Physics of the interaction Process in a typical coaxial virtual cathode oscillator based on computer modeling using MAGIC

Physical basis of the interaction process in a typical coaxial vircator has been studied using MAGIC, a three-dimensional PIC computer code. Detailed investigations of the complex dynamics of electrons in and near the interaction space have revealed that it takes ∼6 ns for the virtual cathode to be formed and oscillations to begin. Once the oscillations have started three groups of electrons can be distinguished: those that pass through the semipermeable anode and form a virtual cathode, those that travel parallel to the cylindrical anode, or even around its inner edge in small circles, and finally those called "stray" electrons which are ejected from the cylindrical anode and land on the walls of the output waveguide. We have then shown that by reducing the influence of stray electrons the output power of the vircator can be increased by as much as 52%. As a test of the accuracy of the simulation model the input impedance of the device and its frequency of oscillations have been reproduced, respectively, to within 5% and 2.5% of their measured values.