investigated to simulate the linear macroscopic electromagnetic reflection and transmission properties of the plasma. A series-resonance circuit is chosen since its representation is capable of covering the measurements from 10 to 40 W of input power and gaps from 1 to 3 mm. With this circuit, a continuous relationship between the impedance, power, and the spatial dimensions of the plasma is found. [ABSTRACT FROM AUTHOR]

Impedance matching plays a vital role in a microwave atmospheric pressure plasma jet (MW-APPJ). However, real-time tuning of MW-APPJ impedance matching has rarely been investigated. In this study, we have found that the dissipated microwave power and length of a MW-APPJ are effected by the application of a DC-bias magnetic field. By placing a MW-APPJ in a gap between two electromagnets, the consumed microwave power varied with the insertion position of the MW-APPJ. When the MW-APPJ was fixed at the center of the electromagnets, the consumed microwave power decreased as the DC magnetic field intensities increased, from 12 to 750 mT. The variation of consumed microwave power was much higher at lower gas velocities, which indicates that the DC magnetic field has a relatively strong effect on microwave plasma with lower gas velocity. The length of the plasma jet also decreased with increasing DC magnetic field, which was mainly due to the variation of the consumed microwave power. To explain these interesting phenomena, the effective permittivity of microwave plasma and the equivalent circuit model of a generator under DC-bias magnetic field have been analyzed. The effective permittivity of the plasma is related to its cyclotron frequency, which is a function of the DC-bias magnetic field. The variation of the effective permittivity changes the load impedance of the plasma generator. Therefore, the reflection coefficient of the plasma generator is adjusted and the length of the plasma jet varies with the change in consumed microwave power. [ABSTRACT FROM AUTHOR]

Particle-in-cell (PIC) simulations of a microwave oven free-running 2.45 GHz “cooker” ten-vane magnetron operating with a “cold” explosive-emission cathode in a uniform axial magnetic field are performed with two computer codes, improved concurrent electromagnetic PIC (ICEPIC), and CST Particle Studio (CST-PS). PIC simulations are done to compare results obtained by these two codes to each other and, in such a way, identify all possible advantages and disadvantages of each code performance as a reliable tool allowing to predict all important characteristics of the magnetron operation. Results of the PIC simulations show that the range of applied voltages within which the magnetron is able to operate in the $\pi $ -mode at an external uniform axial magnetic field 0.19 T is much broader as it is predicted by the CST-PS code, from 4.00 to 4.70 kV, than as it predicted by the ICEPIC code, from 3.90 to 4.10 kV. It is also shown that while the magnetron startup time gradually decreases, as it is predicted by the ICEPIC code, from about 700 ns (3.90 kV) to about 100 ns (4.20 kV) with the applied voltage increase, it initially chaotically varies, as it is predicted by the CST-PS code, between about 1000 ns (4.03 kV) and about 300 ns (4.01 kV) and only then gradually decreases down to 10–20 ns (4.40–4.60 kV) with the applied voltage increase. Additional PIC simulation with MAGIC or VORPAL codes would be interesting to perform as well to compare the obtained with these codes simulation results with results described in this article. [ABSTRACT FROM AUTHOR]

A novel method for measuring microwave plasma impedance is presented. Plasma impedance is measured in real-time using three coupling probes and a microwave detector, rather than using a vector network analyzer or directional coupler, spectrometer. The measured impedance of a plasma filament at atmospheric pressure demonstrates that the impedance changes significantly with power variation, whereas the influence of airflow is minor. This implies that the impedance matching of atmospheric pressure microwave plasmas should take into account the effects of microwave power variations, and the use of a fixed matcher is not recommended for impedance matching of plasma jets unless they are operating at a fixed power. This measurement method avoids the intervention of other microwave power or expensive instruments, which facilitates the development of microwave plasma models and the tuning of efficiency. [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]

In this article, the performance of an unshielded low-noise amplifier (LNA), which is subjected to the incident high power microwave (HPM) pulse waves, is investigated analytically and experimentally. For this purpose, a time-domain algorithm is proposed, which uses the finite difference time domain (FDTD) method and a globally convergent iterative method to solve linear and nonlinear equations of the problem simultaneously. In particular, the effects of external incident electromagnetic (EM) field illumination with different types of waveforms, including HPM pulses and sinusoidal waves, on the nonlinear performance of a microwave LNA are investigated and discussed by this method. Furthermore, using a measurement setup comprised of a transverse EM (TEM) cell, the proposed method is validated by comparing with the measurement results in good agreement. The presented analysis would be useful in EM interference/compatibility (EMI/EMC) analysis, such as radiated susceptibility analysis of RF/microwave nonlinear circuits excited by the incident HPM pulse wave. [ABSTRACT FROM AUTHOR]

