Refining and maintaining the optimal performance of the CEBAF SRF systems

CEBAF at Jefferson Lab is striving to achieve its maximum reliability at the maximum deliverable energy for physics experiments. Most critical are the acceleration systems. Characterizations of the individual limiting characteristics of the 338 superconducting RF (SRF) cavities continue to be refined. The field-emission-stimulated discharges at the cold RF waveguide input windows remain the dominant energy-limiting effect. By refining the cavity-specific dependences of this window arcing, we are able to minimize the resulting lost beam time when CEBAF is run near its maximum energy. Operation at increased RF power levels has produced unanticipated heating in the region near the warm polymeric RF windows on a few cavities. This has stimulated the migration to a more durable ceramic replacement window. During 2000, CEBAF encountered its first cryomodule helium leak into beam vacuum, most likely through an indium wire seal. Characterization of the leak and accommodation methods used will be described. Finally, in situ RF/helium processing of cavities continues to increase the available linac voltage