Dynamics of Mode Competition in the Gyrotron Backward-Wave Oscillator

The dynamics of axial mode competition in the gyrotron backward-wave oscillator (gyro-BWO) has been investigated in theory and experiment. Because of the difference in field-shaping processes, the axial modes of the gyro-BWO each exhibit a distinctive asymmetry in field distribution along the axis. Multi-mode particle simulations and time-frequency analyses reveal a consistent pattern of axial mode competition in which a fast-growing and well-established mode is subsequently suppressed by a slowly-growing mode with a favorable field profile. This is verified in a Ka-band gyro-BWO experiment.