The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Christophe Leys - One of the best experts on this subject based on the ideXlab platform.
-
influence of Helium mole fraction distribution on the properties of cold atmospheric pressure Helium plasma jets
Journal of Applied Physics, 2012Co-Authors: Ranhua Xiong, Anton Nikiforov, Patrick Vanraes, Qing Xiong, Christophe LeysAbstract:The influence of Helium mole fraction distribution in air on the cold atmospheric plasma jets excited by 1.5 kHz rectangular high voltage pulse is studied in this work. Computational fluid dynamics (CFD) with incorporation of large eddy simulation (LES) model is used to simulate the Helium mole fraction distribution in air under the Helium flow from laminar to turbulent regime with increasing Helium outlet velocity. Numerical simulation results are combined with experimental results in order to determine the influence of Helium distribution on the cold plasma jets. It reveals that the structure of the Helium distribution caused by diffusion or by turbulent mixing in turbulent regime determines the characteristics of the cold plasma jets. On the other hand, the curves of plasma jet length (L) versus Helium outlet velocity (V) at different jet diameters (D) are unified in a map of jet Reynolds number (Re = ρHe·V·D/μHe, where μHe is the Helium viscosity constant) versus dimensionless plasma jet length (l = L...
-
influence of Helium mole fraction distribution on the properties of cold atmospheric pressure Helium plasma jets
Journal of Applied Physics, 2012Co-Authors: Ranhua Xiong, Anton Nikiforov, Patrick Vanraes, Qing Xiong, Christophe LeysAbstract:The influence of Helium mole fraction distribution in air on the cold atmospheric plasma jets excited by 1.5 kHz rectangular high voltage pulse is studied in this work. Computational fluid dynamics (CFD) with incorporation of large eddy simulation (LES) model is used to simulate the Helium mole fraction distribution in air under the Helium flow from laminar to turbulent regime with increasing Helium outlet velocity. Numerical simulation results are combined with experimental results in order to determine the influence of Helium distribution on the cold plasma jets. It reveals that the structure of the Helium distribution caused by diffusion or by turbulent mixing in turbulent regime determines the characteristics of the cold plasma jets. On the other hand, the curves of plasma jet length (L) versus Helium outlet velocity (V) at different jet diameters (D) are unified in a map of jet Reynolds number (Re = ρHe·V·D/μHe, where μHe is the Helium viscosity constant) versus dimensionless plasma jet length (l = L...
Ranhua Xiong - One of the best experts on this subject based on the ideXlab platform.
-
influence of Helium mole fraction distribution on the properties of cold atmospheric pressure Helium plasma jets
Journal of Applied Physics, 2012Co-Authors: Ranhua Xiong, Anton Nikiforov, Patrick Vanraes, Qing Xiong, Christophe LeysAbstract:The influence of Helium mole fraction distribution in air on the cold atmospheric plasma jets excited by 1.5 kHz rectangular high voltage pulse is studied in this work. Computational fluid dynamics (CFD) with incorporation of large eddy simulation (LES) model is used to simulate the Helium mole fraction distribution in air under the Helium flow from laminar to turbulent regime with increasing Helium outlet velocity. Numerical simulation results are combined with experimental results in order to determine the influence of Helium distribution on the cold plasma jets. It reveals that the structure of the Helium distribution caused by diffusion or by turbulent mixing in turbulent regime determines the characteristics of the cold plasma jets. On the other hand, the curves of plasma jet length (L) versus Helium outlet velocity (V) at different jet diameters (D) are unified in a map of jet Reynolds number (Re = ρHe·V·D/μHe, where μHe is the Helium viscosity constant) versus dimensionless plasma jet length (l = L...
-
influence of Helium mole fraction distribution on the properties of cold atmospheric pressure Helium plasma jets
Journal of Applied Physics, 2012Co-Authors: Ranhua Xiong, Anton Nikiforov, Patrick Vanraes, Qing Xiong, Christophe LeysAbstract:The influence of Helium mole fraction distribution in air on the cold atmospheric plasma jets excited by 1.5 kHz rectangular high voltage pulse is studied in this work. Computational fluid dynamics (CFD) with incorporation of large eddy simulation (LES) model is used to simulate the Helium mole fraction distribution in air under the Helium flow from laminar to turbulent regime with increasing Helium outlet velocity. Numerical simulation results are combined with experimental results in order to determine the influence of Helium distribution on the cold plasma jets. It reveals that the structure of the Helium distribution caused by diffusion or by turbulent mixing in turbulent regime determines the characteristics of the cold plasma jets. On the other hand, the curves of plasma jet length (L) versus Helium outlet velocity (V) at different jet diameters (D) are unified in a map of jet Reynolds number (Re = ρHe·V·D/μHe, where μHe is the Helium viscosity constant) versus dimensionless plasma jet length (l = L...
Brian D Wirth - One of the best experts on this subject based on the ideXlab platform.
