Successful Nitrogen Doping of 1.3GHz Single Cell Superconducting Radio-Frequency Cavities

A high intrinsic quality factor (Q_0) of a superconducting radio-frequency cavity is beneficial to reducing the operation costs of superconducting accelerators. Nitrogen doping (N-doping) has been demonstrated as a useful way to improve Q_0 of the superconducting cavity in recent years. N-doping researches with 1.3 GHz single cell cavities are carried out at Peking University and the preliminary results are promising. Our recipe is slightly different from other laboratories. After 250 μm polishing, high pressure rinsing and 3 h high temperature annealing, the cavities are nitrogen doped at 2.7–4.0 Pa for 20 min and then followed by 15 μm electropolishing. Vertical test results show that Q_0 of a 1.3 GHz single cell cavity made of large grain niobium has increased to 4\times10^10 at 2.0 K and medium gradient.