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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]

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 investigates the external circuit effect in corona discharge by means of numerical simulation, while the effect is usually disregarded in previous plasma simulations. A general numerical solution method of serial external circuit, which can compute surface charges on any shape of electrodes adaptively and solve electrode potential and circuit current simultaneously, is developed to support the investigation, due to lack of theoretical solution in irregular electrode systems. Brief description and validation of the scheme are presented in section 2. In general, the accuracy of numerical solution improves with mesh refinement in orthogonal mesh, due to stair step approximation. Simulations are performed in our self-developed 3D PIC-MCC (particle-in-cell, Monte Carlo collision) code with photoionization and external circuit. The simulation model including recently developed photoionization model is described briefly in section 3. Then the simulation results in a needle-plate electrode in air, such as spatiotemporal evolution of corona discharge and waveforms of electrode voltage and circuit current, are presented. Physical mechanisms of formation of branched corona discharge and self-consistent adjustment of electrode voltage and circuit current are discussed. The waveforms of voltage and current in this simulation are generally consistent with experimental result. The external circuit has negative feedback effect on the discharge, and can adjusts electrode voltage self-consistently. The application of external circuit improves the applicability of particle simulation method to the simulation of discharge phenomenon in actual devices. [ABSTRACT FROM AUTHOR]

Self-organization of periodic, streamer-like ionization waves in planar microplasma devices having a dielectric barrier discharge structure is observed. In contrast to plasma propagation in arrays of microchannels or microcavities, the ionization waves originate from a single point but rapidly sub-divide into as many as 10 'branch' plasma wave packets that eventually recombine. In less than 70 ns, the self-organization of the spatially-periodic array of co-propagating branches is complete and two successive sets of waves, separated in distance and time by ∼1.8 mm and ∼50 ns, respectively, are generated. The mean propagation velocity of each plasma packet is greater than 70 km s−1 but values as large as 150 km s−1 have been measured. Because the propagation path for all subsequent streamers is established by the first set of plasma packets, the intensity of the second set is noticeably enhanced. The average length of the primary branches is ∼1.5 mm but reaches a maximum of ∼4.5 mm as the wave packets travel an overall distance of 1 cm. These phenomena are interpreted in terms of photoelectron emission from the floor and walls of the shallow dielectric microcavity, induced by radiation from the advancing packets, and the rapid collapse of the sheath of each microplasma owing to the accumulation of charge on the underlying dielectric. The spatial profiles of the propagating plasmas suggest that generating and probing plasma solitons may now be feasible. [ABSTRACT FROM AUTHOR]