Overview of the First Five Refurbished CEBAF Cryomodules

The Thomas Jefferson National Accelerator Facility is currently engaged in a cryomodule refurbishment project known as the C50 project. The goal of this project is robust 6 GeV, 5 pass operation of the Continuous Electron Beam Accelerator Facility (CEBAF). The scope of the project includes removing, refurbishing and replacing ten CEBAF cryomodules at a rate of three per year. Refurbishment includes reprocessing of SRF cavities to eliminate field emission and increase the nominal gradient from the original 5 MV/m to 12.5 MV/m. New "dogleg" couplers between the cavity and helium vessel flanges will intercept secondary electrons that produce arcing at the 2 K ceramic window in the fundamental Power Coupler (FPC). Modifications of the external Q (Qext) of the FPC will allow higher gradient operations. Other changes include new ceramic RF windows for the air to vacuum interface of the FPC and improvements to the mechanical tuner. Any damaged or worn components will be repla