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We investigated the use of single-stepped cavities instead of typical tapered cavities in an A6 magnetron with diffraction output (MDO) and a 12-cavity MDO through particle-in-cell (PIC) simulations using MAGIC [1] and UNIPIC [2] in our earlier publications [3]–[5]. The interaction space, where the charged particles interact with the induced RF waves, was increased by replacing tapered cavities with single-stepped cavities in a 12-cavity rising-sun relativistic magnetron with diffraction output (RMDO) that the electronic efficiency of \pi -mode generation in a 12-cavity rising-sun RMDO with single-stepped cavities driven by a transparent cathode [6] with gigawatt output power level can be as high as 83% for \alpha = 12.5^{\circ } , 79% for \alpha = 17.5^{\circ } , and 82% for \alpha = 18.2^\circ at \beta = 32^\circ , where \alpha is the angle between the inner wall and the z -axis, and \beta is the angle between the outer wall and the z -axis. When \alpha , the angle between the inner wall and the z -axis, is changed, the depth of single-stepped cavities was changed. This would lead to the coupling between deep cavities and shallow cavities in the 12-cavity rising-sun MDO changing too, and which finally results in different frequencies of magnetron operation in the \pi and \beta = 32^\circ , the peak efficiency of \pi -mode generation in a 12-cavity rising-sun MDO with single-stepped cavities design is around 82% and occurs for voltage $V\sim 400$ kV ± 50 kV. This paper describes optimizing the parameters in a 12-cavity rising-sun RMDO for the desired $\pi $ -mode operation. [ABSTRACT FROM AUTHOR]

The possibility of using single-stepped cavities to replace the common tapered cavities was studied using particle-in-cell simulations in an A6 magnetron with diffraction output (MDO). The replacing of the tapered cavities by the single-stepped cavities in a 12-cavity MDO increases the interaction space where the charged particles interact with the induced RF waves. The electronic efficiency of the 12-cavity MDO with single-stepped cavities driven by the transparent cathode [2] of GW output power level can be as high as 73% for \alpha=18.2^\circ , 74% for \alpha=17.5^\circ , and 72% for \alpha=12.5^\circ at \beta=32^\circ , where $\alpha$ is the angle between the outer wall and z$ -axis, and \beta$ is the angle between the inner wall and z$ -axis. The depth of single-stepped cavities is changed when \alpha . The results presented in this paper provide references for relativistic magnetron mode selection or mode switching experiments when choosing the input parameters (magnetic field and accelerating voltage) allowing the magnetron to operate in the desired operation mode. [ABSTRACT FROM PUBLISHER]

The breakdown characteristics of C4F7N/CO2 mixtures under dc condition are investigated with a particle-in-cell method. The processes of elastic, excitation, ionization, and attachment collisions are all considered. The elastic cross section of electron scattering from C4F7N is modeled through quantum mechanical spherical complex optical potential formalism. Based on the cross-sectional data, the dielectric strength of pure C4F7N is studied. The threshold of breakdown is in good agreement with the experiment. Besides, the dielectric strength of C4F7N/CO2 mixtures is also obtained. The threshold of breakdown in 80% C4F7N and 20% CO2 is larger than that of pure C4F7N when the gas pressure is larger than 1300 torr. The results show that the energy loss of electrons is mainly caused by excitation collision with CO2 when the energy of electrons ${T}_{e}$ is smaller than 5.5 eV. When ${E}/{P}$ is small, the proportion of low-energy electrons is large and ${T}_{e}$ increases with the ratio of C4F7N. Therefore, the effective ionization rate first decreases and then increases as the ratio of C4F7N increases. [ABSTRACT FROM AUTHOR]

We present an S-band high-power microwave (HPM) oscillator based on crossed-elliptical metamaterial (MTM) rings in a circular waveguide and powered by a high-power electron beam. Particle-in-cell (PIC) simulations demonstrate that when an output horn antenna of radius of 200 mm is used, an output power of 443 MW of a backward wave TE41 mode below its cutoff frequency at 2.80 GHz can be generated using a pulsed electron beam with a voltage of 990 kV and a current of 1.736 kA in a 1.8-T solenoidal magnetic field, corresponding to an electronic efficiency up to 26%. Meanwhile, another degenerate frequency of 2.80 GHz of a forward wave in the TM01 mode with an output power of 9 MW is also observed. When an output horn antenna of radius 150 mm is used, this crossed-elliptical MTM oscillator operates mainly in a forward TM01 mode at 2.80 GHz with an output power of 325 MW at an electronic efficiency of 19%, and at the same time, a backward wave TE41 mode below its cutoff frequency of 2.80 GHz with an output power of 8 MW can be observed. Simulations indicate that this slow-wave structure (SWS) consisting of a periodically crossed-elliptical MTM loaded circular waveguide can support degenerate mode operation. This result suggests that this configuration is favorable for mode switching and this work seeks to design a compact HPM source. [ABSTRACT FROM AUTHOR]

