Broadband efficient low-relativistic gyro-TWT with helically grooved waveguide

Summary form only given. The gyrotron traveling wave tube (gyro-TWT) is a well-known amplifier variety of the gyro-devices, which may have a wide instantaneous frequency bandwidth because of the operation with an electromagnetic wave possessing large group velocity. For a microwave system in the form of a smooth cylindrical waveguide a large wave group velocity inevitably leads to a large axial wavenumber, which makes this device significantly more sensitive to particle velocity spread in comparison with a gyrotron. The most favorable wave dispersion for a gyro-TWT is that when the wave group velocity is sufficiently large and constant in the region of close-to-zero axial wavenumber. A similar dispersion can be realized in an oversized circular waveguide with special helical ripples of its inner surface A theoretical analysis demonstrates important advantages of the "helical" gyro-TWTs over the analogous "smooth" ones in sensitivity to electron velocity spread, frequency bandwidth and stability to parasitic self-oscillations. The proof-of-principle experiments exploiting moderately relativistic (200-300 keV) short-pulse (20-100 ns) field-emission electron beams have proved the main theoretical predictions. Based on the first successful experiments and the developed theory, a project was started aimed at the creation of a more applicable device. The main goal of this project is the realization of a Ka-band gyro-TWT with a low-relativistic electron beam produced by a gun with a thermionic cathode.