A theoretical analysis is presented which is capable of predicting the starting oscillation condition and the eigenmode temporal growth rate of gyro backward wave oscillators. The theoretical predictions are confirmed by computer simulations. The nonlinear saturation mechanism is due to that in the unstable system, the nonlinear electron phase shift induced by the interaction with the wave field results in a virtual end plane which tends to shorten the effective interaction length and brings the system into the marginal stable state. In the system far above threshold, the virtual end plane first oscillates about and eventually approaches the steady state location. This early oscillating behavior of the end plane strongly correlates to the initial pronounced spiking temporal structure in the output power. The spiking structure could be smoothed out if the magnetic field is tapered.
展开▼
