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Innovative Severe Plastic Deformation Of Niobium With Application To Superconducting Radio Frequency Cavities
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Book Synopsis Innovative Severe Plastic Deformation of Niobium with Application to Superconducting Radio Frequency Cavities by : Nicholas Gutzmore Bembridge
Download or read book Innovative Severe Plastic Deformation of Niobium with Application to Superconducting Radio Frequency Cavities written by Nicholas Gutzmore Bembridge and published by . This book was released on 2011 with total page 276 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Microstructure Development in Bulk Niobium Following Severe Plastic Deformation and Annealing by : Shreyas Balachandran
Download or read book Microstructure Development in Bulk Niobium Following Severe Plastic Deformation and Annealing written by Shreyas Balachandran and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Niobium (Nb) finds application in the fabrication of Nb3Sn superconducting wires for superconducting magnet applications, and SRF cavity applications. These applications need a favorable starting microstructure in precursor Nb to increase manufacturing reliability, reduce costs, and advance technology. The main problem with traditional Nb processing is that pure Nb is obtained by electron beam melting (EBM), which produces initial polycrystals tens to hundreds of centimeters in width/length, and can be comparable to the dimensions of the initial ingot. Breakdown of these initial cast microstructures, and to obtain consistent, fine grain microstructures in bulk product is a processing challenge. Generally, pure Nb, traditional thermo-mechanical processing methodologies such as: rolling, swaging, forging have been unable to effectively breakdown initial cast structures. An objective of the thesis is to develop thermo-mechanical processing strategies involving severe plastic deformation (SPD) by Equal Channel Angular Extrusion (ECAE) for bulk Nb. ECAE enables grain refinement without appreciable crossectional area changes to the workpiece, which is a hallmark of ECAE. The microstructure refinement process by ECAE is not well understood for the breakdown of large grain Nb. We have shown that ECAE produces continuous orientation splitting, and hence grain refinement even when processed under a strain path that is perceived to be structure conserving (route 2C). Initial bi-crystal results indicate that significant convergence in microstructure is possible within two ECAE passes for extremely large grain Nb. Processing strategies have been developed for effective control of grain size and texture in polycrystalline microstructures. The main results include effective grain size control leading to uniform recrystallized grain sizes in the range of tens of microns, and texture control in Nb bars. Nb bars processed by this technique have better co-deformation characteristics as observed in Cu-Nb monocore wire experiments where a circularity greater than 0.85 is obtained for several textures, as compared to circularities of 0.5-0.7 using traditional processing. The methodology to adopt precursor Nb processed by thermomechanical processing by SPD to traditional tube development techniques such as area reduction extrusion are presented. The tubes formed by this approach show sufficient ductility (greater than 30%) along the circumferential and extrusion directions with tensile properties being very similar in perpendicular directions. The development of tube ECAE (tECAE) process produces textures very close to f111g parallel to tube normal directions that are considered to be favorable for hydroforming applications. This is the first report of such textures in a seamless tube. The processing strategies developed are able to homogenize and converge the microstructures in Nb leading to similar deformation behavior irrespective of the starting microstructure. The grain refinement strategies for Nb presented in this thesis have the potential to be scaled up, and similar performance are expected irrespective of the Nb workpiece dimensions. The same processing strategies can be adapted to other bcc refractory metals including: tantalum (Ta), molybdenum (Mo), and tungsten (W) where the processing needs to be done at similar homologous temperatures/conditions where similar deformation mechanisms are active. \indent An objective of the thesis is to develop thermo-mechanical processing strategies involving severe plastic deformation (SPD) by Equal Channel Angular Extrusion (ECAE) for bulk Nb. ECAE enables grain refinement without appreciable crossectional area changes to the workpiece, which is a hallmark of ECAE. The microstructure refinement process by ECAE is not well understood for the breakdown of large grain Nb. We have shown that ECAE produces continuous orientation splitting, and hence grain refinement even when processed under a strain path that is perceived to be "structure conserving" (route 2C). Initial bi-crystal results indicate that significant convergence in microstructure is possible within two ECAE passes for extremely large grain Nb.\\ \indent Processing strategies have been developed for effective control of grain size and texture in polycrystalline microstructures. The main results include effective grain size control leading to uniform recrystallized grain sizes in the range of tens of microns, and texture control in Nb bars. Nb bars processed by this technique have better co-deformation characteristics as observed in Cu-Nb monocore wire experiments where a circularity greater than 0.85 is obtained for several textures, as compared to circularities of 0.5-0.7 using traditional processing. The methodology to adopt precursor Nb processed by thermomechanical processing by SPD to traditional tube development techniques such as area reduction extrusion are presented. The tubes formed by this approach show sufficient ductility (greater than 30\%) along the circumferential and extrusion directions with tensile properties being very similar in perpendicular directions. The development of tube ECAE (tECAE) process produces textures very close to $\lbrace111\rbrace$ parallel to tube normal directions that are considered to be favorable for hydroforming applications. This is the first report of such textures in a seamless tube. The processing strategies developed are able to homogenize and converge the microstructures in Nb leading to similar deformation behavior irrespective of the starting microstructure.\\ \indent The grain refinement strategies for Nb presented in this thesis have the potential to be scaled up, and similar performance are expected irrespective of the Nb workpiece dimensions. The same processing strategies can be adapted to other bcc refractory metals including: tantalum (Ta), molybdenum (Mo), and tungsten (W) where the processing needs to be done at similar homologous temperatures/conditions where similar deformation mechanisms are active. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/155305
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 Springback in Deep Drawn High Purity Niobium for Superconductor Cavities by : Ganapati Rao Myneni
Download or read book Springback in Deep Drawn High Purity Niobium for Superconductor Cavities written by Ganapati Rao Myneni and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Superconducting radio frequency (SRF) cavities made from deep drawn high-purity niobium have become a popular approach for the design of particle accelerators. A number of current accelerators use this technology and it is a leading candidate for future designs. The development of this technology has required significant advances in many scientific fields including metallurgy, high vacuum physics, surface science, and forming. Recently proposed modifications to the current process for fabrication of these cavities has resulted in increased concern about the distribution of deformation, residual stress patterns, and springback. This presentation will report on the findings of a recently initiated program to study plastic flow and springback in the fabrication of these cavities and the influence of metallurgical variables including grain size and impurity content.