As a low operating cost microwave source, magnetron has been fully considered for superconducting radio frequency (SRF) accelerator. A 1497-MHz, 13.5-kW continuous-wave (CW) magnetron for SRF accelerator is designed and manufactured, and the test results meet the design requirements. Two simulation steps of designing magnetron with Computer Simulation technology (CST) Studio Suite are presented. First, the Microwave Studio helped to simulate the microwave coupled output structure and the resonant cavity. Then, the output performance of magnetron was simulated with particle-in-cell (PIC) solver. The cold test results show that the circuit efficiency is 93.14 %. A magnetron hot test platform was used to measure an output power of 14.23 kW and an electronic efficiency of 84.23 %. The injection locking experiment is completed at 4.5 kW. The frequency of the magnetron is adjustable, with a tunable bandwidth of 7 MHz through a mechanical tuning rod. The problems and solutions in the process of design and manufacture are summarized, which can provide a reference for the development of high-power magnetron with different frequency. The development of 1497-MHz magnetron broadens the selectable frequency of high-power magnetron, which is beneficial to its industrial applications. [ABSTRACT FROM AUTHOR]

This article presents a dual-band bandpass filter based on the double-sided spoof surface plasmon polaritons-line. The whole structure consists of a dual-band filtering part and two SSPPs lowpass filtering parts. Simulated results show that the proposed dual-band bandpass filter has an excellent dual-band filtering performance and wide upper band suppressions. Simulated bandwidths of two passbands are 41% (2.36–3.58 GHz) and 13.9% (6.7–7.7 GHz). It can realize the suppression of $S_{21}$ below −40 dB from 9.6 to 39.7 GHz. A prototype has been fabricated and measured. Measured results are in a good agreement with simulated ones, which validates our design concepts and methods. The proposed dual-band bandpass filter will have significance in microwave device designing, especially in the plasmonic device in microwave frequencies. [ABSTRACT FROM AUTHOR]

In this article, an equivalent circuit approach has been used to study the bifrequency generation by the azimuthally partitioned axially periodic metal disk-loaded coaxial structure. Considering the effect of all harmonics present within the structure and using an equivalent circuit approach, the expression of the equivalent series inductance per unit length and equivalent shunt capacitance per unit length has been obtained for this equivalent transmission line. In addition, with the help of computed equivalent series induction and equivalent shunt capacitance, expressions for the dispersion relation, phase velocity, and characteristic impedance have been obtained. The maximum possible frequency difference (i.e., bandwidth) between the modes (i.e., resonating frequency) and its region of operation have also been analytically computed. Finally, the parametric studies have been performed to find out the effect of structural parameter variation on dispersion behavior. In order to validate the numerical analysis, the structure has been first simulated with the help of CST microwave studio, and then, the analytically obtained results (such as dispersion behavior and phase velocity) have been compared with the results obtained from simulation. The comparison of results shows that the relative error is below than 5%, which shows a good agreement between them. [ABSTRACT FROM AUTHOR]

This article presents the amplification of the propagating spoof surface plasmon polariton (SSPP) modes in the ring resonator-based filtering structure. SSPP-based corrugated ring resonator has been used to design a high- $Q$ dual-band bandpass filter (BPF). Afterward, a subwavelength scale amplifier has been embedded on the output port of the designed BPF to provide loss-compensation as well as amplification at the specified frequency bands of the filtering structure. A microwave laminate with a dielectric constant of 3.38 and a height of 1.52 mm is used to develop the proposed circuit. An 8.2 and 9 - dB gains have been obtained at the two frequency bands, respectively. Good agreement has been achieved between simulated and measured results. The proposed loss compensation and amplification of the SSPP modes in the ring resonator-based structure paves a path to develop active biosensing applications and ultracompact spoof plasmonics-based radio frequency (RF)-to-terahertz (THz) transceiver systems. [ABSTRACT FROM AUTHOR]

