7 research outputs found
Influence of re-deposited layer thickness and sample structure on deuterium retention in tungsten
No full textDynamic erosion and stability analysis of nano-columnar tungsten
Full text linkDie Wahl des ersten Wandmaterials für künftige Fusionsreaktoren ist eine der Herausforderungen, die es zu bewältigen gilt, um die Aufwärtsskalierung zu kommerziellen Kraftwerken zu ermöglichen. Aufgrund seiner Hitzebeständigkeit, seiner hohen Sputtering-Schwelle und vieler weiterer vorteilhafter Eigenschaften ist Wolfram (W) bisher einer der vielversprechendsten Kandidaten. Dennoch gibt es eine Reihe von nachteiligen Effekten, wenn W in Fusionsgeräten mit magnetischem Einschluss verwendet wird, wie z. B. Blasen- und "W-Fuzz"-Bildung, die die Effizienz der Reaktoren beeinträchtigen. In früheren Studien wurde gezeigt, dass die Nanostrukturierung von W in Form von Nanosäulen zu einer höheren Strahlungsresistenz und einer geringeren Sputterausbeute führt.Um den Erosionsprozess von nanosäulenförmigem W (NCW) besser zu verstehen, wurde eine dünne Schicht von NCW, die zuvor auf einen mit Gold-Elektroden ausgestatteten Quarzkristall abgeschieden worden war, unter 2 keV Ar Ionenbestrahlung bei einem Einfallswinkel des Ionenstrahls von ° zur Oberflächennormalen schrittweise erodiert. Nach jedem Erosionsschritt wurde die winkelabhängige Sputterausbeute gemessen und die Oberflächentopographie mittels SEM und AFM abgebildet. Zusätzlich wurden die AFM-Messungen und eine nach den verfügbaren SEM-Bildern modellierte Struktur als Input für einen Simulationscode (SPRAY-Code) verwendet, der auf Basis der sogenannten binary collision approximation (BCA) in Kombination mit einem Raytracing Algorithmus entwickelt wurde.Es wurde festgestellt, dass die SPRAY-Simulationen die gemessene statische Sputterausbeute erst nach einer signifikanten Erosion der NCW-Probe gut reproduzieren konnten. Dies wurde hauptsächlich auf die Ungenauigkeiten bei der Reproduktion der Oberflächentopologie mittels AFM-Abbildung zurückgeführt. Andererseits stellt die Modellstruktur zwar die tiefen Kanäle in den NCW-Topologien besser dar, gibt aber die Oberflächenrauheit nicht genau wieder und konnte daher auch keine fehlerfreien simulierten Sputtererträge für NCW liefern.Die Messung der dynamischen Sputterausbeute liefert die erste experimentell ermittelte Quantifizierung der Stabilität von NCW bei längerem Sputtern mit energiereichen (keV-Bereich) Ionen. Während die anwendbaren Fluenzen bisher nur durch Simulationen untersucht wurden, untermauert das Experiment den vorhergesagten Wert mit guter Übereinstimmung. Darüber hinaus wurde die Betriebszeit des NCW unter fusionsrelevanten Bedingungen abgeschätzt, sodass Hochrechnungen für die Betriebszeit in unterschiedlichen Betriebsmodi möglich ist.The choice of the first wall material in future fusion reactors is one of the challenges that need to be addressed, in order to enable the up scaling of research reactors to commercial power plants. Because of its heat resistance, high sputtering threshold and many other beneficial properties, to date, tungsten (W) is one of the most promising candidates. Nevertheless, there are a number of detrimental effects when using W in Magnetic Confinement Fusion (MCF), such as blistering and W-fuzz formation, which inhibit the efficiency of the reactors. In previous studies, it was shown that nano-structuring of W into nano-columns or nano-foam results in higher radiation resistance and lower sputter yield.In order to better understand the erosion process of nano-columnar W (NCW), a thin layer of NCW deposited onto a quartz crystal was gradually eroded under 2\,keV Ar ion irradiation at an ion beam incidence angle of ° towards the surface normal. After each erosion step the angle dependence of the sputter yield was measured and the surface topography was imaged via SEM and AFM. Additionally, the AFM measurements and a structure modeled according to the available SEM images were used as input for a simulation code (SPRAY), which was developed on the basis of the so-called Binary Collision Approximation (BCA) in combination with a ray-tracing algorithm.It was found that the SPRAY simulations could only reproduce the measured static sputter yield well after significant erosion of the NCW sample. This was mainly attributed to the inaccuracies in the reproduction of the surface topology via AFM imaging. On the other hand, the model structure, while better representing the deep channels present in the NCW topologies, did not reproduce the surface roughness precisely and, therefore as well, could not provided accurate simulated sputter yields for NCW.The dynamic sputter yield measurement provides the first experimentally determined quantification of the stability of NCW under prolonged sputtering with energetic (keV range) ions. While previously the applicable fluences were only investigated through simulations, the experiment supports the predictions with good agreement. Furthermore, an operational time of NCW in fusion relevant conditions was estimated, which can be up-scaled to possible reactor scenarios
