A gyro-TWT with a weak sensitivity to electron velocity spread

A new microwave system for a gyro-TWT in the form of a circular waveguide with a helically grooved inner surface is proposed and studied. The corrugation radically changes the wave dispersion in the region of small axial wavenumbers: at “nearly infinite” phase velocity the group velocity of the wave is finite and constant in a broad frequency band. According to the theory, this allows significant reduction in the sensitivity of the amplifier to the axial velocity spread and an increase in its efficiency and frequency bandwidth. The helical gyro-TWT is realized for the first time experimentally. In the regime of single-frequency amplification, the gyro-TWT operating at the second cyclotron harmonic with a 200 keV/25 A electron beam having a large axial velocity spread of 30% and moving in a relatively weak magnetic field of 2.2 kG yields in the X-band, a high output power of 1 MW, a gain of 23 dB and an efficiency of 20%