Influence of the Aftercavity Interaction on the Output Power of a Gyrotron Operating at a High-Order Axial Mode

An unexpected abrupt increase of the output power at magnetic field values corresponding to the excitation of high-order axial modes (HOAM) was observed experimentally and is explained theoretically through an after-cavity interaction of the bunched electron beam with the next radial mode. The calculations showed that under certain conditions this effect can be either useful for a power increase at the HOAM operation of the frequency-tunable gyrotron or harmful for high cyclotron harmonic operation due to an expansion of the zone of fundamental cyclotron resonance mode excitation.