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The Effect Of Defects On Functional Properties Of Niobium For Superconducting Radio Frequency Cavities
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Book Synopsis The Effect of Defects on Functional Properties of Niobium for Superconducting Radio-frequency Cavities by : Pulkit Garg
Download or read book The Effect of Defects on Functional Properties of Niobium for Superconducting Radio-frequency Cavities written by Pulkit Garg and published by . This book was released on 2019 with total page 97 pages. Available in PDF, EPUB and Kindle. Book excerpt: Niobium is the primary material for fabricating superconducting radio-frequency (SRF) cavities. However, presence of impurities and defects degrade the superconducting behavior of niobium twofold, first by nucleating non-superconducting phases and second by increasing the residual surface resistance of cavities. In particular, niobium absorbs hydrogen during cavity fabrication and promotes precipitation of non-superconducting niobium hydride phases. Additionally, magnetic flux trapping at defects leads to a normal conducting (non-superconducting) core which increases surface resistance and negatively affects niobium performance for superconducting applications. However, undelaying mechanisms related to hydride formation and dissolution along with defect interaction with magnetic fields is still unclear. Therefore, this dissertation aims to investigate the role of defects and impurities on functional properties of niobium for SRF cavities using first-principles methods. Here, density functional theory calculations revealed that nitrogen addition suppressed hydrogen absorption interstitially and at grain boundaries, and it also decreased the energetic stability of niobium hydride precipitates present in niobium. Further, hydrogen segregation at the screw dislocation was observed to transform the dislocation core structure and increase the barrier for screw dislocation motion. Valence charge transfer calculations displayed a strong tendency of nitrogen to accumulate charge around itself, thereby decreasing the strength of covalent bonds between niobium and hydrogen leading to a very unstable state for interstitial hydrogen and hydrides. Thus, presence of nitrogen during processing plays a critical role in controlling hydride precipitation and subsequent SRF properties. First-principles methods were further implemented to gain a theoretical perspective about the experimental observations that lattice defects are effective at trapping magnetic flux in high-purity superconducting niobium. Full-potential linear augmented plane-wave methods were used to analyze the effects of magnetic field on the superconducting state surrounding these defects. A considerable amount of trapped flux was obtained at the dislocation core and grain boundaries which can be attributed to significantly different electronic structure of defects as compared to bulk niobium. Electron redistribution at defects enhances non-paramagnetic effects that perturb superconductivity, resulting in local conditions suitable for flux trapping. Therefore, controlling accumulation or depletion of charge at the defects could mitigate these tendencies and aid in improving superconductive behavior of niobium.
Book Synopsis Effect of Microscopic Defects on Superconducting Properties of High Purity Niobium Used for SRF Cavities by : Mingmin Wang
Download or read book Effect of Microscopic Defects on Superconducting Properties of High Purity Niobium Used for SRF Cavities written by Mingmin Wang and published by . This book was released on 2020 with total page 193 pages. Available in PDF, EPUB and Kindle. Book excerpt: High purity niobium has been used to fabricate superconducting radio-frequency (SRF) cavities for linear particle accelerator applications for decades due to its high critical temperature (9.3 K) and critical magnetic field. Great progress has been made in achieving high accelerating gradients and quality factors (a measure of efficiency). However, the performance of Nb cavities still suffers from the variability of the material such that high quality factors and accelerating gradients cannot be consistently produced.Trapped magnetic flux is well known for causing significant radio-frequency losses. Both local flux penetration and flux trapping indicate the local suppression of superconductivity. Magnetic flux from both unshielded earth field and thermoelectric currents can be trapped when a cavity is cooled through its superconducting transition temperature. Microstructural defects including hydrogen, grain boundaries, and dislocations are possible causes for flux trapping. However, the details of magnetic flux trapping mechanisms and conditions that enable it are still not clear. Research on this topic has been very active in the SRF community. Cavity studies on flux expulsion after different heat treatments and cooldown procedures have been performed in recent years, but the study of flux trapping mechanisms at the microscopic level is still lacking.In order to study the effect of microscopic defects on flux trapping, single crystal and bicrystal samples were designed with strategically chosen tensile axes to intentionally introduce defects by a 5% tensile strain. Magneto-Optical (MO) Imaging was used to visualize locations where magnetic flux was trapped, and the dislocation substructures were studied using Electron Channeling Contrast Imaging (ECCI).The results show that high angle grain boundaries (HAGB) and low angle grain boundaries (LAGBs) have different flux penetration behaviors. LAGBS could be hydrogen segregation sites leading to precipitation of normal conducting hydrides along LAGBs at ~100-130 K during cooling. In hydrogen contaminated single-crystal samples, large hydride scars (locations where a hydride formed and then dissolved during heating) were observed both at the LAGBs and within the grain after MO cooling; however, only hydrides at the LAGBs appeared to cause premature flux penetration. Flux trapping related to LAGBs could still be observed after the heat treatment removed most of the hydrogen. By contrast, the flux penetration along a HAGB could be turned off by heat treatment that removed hydrogen and restored by reintroducing hydrogen into the sample. This work suggests that HAGBs are not as effective at causing flux penetration or trapping as hydrides and LAGBs.Some deformed bi-crystal samples show correlations between a larger amount of deformation or a higher density of dislocations and more trapped flux. Deformation led to the development of dislocation substructures; however, the effect of dislocation arrangements on flux penetration could not be observed in the current work. Further study with flux measurement techniques of a higher resolution and sensitivity is necessary to understand what kinds of dislocation substructures are most likely to cause flux penetration.
