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Abstract While Nb3Sn theoretically offers better superconducting radio-frequency (RF) cavity performance (Q0and ) to Nb at any given temperature, peak RF magnetic fields consistently fall short of the ∼400 mT prediction. The relatively rough topography of vapor-diffused Nb3Sn is widely conjectured to be one of the factors that limit the attainable performance of Nb3Sn-coated Nb cavities prepared via Sn vapor diffusion. Here we investigate the effect of coating duration on the topography of vapor-diffused Nb3Sn on Nb and calculate the associated magnetic field enhancement and superheating field suppression factors using atomic force microscopy topographies. It is shown that the thermally grooved grain boundaries are major defects which may contribute to a substantial decrease in the achievable accelerating field. The severity of these grooves increases with total coating duration due to the deepening of thermal grooves during the coating process.
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Surface oxides, carbides, and impurities on RF superconducting Nb and Nb 3 Sn: a comprehensive analysis
Abstract Surface structures on radio-frequency (RF) superconductors are crucially important in determining their interaction with the RF field. Here we investigate the surface compositions, structural profiles, and valence distributions of oxides, carbides, and impurities on niobium (Nb) and niobium–tin (Nb3Sn)in situunder different processing conditions. We establish the underlying mechanisms of vacuum baking and nitrogen processing in Nb and demonstrate that carbide formation induced during high-temperature baking, regardless of gas environment, determines subsequent oxide formation upon air exposure or low-temperature baking, leading to modifications of the electron population profile. Our findings support the combined contribution of surface oxides and second-phase formation to the outcome of ultra-high vacuum baking (oxygen processing) and nitrogen processing. Also, we observe that vapor-diffused Nb3Sn contains thick metastable oxides, while electrochemically synthesized Nb3Sn only has a thin oxide layer. Our findings reveal fundamental mechanisms of baking and processing Nb and Nb3Sn surface structures for high-performance superconducting RF and quantum applications.
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- Award ID(s):
- 1719875
- PAR ID:
- 10468623
- Publisher / Repository:
- IOP Publishing
- Date Published:
- Journal Name:
- Superconductor Science and Technology
- Volume:
- 36
- Issue:
- 11
- ISSN:
- 0953-2048
- Format(s):
- Medium: X Size: Article No. 115030
- Size(s):
- Article No. 115030
- Sponsoring Org:
- National Science Foundation
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