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 Q₀ of 1.3 GHz single cavity after medium-temperature baking can be 2–3×10¹⁰ 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 Q₀ 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.