SPRAY – SPuttering simulation via RAYtracing of particles
No full text<h1>SPRAY – SPuttering simulation via RAYtracing of particles</h1>
<p>Python 3 Code for simulation of rough surface sputtering / ion reflection, using repository data from one-dimensional BCA simulations and microscopy image input Independent on lateral / vertical height of image or resolution (as long as enough RAM is provided). The working principle is described in greater detail in the supplementary material to the following publication:</p>
<p>C. Cupak, P.S. Szabo, H. Biber, R. Stadlmayr, C. Grave, M. Fellinger, J. Brötzner, R.A. Wilhelm, W. Möller, A. Mutzke, M.V. Moro, F. Aumayr, Sputter yields of rough surfaces: Importance of the mean surface inclination angle from nano- to microscopic rough regimes, Appl. Surf. Sci. 570 (2021) 151204. <a href="https://doi.org/10.1016/j.apsusc.2021.151204">https://doi.org/10.1016/j.apsusc.2021.151204</a>.</p>
<h2>Files contained:</h2>
<ul>
<li>SPRAY_V4_73.py – the main code; Run this to run the simulation</li>
<li>roughness2D.py – provides all necessary classes and methods </li>
<li>read_data.py – provides methods to read in the 1D BCA input data</li>
<li>Data.zip – example for 1D BCA data structure necessary to run SPRAY simulations. Should be extracted such that the directory "Data" is in the same directory as SPRAY_V4_73.py
<ul>
<li>Data/SDtrimSP_AngleEnergySweep.dat is a table of relevant sputter yields for all target species as a function of energy and incidence angle</li>
<li>Data/table1.txt gives data on atomic masses, etc.</li>
<li>Data/Atoms/ contains emission files for the sputtered recoils. Follow the naming convention: The integer in the file name gives the projectile incidence angle.</li>
<li>Data/Ions/ contains emission files for the reflected projectiles. Same naming convention as above</li>
</ul>
</li>
<li>README.md – a description of the code, the inputs and outputs; basically this description</li>
<li>SPRAY.inp – an exemplary input file containing all necessary input parameters</li>
</ul>
<p>The necessary inputs are described in greater detail below.</p>
<h2>System requirements:</h2>
<p>Tested and developed for usage under LINUX (Ubuntu 20.04.2 LTS and newer); For (old version) ready for Win10, contact the depositors.<br>Recommended PC specification: </p>
<ul>
<li>16GB RAM (for larger + high resoluted images, more is always better),</li>
<li>4 physical CPU Cores (the more you have, the faster it should work)</li>
<li>Some GB empty space on disk. For high statisical parameters for SPRAY simulation (pi, ns, ss), the emission list files can easily reach data volume in GB range</li>
</ul>
<h2>Required Python3.8 libraries:</h2>
<p>To be installed prior execution by pip install; the listed versions provided stable execution during benchmarking:</p>
<ul>
<li>numpy (1.20.2)</li>
<li>matplotlib (3.4.1)</li>
<li>psutil (5.8.0)</li>
<li>numpy-stl (2.16)</li>
<li>pandas (1.2.3)</li>
<li>vtk (9.0.1)</li>
<li>all other libraries should be available by default</li>
</ul>
<p>For convenience, a <code>requirements.txt</code> is provided; can be used with <code>pip install -r requirements.txt</code></p>
<h2>Necessary Input:</h2>
<h3>Input file "SPRAY.inp": </h3>
<p>General user input parameters need to be defined in the "SPRAY.inp" file</p>
<ul>
<li>number of primary ions <strong>pi</strong></li>
<li>number of sputtered atoms per primary ion <strong>ps</strong></li>
<li>number of secondary sputtered atoms <strong>ss</strong> (if ss larger than 0, also ri needs to be larger than 0)</li>
<li>number of CPU cores (or available virtual cores) used for this simulation <strong>np</strong></li>
<li>desired incidence angles for simulation <strong>(sa, ba, ia)</strong> = starting, last and increment step of angles</li>
<li>List of elements, starting with the ion species, for the composition of the target. Order should be consistent with order in provided repository data (see below). <strong>et</strong></li>
<li>declaration of path to repository data directory. if "loc" is listed, then the data repo needs to be locally in the same directory as SPRAY executable <strong>di</strong></li>
