Design of one-octave bandwidth gyro-BWO with zigzag quasi-optical transmission line

Design of a proof-of-principle experiment on 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 the mirrors direct a Gaussian wave beam 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 at 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 frequency band) tuning in the short-millimeter wavelength 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.