Operation of a Highly Overmoded, Harmonic-Multiplying, Wideband Gyrotron Amplifier

Experiments on a unique, high-power, millimeter wave amplifier (a phase-coherent, harmonic-multiplying, inverted gyrotwystron) are reported. Superior stability resulted from two factors: (1) interaction between a relatively low order waveguide mode (TE₂₂) and the beam wave at the fundamental cyclotron frequency in the input section, and (2) an internal mode filter in the highly overmoded (TE₄₂), second harmonic output cavity. Bandwidth was 1.3% with peak gain of 33 dB around 31.8 GHz. The gain-bandwidth performance is a significant advance for gyrotron amplifiers operating in such high order modes.