Helium Nano Bubble Formation In Tungsten
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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.
Measuring Helium Nano Bubble Formation In Tungsten With Grazing Incidence Small Angle X Ray Scattering
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Author : Matt Andrew Trevor Thompson
language : en
Publisher:
Release Date : 2017
Measuring Helium Nano Bubble Formation In Tungsten With Grazing Incidence Small Angle X Ray Scattering written by Matt Andrew Trevor Thompson 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.
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.
Helium Induced Bubble Formation In Ultrafine And Nanocrystalline Tungsten Under Different Extreme Conditions
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Author :
language : en
Publisher:
Release Date : 2014
Helium Induced 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.
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.
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.
On The Edge Of Magnetic Fusion Devices
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Author : Sergei Krasheninnikov
language : en
Publisher: Springer Nature
Release Date : 2020-09-07
On The Edge Of Magnetic Fusion Devices written by Sergei Krasheninnikov and has been published by Springer Nature this book supported file pdf, txt, epub, kindle and other format this book has been release on 2020-09-07 with Science categories.
This book reviews the current state of understanding concerning edge plasma, which bridges hot fusion plasma, with a temperature of roughly one million degrees Kelvin with plasma-facing materials, which have melting points of only a few thousand degrees Kelvin. In a fact, edge plasma is one of the keys to solution for harnessing fusion energy in magnetic fusion devices. The physics governing the processes at work in the edge plasma involves classical and anomalous transport of multispecies plasma, neutral gas dynamics, atomic physics effects, radiation transport, plasma-material interactions, and even the transport of plasma species within the plasma-facing materials. The book starts with simple physical models, then moves on to rigorous theoretical considerations and state-of-the-art simulation tools that are capable of capturing the most important features of the edge plasma phenomena. The authors compare the conclusions arising from the theoretical and computational analysis with the available experimental data. They also discuss the remaining gaps in their models and make projections for phenomena related to edge plasma in magnetic fusion reactors.
Hydrogen And Helium Recycling At Plasma Facing Materials
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Author : Ahmed Hassanein
language : en
Publisher: Springer Science & Business Media
Release Date : 2002-03-31
Hydrogen And Helium Recycling At Plasma Facing Materials written by Ahmed Hassanein and has been published by Springer Science & Business Media this book supported file pdf, txt, epub, kindle and other format this book has been release on 2002-03-31 with Mathematics categories.
Proceedings of the NATO Advanced Research Workshop on Hydrogen Isotope Recycling at Plasma Facing Materials in Fusion Reactors, Argonne, Illinois, USA from 22-24 August 2001
Molecular Dynamics Study Of Hydrogen Trapping And Helium Clustering In Tungsten
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Author : Ashok Gurung
language : en
Publisher:
Release Date : 2018
Molecular Dynamics Study Of Hydrogen Trapping And Helium Clustering In Tungsten written by Ashok Gurung and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2018 with Physics categories.
The field of plasma confinement and path toward achieving thermonuclear fusion started with experimental devices like tokamak and has evolved into other more complex variants of magnetic plasma confinement such as stellarator and spherical-tokamaks. As the plasma confinement machines advance towards higher temperature and plasma density (thermonuclear fusion conditions) the role and nature of plasma-wall interaction such as possible edge plasma regimes, particle recycling at the walls and its consequence for erosion, migration and re-deposition of wall material and impurity generation, transport and radiation as well as issues of particle exhaust continues to be a dominant limiting factor due to the close proximity of the wall. The selection of optimal wall-material for the plasma-wall components is a complex process, and till date, it continues to be an important and challenging area in the field of study of plasma-wall interaction. Various metals, ceramics or graphites with desirable response to severe thermal loads and varying mechanical properties towards elastic deformation, plastic deformation, fatigue, and toughness have been proposed. Sputtering and wall-erosion which results in plasma contamination is an important determining factor for wall-material selection. Tungsten is considered as a possible candidate for plasma facing material because of its high thermal conductivity, low hydrogen retention, high atomic mass (high-Z), and, high melting point. In both, limiter and divertor configurations there is substantial recycling of particles on the wall due to continuous bombardment of wall material by both charged and neutral particles. Experimental studies have shown that the light particle species such as hydrogen and helium are able to penetrate into the tungsten wall and substantial trapping of helium in tungsten has been observed. Among other issues, blistering, fuzz formation, tritium retention, surface roughening, and intergranular embrittlement are major issues to be addressed. Considerable effort is invested towards developing a better understanding of the interactions of hydrogen, helium in tungsten matrix. In the present study we use classical molecular dynamics (MD) approach to study (a) hydrogen retention, (b) helium bubble formation in tungsten, and, (c) study the effect of the presence of helium bubbles in tungsten matrix on hydrogen retention. The hydrogen bombardment simulations span an energy range from 30 eV to 100 eV at three different substrate temperatures - 500K, 1200K and 2000K. The variation of hydrogen trapping on tungsten matrix surface orientation is examined by performing MD simulation for 100 and 111 surface orientations. The growth of helium clusters in tungsten matrix as a function of temperature and a varying number of helium atoms at the start of the simulation is performed to study solute saturation effects. The trapping of hydrogen in the presence of helium is studied through molecular dynamics study of the bombardment of hydrogen atoms on tungsten substrate with helium cluster distributed throughout the tungsten matrix.The results of this study show that the hydrogen trapping fraction grows almost linearly over the intermediate bombarding energy range with the exception of low incident energy for which higher hydrogen trapping is observed. The effect of substrate temperature for low energy hydrogen bombardment is found to be different from the high-energy incidence indicating a complex dynamics of atomic diffusion within the tungsten matrix. The surface orientation of the substrate also affects the trapping percentage of hydrogen. The formation and growth of helium cluster are found to be dependent on the temperature and the number of helium atoms per unit cell. In the presence of helium cluster, the trapping percentage of hydrogen is significantly affected, especially at low energy
Helium Bubble Formation And Swelling In Metals
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Author : B. B. Glasgow
language : en
Publisher:
Release Date : 1981
Helium Bubble Formation And Swelling In Metals written by B. B. Glasgow and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1981 with categories.