Morphology Changes Due To Energetic Helium Ion Irradiation Of Tungsten Surfaces At High Temperatures
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Morphology Changes Due To Energetic Helium Ion Irradiation Of Tungsten Surfaces At High Temperatures
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Author : Karla Brittany Hall
language : en
Publisher:
Release Date : 2019
Morphology Changes Due To Energetic Helium Ion Irradiation Of Tungsten Surfaces At High Temperatures written by Karla Brittany Hall and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2019 with categories.
The Materials Irradiation Experiment (MITE-E) at the University of Wisconsin-Madison in the Inertial Electrostatic Confinement Laboratory was used to simulate helium ion (He+) irradiation of tungsten at fusion reactor relevant ion fluences and temperatures. Single and polycrystalline tungsten (SCW and PCW) samples were irradiated with 30-55 keV He+ at normal incidence with fluences of 3x1017 to 1019 He+/cm2 at temperatures from 500-900 oC. Post-irradiation analysis of the samples irradiated in the MITE-E device revealed several unique surface morphologies when the ion energy, temperature, and fluence were varied. Surface erosion due to energetic He+ irradiation was determined by mass loss measurements of samples pre- and post-irradiation. Past studies in the MITE-E revealed a surface orientation near {001} on PCW had considerably less erosion from He+ irradiation than surrounding grains Morphology development and mass loss measurements on [110] and [100] SCW revealed that the [100] crystal orientation lead to decreased surface erosion below 10^18 He+/cm2. Simulating what a fusion reactor component would likely experience, a sequentially increasing and decreasing multi-energy He+ irradiation on PCW was explored. Samples irradiated with increasing and decreasing multi-energy (35, 45, and 55 keV) He+ showed more surface damage than samples irradiated with mono-energetic (30 keV) He+. However, the multi-energy ion irradiated samples had less mass loss than the mono-energetic ion irradiated samples under similar parameters. Varying the temperature of samples under mono-energetic and multi-energy He+ irradiation at the same fluence caused an increase in mass loss as the temperature was decreased. The amount of mass loss and morphologies that developed on all samples point to He+ as a contributing mechanism in the undesired creation of W dust in a fusion reactor.
Characterization Of The Dynamic Formation Of Nano Tendril Surface Morphology On Tungsten While Exposed To Helium Plasma
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Author : Kevin Benjamin Woller
language : en
Publisher:
Release Date : 2017
Characterization Of The Dynamic Formation Of Nano Tendril Surface Morphology On Tungsten While Exposed To Helium Plasma written by Kevin Benjamin Woller and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2017 with categories.
Tungsten undergoes surface morphology changes on the nanometer scale when subjected to low energy helium ion bombardment. This is due in part to the ion bombardment causing tungsten atoms to move on the surface, but also because of helium implantation and bubble development in the near surface at a depth 30 nm. At high enough surface temperatures, T/TM /~ 0.2, where TM is the melting temperature, nanoscale tendrils form on the surface and grow longer with additional bombardment by helium, but will decompose at the same temperature without helium bombardment. A tungsten surface that develops a densely packed layer of nano-tendrils over macroscopic areas greater than the grain size is referred to as tungsten fuzz, and is under intense study in fusion energy research, both for better understanding of how tungsten fuzz forms and of how tungsten fuzz affects the performance of plasma-facing components. The necessity of helium irradiation of the surface to induce nano-tendril growth motivates investigation into the dynamic process of helium implantation and accumulation in the surface. In this thesis, in situ elastic recoil detection is developed and used to measure the dynamic concentration of helium within a tungsten surface during the active growth of tungsten fuzz. During the development of in situ elastic recoil detection analysis, a variant of tungsten nano-tendril growth was discovered featuring drastically isolated bundles of nano-tendrils that grow at a higher rate than tungsten fuzz. The variation in nano-tendril morphology is correlated with incident helium ion energy modulation. The dependence on ion energy modulation and isolated nature of the nano-tendril bundles reveals clearly that nano-tendril growth is sensitive to surface kinetic effects. In this thesis, the structure and parameter space of the newly discovered nano-tendril bundle growth is analyzed with a suite of electron-based surface science techniques.
Improving The Materials Irradiation Xperimental Facility And Increasing Understanding Of Helium Irradiation Of Tungsten
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Author :
language : en
Publisher:
Release Date : 2013
Improving The Materials Irradiation Xperimental Facility And Increasing Understanding Of Helium Irradiation Of Tungsten written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2013 with categories.
