Nonlinear analysis of low frequency Oscillations in gyrotrons

Summary form only given: Low frequency oscillations attributed to reflected electrons bouncing between the electron gun and the interaction space have been observed in many gyrotrons. A nonlinear model is considered which allows one to develop the theory based on PIC simulations and apply it to the analysis of these oscillations. Compared to our previous analytical linear theory, in the present nonlinear model the velocity spread is taken into consideration which shows how the velocity spread influences the period, growth rate and amplitude of the low frequency oscillations. The nonlinear analysis shows how the space charge field of trapped electrons modifies the potential well in which they oscillate and results in the low frequency oscillations.