First Experimental Results on Gyrotron Backward-Wave Oscillator With Zigzag Quasi-Optical Transmission Line

The design and results of the first hot-test experiment on a gyrotron backward-wave oscillator (gyro-BWO) using a newly proposed microwave circuit are presented. The gyro-BWO employs an interaction circuit based on a quasi-optical transmission line that directs a Gaussian wave beam along a zigzag path with vertical and oblique segments periodically spaced along the longitudinal axis. A resonant cyclotron beam-wave interaction occurs in the regions where the beam intersects the wave perpendicularly, resulting in low sensitivity to particle velocity spread, similar to that of a gyrotron. The device was hot-tested in a continuous wave (CW) mode, generating microwave radiation in the form of a Gaussian beam with powers of 0.2-1.2 kW and frequencies in the 90–195 GHz range. 15 bands were measured, within which the generation frequency linearly and continuously changed as the magnetic field or accelerating voltage were varied. Due to the unique dispersion properties of the zigzag gyro-BWO, these bands cover the entire operating range with a fill-factor of approximately 70%. This is significantly greater than that of any other experimentally tested gyrotron-type device.