Nonlinear theory of induced cyclotron and synchrotron radiation from relativistic electron beams at the harmonics of the gyrofrequency

Induced gyroharmonic radiation from an electron beam is analyzed for a cyclotron resonance maser with a double-mirror quasi-optical resonator. The induced cyclotron radiation at the gyrofrequency harmonics has a high electronic efficiency which decreases slowly with the harmonic number under nearly autoresonant conditions when a wave propagates nearly parallel to a uniform magnetic field. It is also shown that the efficiency is relatively low for induced synchrotron radiation at an isolated harmonic with a large harmonic number; the operating current rises only very slowly with the harmonic number.