The Experts below are selected from a list of 39162 Experts worldwide ranked by ideXlab platform
Laifa Boufendi - One of the best experts on this subject based on the ideXlab platform.
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Nonlinear Oscillations of a Dust Cloud in a rf Plasma
2010Co-Authors: Maxime Mikikian, Laifa Boufendi, LÉnaÏc Couedel, Marjorie Cavarroc, Yves Tessier, Olivier ValléeAbstract:In a plasma, Dust particles acquire a negative charge. Thus, a high density of Dust particles strongly reduces the free electron density and can drastically alter the plasma equilibrium leading to a wide variety of instabilities (as in electronegative plasmas). One of these instabilities concerns the Dust-free region (void) often appearing in the center of the discharge. This void is maintained by two forces of opposite directions and a break in this equilibrium can lead to strongly nonlinear oscillations of the void size. In this presentation we analyze these low-frequency oscillations on the Dust Cloud and the plasma thanks to high-speed imaging. Correlations are made with the evolution of the discharge current which shows a nonlinear behavior similar to mixed-mode oscillations (MMOs) well- known in other fields like chemistry or neuronal science. We perform an analogy between MMOs in these fields and the ones we obtained. These MMOs are also highly studied through dynamical system theories which can provide a new approach for studying plasma instabilities.
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Threshold phenomena in a throbbing Dusty plasma
2010Co-Authors: Maxime Mikikian, LÉnaÏc Couedel, Marjorie Cavarroc, Yves Tessier, Laifa BoufendiAbstract:A Dust Cloud trapped in a plasma often contains a Dust-free region ("void") near the plasma center. This void has important effects: it induces a spatial inhomogeneity of the Dust particle distribution and is at the origin of many intricate unstable phenomena. One of this behavior is the heartbeat instability consisting of successive contractions and expansions of the void. This instability is characterized by a strong nonlinear dynamics which can reveal the occurrence of incomplete sequences corresponding to failed contractions. Experimental results based on high-speed imaging are presented for the first time and underline this threshold effect in both the Dust Cloud motion and the evolution of the plasma light emission.
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Dusty plasmas: synthesis, structure and dynamics of a Dust Cloud in a plasma
European Physical Journal: Applied Physics, 2010Co-Authors: Maxime Mikikian, LÉnaÏc Couedel, Marjorie Cavarroc, Yves Tessier, Laifa BoufendiAbstract:Plasmas are energetic media that can give birth to Dust particles due to the presence of reactive gases or plasma-surface interactions. InDustrial plasmas are often concerned by these Dust particles that can be either unwanted or useful for the process. For fusion plasmas, production of Dust particles from wall erosion is a serious issue for performance and safety reasons. In this article, some aspects of Dusty plasmas with potential implications for plasma experimenters will be discussed. Convenient ways for detecting the presence or the growth of Dust particles will be presented. The spatial distribution of the Dust Cloud during the plasma phase determines the subsequent Dust particle deposition. It will be shown that some reactor regions can attract or repeal these Dust particles. Finally, the Dust particle dynamics after the plasma extinction will be investigated. A special attention will be paid on the residual electric charge that can stay attached on the Dust particle surface and on its implications for Dust particle control or deposition.
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Dust Successive Generations in Ar/SiH4: Dust Cloud Dynamics
2008Co-Authors: Marjorie Cavarroc, Maxime Mikikian, Yves Tessier, Laifa BoufendiAbstract:Successive generations of Dust particles in an Ar/SiH4 plasma, are shown to take place in the void region. We evidence that this cyclic phenomenon is also related to self-excited low frequency oscillations. These different results are obtained by correlating several diagnostics. We studied Dust particle successive generations and the related Dust Cloud dynamics in silane based plasmas. Indeed, the growth of silicon nanoparticles is known to follow a well-defined cycle. Thanks to the correlation of various diagnostics (electrical, optical, ex-situ SEM), we evidenced a void region in the plasma and its specific structure. We especially showed that Dust new generations grow inside this void region close to the plasma center. Moreover, an instability phenomenon linked to this cyclic growth in the void has been brought to the fore.