-
Helium diffusion and bubble evolution in tungsten nanotendrils
Computational Materials Science, 2020Co-Authors: M A Cusentino, Brian D WirthAbstract:Abstract We describe molecular dynamics simulations of Helium implantation in geometries resembling tungsten nanotendrils observed in Helium plasma exposure experiments. Helium atoms self-cluster and nucleate bubbles within the tendrillike geometries. However, Helium retention in these geometries is lower than planar surfaces due to higher surface area to volume ratio which allows for continual bubble expansion and non-destructive release of Helium atoms from the nanotendril. Limited diffusion of Helium atoms deeper into the tendril was observed, and diffusion was enhanced with pre-existing, subsurface Helium bubbles. Diffusion coefficients on the order of 10−12–10−11 m 2 s - 1 were calculated. This suggests that while Helium diffusion is low, it is still feasible that Helium can diffuse to the base of a nanotendril to continue to drive fuzz growth.
-
crystal orientation effects on Helium ion depth distributions and adatom formation processes in plasma facing tungsten
Journal of Applied Physics, 2014Co-Authors: Karl D Hammond, Brian D WirthAbstract:We present atomistic simulations that show the effect of surface orientation on Helium depth distributions and surface feature formation as a result of low-energy Helium plasma exposure. We find a pronounced effect of surface orientation on the initial depth of implanted Helium ions, as well as a difference in reflection and Helium retention across different surface orientations. Our results indicate that single Helium interstitials are sufficient to induce the formation of adatom/substitutional Helium pairs under certain highly corrugated tungsten surfaces, such as {1 1 1}-orientations, leading to the formation of a relatively concentrated layer of immobile Helium immediately below the surface. The energies involved for Helium-induced adatom formation on {1 1 1} and {2 1 1} surfaces are exoergic for even a single adatom very close to the surface, while {0 0 1} and {0 1 1} surfaces require two or even three Helium atoms in a cluster before a substitutional Helium cluster and adatom will form with reasonable probability. This phenomenon results in much higher initial Helium retention during Helium plasma exposure to {1 1 1} and {2 1 1} tungsten surfaces than is observed for {0 0 1} or {0 1 1} surfaces and is much higher than can be attributed to differences in the initial depth distributions alone. The layer thus formed may serve as nucleation sites for further bubble formation and growth or as a source of material embrittlement or fatigue, which may have implications for the formation of tungsten “fuzz” in plasma-facing divertors for magnetic-confinement nuclear fusion reactors and/or the lifetime of such divertors.
-
spatially dependent cluster dynamics modeling of microstructure evolution in low energy Helium irradiated tungsten
Modelling and Simulation in Materials Science and Engineering, 2014Co-Authors: T Faney, Brian D WirthAbstract:In fusion reactors, plasma facing components (PFC) and in particular the divertor will be irradiated with high fluxes of low energy (~100 eV) Helium and hydrogen ions. Tungsten is one of the leading candidate divertor materials for ITER and DEMO fusion reactors. However, the behavior of tungsten under high dose, coupled Helium/hydrogen exposure remains to be fully understood. The PFC response and performance changes are intimately related to microstructural changes, such as the formation of point defect clusters, Helium and hydrogen bubbles or dislocation loops. Computational materials modeling has been used to investigate the mechanisms controlling microstructural evolution in tungsten following high dose, high temperature Helium exposure. The aim of this study is to understand and predict Helium implantation, primary defect production and defect diffusion, Helium-defect clustering and interactions below a tungsten surface exposed to low energy Helium irradiation. The important defects include interstitial clusters, vacancy clusters, Helium interstitials and Helium-vacancy clusters. We report results from a one-dimensional, spatially dependent cluster dynamics model based on the continuum reaction–diffusion rate theory to describe the evolution in space and time of all these defects. The key parameter inputs to the model (diffusion coefficients, migration and binding energies, initial defect production) are determined from a combination of atomistic materials modeling and available experimental data.
-
thermal stability of Helium vacancy clusters in iron
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 2003Co-Authors: K Morishita, R Sugano, Brian D Wirth, Diaz T De La RubiaAbstract:Molecular dynamics calculations were performed to evaluate the thermal stability of Helium–vacancy clusters (HenVm) in Fe using the Ackland Finnis–Sinclair potential, the Wilson–Johnson potential and the Ziegler–Biersack–Littmark–Beck potential for describing the interactions of Fe–Fe, Fe–He and He–He, respectively. Both the calculated numbers of Helium atoms, n, and vacancies, m, in clusters ranged from 0 to 20. The binding energies of an interstitial Helium atom, an isolated vacancy and a self-interstitial iron atom to a Helium–vacancy cluster were obtained from the calculated formation energies of clusters. All the binding energies do not depend much on cluster size, but they primarily depend on the Helium-to-vacancy ratio (n/m) of clusters. The binding energy of a vacancy to a Helium–vacancy cluster increases with the ratio, showing that Helium increases cluster lifetime by dramatically reducing thermal vacancy emission. On the other hand, both the binding energies of a Helium atom and an iron atom to a Helium–vacancy cluster decrease with increasing the ratio, indicating that thermal emission of self-interstitial atoms (SIAs) (i.e. Frenkel-pair production), as well as thermal Helium emission, may take place from the cluster of higher Helium-to-vacancy ratios. The thermal stability of clusters is decided by the competitive processes among thermal emission of vacancies, SIAs and Helium, depending on the Helium-to-vacancy ratio of clusters. The calculated thermal stability of clusters is consistent with the experimental observations of thermal Helium desorption from α-Fe during post-He-implantation annealing.
