Molecular Dynamics Study Of Hydrogen Trapping And Helium Clustering In Tungsten
DOWNLOAD
Download Molecular Dynamics Study Of Hydrogen Trapping And Helium Clustering In Tungsten PDF/ePub or read online books in Mobi eBooks. Click Download or Read Online button to get Molecular Dynamics Study Of Hydrogen Trapping And Helium Clustering In Tungsten book now. This website allows unlimited access to, at the time of writing, more than 1.5 million titles, including hundreds of thousands of titles in various foreign languages. If the content not found or just blank you must refresh this page
Molecular Dynamics Study Of Hydrogen Trapping And Helium Clustering In Tungsten
DOWNLOAD
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
Surface Response Of Tungsten To Helium And Hydrogen Plasma Flux As A Function Of Temperature And Incident Kinetic Energy
DOWNLOAD
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.
Discovering Key Unknowns For Tungsten Hydrogen Helium Plasma Material Interactions Using Molecular Dynamics
DOWNLOAD
Author : Mary Alice Cusentino
language : en
Publisher:
Release Date : 2018
Discovering Key Unknowns For Tungsten Hydrogen Helium Plasma Material Interactions Using Molecular Dynamics written by Mary Alice Cusentino and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2018 with Helium categories.
Molecular dynamics simulations have been used to study plasma material interactions to better understand the performance of a tungsten divertor. A tendril-like geometry was modeled to study the diffusion of helium in nanotendrils and its relation to fuzz growth. The tendrils remain stable throughout the simulation and a modified helium release mechanism is found that allows the helium retention to reach a steady state within the tendril. The helium retention within the tendril inversely depends on the surface to volume ratio. There is limited diffusion deep into the tendril and extrapolating the flux calculated to experimentally relevant time scales indicates that helium diffusion is not sufficient to drive fuzz growth. Helium implantation near a grain boundary, but not directly on the grain boudary itself, was performed. Helium behavior within the implantation zone is consistent with previous simulations of helium in defect-free tungsten. Some helium diffuses to the grain boundary where it forms small helium clusters but virtually no helium atoms diffuse over the grain boundary. The sink strength of the grain boundary and helium bubbles are calculated and the values are comparable, indicating that the grain boundary sink strength only matters at the beginning of the simulation before the helium bubbles form. Simulations of hydrogen and helium were performed to assess the interaction between the two gas atom species in tungsten. Simulations of small subsurface mixed hydrogen-helium bubbles indicate that hydrogen diffuses to the helium bubble periphery region and becomes trapped there. A binding energy of 2 eV is calculated. Modeling of hydrogen implantation in helium pre-implanted tungsten were performed and the presence of helium modifies the depth distribution and blocks the deeper diffusion of hydrogen when compared with hydrogen implantation in pure tungsten. This could potentially have a significant impact on tritium retention and material performance.
Helium Nano Bubble Formation In Tungsten
DOWNLOAD
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.
Helium Segregation And Migration Behavior Near Symmetric Tilt Grain Boundaries In Tungsten
DOWNLOAD
Author : Zhoucen Yang
language : en
Publisher:
Release Date : 2018
Helium Segregation And Migration Behavior Near Symmetric Tilt Grain Boundaries In Tungsten written by Zhoucen Yang and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2018 with categories.
Tungsten, one of the most important divertor materials in nuclear fusion devices, will be subject to high-flux helium plasma, which can lead to unexpected structural defects and irregular microstructure such as fuzz and blistering. Helium transport in tungsten is affected by grain boundary (GB) defects in the metal. To improve the lifetime and long-term performance of plasma-facing tungsten, it is important to have a better understanding of helium behavior near GBs. In the first part of this thesis, helium cluster transport near symmetric tilt GBs is studied by molecular dynamics (MD) simulation. We find that helium cluster diffusion is significantly impeded, compared to its bulk diffusion rate, near various symmetric tilt GBs with different tilt angles and [sigma] values. Secondly, various cluster-GB interactions and the resulting drift forces for helium cluster transport near GBs are quantified by molecular statics (MS) simulations and continuum elastic inclusion theory. We conclude that the GB sink strength for helium cluster segregation increases with cluster size and depends strongly on various GB properties. The third part of this thesis focuses on analyzing small helium cluster migration on symmetric tilt GBs. We find that small helium clusters show much higher migration energies when bound to the GB than in the bulk. Helium cluster migration is highly affected by the size of helium cluster and the structure of the GB. Vacancy migration energies are relatively low compared to the bulk, and are also much lower than helium cluster migration energies on the GB plane. This suggests that helium cluster migration on grain boundaries is actually governed by the rate of vacancy migration.