A novel four-port circulator is presented which uses an inline ferromagnetic element to allow for transmission or reflection depending on the sense of the incident circularly polarized wave. This configuration has been shown to reduce the dependency on ferrite anisotropy and support higher power, low rf loss, operation. An analytic analysis of this device is presented alongside corroborating cold test data of the first prototype. High-power operation was performed at 2.856 GHz, with input power levels up to 8 MW for $3.5~\mu \text{s}$ in a pressurized nitrogen environment. The results from this research not only demonstrate ability to eliminate the use of greenhouse insulators, such as SF6, but also provide conceptual groundwork for a new class of ultrahigh power (50 MW+) nonreciprocal networks including circulators, isolators, phase shifters, and rf switches. [ABSTRACT FROM AUTHOR]

In this article, a high-power microwave (HPM) oscillator magnetically insulated line oscillator (MILO) design study has been carried out to improve its performance. Impedances of different subsections of the device have been matched. An equivalent circuit approach, which is simpler and easy to handle, has been adopted for this purpose. First, the input impedance of the tapered inner conductor of the coaxial structure has been matched with the impedance of the choke disks. Then, the extractor inner radius and extractor gap impedance have been optimized at the output section. This impedance matching scheme provides the maximum efficiency of the device with the maximum RF transmission. The optimum position of the stub to match the impedance with the output side has also been analyzed. To validate our concept, initially, an experimentally reported $L$ -band MILO has been simulated using commercial particle-in-cell (PIC) code, which provides an RF output power of 1.38 GW with the efficiency of 7.8%. The PIC simulation results have been found in agreement of ~5% with the experimental values. Furthermore, the PIC simulation with the optimized design parameters has improved the RF output power of 2.5 GW with an efficiency of 14.4%. [ABSTRACT FROM AUTHOR]

The thermal burnout effect of a gallium arsenide (GaAs) pseudomorphic high electron mobility transistor (PHEMT) low-noise amplifier (LNA) caused by repetitive microwave pulses is studied by theoretical analyses, simulations, and experiments. The theoretical model for thermal burnout under a single microwave pulse injection is first acquired by analyzing the power absorption in the electrical procedure and the heat distribution in the thermal procedure. By adopting two new assumptions and using the linear superposition theorem, the theoretical model for thermal burnout under a repetitive microwave pulse injection is acquired by further extension. Through derivation, the analytical relationship among the thermal burnout power threshold, the pulsewidth in a cycle, the pulse repetition frequency (PRF) and the pulse number is acquired. Because some assumptions and approximations are adopted, both the pulsewidth in a cycle and the total repetitive microwave pulselength must be between 10-ns scale and 1- $\mu \text{s}$ scale. It shows that the theoretical results agree well with the simulation and experimental results. A minimum of two sets of data by experiment or simulation are needed to fit the analytical relationship. Therefore, experimental or simulation costs can be substantially reduced, and a helpful reference for the design and protection of wireless receivers can be provided. [ABSTRACT FROM AUTHOR]

High-frequency power amplifiers can be equipped with complementary pulse-compressor systems to fulfill the advanced cavity power requirements. Microwave pulse compression is a power extraction method based on pulsewidth reduction and electronic triggering. The cavity is fed by pulsed-RF source, the resonance is evolved at $t\geq t_{0}$ , $t_{0}=\textrm {cavity}$ filling time. Established standing waves or resonance condition is brokendown by triggered plasma switch programmed with adjustable delay and pulsewidth. This causes the stored energy to be transmitted as shorter output RF-pulse. The implementation of a microwave pulse compression system requires careful measurements and structural modifications to be able to tune design parameters for optimal setup. In the scope of this paper, the experimental results are obtained for different waveguide lengths and various load configurations (to exploit new opportunities). All connections, iris configuration, and precise adjustment of plasma triggering have been set up cautiously. The cavity gain is increased up to 23 dB with trigatron driving improvements. High power requirements and demands are investigated for many applications, particularly for biomedical science projects. [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 seven-channel microwave interferometer (100 GHz) is designed, developed, and used to measure the radial profile of the plasma density $({\mathbf {n}}_{\mathbf {e}})$ in Aditya tokamak. The resolution of the density measurement is ${n}_{e}=2 \times {10}^{11}\,\,{\text {cm}}^{-3}$. The spatial and time resolutions are 7 cm and $10~\mu \text{s}$ , respectively. The chord-averaged measurements from seven channels are Abel inverted to obtain the radial profile of the plasma density. Plasma density measured by the microwave interferometer is well matched with that measured by the Thomson scattering diagnostics. [ABSTRACT FROM AUTHOR]

