WEIAA02
PKU, Beijing, People’s Republic of China
PKU, Beijing, People’s Republic of China
PKU, Beijing, People’s Republic of China
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WEIAA02 |
Temperature Responses of Superconducting Niobium Properties in Experiment and Simulation | |
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| Mild, medium, and high temperature baking has been researched to obtain high-Q₀ SRF niobium cavities in past decades. It suggests that niobium has different properties when treated at different temperatures. We conducted various experiments on SRF-cavity-class niobium samples, and the systematic measurements included not only impurity analysis via TOF-SIMS, in-situ XPS, in-situ ESEM, HRTEM, but also superconductor measurements via in-situ ARPES. We also performed quantitative atomic simulation of the impurities in niobium bulks at zero temperature, and found interstitial carbon had similar trapping effect on interstitial hydrogen as interstitial nitrogen and oxygen did. We found the mildly increased interstitial carbons and oxygens during medium temperature baking not only suppressed the hydrogen accumulation and hydride precipitation during cooling down, but also reduced the electron mean free path to the optimal range which yielded declined BCS resistance. Therefore, the surface resistances of the cavities were reduced and the Q₀ values were improved correspondingly. | ||
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Slides WEIAA02 [15.615 MB] | |
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| WEPWB045 | The Oxidizing Responses of Baked Niobium Exposed to Various Gases via In-situ NAXPS | 662 |
| SUSPB040 | use link to see paper's listing under its alternate paper code | |
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| We carried out in-situ NAXPS (Near-atmospheric X-ray Photoelectron Spectroscopy) on SRF-cavity class niobium to observe its oxidizing responses when exposed to various gases. The niobium samples were baked at 800°C until the peaks of niobium oxides disappeared in the spectrum. Then the revealed pure niobium samples were exposed to the air-proportion mixture of nitrogen and oxygen, pure oxygen, and pure water vapor respectively. And for the pure oxygen and water vapor group, we also carried out TOF-SIMS (Time-of-Flight Secondary Ion Mass Spectroscopy) measurements before and after the baking and oxidation experiments. We found that pure oxygen and water vapor could oxidize niobium at similar rate which was faster than the N2/O2 mixture. After re-oxidized by pure oxygen and water vapor, the niobium sample presented a significant increase of interstitial carbon and a moderate increase of interstitial oxygen in the magnetic penetration depth, while it showed a mild decrease of interstitial hydrogen. | ||
| DOI • | reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEPWB045 | |
| About • | Received ※ 15 June 2023 — Revised ※ 23 June 2023 — Accepted ※ 25 June 2023 — Issue date ※ 31 July 2023 | |
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| WEPWB084 | The Interaction among Interstitial C/N/O/H and Vacancy in Niobium via First-Principles Calculation | 778 |
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| We calculate the interaction among zero dimensional defects in niobium lattice through first-principles calculation. And we compare the trapping effect of hydrogen among carbon, nitrogen, and oxygen as well as the trapping effect of interstitial atoms by vacancy. We find that the interstitial C/N/O have similar effect of trapping interstitial hydrogen in niobium lattice, and the vacancy can trap interstitial C/N/O/H in adjacent protocells and strengthen their chemical bond with Nb. These calculations give some explanation for improving superconducting performance of niobium cavities through medium temperature baking. | ||
| DOI • | reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEPWB084 | |
| About • | Received ※ 15 June 2023 — Revised ※ 25 June 2023 — Accepted ※ 29 June 2023 — Issue date ※ 03 July 2023 | |
| Cite • | reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml) | |