Passive intermodulation (PIM) interference that occurs in communication systems could limit the communication capacity and increase the manufacturing and maintenance costs. In this letter, a composite exponential model is developed to characterize the weak nonlinearity of passive components that causes PIM generation accurately. This proposed model fully considers the correlation between the PIM products on each order and the relation of PIM products with variation of carrier powers. For verification, a microwave filter is given to demonstrate the effectiveness of this composite model, and the reliability of this model is proved by the sensitivity analysis due to measurement uncertainty. Besides, the good agreement between the calculated powers of PIM products and the measured data shows that it can provide a theoretical guidance for PIM performance assessment in engineering application, thereby evaluating the influence of PIM interference on communication quality effectively. [ABSTRACT FROM AUTHOR]

Many radio frequency measurement systems require multicarrier signals with coherent phases between carriers with different frequencies. A typical example is the signal generator which is used in multicarrier multipactor (MM) testing systems. In this paper, we propose a new approach for the generation of coherent multicarrier signals based on a state-of-the-art phase-locked loops technique. Different from existing systems that rely on a heavy use of commercial microwave instruments, this generator can be implemented with on-shelf chips and devices. As an example, an ultrahigh frequency band generator is implemented and how to implement the in-system calibration of this generator in an experimental multipactor testing system is demonstrated. Based on the proposed approach, performing a quantitative experimental research on MM becomes affordable for an ordinary microwave laboratory, which may promote the in-depth experimental study in this area. It can also be used in a wide range of applications such as MIMO and phased array systems. [ABSTRACT FROM AUTHOR]

The newly discovered “long-term” multicarrier multipactors that can be induced by low-energy electric fields potentially threatens the reliability of spaceborne microwave systems. It also causes a new technical challenge to the prediction of the global occurrence threshold of multicarrier multipactors. In this paper, we propose efficient approaches to rapidly compute the fluctuation of space electrons in the evolving process of a multicarrier multipactor, based on which Monte Carlo approaches are developed to efficiently find the global “worst case” waveforms and the occurrence thresholds for both “single-event” and “long-term” multipactors. The proposed approaches can be used for wideband devices, providing an efficient integrated solution for the multicarrier multipactor analysis for practical high-power microwave devices with inhomogeneous field distribution. [ABSTRACT FROM PUBLISHER]

Microchannel plates (MCPs) are widely used as electron, ion, and X-ray detectors. The gain factor and time resolution of the MCP are strongly dependent on its operating and geometry parameters (applied voltage, length-to-diameter ratio, bias angle, and electrode penetration depth). Measurements about this dependence are sparse and do not cover the full range of the parameters. In this paper, 3-D single channel models are developed in computer simulation technology studio suit to systematically and comprehensively calculate the MCP gain and time resolution for various operating and geometry parameters. Furman secondaries electron emission model is employed in our simulation. Simulated result of the gain versus bias voltage is validated by the available experimental data. Finally, geometry parameters of L = 373.6~\mu \textm , D =10~\mu \textm , $h_{{{\text {in}}}}=h_{{{\text {out}}}}= 5~\mu \text{m}$ , and \theta =12^{\circ } are proposed to optimize the MCP performances. Simulation results show that the gain, mean transit time, and transit time spread of the optimized MCP are expected to reach 128 012, 128 ps and 19 ps at the applied voltage of 1000 V. [ABSTRACT FROM AUTHOR]

In this paper, the light images of addressing discharge by plasma in subpixel cells of plasma display panel are presented. The evolution of plasma discharge was recorded using an intensified charge-coupled device digital camera with nanosecond exposure time. The discharge images using a new ramp setup waveform show an improvement of addressing discharge speed. [ABSTRACT FROM AUTHOR]

