Extract from CST PARTICLE STUDIO
This workflow example considers a particle beam passing through a pillbox cavity. Since only the vacuum parts of the structure need to be modeled, it is very easy to set up the geometrical description. It consists only of two added cylinders with a couple of blended edges. The following picture shows the structure of interest. It is shown in a transparent way, in order to see the particle beam axis.
CST PARTICLE STUDIO allows you to define the properties of the background material. Anything you do not fill with a particular material will automatically be considered as background material. For this structure, it is sufficient to model only the vacuum space. The background properties will be set to PEC (Perfect Electric Conductor).
Further information can be obtained from the "Workflow and Solver Overview" documentation.