Minimizing damage to plasma facing components is a key issue that needs to be resolved before realizing commercial fusion reactors. The Materials Irradiation Experiment (MITE-E) at the University of Wisconsin Inertial Electrostatic Confinement (UW-IEC) Laboratory simulates fusion reactor conditions of light ion bombardment at high temperatures. Past experiments done in the MITE-E revealed that different morphologies developed on different grains of tungsten after irradiation with 30 keV helium ions at 900 oC. In this thesis, these structures have been correlated with the underlying crystal structure. Grains with orientations near {0 0 1} formed plateaus that were less eroded, while grains near {1 0 1} formed ripples parallel to 0 1 0. The connection of morphology to crystal orientation was made possible by the development of a new sample marking technique that allows the same location on a sample to be analyzed with the scanning electron microscope and the electron backscatter diffraction technique. It was also discovered that the sample pre-irradiation surface treatment has a large impact on the morphologies that develop after irradiation. A sample irradiated with helium ions over a spectrum of energies developed a more damaged surface structure than samples irradiated to the same fluence with mono-energetic helium. The sample with multiple energy implantation did not develop blisters, which had been seen previously on mono-energetically implanted samples in the MITE-E. In a separate experiment, samples of ZrB2, made with isotopically separated 11B, were irradiated with 30 keV helium ions in the MITE-E, and the results were compared to other materials irradiated under similar conditions. The rates and levels of damage observed on all samples would have a significant impact on fusion reactor divertor plates and first walls.
Surface Response Of Tungsten To Helium And Hydrogen Plasma Flux As A Function Of Temperature And Incident Kinetic Energy
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Author : Faiza Sefta
language : en
Publisher:
Release Date : 2013
Surface Response Of Tungsten To Helium And Hydrogen Plasma Flux As A Function Of Temperature And Incident Kinetic Energy written by Faiza Sefta and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2013 with categories.
Tungsten is a leading candidate material for the diverter in future nuclear fusion reactors. Previous experiments have demonstrated that surface defects and bubbles form in tungsten when ex- posed to helium and hydrogen plasmas, even at modest ion energies. In some regimes, between 1000K and 2000K, and for He energies below 100eV, "fuzz" like features form. The mechanisms leading to these surfaces comprised of nanometer sized tungsten tendrils which include visible helium bubbles are not currently known. The role of helium bubble formation in tendril morphology could very likely be the starting point of these mechanisms. Using Molecular dynamics (MD) simulations, the role of helium and hydrogen exposure in the initial formation mechanisms of tungsten "fuzz" are investigated. Molecular dynamics simulations are well suited to describe the time and length scales associated with initial formation of helium clusters that eventually grow to nano-meter sized helium bubbles. MD simulations also easily enable the modeling of a variety of surfaces such as single crystals, grain boundaries or "tendrils". While the sputtering yield of tungsten is generally low, previous observations of surface modification due to plasma exposure raise questions about the effects of surface morphology and sub-surface helium bubble populations on the sputtering behavior. Results of computational molecular dynamics are reported that investigate the influence of sub-surface helium bubble distributions on the sputtering yield of tungsten (100) and (110) surfaces induced by helium ion exposure in the range of 300 eV to 1 keV. The calculated sputtering yields are in reasonable agreement with a wide range of experimental data; but do not show any significant variation as a result of the pre-existing helium bubbles. Molecular dynamics simulations reveal a number of sub-surface mechanisms leading to nanometer- sized "fuzz" in tungsten exposed to low-energy helium plasmas. We find that during the bubble formation process, helium clusters create self-interstitial defect clusters in tungsten by a trap mutation process, followed by the migration of these defects to the surface that leads to the formation of layers of adatom islands on the tungsten surface. As the helium clusters grow into nanometer sized bubbles, their proximity to the surface and extremely high gas pressures can cause them to rupture the surface thus enabling helium release. Helium bubble bursting induces additional surface damage and tungsten mass loss which varies depending on the nature of the surface. We then show tendril-like geometries have surfaces that are more resilient to helium clustering and bubble formation and rupture. Finally, the study includes hydrogen to reveal the effect of a mixed 90%H-10%He plasma mix on the tungsten surface. We find that hydrogen greatly affects the tungsten surface, with a near surface hydrogen saturation layer, and that helium clusters still form and are attractive trapping sites for hydrogen. Molecular dynamics simulations have also investigated the effect of sub-surface helium bubble evolution on tungsten surface morphology. The helium bubble/tungsten surface interaction has been systematically studied to determine how parameters such as bubble shape and size, temperature, tungsten surface orientation and ligament thickness above the bubble impact bubble stability and surface evolution. The tungsten surface is roughened by a combination of adatom islands, craters and pinholes. The study provides insight into the mechanisms and conditions leading to various tungsten topology changes, most notably the formation of nanoscale fuzz. An atomistic study of the mechanisms behind initial phases of tungsten nano-fuzz growth has determined that tungsten surfaces are affected by sub-displacement energy helium and hydrogen fluxes through a series of mechanisms. Sub-surface helium atom clustering, bubble nucleation, growth and rupture lead to tungsten surface deformation. Helium clustering processes vary near grain boundaries or in tendril-like surface geometries. In the presence of hydrogen, these mechanisms are coupled with hydrogen surface saturation. Finally, further investigation to connect these atomistic mechanisms to nano-size tungsten fuzz growth is needed to get a comprehensive under- standing of the effects of low energy helium and hydrogen on tungsten.