The particle-in-cell (PIC) simulation of an A6 magnetron with diffraction output (MDO) in our earlier work shows the peak output power (especially the short power pulse with several nanoseconds duration) is lowered when electrons with high energy strike the anode block, which leads to the emission of secondary and backscattered electrons. In addition, the PIC simulation for a 12-cavity MDO also shows when secondary electron emission occurs, the boundary for neighboring modes becomes more complicated than before. Replacing tapered cavities by single-stepped cavities in a relativistic MDO increases the interaction space where the charged particles interact with the induced RF waves. The electronic efficiency of the A6 relativistic MDO as well as the 12-cavity MDO with single-stepped cavities driven by the transparent cathode can be over 70% with gigawatts output power level. And with single-stepped cavities, the distance between the cathode and the wall of relativistic MDO is increased such that the possibility for electrons with high energy striking on the wall is decreased, which results in less emission of secondary and backscattered electrons under the same applied voltage. The PIC simulation demonstrated that in the 12-cavity MDO with single-stepped cavities driven by the transparent cathode with 400-kV applied voltage, the electrons with above 500 eV from cathode under the crossed electromagnetic field can strike on the anode block of MDO, resulting in a secondary and backscattered electron current that can cause different modes to be prevalent or stop the designed mechanism from working. Especially when applied with short voltage pulse with 10-ns duration, the output power pulse is shorted with peak power lowered. The simulation results presented in this paper possibly provide references for multicavity resonator when considering mode selection or mode switching experiments. [ABSTRACT FROM PUBLISHER]

This paper deals with the theory of plasma development in the nanosecond high-power microwave breakdown at the dielectric/air interface. Utilizing the Poisson and Boltzmann equations, the basic physics are explored and investigated. Corresponding to the incident electric field, electrons moving back and forth bring about the negative charge accumulation at the interface. This process generates an extra electric field, strengthening the total amplitude. Simultaneously, deviations of electrons and ions lead to a sheath region providing a space charge field. Secondary electrons are strongly accelerated in the sheath region, eventually leading to an ionization avalanche in a very short time. Both the densities and energies of particles reach the maximums near the sheath region, and that is why the illumination is most significant near the interface. The theory is in good accordance with an experiment conducted under the same conditions. [ABSTRACT FROM PUBLISHER]

We report the performance of an A6 relativistic magnetron with single-stepped cavities output. Particle-in-cell simulation shows the electronic efficiency of an A6 relativistic magnetron with an anode block made of six single-stepped cavities can be up to 78% with an output power of one gigawatt for an applied voltage of 400 kV. When the A6 relativistic magnetron with axial extraction using six single-stepped cavities is applied with a voltage of \(V \sim 400~{\rm kV}\pm 50\) kV the electronic efficiency can be as high as 60%, while the output power can be as high as 1 GW. And, when a 10-ns voltage pulse of 400 kV is applied on this magnetrons with diffraction output using single-stepped cavities, the output power pulse can be as high 1.2 GW. The results in this paper will provide a reference for choosing a cavity that is easily manufactured, so that a physical experiment is more feasible. [ABSTRACT FROM PUBLISHER]

The corona discharge process in a point-plane structure has been simulated using the 3-D particle-in-cell code VORPAL. The motivation behind these simulations was to understand how the corona needle worked in the gas switch, and to look for the methods to improve the stability of the gas switch by achieving a steady corona discharge. The influences of three parameters on ionization region were investigated, the needle size, the gas pressure, and the voltage applied across the electrodes. The needle size varied from 0.05 to 0.25 mm, the air pressure varied from 1.0 to 3.0 atm and the applied voltage varied from 1.2 to 2.3 kV. The voltage polarity was also changed. From the simulations, we obtained the electric field distribution, the distribution of the ionization region, and the current–voltage characteristic. All these parameters have an effect on the corona. Different voltage polarity would result in a different corona shape. Unlike the voltage polarity, the needle size, the air pressure, and the applied voltage have no effect on the shape of the corona. However, with an increase in needle size, or applied voltage, the corona size will also increase, while the corona size will decrease when the air pressure increases. The degree of influence is different; that of the applied voltage is the highest followed by the needle size, while that of the air pressure is the lowest. [ABSTRACT FROM AUTHOR]

By introducing a compensated Monte Carlo collision (MCC) model into the particle-in-cell/MCC method, the streamer initiation process in a laser-triggered gas switch is simulated with a large time step. The spatial distributions of electron density at various pressures and voltages are obtained. [ABSTRACT FROM AUTHOR]

A positive streamer in a strong electric field in air at 1-atm pressure is investigated with particle-in-cell/Monte Carlo collision method including a photoionization model. The simulation results of streamer discharge in parallel plate air gap with and without the photoionization model are compared. It is shown that the seed electrons produced by photoionization generate secondary avalanches which lead to the formation of the streamer. No streamer is observed without photoionization model. [ABSTRACT FROM AUTHOR]