<li>a factor corresponding to the size of central irradiated area of the surface (0.8 = 80% recommended to prevent corner effects) <strong>as</strong></li>
<li>declaration of the surface input file type (either "xyz" or "stl" is supported) <strong>sf</strong></li>
<li>number of reflected ions per primary ion <strong>ri</strong></li>
<li>azimuthal angle mode <strong>aa</strong> (x, rand); x = classic from x axis, rand = random azimuthal impact </li>
<li>flag for display setting <strong>ds</strong>. Default option "no" (e.g., for headless computers without screen). "No" activates Xvfb environment to create a virtual desktop. </li>
</ul>
<h3>Microscopy images:</h3>
<p>A flexible number (at least one) of microscopy images can be provided:</p>
<ul>
<li>should be in form of a text file with .xyz file ending</li>
<li>Header lines needs to be marked with "#"</li>
<li>Take care: Greek letters or special characters like ä, ö, ü etc... may cause encoding troubles!</li>
<li>The shape of the data should be in 3 columns, representing the lateral x and y and vertical height z values</li>
<li>The unit should be in m, (will be converted to microns during SPRAY execution); </li>
<li>all 3 coordinates need to be in the same unit</li>
<li>ideally, the minimum surface height and xy coordinate is set to 0. </li>
<li>ATTENTION: Surface may not be properly hit by primary ions if the surface consists of a rather smooth, flat plane with some single spikes under grazing ion incidence! Especially important for AFM images with artifacts</li>
</ul>
<h3>STL file inputs:</h3>
<p>A flexible number (at least one) of .stl files can be provided:</p>
<ul>
<li>can be generated by any method, e.g., Solidworks,...</li>
<li>both surfaces, but also closed volumes should be supported</li>
<li>the units in the file should be in microns (principally the simulation is scale independent, but the print outputs are declared as microns)</li>
<li>the reference frame must be the following: lateral coordinates are x and y. Positive z values correspond to height value sthe ion beam (if ion incidence angle > 0°) comes from the positive x axis.</li>
<li>the lateral coordinates of the computational volume must start at x = y = 0, and should be strictly positive.</li>
<li>ideally, also the minimum z value should be 0</li>
</ul>
<h3><br>BCA simulation repositories: </h3>
<p>all stored in the folder Data</p>
<ul>
<li><strong>ATTENTION:</strong> <strong>This record contains just dummy data for illustration purposes</strong>, since this repository is usually large in volume (GB range). Moreover, a it has to be provided by the user for every target-projectile combination anyway.</li>
<li>Principally, any BCA code can be used for repository creation, but the shape of the data needs to be suitable</li>
<li>Sweep file (fine discretisation for 0-89° ion incidence and for 50eV - max. energy), which provides Sputter Yields and reflection coefficients for all target elements and reflection coefficients for the ions. Name = "*_AngleEnergySweep.dat" </li>
<li>Periodic table of elements (Name = "table1.txt"); necessary to load amu for given elemental species</li>
<li>Repository files including emission trajectories of both sputtered ions and reflected ions. These simulations need to be performed assuming a flat target of the same composition as also used for the Sputteryield Sweep file (see -> before). A set of simulations is required, where various ion incidence angles are used with relatively fine discretisation. It is important that the simulated angles range from 0 to 85 deg, 5deg increments. For repository simulations using Tri3dyn (2019-2020) or SDtrimSP (V6), useful python routines for data shaping are available by the authors. Ask the depositors if required.</li>
<li><strong>emission list files sputtered atoms</strong>: individual files with the trajectories of a single atom species of the target need to be provided (no mixed emission files) for each incidence angle simulated. Files need to be located in folder structure: Data/Atoms/angle/... (each inc. angle case is collected in a subfolder) coordinates in accordance to system of TRI3DYN. It is recommended to compare the shape of these files according to the provided dummy repository data: Data/Atoms/... principally columnar shape like: x,y,z (directional vector components, normalised)</li>
