Stability and Tunability of a Gyrotron Backward-wave Oscillator

Stability issues have been a major concern for the realization of broadband tunability of the gyrotron backward wave-oscillator (gyro-BWO). A time-dependent code is employed to examine the stability properties of the gyro-BWO over a wide range in magnetic field and electron beam voltage. On the basis of the results, an optimized Ka-band gyro-BWO experiment has been designed and conducted. Continuous and smooth tunability, in magnetic field and in beam voltage, was demonstrated with high interaction efficiencies. A 3-dB tuning range of 1.4 GHz with a peak power of 130 kW at 27% efficiency was achieved.