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THEORY WORK ON SRF MATERIALS

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Abstract

Superconducting radio-frequency (SRF) devices have extremely high quality factors which makes them ideal for applications in particle detection, in quantum computing, and in particle accelerators. From a fundamental standpoint, SRF cavities for particle accelerators are a particularly interesting use case because both high quality factor and high electromagnetic field amplitude are necessary. I use density-functional theory to build a better understanding of superconducting surface behavior under extreme conditions, to develop new recipes for higher quality factors and higher fields, and to study novel materials for SRF applications. I begin with my research on niobium, the gold-standard material for cavities and other SRF applications, focusing on the properties of niobium hydride defects and ω-phase defects. I present new theories for the formation of both of these defects, addressing inconsistencies in the literature, explaining the effect of these defects on SRF performance, and developing new recipes. Next I discuss my work on the compound superconductor Nb3Sn, which theoretically has the potential to far outperform niobium, but so far has been unable to reach high fields. Here I focus on developing new models for the nucleation and growth of the Nb3Sn layer, especially concerning the behavior of antisite defects. I present my progress toward developing new recipes to improve layer uniformity and enhance cavity performance by minimizing the effect of compositional defects. Finally, I cover zirconium-doping recipes for SRF — a brand new area of research which I helped usher into existence. My calculations show the potential for zirconium to enhance superconducting properties significantly both in the bcc phase and in the rocksalt phase. I show that the previously-overlooked niobium-zirconium system is a promising pathway towards next-generation SRF technology.

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163 pages

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Date Issued

2022-12

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Keywords

Density Functional Theory; Radio-Frequency Superconductivity

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Union Local

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Committee Chair

Arias, Tomas

Committee Co-Chair

Committee Member

Mueller, Erich
Liepe, Matthias

Degree Discipline

Physics

Degree Name

Ph. D., Physics

Degree Level

Doctor of Philosophy

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Government Document

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Attribution-NonCommercial-ShareAlike 4.0 International

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dissertation or thesis

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