Book Synopsis Investigation of the Superconducting Properties of Niobium Radio-frequency Cavities by : Gianluigi Ciovati
Download or read book Investigation of the Superconducting Properties of Niobium Radio-frequency Cavities written by Gianluigi Ciovati and published by . This book was released on 2005 with total page 398 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis First-principles Calculations of Niobium Hydride Formation in Superconducting Radio-frequency Cavities by :
Download or read book First-principles Calculations of Niobium Hydride Formation in Superconducting Radio-frequency Cavities written by and published by . This book was released on 2013 with total page 95002 pages. Available in PDF, EPUB and Kindle. Book excerpt: Niobium hydride is suspected to be a major contributor to degradation of the quality factor of niobium superconducting radio-frequency (SRF) cavities. In this study, we connect the fundamental properties of hydrogen in niobium to SRF cavity performance and processing. We modeled several of the niobium hydride phases relevant to SRF cavities and present their thermodynamic, electronic, and geometric properties determined from calculations based on density-functional theory. We find that the absorption of hydrogen from the gas phase into niobium is exothermic and hydrogen becomes somewhat anionic. The absorption of hydrogen by niobium lattice vacancies is strongly preferred over absorption into interstitial sites. A single vacancy can accommodate six hydrogen atoms in the symmetrically equivalent lowest-energy sites and additional hydrogen in the nearby interstitial sites affected by the strain field: this indicates that a vacancy can serve as a nucleation center for hydride phase formation. Small hydride precipitates may then occur near lattice vacancies upon cooling. Vacancy clusters and extended defects should also be enriched in hydrogen, potentially resulting in extended hydride phase regions upon cooling. We also assess the phase changes in the niobium-hydrogen system based on charge transfer between niobium and hydrogen, the strain field associated with interstitial hydrogen, and the geometry of the hydride phases. The results of this study stress the importance of not only the hydrogen content in niobium, but also the recovery state of niobium for the performance of SRF cavities.
Book Synopsis Insights to Superconducting Radio-Frequency Cavity Processing from First Principles Calculations and Spectroscopic Techniques by :
Download or read book Insights to Superconducting Radio-Frequency Cavity Processing from First Principles Calculations and Spectroscopic Techniques written by and published by . This book was released on 2013 with total page 127 pages. Available in PDF, EPUB and Kindle. Book excerpt: Insights to the fundamental processes that occur during the manufacturing of niobium superconducting radio-frequency (SRF) cavities are provided via analyses of density functional theory calculations and Raman, infrared, and nuclear magnetic resonance (NMR) spectra. I show that during electropolishing fluorine is bound and released by the reaction of the acid components in the solution: HF + H2SO4 - HFSO3 + H2O. This result implies that new recipes can possibly be developed on the principle of controlled release of fluorine by a chemical reaction. I also show that NMR or Raman spectroscopy can be used to monitor the free fluorine when polishing with the standard electropolishing recipe. Density functional theory was applied to calculate the properties of common processing impurities - hydrogen, oxygen, nitrogen, and carbon - in the niobium. These impurities lower the superconducting transition temperature of niobium, and hydride precipitates are at best weakly superconducting. I modeled several of the niobium hydride phases relevant to SRF cavities, and explain the phase changes in the niobium hydrogen system based on the charge transfer between niobium and hydrogen and the strain field inside of the niobium. I also present evidence for a niobium lattice vacancy serving as a nucleation center for hydride phase formation. In considering the other chemical impurities in niobium, I show that the absorption of oxygen into a niobium lattice vacancy is preferred over the absorption of hydrogen, which indicates that oxygen can block these phase nucleation centers. I also show that dissolved oxygen atoms can trap dissolved hydrogen atoms to prevent niobium hydride phase formation. Nitrogen and carbon were studied in less depth, but behaved similarly to oxygen. Based on these results and a literature survey, I propose a mechanism for the success of the low-temperature anneal applied to niobium SRF cavities. Finally, I present the beginning of a model to describe magnetic impurities in niobium SRF cavities, which can cause a loss of local superconductivity. I calculated magnetic configurations of niobium hydrides and oxides, and show that stoichiometric hydride and oxide structures are nonmagnetic, but defective oxide structures retain local magnetic moments.
