Measurement of the interaction between a beam and a beam line higher-order mode absorber in a storage ring

A phased luminosity upgrade of the CESR e⁺e^- storage ring has been initiated. The upgrade program calls for the eventual installation of superconducting cavities with strongly damped high-order modes. The cavity is designed to allow all HOMs to propagate into the beam pipe, so that they may be damned by a layer of microwave absorbing ferrite. RF measurements with a full-size copper cavity and loads made of TT2-111R ferrite indicate that the design gives adequate HOM damping. The coupling impedance of the ferrite loads and the consequences for beam stability in a high-current ring have been predicted. Prototypes for the cavity, cryostat and HOM loads were subjected to a beam test in CESR. To further test our understanding of the beam-ferrite interaction, beam measurements were done in CESR in December 1994 on a ferrite load of magnified coupling impedance