The Effects Of Tungsten S Pre Irradiation Surface Condition On Helium Irradiated Morphology
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Author :
language : en
Publisher:
Release Date : 2015
The Effects Of Tungsten S Pre Irradiation Surface Condition On Helium Irradiated Morphology written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2015 with categories.
Erosion is a concern associated with the use of tungsten as a plasma-facing component in fusion reactors. To compare the damage progression, polycrystalline tungsten (PCW) and (110) single crystal tungsten (SCW) samples were prepared with (1) a mechanical polish (MP) with roughness values in the range of 0.018-0.020 [mu]m and (2) an MP and electropolish (MPEP) resulting in roughness values of 0.010-0.020 [mu]m for PCW and 0.003-0.005 [mu]m for SCW samples. Samples were irradiated with 30 keV He+ at 1173 K to fluences between 3 × 1021 and 6 × 1022 He/m2. The morphologies that developed after low-fluence bombardment were different for each type of sample--MP SCW, MPEP SCW, MP PCW, and MPEP PCW. At the highest fluence, the SCW MPEP sample lost significantly more mass and developed a different morphology than the MP SCW sample. The PCW samples developed a similar morphology and had similar mass loss at the highest fluence. Surface preparation can have a significant effect on post-irradiation morphology that should be considered for the design of future fusion reactors such as ITER and DEMO.
Helium Nano Bubble Formation In Tungsten
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Author : Matt Thompson
language : en
Publisher: Springer
Release Date : 2018-08-01
Helium Nano Bubble Formation In Tungsten written by Matt Thompson and has been published by Springer this book supported file pdf, txt, epub, kindle and other format this book has been release on 2018-08-01 with Science categories.
This PhD thesis characterises the damage that occurs in tungsten when it is exposed to a fusion-like environment. The book presents pioneering work on the use of grazing-incidence small-angle X-ray scattering (GISAXS) to measure nano-bubble formation in tungsten exposed to helium plasma. The phenomenon of nanoscale bubble formation within metals during helium plasma exposure can lead to undesirable changes in the material properties, such as complex nanoscale surface modification or a reduction in thermal conductivity. As a result of this work, it is now possible to quantify how nanobubble behaviour changes within different materials, and under different plasma conditions. In 2015 the author published the first GISAXS study of helium-induced nanobubble formation in tungsten, demonstrating the viability of using GISAXS for this work. This paper has generated significant interest from the international fusion community and was selected as one of the highlights for the journal Nuclear Fusion.
Iter Physics
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Author : C Wendell Horton, Jr
language : en
Publisher: World Scientific
Release Date : 2015-06-25
Iter Physics written by C Wendell Horton, Jr and has been published by World Scientific this book supported file pdf, txt, epub, kindle and other format this book has been release on 2015-06-25 with Science categories.
The promise of a vast and clean source of thermal power drove physics research for over fifty years and has finally come to collimation with the international consortium led by the European Union and Japan, with an agreement from seven countries to build a definitive test of fusion power in ITER. It happened because scientists since the Manhattan project have envisioned controlled nuclear fusion in obtaining energy with no carbon dioxide emissions and no toxic nuclear waste products.This large toroidal magnetic confinement ITER machine is described from confinement process to advanced physics of plasma-wall interactions, where pulses erupt from core plasma blistering the machine walls. Emissions from the walls reduce the core temperature which must remain ten times hotter than the 15 million degree core solar temperature to maintain ITER fusion power. The huge temperature gradient from core to wall that drives intense plasma turbulence is described in detail.Also explained are the methods designed to limit the growth of small magnetic islands, the growth of edge localized plasma plumes and the solid state physics limits of the stainless steel walls of the confinement vessel from the burning plasma. Designs of the wall coatings and the special 'exhaust pipe' for spent hot plasma are provided in two chapters. And the issues associated with high-energy neutrons — about 10 times higher than in fission reactions — and how they are managed in ITER, are detailed.