Anton Nikiforov - One of the best experts on this subject based on the ideXlab platform.
-
influence of Helium mole fraction distribution on the properties of cold atmospheric pressure Helium plasma jets
Journal of Applied Physics, 2012Co-Authors: Ranhua Xiong, Anton Nikiforov, Patrick Vanraes, Qing Xiong, Christophe LeysAbstract:The influence of Helium mole fraction distribution in air on the cold atmospheric plasma jets excited by 1.5 kHz rectangular high voltage pulse is studied in this work. Computational fluid dynamics (CFD) with incorporation of large eddy simulation (LES) model is used to simulate the Helium mole fraction distribution in air under the Helium flow from laminar to turbulent regime with increasing Helium outlet velocity. Numerical simulation results are combined with experimental results in order to determine the influence of Helium distribution on the cold plasma jets. It reveals that the structure of the Helium distribution caused by diffusion or by turbulent mixing in turbulent regime determines the characteristics of the cold plasma jets. On the other hand, the curves of plasma jet length (L) versus Helium outlet velocity (V) at different jet diameters (D) are unified in a map of jet Reynolds number (Re = ρHe·V·D/μHe, where μHe is the Helium viscosity constant) versus dimensionless plasma jet length (l = L...
-
influence of Helium mole fraction distribution on the properties of cold atmospheric pressure Helium plasma jets
Journal of Applied Physics, 2012Co-Authors: Ranhua Xiong, Anton Nikiforov, Patrick Vanraes, Qing Xiong, Christophe LeysAbstract:The influence of Helium mole fraction distribution in air on the cold atmospheric plasma jets excited by 1.5 kHz rectangular high voltage pulse is studied in this work. Computational fluid dynamics (CFD) with incorporation of large eddy simulation (LES) model is used to simulate the Helium mole fraction distribution in air under the Helium flow from laminar to turbulent regime with increasing Helium outlet velocity. Numerical simulation results are combined with experimental results in order to determine the influence of Helium distribution on the cold plasma jets. It reveals that the structure of the Helium distribution caused by diffusion or by turbulent mixing in turbulent regime determines the characteristics of the cold plasma jets. On the other hand, the curves of plasma jet length (L) versus Helium outlet velocity (V) at different jet diameters (D) are unified in a map of jet Reynolds number (Re = ρHe·V·D/μHe, where μHe is the Helium viscosity constant) versus dimensionless plasma jet length (l = L...
Qing Xiong - One of the best experts on this subject based on the ideXlab platform.
-
influence of Helium mole fraction distribution on the properties of cold atmospheric pressure Helium plasma jets
Journal of Applied Physics, 2012Co-Authors: Ranhua Xiong, Anton Nikiforov, Patrick Vanraes, Qing Xiong, Christophe LeysAbstract:The influence of Helium mole fraction distribution in air on the cold atmospheric plasma jets excited by 1.5 kHz rectangular high voltage pulse is studied in this work. Computational fluid dynamics (CFD) with incorporation of large eddy simulation (LES) model is used to simulate the Helium mole fraction distribution in air under the Helium flow from laminar to turbulent regime with increasing Helium outlet velocity. Numerical simulation results are combined with experimental results in order to determine the influence of Helium distribution on the cold plasma jets. It reveals that the structure of the Helium distribution caused by diffusion or by turbulent mixing in turbulent regime determines the characteristics of the cold plasma jets. On the other hand, the curves of plasma jet length (L) versus Helium outlet velocity (V) at different jet diameters (D) are unified in a map of jet Reynolds number (Re = ρHe·V·D/μHe, where μHe is the Helium viscosity constant) versus dimensionless plasma jet length (l = L...
-
influence of Helium mole fraction distribution on the properties of cold atmospheric pressure Helium plasma jets
Journal of Applied Physics, 2012Co-Authors: Ranhua Xiong, Anton Nikiforov, Patrick Vanraes, Qing Xiong, Christophe LeysAbstract:The influence of Helium mole fraction distribution in air on the cold atmospheric plasma jets excited by 1.5 kHz rectangular high voltage pulse is studied in this work. Computational fluid dynamics (CFD) with incorporation of large eddy simulation (LES) model is used to simulate the Helium mole fraction distribution in air under the Helium flow from laminar to turbulent regime with increasing Helium outlet velocity. Numerical simulation results are combined with experimental results in order to determine the influence of Helium distribution on the cold plasma jets. It reveals that the structure of the Helium distribution caused by diffusion or by turbulent mixing in turbulent regime determines the characteristics of the cold plasma jets. On the other hand, the curves of plasma jet length (L) versus Helium outlet velocity (V) at different jet diameters (D) are unified in a map of jet Reynolds number (Re = ρHe·V·D/μHe, where μHe is the Helium viscosity constant) versus dimensionless plasma jet length (l = L...
