Linear gain of a gyro-TWT with a slotted-waveguide interaction space

Summary form only given. The single-mode operation of a millimeter wave gyro-TWT amplifier can be provided by using a mode selective slotted waveguide. At operating frequencies of 100 GHz and higher it is expedient to apply a quasi-optical slotted waveguide. We selected the slotted waveguide with two cylindrical confocal mirrors. It is possible to selectively excite a Gaussian-like mode in such a waveguide. As a result, we can achieve single-mode operation. However, the inhomogeneous azimuthal field distribution of the Gaussian-like mode decreases the gain as compared to the gain of the conventional circular-waveguide based gyro-TWT amplifier. We have developed a small-signal theory of the gyro-TWT amplifier with a confocal waveguide and an annular electron beam. The analysis of the 140 GHz amplifier includes calculations of the operating Gaussian-like mode gain, the operating and spurious mode attenuation due to diffraction in the slotted waveguide, and the starting current for parasitic BWO generation in the amplifier.