Self-Consistent Calculation of Start-Oscillation Conditions in a Gyrotron with Reflections

The method for calculation of start-oscillation conditions based on the stationary theory of a gyrotron with non-fixed (self-consistent) axial profile of the RF field is described. The calculations of start-oscillation currents and start-oscillation frequencies are presented for the 0.4-THz second-harmonic gyrotron with delayed reflections from the remote load at different parameters of the reflected signal. Increase of the reflection magnitude leads to increase of the number of oscillation zones observed at fixed beam current and, thus, to is extension of the frequency tunability range.