Selective mode suppression in a W-band second harmonic coaxial-waveguide gyrotron backward-wave oscillator

A gyrotron backward-wave oscillator (gyro-BWO) encounters increasingly severe mode competition problems during development toward the goal of higher power at high frequencies. A coaxial interaction waveguide with distributed losses is proposed to enhance the stability and frequency tunability of a W-band second harmonic gyro-BWO. The losses of the inner and outer cylinders complement each other and effectively stabilize all of the competing modes while having minor effects on the operating mode. Under stable operating conditions, the W-band second harmonic coaxial gyro-BWO has a predicted peak output power of 71 kW with a magnetic tuning bandwidth of 1.0 GHz.