HOM Studies of the Cornell ERL Main Linac Cavity in the Horizontal Test Cryomodule

The Cornell energy recovery linac will accelerate a 100 mA beam to 5 GeV, while maintaining very low emittance (30 pm at 77 pC bunch charge). A major challenge to running such a large current continuously through the machine is the effect of strong higher-order modes (HOMs) in the SRF cavities that can lead to beam breakup. This paper presents the results of HOM studies for the prototype 7cell cavity installed in a horizontal test cryomodule (HTC). HOM measurements were done for three HTC assembly stages, from initial measurements on the bare cavity to being fully outtted with side-mounted RF input coupler and beam line HOM absorbers. We compare the simulated results of the optimized cavity geometry with measurements from all three HTC experiments, demonstrating excellent damping of all dipole higher order modes.