Download or read book מעשה ברבי משה בן מימון written by and published by . This book was released on 18?? with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
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 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 Surface Polishing of Niobium for Superconducting Radio Frequency (SRF) Cavity Applications by :
Download or read book Surface Polishing of Niobium for Superconducting Radio Frequency (SRF) Cavity Applications written by and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Niobium cavities are important components in modern particle accelerators based on superconducting radio frequency (SRF) technology. The interior of SRF cavities are cleaned and polished in order to produce high accelerating field and low power dissipation on the cavity wall. Current polishing methods, buffered chemical polishing (BCP) and electro-polishing (EP), have their advantages and limitations. We seek to improve current methods and explore laser polishing (LP) as a greener alternative of chemical methods. The topography and removal rate of BCP at different conditions (duration, temperature, sample orientation, flow rate) was studied with optical microscopy, scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD). Differential etching on different crystal orientations is the main contributor to fine grain niobium BCP topography, with gas evolution playing a secondary role. The surface of single crystal and bi-crystal niobium is smooth even after heavy BCP. The topography of fine grain niobium depends on total removal. The removal rate increases with temperature and surface acid flow rate within the rage of 0~20 °C, with chemical reaction being the possible dominate rate control mechanism. Surface flow helps to regulate temperature and avoid gas accumulation on the surface. The effect of surface flow rate on niobium EP was studied with optical microscopy, atomic force microscopy (AFM), and power spectral density (PSD) analysis. Within the range of 0~3.7 cm/s, no significant difference was found on the removal rate and the macro roughness. Possible improvement on the micro roughness with increased surface flow rate was observed. The effect of fluence and pulse accumulation on niobium topography during LP was studied with optical microscopy, SEM, AFM, and PSD analysis. Polishing on micro scale was achieved within fluence range of 0.57~0.90 J/cm2, with pulse accumulation adjusted accordingly. Larger area treatment was proved possible by overlapping laser tracks at proper ratio. Comparison of topography and PSD indicates that LP smooths the surface in a way similar to EP. The optimized LP parameters were applied to different types of niobium surfaces representing different stages in cavity fabrication. LP reduces the sharpness on rough surfaces effectively, while doing no harm to smooth surfaces. Secondary ion mass spectrometer (SIMS) analysis showed that LP reduces the oxide layer slightly and no contamination occurred from LP. EBSD showed no significant change on crystal structure after LP.
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 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 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 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 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 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 Superconducting Radio-frequency Cavities Made from Medium and Low-purity Niobium Ingots by :
Download or read book Superconducting Radio-frequency Cavities Made from Medium and Low-purity Niobium Ingots written by and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Superconducting radio-frequency cavities made of ingot niobium with residual resistivity ratio (RRR) greater than 250 have proven to have similar or better performance than fine-grain Nb cavities of the same purity, after standard processing. The high purity requirement contributes to the high cost of the material. As superconducting accelerators operating in continuous-wave typically require cavities to operate at moderate accelerating gradients, using lower purity material could be advantageous not only to reduce cost but also to achieve higher Q0-values. In this contribution we present the results from cryogenic RF tests of 1.3-1.5 GHz single-cell cavities made of ingot Nb of medium (RRR = 100-150) and low (RRR = 60) purity from different suppliers. Cavities made of medium-purity ingots routinely achieved peak surface magnetic field values greater than 70 mT with an average Q0-value of 2 × 1010 at 2 K after standard processing treatments. As a result, the performances of cavities made of low-purity ingots were affected by significant pitting of the surface after chemical etching.
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 Surface Studies of Niobium Chemically Polished Under Conditions for Superconducting Radiofrequency Cavity Production by :
Download or read book Surface Studies of Niobium Chemically Polished Under Conditions for Superconducting Radiofrequency Cavity Production written by and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The performance of niobium superconducting radiofrequency accelerator cavities is strongly impacted by the topmost several nanometers of the active (interior) surface, especially by the final surface conditioning treatments. We examined the effect of the most commonly employed treatment, buffered chemical polishing (BCP), on polycrystalline niobium sheet over a range of realistic solution flow rates using electron back scatter diffraction (EBSD), stylus profilometry, atomic force microscopy, laboratory XPS and synchrotron (variable photon energy) XPS, seeking to collect statistically significant data sets. We found that the predominant general surface orientation is (100), but others are also present and at the atomic-level details of surface plane orientation are more complex. The post-etch surface exhibits micron-scale roughness, whose extent does not change with treatment conditions. The outermost surface consists of a few-nm thick layer of niobium pentoxide, whose thickness increases with solution flow rate to a maximum of 1.3 - 1.4 times that resulting from static solution. The standard deviation of the roughness measurements is?? 30% and that of the surface composition is?? 5%.
