The investigation of nonlinear transient characteristics of gallium arsenide (GaAs) photoconductive semiconductor switches (PCSS) is of great significance for its applications in pulsed power technology. In this letter, the laser diode (LD) energy of $2~\mu \text{J}$ is employed to trigger the opposed-electrode GaAs PCSS. The compressed pulse width and increased amplitude are obtained as the bias electric field increases from 6kV/cm to 34kV/cm. It is numerically modeled the transient electric field distribution along the photogenerated carriers’ transport. Results reveal that pulse compression effect (PCE) can be attributed to the negative differential mobility (NDM) and electric-field screening (EFS) effect. The compression of pulse width on time scale provides a possibility to relieve the heat accumulation on time scale, and further to suppress the device failure for the potential high-repetition-rate applications.

The transient performance of gallium arsenide (GaAs) photoconductive semiconductor switches (PCSSs) triggered by laser diodes (LDs) at nano-joules (nJ) energy is of great significance for the potential high-power applications at high repetition rates. An opposed-contact GaAs PCSS with Ni/AuGe/WTi/Au electrodes is presented at single-shot and 1-kHz excitation. The influences of bias electric field up to 80 kV/cm on nonlinear characteristics are investigated quantitatively with a carriers’ avalanche multiplication factor as high as $0.8\times 10^{{4}}$ . The effect of electric field on the carriers’ dynamic process and thermal accumulation in repetitive operation is analyzed. The transient electric field distribution is demonstrated by an ensemble Monte Carlo simulation.

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.

To suppress microwave window breakdown, an external parallel dc bias electric field is applied to sweep out the electrons from the discharge zone. The development of microwave window breakdown under an external dc electric field is investigated using particle-in-cell and Monte Carlo collision simulation. The results show that the number of multipactor electrons decreases with the strength of the external unidirectional dc electric field when the size of the microwave window is finite. In addition, the threshold of breakdown is strongly influenced by the direction of the external bidirectional dc electric field. When the electric field is directed from the center to the edge of the microwave window, breakdown occurs more readily than in the absence of the electric field. However, when the electric field is directed toward the center of the microwave window, the discharge process starts at the edge of the window and develops to the center of the window. This is because a smaller density of electrons at the window edge results in a smaller gas pressure and the low gas pressure above the dielectric surface thus makes formation of the plasma more difficult. As a result, the early stage of breakdown is suppressed and the maximum transmitting power is enhanced.

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 t_c of microwave window breakdown decreases exponentially with the gas desorption rate. Besides, t_c decreases with the energy of the first crossover point of the secondary electron emission curve when the strength of microwave electric field E_rf is small. This dynamical model provides a solution to designing the microwave window.

Relativistic backward oscillator (RBWO) has been developing toward the millimeter wave, which is easy to cause RF breakdown due to the reduction in device size. Using the overmoded slow wave structure (SWS) and selecting high-order mode to operate can effectively prevent RF breakdown. In this article, we analyzed the physical mechanism of the overmoded SWS dispersion curve, especially the asymmetric mode, and quantitatively obtained the variation laws of the dispersion curve and approximate methods by a concise mathematical formula. Based on these laws, we proposed methods for controlling the quality factor effectively and calculating the coupling impedance. The mode control method considering asymmetric mode is verified through 3-D PIC simulation.