Ultrahigh Gain Gyrotron Traveling Wave Amplifier

Mode competition in the gyrotron traveling wave amplifier is shown to be intricately connected to the interplay between the absolute/convective instabilities, circuit losses, and reflective feedback. Physical origins of spurious oscillations are analyzed and characterized. Fundamental understanding of these processes leads to a device concept which provides zero-drive stability at ultrahigh gain. The scheme was verified in a proof-of-principle experiment in the $\mathrm{Ka}$ band, producing 93 kW saturated peak power at $26.5%$ efficiency, 70 dB gain, and a 3 dB bandwidth of 3 GHz.