Radiation Damage In Materials
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Author : Yongqiang Wang
language : en
Publisher: MDPI
Release Date : 2020-12-28
Radiation Damage In Materials written by Yongqiang Wang and has been published by MDPI this book supported file pdf, txt, epub, kindle and other format this book has been release on 2020-12-28 with Science categories.
The complexity of radiation damage effects in materials that are used in various irradiation environments stems from the fundamental particle–solid interactions and the subsequent damage recovery dynamics after the collision cascades, which involves multiple length and time scales. Adding to this complexity are the transmuted impurities that are unavoidable from accompanying nuclear processes. Helium is one such impurity that plays an important and unique role in controlling the microstructure and properties of materials used in fast fission reactors, plasma-facing and structural materials in fusion devices, spallation neutron target designs, actinides, tritium-containing materials, and nuclear waste. Their ultra-low solubility in virtually all solids forces He atoms to self-precipitate into small bubbles that become nucleation sites for further void growth under radiation-induced vacancy supersaturations, resulting in material swelling and high-temperature He embrittlement, as well as surface blistering under low-energy and high-flux He bombardment. This Special Issue, “Radiation Damage in Materials—Helium Effects”, contains review articles and full-length papers on new irradiation material research activities and novel material ideas using experimental and/or modeling approaches. These studies elucidate the interactions of helium with various extreme environments and tailored nanostructures, as well as their impact on microstructural evolution and material properties.
Helium Bubble Formation In Ultrafine And Nanocrystalline Tungsten Under Different Extreme Conditions
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Author :
language : en
Publisher:
Release Date : 2014
Helium Bubble Formation In Ultrafine And Nanocrystalline Tungsten Under Different Extreme Conditions written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2014 with categories.
We investigated the effects of helium ion irradiation energy and sample temperature on the performance of grain boundaries as helium sinks in ultrafine grained and nanocrystalline tungsten. Irradiations were performed at displacement and non-displacement energies and at temperatures above and below that required for vacancy migration. Microstructural investigations were performed using Transmission Electron Microscopy (TEM) combined with either in-situ or ex-situ ion irradiation. Under helium irradiation at an energy which does not cause atomic displacements in tungsten (70 eV), regardless of temperature and thus vacancy migration conditions, bubbles were uniformly distributed with no preferential bubble formation on grain boundaries. Moreover, at energies that can cause displacements, bubbles were observed to be preferentially formed on the grain boundaries only at high temperatures where vacancy migration occurs. Under these conditions, the decoration of grain boundaries with large facetted bubbles occurred on nanocrystalline grains with dimensions less than 60 nm. Finally, we discuss the importance of vacancy supply and the formation and migration of radiation-induced defects on the performance of grain boundaries as helium sinks and the resulting irradiation tolerance of ultrafine grained and nanocrystalline tungsten to bubble formation.
Issues In Nuclear Energy Technologies 2013 Edition
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Author :
language : en
Publisher: ScholarlyEditions
Release Date : 2013-05-01
Issues In Nuclear Energy Technologies 2013 Edition written by and has been published by ScholarlyEditions this book supported file pdf, txt, epub, kindle and other format this book has been release on 2013-05-01 with Technology & Engineering categories.
Issues in Nuclear Energy Technologies / 2013 Edition is a ScholarlyEditions™ book that delivers timely, authoritative, and comprehensive information about Fusion Energy. The editors have built Issues in Nuclear Energy Technologies: 2013 Edition on the vast information databases of ScholarlyNews.™ You can expect the information about Fusion Energy in this book to be deeper than what you can access anywhere else, as well as consistently reliable, authoritative, informed, and relevant. The content of Issues in Nuclear Energy Technologies: 2013 Edition has been produced by the world’s leading scientists, engineers, analysts, research institutions, and companies. All of the content is from peer-reviewed sources, and all of it is written, assembled, and edited by the editors at ScholarlyEditions™ and available exclusively from us. You now have a source you can cite with authority, confidence, and credibility. More information is available at http://www.ScholarlyEditions.com/.