Slit-Type Cavities for Cyclotron Resonance Masers Operating at TM Modes

We present a theory of cavities with longitudinal slits which allow the external Q-factor of modes to be evaluated. We also propose a cavity design with a regular section made of a set of metallic blades separated by slits. 3-D-PIC simulation of a V-band gyrotron operating at the TM
_{12, 1}
mode with an output of about 0.5 GW is carried out.