Cerenkov radiation in slow-wave guiding structures

Cerenkov radiation of a prebunched beam in a dielectric tube waveguide is here shown to be about an order of magnitude higher than that in a comparable slab of dielectric material. Furthermore, two distinct types of interaction are analyzed: multibunch, and bunch-by-bunch radiation, wherein integral transform methods are used. Multibunch Cerenkov radiation in a helix waveguide is used to show the identity with TWT interaction. It is subsequently shown that for open boundary inhomogeneous waveguides a TWT type analysis will give the same results as multibunch Cerenkov radiation based on integral transform methods. For single bunch or a bunch-by-bunch type of interaction in such structures where energy orthogonality and completeness of the eigenfunctions do not hold, an integral transform method is used. The underlying difference between bunch-by-bunch and multibunch radiation is discussed. The utility of Cerenkov radiation in a dielectric tube waveguide for the generation of coherent electromagnetic power in the millimeter range is pointed out. Numerical results are given to show the variation of power with respect to various parameters. Experimental results from a 0.8-Mev beam are shown to agree satisfactorily with theory.