Comprehensive Nuclear Materials
DOWNLOAD
Author :
language : en
Publisher: Elsevier
Release Date : 2020-07-22
Comprehensive Nuclear Materials written by and has been published by Elsevier this book supported file pdf, txt, epub, kindle and other format this book has been release on 2020-07-22 with Science categories.
Materials in a nuclear environment are exposed to extreme conditions of radiation, temperature and/or corrosion, and in many cases the combination of these makes the material behavior very different from conventional materials. This is evident for the four major technological challenges the nuclear technology domain is facing currently: (i) long-term operation of existing Generation II nuclear power plants, (ii) the design of the next generation reactors (Generation IV), (iii) the construction of the ITER fusion reactor in Cadarache (France), (iv) and the intermediate and final disposal of nuclear waste. In order to address these challenges, engineers and designers need to know the properties of a wide variety of materials under these conditions and to understand the underlying processes affecting changes in their behavior, in order to assess their performance and to determine the limits of operation. Comprehensive Nuclear Materials, Second Edition, Seven Volume Set provides broad ranging, validated summaries of all the major topics in the field of nuclear material research for fission as well as fusion reactor systems. Attention is given to the fundamental scientific aspects of nuclear materials: fuel and structural materials for fission reactors, waste materials, and materials for fusion reactors. The articles are written at a level that allows undergraduate students to understand the material, while providing active researchers with a ready reference resource of information. Most of the chapters from the first Edition have been revised and updated and a significant number of new topics are covered in completely new material. During the ten years between the two editions, the challenge for applications of nuclear materials has been significantly impacted by world events, public awareness, and technological innovation. Materials play a key role as enablers of new technologies, and we trust that this new edition of Comprehensive Nuclear Materials has captured the key recent developments. Critically reviews the major classes and functions of materials, supporting the selection, assessment, validation and engineering of materials in extreme nuclear environments Comprehensive resource for up-to-date and authoritative information which is not always available elsewhere, even in journals Provides an in-depth treatment of materials modeling and simulation, with a specific focus on nuclear issues Serves as an excellent entry point for students and researchers new to the field
Fusion Science And Technology
DOWNLOAD
Author :
language : en
Publisher:
Release Date : 2006
Fusion Science And Technology written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2006 with Fusion reactors categories.
Delft Progress Report
DOWNLOAD
Author :
language : en
Publisher:
Release Date : 1976
Delft Progress Report written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1976 with Engineering categories.
Classical And Quantum Dynamics In Condensed Phase Simulations Proceedings Of The International School Of Physics
DOWNLOAD
Author : Bruce J Berne
language : en
Publisher: World Scientific
Release Date : 1998-06-17
Classical And Quantum Dynamics In Condensed Phase Simulations Proceedings Of The International School Of Physics written by Bruce J Berne and has been published by World Scientific this book supported file pdf, txt, epub, kindle and other format this book has been release on 1998-06-17 with Science categories.
The school held at Villa Marigola, Lerici, Italy, in July 1997 was very much an educational experiment aimed not just at teaching a new generation of students the latest developments in computer simulation methods and theory, but also at bringing together researchers from the condensed matter computer simulation community, the biophysical chemistry community and the quantum dynamics community to confront the shared problem: the development of methods to treat the dynamics of quantum condensed phase systems.This volume collects the lectures delivered there. Due to the focus of the school, the contributions divide along natural lines into two broad groups: (1) the most sophisticated forms of the art of computer simulation, including biased phase space sampling schemes, methods which address the multiplicity of time scales in condensed phase problems, and static equilibrium methods for treating quantum systems; (2) the contributions on quantum dynamics, including methods for mixing quantum and classical dynamics in condensed phase simulations and methods capable of treating all degrees of freedom quantum-mechanically.
Ion Solid Interactions
DOWNLOAD
Author : Michael Nastasi
language : en
Publisher: Cambridge University Press
Release Date : 1996-03-29
Ion Solid Interactions written by Michael Nastasi and has been published by Cambridge University Press this book supported file pdf, txt, epub, kindle and other format this book has been release on 1996-03-29 with Science categories.
Comprehensive guide to an important materials science technique for students and researchers.