Alternate Electrolyte Composition for Electropolishing of Niobium Surfaces

Electropolishing has shown promising results for the treatment of Nb cavities to be used in particle accelerators, particularly in the attainment of high surface electric fields. In support of the CEBAF Upgrade project and as part of a longer-term R and D program, we have investigated the properties of several electrolyte recipes. A particularly promising one consists of a mixture of lactic, sulfuric, and hydrofluoric acids. Initial tests reveal that smooth Nb surfaces can be achieved with no observable grain boundaries under optical microscope. We report on the results of the investigations of the parameters that control the polishing process using this particular acid mixture