A dynamical model of microwave window breakdown at vacuum/dielectric interface

Abstract

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.