Numerical simulations of electrostatic instabilities in magnetron diodes

The electron dynamics in a crossed-field cylindrical diode are analysed by using a two-dimensional code based on particle-in-cell techniques. Depending on the prescribed emission surface current of the cathode, the numerical simulations reveal the existence of two types of regime in which the system can operate: an emission limited regime and a space-charge limited regime. In both types of regime, electrostatic modes are shown to be excited, the frequencies of which being of the same order of magnitude as the cyclotron frequency. The saturated states of these instabilities result in the persistence of large-amplitude coherent structures.