Advance in vertical buffered electropolishing on niobium for particle accelerators

Niobium (Nb) is the most common material that has been employed for making superconducting radio frequency (SRF) cavities for use in particle accelerators over the last couple of decades. One of the most important steps in fabricating Nb SRF cavities is the final chemical removal of 150 ??m of Nb from the inner surfaces of the SRF cavities. This is usually done by either buffered chemical polishing (BCP) or electropolishing (EP). Recently a Nb surface treatment technique called buffered electropolishing (BEP) has been developed at Jefferson Lab. It has been demonstrated that BEP can produce the smoothest surface finish on Nb ever reported in the literature while realizing a Nb removal rate as high as 10 ??m/min that is more than 25 and 5 times faster than those of EP and BCP(112), respectively. In this contribution, recent advances in optimizing and understanding BEP treatment technique are reviewed. Latest results from RF measurements on BEP treated Nb single cell cavities by our unique vertical polishing system will be reported. Copyright ? 2011 by IPAC'11/EPS-AG.EI