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Successive Generations of Dust in Complex Plasmas: A Cyclic Phenomenon in the Void Region
Physical Review Letters, 2008Co-Authors: Marjorie Cavarroc, Maxime Mikikian, Yves Tessier, Laifa BoufendiAbstract:Dust formation and growth in plasmas are in most cases continuous cyclic phenomena. We show that the growth of new Dust generations takes place in a Dust-free region, usually called a void, in the Dust Cloud. The three-step process of new Dust generation is detailed thanks to the correlation between electrical, optical, and ex situ diagnostics. The strong inhomogeneity of both the plasma and the Dust Cloud during this process is underlined.
M. Fulle - One of the best experts on this subject based on the ideXlab platform.
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Dust from short-period comet P/Schwassmann–Wachmann 1 and replenishment of the interplanetary Dust Cloud
Nature, 1992Co-Authors: M. FulleAbstract:IF the current abundance of interplanetary Dust is representative of its long-term value1, there must be a source of Dust replenishing the ∼107 g s–1 (mostly in the form of particles of 10–4 to 1 g) destroyed by dissipative processes2. Short-period comets are the most likely such source3, but their Dust production rate is uncertain. Coma spectrophotometry of several short-period comets excludes significant contributions of Dust from them4,5, but observations by the Infrared Astronomical Satellite6 have suggested the opposite. Here I use a numerical model7 to analyse an optical image of the Dust tail of comet P/Schwassman–Wachmann 1, which contains information about grains 5 μm to 2 cm in diameter, ejected from 900 to 30 days before perihelion. During the three years covered by the model, the mass loss rate reached an estimated (6±3) × 105 g s–1, for an assumed albedo9 of 0.1 at the observation phase angle of 4°. This one short-period comet thus apparently provides ∼6% of the mass required to balance the losses of the interplanetary Dust Cloud.
Frans J M Rietmeijer - One of the best experts on this subject based on the ideXlab platform.
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a comparison of chemistry and Dust Cloud formation in ultracool dwarf model atmospheres
Monthly Notices of the Royal Astronomical Society, 2008Co-Authors: Christiane Helling, Andrew S Ackerman, F Allard, M Dehn, P H Hauschildt, Derek Homeier, Katharina Lodders, Mark S Marley, Frans J M RietmeijerAbstract:The atmospheres of substellar objects contain Clouds of oxides, iron, silicates and other refractory condensates. Water Clouds are expected in the coolest objects. The opacity of these 'Dust' Clouds strongly affects both the atmospheric temperature-pressure profile and the emergent flux. Thus, any attempt to model the spectra of these atmospheres must incorporate a Cloud model. However, the diversity of Cloud models in atmospheric simulations is large and it is not always clear how the underlying physics of the various models compare. Likewise, the observational consequences of different modelling approaches can be masked by other model differences, making objective comparisons challenging. In order to clarify the current state of the modelling approaches, this paper compares five different Cloud models in two sets of tests. Test case 1 tests the Dust Cloud models for a prescribed L-, L-T and T-dwarf atmospheric (temperature T, pressure p, convective velocity υ conv ) structures. Test case 2 compares complete model atmosphere results for given (effective temperature T eff , surface gravity log g). All models agree on the global Cloud structure but differ in opacity relevant details such as grain size, amount of Dust, Dust and gas-phase composition. These models can loosely be grouped into high- and low-altitude Cloud models whereas the first appears generally redder in near-infrared colours than the latter. Comparisons of synthetic photometric fluxes translate into a modelling uncertainty in apparent magnitudes for our L-dwarf (T-dwarf) test case of 0.25 ≤ Am ≤ 0.875 (0.1 ≤ Δm ≤ 1.375), taking into account the Two-Micron All Sky Survey, the UKIRT WFCAM, the Spitzer IRAC and VLT VISIR filters with UKIRT WFCAM being the most challenging for the models. Future developments will need closer links with laboratory astrophysics, and a consistent treatment of the Cloud chemistry and turbulence.
