Mode conversion in a Gyrotron at a waveguide-taper junction

The output power levels of Gyrotron II are very much higher than those predicted when one assumes that a single waveguide mode exists throughout the cavity and output section. In this paper we demonstrate the importance of mode conversion at the point where the uniform waveguide meets the first down-taper.The method of calculating the mode conversion used here is superior to many that appear in the literature. It uses the correct boundary conditions, it treats the wave magnetic field fully and, especially important in relation to cavities, it is applicable to waveguide modes near cutoff.