Excitation of the electromagnetic waves by electronic stream on grating with essentially increased period

We analyze interaction of nonrelativistic electronic stream with microwave field in the regime of synchronism with higher spatial wave of the periodical structure. We have found a possibility to compensate deminution the interaction energetics, caused by high index p of a synchronous wave (adequate to increase of grating´s period). For this purpose we use operation in a band of an Wood´s resonance [1].