This paper puts forward a novel high-voltage pulse generator, which can output a near square waveform across the load. The generator is composed of a conventional Marx generator, an $LC$ filter and a metal–oxide varistor (MOV) in parallel with the load. The Marx generator and the filter form a two-section type-A Guillemin pulse forming network (PFN). The PFN outputs a near square waveform and the MOV further stabilizes the voltage because of the MOV’s nonlinear resistivity. Circuit simulation verifies the working principle. Design parameters for the conventional PFN are derived. Considering the stray inductance of the filter, a more realistic PFN circuit is proposed and its parameters are derived. Preliminary experiments are conducted and verify the concept. Typical output waveforms have 20–30-ns rise time, 1000–1100-ns pulsewidth, and ~7-kV peak voltage. The pulse generator based on this concept is suitable to be used as a compact, long-pulse high power microwave modulator as it has a simple design, a well-defined flat top and it can output near constant voltage even if the load’s impedance varies. [ABSTRACT FROM AUTHOR]

Plasma-based microwave power limitation is experimentally investigated in a microstrip transmission line integrating a direct current (dc) plasma discharge for preionization. Steady state and transient high-power microwave measurements demonstrate that the preionization by the dc plasma discharge helps in reducing limiting power thresholds and time responses to about 30 dBm and tens to few microsecond, respectively. Besides, optical diagnostics also exhibit interesting behaviors of the plasma discharge such as diffusion and parasitic breakdowns. Finally, the effect of plasma confinement is discussed, and it is shown that reducing the volume devoted to plasma expansion leads to a decrease in the dynamic range of the microwave power limitation. [ABSTRACT FROM AUTHOR]

The design and experimental results of a 140-GHz gyro-amplifier that uses a dielectric-loaded, severless confocal waveguide are presented. The gyro-traveling wave amplifier uses the HE06 mode of a confocal geometry with power coupled in and out of the structure with Vlasov-type, quasi-optical couplers. Dielectric loading attached to the side of the confocal structure suppresses unwanted modes allowing zero-drive stable operation at 48 kV and 3 A of beam current. The confocal gyro-amplifier demonstrated a peak circuit gain of 35 dB, a bandwidth of 1.2 GHz, and a peak output power of 550 W at 140.0 GHz. [ABSTRACT FROM PUBLISHER]

In this paper, the multiphysical and frequency-dependent characterization of a microwave argon plasma jet in the GHz range is presented. Three different frequency ranges around 1.3, 2.4, and 3.5GHz are compared using electrical, geometrical, optical, and thermal analyses for different power levels between 2 and 10 W at a constant gas flow. Based on measurements using the large signal S-parameter measuring technique, the plasma base point impedance and microwave conductivity are determined via circuit and finite-element method simulations. Major changes within a small frequency interval are exhibited. Optical measurements are dependent on the geometrical dimension changes of the microwave plasma. It is shown that the geometrical dimensions are strongly dependent on frequency and applied power. These investigated dependencies of the microwave plasma on operation conditions open up new degrees of freedom to match the frequency to the application needs. A description of different applications is given based on the different areas of the measurement results. [ABSTRACT FROM PUBLISHER]

Researchers have investigated plasma-related phenomena and internal breakdowns in the gigawatt–terahertz relativistic backward wave oscillator (RBWO) caused by field emissions from the surfaces of the waveguide circuits in these oscillators. In order to increase the power-handling capability of relativistic electron beam devices, an RBWO is proposed in the form of an oversized structure in which the diameter ( $D$ ) of the electrodynamic structure is increased to several times the free-space wavelength ( $\lambda )$ . An optimal periodic rectangular corrugation structure of which the axial mode is matched to the $\pi $ mode is designed in order to determine only the TM01 mode without mode competition in a slow-wave structure (SWS). The oversized RBWO has a fairly large diameter and uses a resonant reflector to achieve optimum efficiency while also preventing mode competition in the SWS. Absorption of a decelerated electron beam is achieved by the collector, which protects against breakdown and damage. The results of 0.5–0.1 THz from 500 kV–5 kA in the relativistic region are observed by means of a particle-in-cell simulation, and the dispersion relationship is determined by a finite-difference time-domain simulation. The outcomes show that a high-power oversized RBWO can control the selection of the mode and the interaction efficiency. [ABSTRACT FROM PUBLISHER]