Book Synopsis Nanostructural Features Degrading the Performance of Superconducting Radio Frequency Niobium Cavities Revealed by Transmission Electron Microscopy and Electron Energy Loss Spectroscopy by :
Download or read book Nanostructural Features Degrading the Performance of Superconducting Radio Frequency Niobium Cavities Revealed by Transmission Electron Microscopy and Electron Energy Loss Spectroscopy written by and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Nanoscale defect structure within the magnetic penetration depth of ~100 nm is key to the performance limitations of niobium superconducting radio frequency cavities. Using a unique combination of advanced thermometry during cavity RF measurements, and TEM structural and compositional characterization of the samples extracted from cavity walls, we discover the existence of nanoscale hydrides in electropolished cavities limited by the high field Q slope, and show the decreased hydride formation in the electropolished cavity after 120°C baking. Furthermore, we demonstrate that adding 800°C hydrogen degassing followed by light buffered chemical polishing restores the hydride formation to the pre-120°C bake level. We also show absence of niobium oxides along the grain boundaries and the modifications of the surface oxide upon 120°C bake.
Book Synopsis The Influence of Grain Boundaries on the Properties of Superconducting Radio Frequency Cavity Niobium by : Zu Hawn Sung
Download or read book The Influence of Grain Boundaries on the Properties of Superconducting Radio Frequency Cavity Niobium written by Zu Hawn Sung and published by . This book was released on 2010 with total page 115 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Dislocation Substructures on the Functional Properties of Niobium for SRF Cavities, Focusing on Microstructural, Microchemical, and Electromagnetic Characteristic for Florida State University by :
Download or read book Dislocation Substructures on the Functional Properties of Niobium for SRF Cavities, Focusing on Microstructural, Microchemical, and Electromagnetic Characteristic for Florida State University written by and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Funding is being requested pursuant to a proposal that was submitted and reviewed through the Portfolio Analysis and Management System (PAMS). PAMS Proposal ID: 222686. Superconducting cavities are the integral part of many energy-efficient particle accelerators around the world. The current material of choice for superconducting cavities is niobium, which is the material with the highest transition temperature among pure metals. The performance of SRF cavities are influenced by the fabrication and processing steps. We plan to study the microstructural, microchemical and electromagnetic properties of Nb that are processed similar to the cavity processing steps to identify and mitigate the limiting factors to improve the performance of SRF cavities.
Book Synopsis The Effect of Certain Types of Lattice Defects on the Superconducting Properties of Niobium by : Franklin Hadley Cocks
Download or read book The Effect of Certain Types of Lattice Defects on the Superconducting Properties of Niobium written by Franklin Hadley Cocks and published by . This book was released on 1963 with total page 68 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Theory Work on SRF Materials by : Nathan Sitaraman
Download or read book Theory Work on SRF Materials written by Nathan Sitaraman and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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 $\omega$-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 Nb$_3$Sn, 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 Nb$_3$Sn 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.
Book Synopsis Surface Studies of Acid-treated Niobium for Superconducting Radio Frequency Cavities by : David R. Smith
Download or read book Surface Studies of Acid-treated Niobium for Superconducting Radio Frequency Cavities written by David R. Smith and published by . This book was released on 2004 with total page 94 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Mechanical Properties of Niobium Radio-frequency Cavities by :
Download or read book Mechanical Properties of Niobium Radio-frequency Cavities written by and published by . This book was released on 2015 with total page 11 pages. Available in PDF, EPUB and Kindle. Book excerpt: Radio-frequency cavities made of bulk niobium are one of the components used in modern particle accelerators. The mechanical stability is an important aspect of cavity design, which typically relies on finite-element analysis simulations using material properties from tensile tests on sample. This contribution presents the results of strain and resonant frequency measurements as a function of a uniform pressure up to 722 kPa, applied to single-cell niobium cavities with different crystallographic structure, purity and treatments. In addition, burst tests of high-purity multi-cell cavities with different crystallographic structure have been conducted up to the tensile strength of the material. Finite-element analysis of the single-cell cavity geometry is in good agreement with the observed behavior in the elastic regime assuming a Young's modulus value of 88.5 GPa and a Poisson's ratio of 0.4, regardless of crystallographic structure, purity or treatment. However, the measured yield strength and tensile strength depend on crystallographic structure, material purity and treatment. In particular, the results from this study show that the mechanical properties of niobium cavities with large crystals are comparable to those of cavities made of fine-grain niobium.
