Medium-temperature baking of 1.3 GHz superconducting radio frequency single-cell cavity

Background A reliable and repeatable post-processing technology of improving the performance of 1.3 GHz superconducting radio frequency(SRF)cavities is one of the critical technologies for the ILC and XFEL and ERL projects.Methods Three 1.3 GHz single-cell cavities were fabricated and received a baking in temperature 330℃,while the interior of the cavity stayed in ultra-high vacuum(UHV).The cavities were also vertical-tested after electropolishing(EP)with 120℃48-h baking and with nitrogen doping separately for a comparison.Results The Q_(0) of 1.3 GHz single cavity after medium-temperature baking can be 2-3×10^(10) in the accelerating gradient range of 2-35 MV/m in the 2 K vertical test in IHEP.Meanwhile,the outer surface oxidation of niobium cavity caused by baking will decrease the performance of the SRF cavity.Conclusions Medium-temperature(250-400℃)baking on the 1.3 GHz single-cell cavity will improve its Q_(0) in 2 K vertical test compared with EP followed by 120℃48-h baking baseline and reach a similar level of nitrogen doping,and the quench field will lower to a typical range of 20-30 MV/m.Meanwhile,the cavity performance is sensitive to the baking time and temperature,which indicates that a tremendous improvement can be made on the current treatment.