Study on an open column slow-wave grating structure with arbitrarily-shaped slots

The open column slow-wave grating structure, a novel type slow-wave system for Smith-Purcell FEL and relativistic TWT, is presented in this paper. The cold and “hot” dispersion equations of the structure with arbitrarily-shaped slots are derived by means of an approximate field-theory analysis, in which the continuous profile of the groove is approximately replaced by a series of rectangular steps, and the field continuity at the interface of two neighboring steps and the matching conditions at the interface between the groove region and central region are employed. The dispersion characteristics, interaction impedances and the small signal gain of the fundamental wave are numerically calculated and the effects of slot profile are analyzed.