Nonlinear dynamics in a reflex diode

Potentials in high current reflexing electron diodes such as vircators are dominated by space charge effects,¹ and are rapidly time varying and nonlinear because of the oscillating virtual cathode and strong particle bunching. Previous experiments² showed the stochastic character of the oscillating electromagnetic fields. The dynamical behavior of this type of device is studied with the 2 dimensional electromagnetic code MAGIC³ and with a simplified 1 dimensional nonlinear analytic model. Computed particle trajectory phase space plots show several classes of electron trajectories. The 1 dimensional nonlinear model generates a similar set. The calculations show that the stochastic behavior of the electromagnetic fields in both frequency and time are similar to the experimental observations. These models are used to investigate the dependence of spectral bandwidth and the RF fluctuations on the macroscopic system parameters.