Linear analysis of 170 GHz cylindrical and confocal gyrotron

In this paper, the mode density, coupling coefficient, eigenfrequencies, quality factors and starting currents of a 170 GHz cylindrical and confocal gyrotron are studied based on the linear theory. Results show that the mode density in the confocal cavity greatly decrease due to the diffraction properties. Modes in the confocal cavity have lower quality factors than the modes in cylindrical cavity, hence the starting currents are higher than the latter. The confocal gyrotron is more stable than the cylindrical gyrotron when operating at large current. Meanwhile, through altering the mirror width, quality factors together with the starting current of the confocal modes are adjustable.