Proposal for a broadband higher-order-modes suppressor for radiofrequency accelerating cavities

An important task in the design of the radiofrequency cavities for the ELETTRA Synchrotron Light Source is to provide adequate damping for the higher-order modes (HOM) that could be excited in the cavity by the electron beam. In order to satisfy this request, we decided to develop a brosd-band suppressor, which can be used instead of a number of couplers, each tuned at a dangerous cavity mode frequency. A prototype of a waveguide suppressor directly coupled to a cavity has been produced and tested. The measurements on this device show that a large number of HOMs are practically eliminated. A few modes do not disappear, but they are heavily damped. The damping effect on the fundamental mode of the cavity is small and is thus acceptable. (author) 7 refs., 4 figs., 4 tabs