Storage ring cavity higher-order mode dampers for the Advanced Photon Source

Coaxial, mode selective higher-order mode dampers for the Advanced Photon Source storage ring cavities have been fabricated and tested. Two types of dampers will be employed. Electric field probe dampers are positioned in the equatorial plane of the cavity so as to not couple to the fundamental TM₀₁ accelerating mode. Additionally, two magnetic field probe dampers with quarter-wavelength stub rejection filters are positioned in the cavity equatorial plane 90 degrees apart to facilitate dipole mode damping. Both damper types use a vacuum compatible, aluminum nitride (AlN) ceramic RF absorber as the matched load. Measurements were made to optimize the frequency response of the tapered absorber. The design eliminates the need for a ceramic vacuum window