Analysis and preliminary experiments for rectangular grating Cerenkov masers

Abstract

Summary form only given. Pencil and sheet beam propagation over a rectangular deep groove grating structure in a rectangular guide has been considered. A 14-GHz prototype has been analyzed, designed, and fabricated for experimental measurements. The lowest order mode in the rectangular grating in a Ku-band size guide is the hybrid TE/sub x10/ mode. The beam energy ranges from 2.5 kV (backward mode) to 10 kV (forward mode). The fully complex dispersion relation for the beam-wave interaction is analyzed including finite axial beam spread. Growth rates of the electromagnetic wave for a sheet beam case for the forward and backward mode regimes are obtained. Growth rates for the pencil beam case are scaled from that of the sheet beam by a beam filling factor. The absolute and convective nature of the interaction is analyzed utilizing Brigg's criteria and a contour plot technique. It is found that the instability is always convective in the forward mode regime. In the backward wave mode regime, the absolute instability occurs at one particular frequency. At other frequencies, a band of convective growth is obtained.