The results of an experimental study of the S-band magnetron operation with a six-vane anode block and multichannel radial outputs for microwave power extraction are presented. The magnetron was driven by a linear induction accelerator (~350 kV, ~2.5 kA, and 150 ns). In the case of three outputs for microwave power extraction and another three outputs connected to waveguides short circuited by movable plungers for adjusting the magnetron resonance, frequency-stable generation of the microwaves radiation with a total power of 570 MW from these three outputs was demonstrated. This power was equal to the power obtained when the same magnetron with one output was operated with high efficiency ( $\geq 40$ %). In addition, it was shown that the distribution of the generated microwave power between the three outputs allows wedge insulators to be used in the waveguides vacuum–air interface without electrical breakdown. Finally, microwave radiation, extracted in free space by a cluster of horn antennas connected at the output of the waveguides, was coherently added to each other at the desired distance with a three times larger microwave power density than in the case of 570-MW single output magnetron operation. [ABSTRACT FROM PUBLISHER]

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]

A technique has been developed to generate stable Ar plasmas at atmospheric pressure inside of a quartz capillary tube. The microwave plasma in the capillary tube is produced by utilizing a single mode resonant circular cavity applicator with 2.45 GHz frequency excitation. The plasma can be confined or fully exposed outside the cavity as plasma jets depending on the operating conditions. The profile of the plasma front has been characterized as a conical tip or split branching jet plume. The measured discharge length and the power density of the plasma range from 6 to 10 cm and 35 to 75 W $\cdot $ cm ^{-3} , respectively. Addition of CH4 into the Ar plasma results in an increase in the abundances of excited CN and C2 carbon radicals and a concomitant decrease in the intensity of the Ar emission. [ABSTRACT FROM AUTHOR]

In this paper, a novel method for high-repetition-rate high-power radio frequency (RF) pulse generation, which involves only passive solid-state devices and is capable of being used for generating high power microwaves using a low-to-high power converting scheme based on nonlinear self-compression is proposed. The method is also expected to be of low jitter. In the proposed circuit, two high voltage diodes with proper reverse recovery characteristics are used. The simulation results show that the proposed circuit generates RF pulses, with central frequencies up to gigahertz range. By applying a sub-kilowatt power supply, the maximum output power was well over 10 kW. This power can be increased up to megawatt order using power supplies of kilowatt range, as predicted by the theory. Simulations also indicated the possibility of 130-kHz pulse repetition rate as predicted by the theoretical analysis. The proposed method has been shown to work properly by an experimental setup. The setup showed the repetition rates up to 5000 pulses/s, which was capable of being increased to the simulation result using high quality circuit elements just as those used in the simulated circuit. We are currently carrying out a research to achieve the predicted upper limits of the power at gigahertz range RF generation and the results will be presented in their future reports. [ABSTRACT FROM AUTHOR]

Two Cherenkov devices are effectively combined using a circular waveguide T-junction in a simulation study. The microwave sources are driven by the same high voltage pulser to prevent phase difference at the output of the power combiner. This passive power combiner not only combines the microwave power, but also outputs a Gaussian beam when a TM01 mode is used as the input. An efficient serpentine mode converter has been used as the basis of the power combiner design where the fields sum up at the common section of the two mode converters. A combined summation/conversion efficiency was $\sim 90$ % when the output power was more than 1.8 times the input power with a Gaussian output pattern. The combined microwave power was more than 600 MW at 10.2 GHz. [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 nonlinear and damage properties of silicon bipolar junction transistors (Si BJTs) injected with microwave pulses (MWPs) from base are studied in this paper. The experimental results of this injection research show that the feature of the output power of the Si BJT is from linear increase, saturation, reduction to increase again as the input power increases; the feature of the measured output voltage waveform is from linear increase, saturation, reduction to reversion and increase again as the input power increases. Permanent damage occurs to the BJT when the input power is high enough. The 3-D simulation model is established with Technology Computer Aided Design (TCAD) to further analyze the nonlinear and damage properties of the Si BJT injected with MWPs. The simulation results match with the experimental results. [ABSTRACT FROM AUTHOR]

