Aftercavity interaction in gyrotrons

Summary form only given. The theory describing the cyclotron resonance interaction between electrons in a spent beam exiting the cavity and traveling electromagnetic waves propagating from the cavity exit into the output part of a gyrotron is developed. At present it is recognized that this parasitic effect not only reduces the gyrotron interaction efficiency but, more importantly, spoils the energy distribution of spent electrons, thus reducing the possibility to efficiently utilize depressed collectors. Our study shows that a proper consistent optimization of a profile of the waveguide wall in the region of the uptapered output waveguide and quasioptical launcher and axial distribution of the magnetic field of a solenoid may result in significant improvement of situation.