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A new dynamical model is built to describe the process of microwave window breakdown at the vacuum/dielectric interface. In this model, the effects of gas desorption and gas diffusion on breakdown are first taken into account. The evolution of the density of electrons and the neutral gas is analyzed. Particle-in-cell simulations are employed to validate this model, and the agreements of comparisons are favorable. The results show that the density of neutral gas decreases exponentially with the distance away from the dielectric surface. It is concluded that the gas diffusion is the main factor in the density reduction of neutral gas. With the influence of gas ionization, the number of electrons striking the dielectric surface increases. As a result, the gas pressure above the dielectric surface increases rapidly. In addition, the discharge formation time tc of microwave window breakdown decreases exponentially with the gas desorption rate. Besides, tc decreases with the energy of the first crossover point of the secondary electron emission curve when the strength of microwave electric field Erf is small. This dynamical model provides a solution to designing the microwave window. [ABSTRACT FROM AUTHOR]

With the introduction of the gas diffusion model, the surface flashover at the insulator–vacuum interface perpendicular to electrodes is simulated with the particle-in-cell method. The distributions of density of electrons, ions, and neutral gas molecules are obtained, which is consistent with images diagnosed in the experiment. The gas pressure at the dielectric surface near electrodes is much higher than it is at other locations. Furthermore, the processes of vacuum surface flashover for angled dielectric insulators are analyzed. The results show that negative charges will accumulate on the dielectric surface when the negative angle is large. The electric field produced by negative charges weakens the normal electric field and emission current on the cathode triple junction. Moreover, the process of secondary electron emission is completely suppressed when the negative angle is large. With the development of gas desorption, the breakdown will evolve from field emission into gas ionization. Therefore, when the angle is negative, the threshold of surface flashover first decreases then increases with the angle, which is in good agreement with laws obtained in experiments. This study can provide a deep understanding to the vacuum surface flashover. [ABSTRACT FROM AUTHOR]

Abstract: A simple broadband T-shaped waveguide branch in photonic crystals is constructed only by introducing three dielectric rods into the waveguide channels near branch region. Numerical results indicate that the bandwidth of high transmission (the total transmittance is larger than 95%) is over 415nm centered at 1550nm. Owing to its simple structure and broad enough bandwidth, this waveguide branch is expected to be applied to highly dense photonic integrated circuits. [Copyright &y& Elsevier]

The microwave window breakdown due to the plasma formation greatly limits the power handling capability of high-power microwave systems. However, the experimentally-observed fast plasma propagation cannot be explained using previous theory or simulation results. In this paper, the photoionization is considered to investigate the mechanism of microwave window breakdown at the air/dielectric interface by particle-in-cell simulation. The results show that photoelectrons produced by high-speed photons can profoundly promote discharge above the air/dielectric interface. Then a fast plasma formation and propagation occurs. The speed of plasma propagation can reach 1 × 106 m s−1, which agrees well with experiments. As a result, the transmitting power is attenuated more seriously than the case without the photoionization. Furthermore, the effects of size of microwave window, gas pressure, strength of microwave electric field and distribution of microwave electric field on the plasma propagation are investigated. The results show that the total number of electrons is nonlinearly increasing with the size of microwave window when a uniform microwave electric field is applied. The speed of the plasma propagation exponentially increases with the strength of microwave electric field. Therefore, the photoionization is an indispensable process in the microwave window breakdown with high-strength microwave electric field. [ABSTRACT FROM AUTHOR]

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]

Abstract: The striation phenomenon in large-gap coplanar plasma display panel (PDP) has been investigated experimentally in macroscopic cells. The results show that the striations can generate either above anode accompanying the development of discharge or in the weak-field plasma channel near the dielectric surface after the discharge having developed. The surface state of the dielectric layer and the pre-accumulated wall charge play non-important role on the generation of striation. It is supposed that the physical process in the gas volume govern the formation of striation in PDP cells. [Copyright &y& Elsevier]

Influences of wall-charge accumulation on gas dielectric barrier discharge (DBD) breakdown threshold and sustaining voltage margin of alternating current plasma display panel (AC-PDP) were investigated. It is observed that wall-charge accumulation results in a remarkable increase of gas DBD breakdown threshold during sustaining discharge period. Sustaining voltage margin is reduced by the threshold increase. A larger margin can be obtained when the threshold is decreased by removing unfavorable influence of wall-charge accumulation. Compared with normal margin, improved margin has a larger value and a faster linear increase with increasing wall-charge voltage. That indicates a way to improve AC-PDP performances remarkably. [ABSTRACT FROM AUTHOR]