Book Synopsis Niobium Near Surface Composition Relevant for Superconducting Radio-frequency Cavities by : Guilherme Dalla Lana Semione
Download or read book Niobium Near Surface Composition Relevant for Superconducting Radio-frequency Cavities written by Guilherme Dalla Lana Semione and published by . This book was released on 2020 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Surface Polishing of Niobium for Superconducting Radio Frequency (SRF) Cavity Application by : Liang Zhao (Ph. D.)
Download or read book Surface Polishing of Niobium for Superconducting Radio Frequency (SRF) Cavity Application written by Liang Zhao (Ph. D.) and published by . This book was released on 2015 with total page 237 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Nb3Sn Superconducting Radiofrequency Cavities by :
Download or read book Nb3Sn Superconducting Radiofrequency Cavities written by and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A microns-thick film of Nb3Sn on the inner surface of a superconducting radiofrequency (SRF) cavity has been demonstrated to substantially improve cryogenic efficiency compared to the standard niobium material, and its predicted superheating field is approximately twice as high. We review in detail the advantages of Nb3Sn coatings for SRF cavities. We describe the vapor diffusion process used to fabricate this material in the most successful experiments, and we compare the differences in the process used at different labs. We overview results of Nb3Sn SRF coatings, including CW and pulsed measurements of cavities as well as microscopic measurements. We discuss special considerations that must be practised when using Nb3Sn cavities in applications. Lastly, we conclude by summarizing the state-of-the-art and describing the outlook for this alternative SRF material.
Book Synopsis Investigating Single Crystal Plasticity of Niobium with a Dislocation Mechanics-based Model by : Eureka Pai Kulyadi
Download or read book Investigating Single Crystal Plasticity of Niobium with a Dislocation Mechanics-based Model written by Eureka Pai Kulyadi and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: One suggested method to manufacture superconducting radio frequency (SRF) cavities, which are used as driving units in particle accelerators, is the deep-drawing of Niobium (Nb) disks that were cut from large-grained ingots. This is a promising and cost-effective alternative to the current industry standard of deep-drawing rolled poly-crystalline sheets. It is essential to understand the sources of the observed variability in the performance of cavities fabricated by either process in order to define the most suitable fabrication route.Cavity performance is hampered by material defects such as dislocations or crystallite boundaries that can arise and evolve during deformation processes involved in the mechanical shaping of the cavity (mostly by deep-drawing). Such defects can trap magnetic flux causing significant radio frequency (RF) losses leading to reduced performance. Understanding dislocation mechanics in Nb based on deformation experiments allows predictive modeling to enable informed design strategies for optimal cavity fabrication and improved performance.Crystal plasticity (CP) modeling is a powerful and well-established computational materials science tool to investigate mechanical structure-property relations in crystalline materials. A dislocation mechanics-based constitutive description of plastic deformation in body-centered cubic (BCC) metals is used to formulate a CP model for Nb. Uniaxial tension experiments on several Nb single crystals cut from a large-grained ingot disk were conducted at several different strain rates. The specific selection of grains and the in-plane orientation of deformation samples cut from those grains were based on the active slip systems anticipated from SCHMID factor calculations. The results from these specifically designed deformation experiments are used to validate the model.Simulations and corresponding deformation experiments exhibit notable discrepancies in terms of the stress-strain response and lattice reorientation. These discrepancies are rationalized by considering the effect of a distribution in pre-existing dislocation densities across the possible slip systems, which entails a significant variability in the resulting slip system activity and associated crystal reorientation and strain hardening behavior. An exhaustive numerical study probing thousands of initial dislocation density distributions could be condensed into inverse pole figure (IPF) maps that chart the range of crystallographic tensile directions for which stable outcomes can be expected despite a given variability in the pre-existing dislocation density distribution. Consequently, it becomes clear that while single-crystal experiments can be a useful guide toward the development and testing of dislocation mechanics-based models, care must be exercised as to not expect a one-to-one matching between any specific experiment and its corresponding simulation, since the exact values and distribution of pre-existing dislocations in the sample is generally unknown (and likely unknowable).
Book Synopsis Flux Pinning in Superconductors by : Teruo Matsushita
Download or read book Flux Pinning in Superconductors written by Teruo Matsushita and published by Springer Science & Business Media. This book was released on 2007-07-04 with total page 509 pages. Available in PDF, EPUB and Kindle. Book excerpt: The book deals with the flux pinning mechanisms and properties and the electromagnetic phenomena caused by the flux pinning common for metallic, high-temperature and MgB2 superconductors. The loss originates from the ohmic dissipation of normal electrons in the normal core driven by the electric field induced by the flux motion. Readers will learn why the resultant loss is of hysteresis type in spite of such mechanism.
