Higher order mode damping in a pill box cavity

The authors present a method to damp the higher-order modes (HOMs) without excessive damping of the principal mode. This has been demonstrated in a pill box cavity with three slots coupled to waveguides that carry HOM energy to terminating loads. They were concerned primarily with accelerating and deflecting modes: i.e. the TM/sub mnp/ modes of order m=0 and m=1. For the strongest damping, only three m=0 and m=1 modes were detectable. These were the principal TM/sub 010/ mode, the TM/sub 011/ longitudinal mode, and the TM/sub 110/ deflecting mode. In addition, the HOM Qs and the reduction of Q for the principal mode were determined by computer calculation. The measured Q of the first longitudinal mode was 31 and of the first transverse mode 37. The maximum damping was limited by how well the waveguides could be terminated. The computer calculations for the TM/sub 011/ and TM/sub 110/ modes gives values in the range as measured.<>