Cyclotron resonance interaction of microwaves with energetic electrons

Quantum mechanical and classical descriptions of microwave interaction with energetic electrons near cyclotron resonance which underlie the gain mechanism in the electron cyclotron maser are reviewed. Experimental studies designed to test the theory are discussed. A perturbation calculation is given which includes systematically the effects of RF electric and magnetic forces and finite transit time for electrons in the TE
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cavity used in the experiments. Nonlinear extensions of the theory which lead to estimates of the saturation level of this maser are discussed.