SRF2023 - List of Authors (Liu, H.)

Paper	Title	Page
WEIAA02	Temperature Responses of Superconducting Niobium Properties in Experiment and Simulation
	Z.T. Yang, J.K. Hao, H. Liu, K.X. Liu, S.W. Quan PKU, Beijing, People’s Republic of China
	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.
	Slides WEIAA02 [15.615 MB]
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WEPWB084	The Interaction among Interstitial C/N/O/H and Vacancy in Niobium via First-Principles Calculation	778
	H. Liu, J.K. Hao, Z.T. Yang PKU, Beijing, People’s Republic of China
	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)

Paper

Title

Page

WEIAA02

Temperature Responses of Superconducting Niobium Properties in Experiment and Simulation

Z.T. Yang, J.K. Hao, H. Liu, K.X. Liu, S.W. Quan
PKU, Beijing, People’s Republic of China

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.

Slides WEIAA02 [15.615 MB]

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reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPWB084

The Interaction among Interstitial C/N/O/H and Vacancy in Niobium via First-Principles Calculation

778

H. Liu, J.K. Hao, Z.T. Yang
PKU, Beijing, People’s Republic of China

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)