An extended interaction oscillator based on a complex resonator structure

We report experimental investigation of a novel scheme for efficient intera ction between a linear electron beam and an electromagnetic wave in a compl ex extended interaction structure. The structure of interest consists of a high R/Q, five-gap, coupled-cavity resonator that incorporates a coaxial se ction of a quarter plasma wavelength placed between the first and second ca vities. In the coaxial section, beam and wave propagate in separate channel s, The first cavity, strongly coupled to the other cavities through the wav e channel of the coaxial section, serves as a buncher cavity, An inner chan nel running through the center conductor of the coaxial section provides a cutoff drift space for ballistic bunching of electrons, an effect that is s hown to significantly enhance the interaction efficiency, Oscillation power of 2.2 kW at 16.6 GHz was demonstrated with an interaction efficiency of 3 0%, The total efficiency was further increased to 41% by incorporation of a two-stage depressed collector.