Analytical nonlinear theory of the orotron

Abstract

The orotron is a device in which a sheet electron beam excites electromagnetic (EM) oscillations in an open resonator formed by a concave mirror and a periodic grating plate. The first spatial harmonic of a field near the grating has phase velocity close to electron velocity; therefore electrons streaming over the grating surface produce Cherenkov or Smith-Purcell radiation. The orotrons can be configured for producing coherent radiation at short millimeter and submillimeter wavelengths (up to the terahertz range). Typically the amplitude of the EM field in the orotron is rather small. Therefore, for extracting an appreciable part of electron kinetic energy, it is necessary to realize synchronous interaction between electrons and a slow wave at long enough distances. This peculiarity of the orotron operation makes it possible to develop an analytical nonlinear theory of the orotron. Such a theory showing how to optimize the choice of the interaction length and the ratio between ohmic and diffractive losses is developed in the present paper. The theoretical treatment is accompanied with consideration of practical effects limiting the orotron efficiency. © 2006 American Institute of Physics.