Virtual cathode oscillator (vircator) modes

Vircators as high-power microwave sources have been investigated for twenty years now. Computer simulations are important tools for vircator performance investigations. However, such simulations do not show the mechanisms involved. Two basic mechanisms are usually discussed: Bridges and Birdsall oscillations and Barkhausen-Kurz oscillations. There is also virtual cathode interaction, producing time-of-flight dependent oscillations with restricted frequency. Neglecting this effect may lead to a substantial decrease in energy conversion efficiency.