Computer aided design of three-dimensional waveguide loaded cavities

We have developed two simple methods to calculate the power transport through an external waveguide of a loaded cavity utilizing the RF parameters obtained from the frequency domain codes. In the first method the external power loss through an open waveguide is expressed in terms of equivalent circuit coupling parameters between a closed waveguide and a cavity to which it is connected. As we shall see, this equivalent circuit approach is limited in it applicability only to structures with high loaded Q values, say Q/sub L/ < 200. In the second method, the power flow through an external waveguide is calculated from an analysis of the electromagnetic field components of the standing waves in the closed waveguide-cavity structure. Our models make use of the MAFIA code to obtain values of structural parameters and fields when an external waveguide is abruptly terminated with a metal surface. A typical model consists of an output cavity attached via an iris to a short waveguide section ended with a conducting cap. Our methodologies of calculating the loaded Q/sub L/ in terms of the parameters of the closed waveguide-cavity model are described in the following sections. We have obtained reasonable and encouraging results for several loaded cavities whose values of Q/sub L/ have been experimentally measured. Of particular interest is the application to low-Q structures such as the relativistic klystron output cavities. The electromagnetic field method yields good agreement with experimental measurements. This method has also been successfully applied to high gradient accelerating structures with slots for damping out higher modes as recently proposed by Palmer. 5 refs., 9 figs., 2 tabs.