Quasi-Optical Gyro-BWO With Zigzag Transmission Line As One-Octave Bandwith Sub-THz Source

A broadband frequency-tunable gyrotron backward-wave oscillator (gyro-BWO) is discussed. The gyro-BWO under consideration is using a recently proposed interaction circuit in the form of quasi-optical transmission line where a Gaussian wave beam propagates along a zigzag-like path with vertical and inclined segments periodically spaced along longitudinal z-axis. A static B-field and translational electron velocity are directed along z-axis, so that the electron beam periodically intersects with the wave beam. The resonant cyclotron beam-wave interaction occurs in the regions of perpendicular beam-wave intersections resulting in low sensitivity to the particle velocity spread similar to a gyrotron. The 3D PIC simulations show prospects of this “zigzag” gyro-BWO in realization of frequency tunable oscillators capable of high power and unique (octave width) frequency tuning in the sub-THz range. In the paper, a general layout and results of computer modeling of major experimental components (interaction circuit, electron gun, output microwave system etc.) are discussed for a CW device using a cryomagnet with the B-field of 4–8 T. According to CST simulations, the designed gyro-BWO ensures output of nearly Gaussian wave beam of kilowatt power level at any predefined frequency within 107–215 GHz range. A gyro-BWO with a 20-T magnet is also discussed enabling continuous coverage of the 260–530 GHz frequency band.