Theory of the virtual cathode oscillator

Abstract

A one-dimensional analytical theory is developed to describe the behavior of the virtual cathode oscillator. Theoretical predictions for the microwave frequency and efficiency have been obtained. The results suggested that the feedback of the microwave field to the virtual cathode is very important for the microwave efficiency which, under optimum conditions, can be as high as 30%–40%. In addition, the dependence of the microwave efficiency on the electron-beam energy spread and the electron lifetime was determined. The threshold value of the cavity Q, which is necessary to enhance the microwave field, is also estimated.