Determination of bulk and surface superconducting properties of N2-doped cold worked, heat treated and electro-polished SRF grade niobium
In this study, nitrogen-doped cavities show significant performance improvement in the medium accelerating field regime due to a lowered RF surface resistivity. However, the mechanism of enhancement has not been clearly explained. Our experiments explore how N2-doping influences Nb bulk and surface superconducting properties, and compare the N2-doped properties with those obtained previously with conventionally treated samples. High purity Nb-rod was mechanically deformed and post treated based on a typical SRF cavity treatment recipe. The onset of flux penetration at Hc1, and the upper and the surface critical fields, Hc2 and Hc3, were characterized by magnetic hysteresis and AC susceptibility techniques. The surface depth profile responsible for superconductivity was examined by changing AC amplitude in AC susceptibility, and the microstructure was directly observed with EBSD-OIM. We are also investigating surface chemistry for detailed composition using XPS. We have found that N2-doping at 800 °C significantly reduces the Hc3/Hc2 ratio towards the ideal value of ~1.7, and conclude that AC susceptibility is capable of following changes to the surface properties induced by N2-doping.
- Research Organization:
- Florida State Univ., Tallahassee, FL (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), High Energy Physics (HEP)
- Grant/Contract Number:
- SC0009960
- OSTI ID:
- 1244545
- Journal Information:
- Proc. of International Conference on RF Superconductivity, Conference: SRF15, Whistler, BC (Canada), 13-18 Sept 2015
- Country of Publication:
- United States
- Language:
- English
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