HOM (HIGHER-ORDER MODE) DAMPER TESTS OF ADVANCED PHOTON SOURCE STORAGE RING CAVITY WITH a 20-MeV e- BEAM*

A beamline has been assembled with the ANL Chem-istry Division linac (20-MeV e- beam with FWHM of 30 ps) to test the effectiveness of damping techniques of the APS storage ring single-cell cavity. The beamline consists of two sections--the beam collimating section and the cavity measurement section--separated by two single AZ foil windows. The beam diagnostics include a beam position monitor, integrating current transformers, fluores-cent screens, and a Faraday cup. The EPICS (Experimental Physics and Industrial Control System) is used for beam-line control, monitoring, and data acquisition. The cavity was excited by the electron beam to investigate the HOMs. The HOMs were measured with various conditions such as unloaded, critically-coupled, and overcoupled cavity to th