Comparative analysis of gyrotron backward-wave oscillators operating at different cyclotron harmonics

A comparative analysis between the fundamental and second cyclotron harmonics of gyrotron backward-wave oscillators (gyro-BWOs) is presented. The simulation results reveal that nonlinear field contraction is a common feature for both harmonic interactions. Besides, the electron transit angle, used to characterize the axial modes of the fundamental harmonic TE11 mode at the start-oscillation conditions, is found to be applicable even for the second harmonic TE21 mode. Each axial mode of either the fundamental harmonic TE11 or the second harmonic TE21 modes is maintained at a constant value of the electron transit angle while changing the operating parameters, such as magnetic field and beam voltage. Extensive numerical calculations are conducted for the start-oscillation currents and tuning properties. Moreover, single-mode operating regimes are suggested where the second harmonic TE21 gyro-BWO could generate a considerable output power, comparing with the fundamental harmonic TE11 gyro-BWO. © 2004 American Institute of Physics. [DOI: 10.1063/1.1783314]