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An extension of a first-principle combined Monte Carlo method is proposed in this work to obtain the secondary electron emission characteristics of anisotropic crystal Al2O3. Unlike isotropic crystal Cu, density functional theory calculations reveal that the q-dependent energy loss function of Al2O3 in all directions is different. Therefore, an interpolation algorithm is introduced in the Monte Carlo method to determine the loss of energy and inelastic mean free path of electrons. The simulation results are in good agreement with experimental data. This method can be further used to simulate the secondary emission yield of other anisotropic crystal materials. [ABSTRACT FROM AUTHOR]

A microcavity array device decorated by silicon nanowires (SiNWs) is fabricated and the discharge property improvement is investigated. The array device can be operated stably from several kPa to atmospheric pressure of argon, powered by a 20 kHz bipolar nanosecond pulse source. Profiting by electron emission from SiNWs, the microplasma discharge dynamics and emission properties are significantly enhanced. Experimental results manifest that the instantaneous total current of the device decorated by SiNWs is up to ∼20% higher than that of the device without SiNWs and the mean current is increased by ∼12.5% compared with the conventional device (without SiNWs), and the ignition voltage decreased by ∼24%. The setup time is less than 90 ns before the device is fully ignited, and emission intensity enhanced by over 60% compared with the conventional plain surface device. Moreover, calculated by Lissajous figures, the discharge power of proposed device is higher than that of the traditional device with increment of ∼26%, and the impact of SiNWs on microdischarge processes is analyzed. The mechanism of the microplasma property enhancement is discussed through introducing the electric field enhancement effect at SiNWs cap and initial seed electrons emitted from SiNWs. This work combines the characteristic advantages of SiNWs with microcavity gas discharge to achieve the performance improvement of microplasma, and the results reported here has profound impacts on improving microplasma discharge properties and implies potential significance in promoting the performance of plasma applications. [ABSTRACT FROM AUTHOR]

In this paper, emphasis is put on passive intermodulation (PIM) caused by multipaction. The results are calculated by particle-in-cell simulation under the conditions of 2-tone and 4-tone carriers. A temporal evolution of the number of particles with different carrier powers is presented. The input and output signals in the time domain and the power spectrum densities of these signals in the frequency domain under different conditions are compared. The relationship between multipaction and PIM interference is discussed. It shows that the appearance of the PIM phenomenon follows the occurrence of saturation of multipactor discharge and the powers of PIM products basically increase as the carrier powers grow. In addition, to suppress the occurrence of PIM interference, an external magnetic field is added in the direction perpendicular to the electric field, which is a practical way to inhibit multipaction, and the effectiveness and the reliability of this method are also verified by simulation. [ABSTRACT FROM AUTHOR]

With the introduction of an external circuit model and a gas desorption model, the surface flashover on the plane insulator-vacuum interface perpendicular to parallel electrodes is simulated by a Particle-In-Cell method. It can be seen from simulations that when the secondary electron emission avalanche (SEEA) occurs, the current sharply increases because of the influence of the insulator surface charge on the cathode field emission. With the introduction of the gas desorption model, the current keeps on increasing after SEEA, and then the feedback of the external circuit causes the voltage between the two electrodes to decrease. The cathode emission current decreases, while the anode current keeps growing. With the definition that flashover occurs when the diode voltage drops by more than 20%, we obtained the simulated flashover voltage which agrees with the experimental value with the use of the field enhancement factor β = 145 and the gas molecule desorption coefficient γ = 0.25. From the simulation results, we can also see that the time delay of flashover decreases exponentially with voltage. In addition, from the gas desorption model, the gas density on the insulator surface is found to be proportional to the square of the gas desorption rate and linear with time. [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]

Statistical multipactor theories are critical prediction approaches for multipactor breakdown determination. However, these approaches still require a negotiation between the calculation efficiency and accuracy. This paper presents an improved stationary statistical theory for efficient threshold analysis of two-surface multipactor. A general integral equation over the distribution function of the electron emission phase with both the single-sided and double-sided impacts considered is formulated. The modeling results indicate that the improved stationary statistical theory can not only obtain equally good accuracy of multipactor threshold calculation as the nonstationary statistical theory, but also achieve high calculation efficiency concurrently. By using this improved stationary statistical theory, the total time consumption in calculating full multipactor susceptibility zones of parallel plates can be decreased by as much as a factor of four relative to the nonstationary statistical theory. It also shows that the effect of single-sided impacts is indispensable for accurate multipactor prediction of coaxial lines and also more significant for the high order multipactor. Finally, the influence of secondary emission yield (SEY) properties on the multipactor threshold is further investigated. It is observed that the first cross energy and the energy range between the first cross and the SEY maximum both play a significant role in determining the multipactor threshold, which agrees with the numerical simulation results in the literature. [ABSTRACT FROM AUTHOR]