Study of the trapped modes at the vacuum ports

Pumping ports in PEP-II vacuum chamber will be shielded with slots cut in the walls of the beam pipe. The number of slots n{sub s}, their length l, and width w are defined by the required pumping conductance. The present design has 40 slots around the stainless steel round pipe in the straight sections, and, for the rectangular copper chamber of the arcs, there are 18 slots placed in upper and lower decks. Here we want to address two potential problems related to the slots: radiation of the TE HOM-s through the slots, and generation of the trapped modes