Computer Modelling of Two- and Three-Dimensional Cavities

The rf accelerating system is the heart of many low, medium and high energy particle accelerators and in many cases, it is also a major drain of investement money and operational costs. In order to increase efficiency, many computer codes have been developed in the last few decades. Recently, it has been realized that parasitic collective effects can also present serious problems in the most expensive front line high energy physics accelerators. Nowadays, cavity design is no longer only a question of optimizing the shunt impedance but also of optimizing the overall effect of the system. Also, all other non-rf cavities in an accelerator are found to cause many problems. For cylindrically symmetric structures well tested computer codes are in widespread routine use as design tools. Fully three dimensional codes are just coming into common operation. At the present time, we are able to solve almost every two or three dimensional cavity problem either by mode computation or by transient wake field computation.