Suppression of high-power microwave window breakdown by the sweeping-out-electron effect with an external dc bias electric field

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.