Speaker
Description
A new surface treatment method is being developed, wet nitrogen doping, in which nitric acid is added during electro-polishing (EP). In the first trial on a FRIB beta = 0.53 half-wave resonator (HWR), a high quality factor (Q0 = 8E10) was observed at 2 K at low field (accelerating gradient ≤ 0.5 MV/m) without an anti-Q slope. It is known that the Q0 can be increased by shortening the mean free path via surface contamination by oxygen. Low-temperature baking (LTB) can allow oxygen to diffuse into the surface to a depth similar to the RF penetration depth. However, nitrogen cannot diffuse via LTB. Therefore, the mechanism for increasing Q0 with N-doping has not been clearly understood. Moreover, by comparing the behavior of buffered chemical polishing (BCP) processed cavities, it was found that BCP also dopes nitrogen on the SRF surface, and the doped nitrogen hinders the diffusion of oxygen under LTB, making LTB unable to mitigate the high field Q-slope (HFQS).
Funding Agency
U.S. Department of Energy, Office of Science, Office of Nuclear Physics and used resources of the Facility for Rare Isotope Beams (FRIB) Operations under Award Number RC114424
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