Relativistic gyrotrons and cyclotron autoresonance masers

As follows from theory, supported by experiment, if the electron energy grows to ∼ 1 McV the gyroton preserves its capability to produce single-mode radiation in the millimetere wave range with rather high efficiency. If the electron energy is ultra-relativistic (≳ 1 McV), preference must be given to the eyelotron auto-resonance maser, which is, in principle, the most effective type of free electron laser (‘ doppertron’) at milimetere and submillimetre wavelengths.