<li><strong>emission list files reflected ions</strong>: individual files with the trajectories of reflected ions need to be provided for each incidence angle simulated. files need to be located in folder structure: Data/Ions/... (each inc. angle case is collected in a file) coordinates in accordance to system of TRI3DYN. It is recommended to compare the shape of these files according to the provided dummy repository data: Data/Ions/... principally columnar shape like: Energy,x,y,z (directional vector components, normalised) for the reflected ions, also the kinetic energy after reflection needs to be considered, which influences secondary sputtering events.</li>
<li>It has to be noted that the sputteryields / reflection coefficients are taken from the Sweep Repository only. The emission list files are just the basis for the emission distribution utilised in SPRAY, while always a fixed and constant number of trajectories is taken as sample from these emission lists: (i.e.: ps = 100 virtually sputtered atoms for each primary ion impact, ss = 50 virtually secondary sputtered atoms for a reflected ion impact). Therefore, the length of the emission list files or their origin (BCA Code) must not directly be connected to the results of the Sweep Repository. However, a large number of emission trajectories in these files is beneficial to have a representative distribution at hand.</li>
</ul>
<h2>Output of simulations:</h2>
<ul>
<li>effective Sputter Yields</li>
<li>3D emission list files of successfully sputtered atoms and reflected ions (Attention, it's in TRI3DYN coordinates due to historic reasons!) Furthermore, only the azimuthal angle option "x" should be used, as otherwise the emission is a-priori equally distributed. The emission files, however, contain the relevant azimuthal angle in rad which was selected (0.0 for option x, otherwise between 0.0 to 2*pi), which you may use to back-shift those data.</li>
<li>global results file (all surfaces, simulated angles, simulated target elements)</li>
<li>in surface file specific subfolders: specific results (for all simulated incidence angles, elements...)</li>
<li>for each surface, a stl file for visualisation purposes is generated. Also necessary for raytracing</li>
<li>for each surface, a png image of the stl file is provided in the folder Surface_PNGs</li>
</ul>
<h2>Licenses</h2>
<p>The data is licensed under CC-BY, the code is licensed under MIT.</p>
Irradiation Stability of Nano-Columnar Tungsten Under Fusion-Relevant Ion Bombardment
No full textPlasma facing components (PFCs) in magnetic confinement fusion devices are exposed to very high thermal loads and particles fluxes during op- eration. Currently built and planned fusion reac- tors predominantly use tungsten (W) as the ma- terial of choice for their PFCs [1]. This choice is driven by tungsten’s beneficial properties, in- cluding a high melting point, excellent thermal conductivity and low fuel retention [2]. How- ever, at high temperatures (→ 800 K) and high helium fluxes, a porous nano-structure starts to form on its surface. This so called ”W-fuzz” is brittle, non-reflective and facilitates unipolar arc- ing, leading to a quicker degradation of PFCs [3]. It was shown that nano-structured surfaces, e.g. nano-foam or nano-columns, reduce the growth rate of W-fuzz and have a reduced sputter yield at high angles of incidence towards the surface normal [4, 5].
References
[1] P. Barabaschi et al. Fusion Engineering and Design 215 (2025)
[2] M. Kaufmann et al. Fusion Engineering and Design 82 5 (2007)
[3] M. J. Baldwin et al. Nuclear Fusion 48 3 (2008)
[4] W. Qin et al. Acta Materialia 153 (2018)
[5] A. Lopez-Cazalilla et al. Physical Review
Materials 6 7 (2022)
[6] C. Cupak et al. Physical Review Materials 6
7 (2023)
[7] R. Gonza ́lez-Arrabal et al. Nuclear Materi-
als and Energy 40 (2024)
[8] R. Arredondo et al. Nuclear Materials and
Energy 18 (2019)
Cupak et al. simulated the erosion of such a nano-columnar tungsten (NCW) surface under prolonged ion irradiation [6]. This gave a first estimate at the irradiation stability of such a structure in a fusion reactor. We investigated the NCW stability experimentally through ero- sion with a 2 keV Ar+ ion beam and simultane- ously measured the sputter yield via the means of a highly sensitive Quartz-Crystal-Microbalance (QCM). To enable the QCM measurement, the thin NCW layer was deposited directly onto a quartz resonator by magnetron sputter deposi- tion [7]. Erosion was conducted in three steps to enable investigation of surface topography changes, which significantly impact the sput- ter yield, via atomic force and scanning elec- tron microscopy in between. For a qualitative analysis of the experimental data, accompanyin
Impact of boron intermixing on W-based PFCs: Atomic, structural and mechanical characteristics
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