Large-signal operation of a third-harmonic slotted gyro-TWT amplifier

The large-signal characteristics are reported for a slotted third-harmonic gyrotron traveling-wave tube (gyro-TWT) amplifier. The slotted interaction circuit yields strong harmonic interaction for relatively low-energy axis-encircling electrons. The circuit was sliced to suppress competing modes by interrupting their wall currents. The experiment was conducted in the X-band as a scaled test of a 95-GHz amplifier design developed in collaboration with CPI/Varian. A gyroresonant RF accelerator was employed to produce the required axis-encircling electron beam. The two-stage slotted third-harmonic gyro-TWT with a beam current equal to 60% of the design value was stable and yielded an output power of 6 kW with 5% efficiency and 11-dB saturated gain over a bandwidth of 3%