The Viton gate valves installed in the CEBAF beamline have significantly degraded after long-term operation in a radiation environment, generating numerous particles that cause heavy contamination and strong field emission. As a replacement, all-metal gate valves have been proposed for installation in the CEBAF beamline. In this paper, we present thorough comparison tests between the Viton gate valves and the all-metal gate valves, including evaluations of particle levels, aging tests of the gate valves, and analysis of the particle material.

The bipolar pulsed electropolishing (BPEP), due to its HF-free feature, can offer much safer, more environmentally friendly, and lower-cost operation compared to the conventional electropolishing, using concentrated HF and H2SO4 as electrolyte. Jefferson Lab has developed the BPEP system using diluted H2SO4 only for implementing final surface processing of niobium SRF cavities, including single cells, 7-cell CEBAF C100 cavity, and 9-cell TESLA-style cavities. The BPEP-treated cavity, followed by 120°C baking, has achieved an accelerating gradient (Eacc) of 37 MV/m with a quality factor (Q0) above 1e10 at 2K, which demonstrated the success of the system's development. The detailed BPEP parameter optimization and study of the surface engineering by BPEP will also be presented.