Microwave (MW) technology is a promising alternative to conventional heating. It also resides in the new domain of materials science, namely, microscopic and strong thermal nonequilibrium systems. The application of MWs in the iron industry may be characterized by a high potential for an essential reduction of carbon dioxide emission. A series of experiments has been conducted to prove the effectiveness of rapid and high-purity refinement under an oxygen-containing environment by means of MW application, and achieved highly positive results. That has led to feasibility studies using a compact 30-GHz gyrotron system at the Karlsruhe Institute of Technology. Potential MW effects have been investigated. High-quality pig iron has been made from powder samples of mixed magnetite and carbon by 30-GHz millimeter-wave heating. This paper discusses the experimental results obtained recently and the estimated MW power for the iron production. [ABSTRACT FROM PUBLISHER]

The virtual cathode oscillator (vircator), which is one of the microwave sources, has been widely studied for about 40 years, since it has advantages, such as its simple structure and high-power radiation. To implement the behavior of the vircator, a simulation model of the axial vircator using circuit elements is studied in this paper. There are two steps in simulation of this paper: 1) obtaining the optimized case in the fixed input power that has a maximum efficiency and 2) at the case, conducting the circuit modeling. Passive elements and switches are used to model the power losses, emission threshold, etc. This circuit analysis is simulated by the Electro Magnetic Transient Program. Through the simulation model of the axial vircator using circuit elements, the high-power electromagnetic system can be handled as an integrated system, which contains a prime power part, a pulsed power part, a microwave source part, etc. This means that the circuit analysis can be carried out from the prime power to the vircator. [ABSTRACT FROM PUBLISHER]

The linear interactions between two electromagnetic waves arising from high-speed electrons in the resonant cavity are studied. The first electromagnetic wave arises from the high speed electrons in the corona discharges occurring at the helix. The second electromagnetic wave is due to the high speed electrons in the gas discharges taking place in small gaps. Many experimental data are analyzed and seven examples are presented. [ABSTRACT FROM AUTHOR]

This paper introduces a novel microwave plasma source based on inductive coupling window—rectangular resonator. It consists of a WR430 waveguide, an inductive coupling window, a rectangular resonator, a closed cuboid quartz cavity, and a sliding short-circuit plunger. This microwave plasma source can produce a large-volume stable atmospheric air microwave plasma, and the plasma size is at the smallest 63 mm $\times\,$ (40–50) mm $\times\,$ 30 mm. The microwave reflectance ratio of the microwave plasma source exactly at higher power is roughly unrelated to the input microwave power before the plasma is produced. After the plasma is generated, the reflectance ratio increases with the increase in the input microwave power and the ratio at lower power is even smaller than that before the plasma is produced. The gas temperature of the atmospheric air microwave plasma is approximately changeless with the input microwave power. The atmospheric air microwave plasma cuts off the microwave with the frequency of 2450 MHz. [ABSTRACT FROM AUTHOR]

We describe the technology and experimental work done at Polarix Corporation on photoconductive switch-based high-power microwaves systems for airborne counter-improvised explosive device (IED) applications. We address the fluence requirement for nanosecond pulse range for coupling to IED harnesses both theoretically and experimentally. We describe some of the key elements of the technology and the system being developed. They include silicon backed biased junction switch technology, low inductance–high current switch integration with thin film Blumlein type circuits, multiswitch multicycle generation, and radiation concepts using asymmetric Wheeler–Chu apertures for side firing small diameter but long unmanned aerial vehicles platforms. We will also present the experimental results showing switch source and radiator performance. [ABSTRACT FROM PUBLISHER]

In this paper, we present a design approach of a single-line nanosecond pulse source by using a thorough analytical investigation and by verification with CST MICROWAVE STUDIO. Through detailed analysis and simulation, we arrive at a design for a fast rise time variable pulse duration pulse source which is able to produce 1–10 ns pulses with tens of kilovolt amplitude and less than hundreds of picoseconds rise time. This variable pulse duration is achieved by using telescopic antennas and ferrites in the pulse-forming line of the pulse source. Finally, we present a first implementation of a 5-ns pulse source with an oil spark gap for fast switching. [ABSTRACT FROM AUTHOR]

