Abstract：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.
Kasprzak K, Wiencek M, Zwozniak A et al 2017 Proceedings of SRF2017, Test Results of the European XFEL Serial-production Accelerator Modules (Lanzhou, China 17–21 July 2017) p MOPB106
[2]
Grassellino A, Romanenko A, Posen S et al 2015 Proceedings of SRF2015, N Doping: Progress in Development and Understanding (Whistler, Canada 13–18 September 2015) p 48
[3]
Galayda J 2014 Proceedings of Linac2014, The New LCLS-II Project: Status and Challenges (Geneva, Switzerland 31 August–5 September 2014) p 404
[4]
Chen S, Hao J K, Quan S W et al 2017 Proceedings of SRF2017, Flux Pinning Study of OTIC Niobium Material (Lanzhou, China 17–21 July 2017) p THPB028
[5]
Palczewski A D 2017 Proceedings of SRF2017 (Lanzhou, China 17–21 July 2017) p TUXBA06
[6]
Merio M, Checchin M, Crawford A et al 2015 Proceedings of SRF2015, Furnace N2 Doping Treatments at Fermilab (Whistler, Canada 13–18 September 2015) p 423
[7]
Ge M, Eichhorn R, Elmore B et al 2015 Proceedings of SRF2015, Performance of Nitrogen-Doped 9-Cell SRF Cavities in Vertical Tests at Cornell University (Whistler, Canada 13–18 September 2015) p 328
2018, Vol. 35 