A novel phase shifter used to adjust the output phase of high-power microwave (HPM) is investigated. It is noticed that the waveguide wavelength and propagation constant of the TE10 mode are functions of the wide side dimension of the rectangular waveguide, and therefore the output phase of the microwave can be adjusted by changing the wide side dimension. In this paper, an HPM waveguide phase shifter with the wide side dimension adjustable is designed and analyzed numerically. No dielectric or metal pins are involved in this phase shifter, and the microwave propagates in the TE10 mode. In addition, it has a high power-handling capacity. Results show that the phase shifter could operate at a frequency of 15.2 GHz, and the phase of the wave can be adjustable in a range of 0^\circ–360^\circ with a transmit efficiency over 96%. The dimensions of the phase shifter are 13.8 mm \times\,7.9 mm with a phase shifting length of 139 mm. This novel phase shifter is of interest to HPM applications and higher microwave band. [ABSTRACT FROM AUTHOR]

This paper offers a simple method to recognize the coherence effect that is responsible for the pulse shortening in microwave devices. To apply this method, it is necessary to observe the experimental fast Fourier transform curve and the experimental waveform and compare these data with the PSPICE simulation. [ABSTRACT FROM PUBLISHER]

The results of experimental research on the stabilization and tuning of the frequency of a relativistic S-band six-resonator magnetron powered by a linear induction accelerator (U\approx 300~\kappaB, I\approx 2.5~kA, and \tau\approx 150~ns) are presented. The frequency of the microwaves was stabilized using a partial reflection of the generated microwave power P\approx 300~MW from the output of the magnetron and a proper adjustment of the phase of the reflected microwaves. [ABSTRACT FROM PUBLISHER]

Microwave amplification in relativistic backward wave oscillator operating below its self-excitation threshold is considered. The conditions that allow to achieve high gain provided with stable operation of the backward wave amplifier (BWA) were found. Several schemes of use of the relativistic BWA providing high power microwave amplification were studied. It is shown that employing a BWA in regenerative amplification regime allows to obtain more than 40 dB gain with efficiency over 20%. [ABSTRACT FROM AUTHOR]

A numerical simulation analysis is made of the effect of signal transmission using the quadrature phase-shift keying of a constant-amplitude RF carrier wave on the initiation of multipactor breakdown in RF devices operating under close-to-vacuum conditions. It is found that this form of signal modulation has a suppressing effect on the growth of the multipactor electron avalanche that depends on the parameters of the system. However, for technically realistic values of signal and phase-shift frequencies, the effect is found to be small. [ABSTRACT FROM AUTHOR]

In this paper, computer-aided design (CAD) of two types of RE windows, namely, double-disk RF window and pillbox-type RF window, is presented for use in high-power microwave/millimeter-wave sources. The design of double-disk RF window was carried out for 42-GHz band (TE0,3 mode) and 170-GHz band (Gaussian mode), while the design of pillbox-type RF window was carried out for 2.856-GHz band. The requirement for the design of RE window is to minimize the reflections with exact matching at desired resonant frequency. In the present approach, a scattering-matrix code was invoked with recently developed particle swarm optimization (PSO) method in order to optimize the geometrical parameters of the window. Multiobjective optimizations using PSO have been used to achieve optimized tradeoff between matching of desired resonant frequency and minimizing the power reflections in the desired band of operation. [ABSTRACT FROM AUTHOR]

Most of the present-day millimeter-wave gyrotrons developed for plasma experiments in controlled fusion reactors utilize cylindrical cavities operating in high-order modes. The choice of modes should obey certain restrictions dictated by the achievable mode selection and the maximum admissible level of the density of microwave ohmic losses in the cavity walls. Even with these restrictions, developers have successfully manufactured quasi-continuous-wave gyrotrons operating in the short millimeter wave- length bands that are capable of delivering microwave power on the order of 1 MW. To upgrade gyrotron power to the level of several megawatts, more complicated coaxial microwave circuits should be used. This statement is also valid for relativistic gyroklystrons, which are currently under development for driving future linear accelerators. This paper presents an overview of the history of the development of coaxial gyrodevices, a discussion of the physics-based issues which are the most important for their operation, a description of the state of the art in the development of coaxial gyrodevices for the above-mentioned applications, and a brief forecast for their future. [ABSTRACT FROM AUTHOR]

Presents a study which introduced the design of a coaxial gyroklystron experiment. Applications of the design in radars and linear accelerators; Details on the microwave circuit of the design; Summary.

Presents a three-cavity design of a gyroklystron amplifier at 95 gigahertz. Details on the magnetron injection gun design; Presentation of the microwave circuit; Discussion of the results.