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a comparison of chemistry and Dust Cloud formation in ultracool dwarf model atmospheres
arXiv: Astrophysics, 2008Co-Authors: Christiane Helling, Andrew S Ackerman, F Allard, M Dehn, P H Hauschildt, Derek Homeier, Katharina Lodders, Mark S Marley, Frans J M RietmeijerAbstract:The atmospheres of substellar objects contain Clouds of oxides, iron, silicates, and other refractory condensates. Water Clouds are expected in the coolest objects. The opacity of these `Dust' Clouds strongly affects both the atmospheric temperature-pressure profile and the emergent flux. Thus any attempt to model the spectra of these atmospheres must incorporate a Cloud model. However the diversity of Cloud models in atmospheric simulations is large and it is not always clear how the underlying physics of the various models compare. Likewise the observational consequences of different modeling approaches can be masked by other model differences, making objective comparisons challenging. In order to clarify the current state of the modeling approaches, this paper compares five different Cloud models in two sets of tests. Test case 1 tests the Dust Cloud models for a prescribed L, L--T, and T-dwarf atmospheric (temperature T, pressure p, convective velocity vconv)-structures. Test case 2 compares complete model atmosphere results for given (effective temperature Teff, surface gravity log g). All models agree on the global Cloud structure but differ in opacity-relevant details like grain size, amount of Dust, Dust and gas-phase composition. Comparisons of synthetic photometric fluxes translate into an modelling uncertainty in apparent magnitudes for our L-dwarf (T-dwarf) test case of 0.25 < \Delta m < 0.875 (0.1 < \Delta m M 1.375) taking into account the 2MASS, the UKIRT WFCAM, the Spitzer IRAC, and VLT VISIR filters with UKIRT WFCAM being the most challenging for the models. (abr.)
F Allard - One of the best experts on this subject based on the ideXlab platform.
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a comparison of chemistry and Dust Cloud formation in ultracool dwarf model atmospheres
Monthly Notices of the Royal Astronomical Society, 2008Co-Authors: Christiane Helling, Andrew S Ackerman, F Allard, M Dehn, P H Hauschildt, Derek Homeier, Katharina Lodders, Mark S Marley, Frans J M RietmeijerAbstract:The atmospheres of substellar objects contain Clouds of oxides, iron, silicates and other refractory condensates. Water Clouds are expected in the coolest objects. The opacity of these 'Dust' Clouds strongly affects both the atmospheric temperature-pressure profile and the emergent flux. Thus, any attempt to model the spectra of these atmospheres must incorporate a Cloud model. However, the diversity of Cloud models in atmospheric simulations is large and it is not always clear how the underlying physics of the various models compare. Likewise, the observational consequences of different modelling approaches can be masked by other model differences, making objective comparisons challenging. In order to clarify the current state of the modelling approaches, this paper compares five different Cloud models in two sets of tests. Test case 1 tests the Dust Cloud models for a prescribed L-, L-T and T-dwarf atmospheric (temperature T, pressure p, convective velocity υ conv ) structures. Test case 2 compares complete model atmosphere results for given (effective temperature T eff , surface gravity log g). All models agree on the global Cloud structure but differ in opacity relevant details such as grain size, amount of Dust, Dust and gas-phase composition. These models can loosely be grouped into high- and low-altitude Cloud models whereas the first appears generally redder in near-infrared colours than the latter. Comparisons of synthetic photometric fluxes translate into a modelling uncertainty in apparent magnitudes for our L-dwarf (T-dwarf) test case of 0.25 ≤ Am ≤ 0.875 (0.1 ≤ Δm ≤ 1.375), taking into account the Two-Micron All Sky Survey, the UKIRT WFCAM, the Spitzer IRAC and VLT VISIR filters with UKIRT WFCAM being the most challenging for the models. Future developments will need closer links with laboratory astrophysics, and a consistent treatment of the Cloud chemistry and turbulence.
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a comparison of chemistry and Dust Cloud formation in ultracool dwarf model atmospheres
arXiv: Astrophysics, 2008Co-Authors: Christiane Helling, Andrew S Ackerman, F Allard, M Dehn, P H Hauschildt, Derek Homeier, Katharina Lodders, Mark S Marley, Frans J M RietmeijerAbstract:The atmospheres of substellar objects contain Clouds of oxides, iron, silicates, and other refractory condensates. Water Clouds are expected in the coolest objects. The opacity of these `Dust' Clouds strongly affects both the atmospheric temperature-pressure profile and the emergent flux. Thus any attempt to model the spectra of these atmospheres must incorporate a Cloud model. However the diversity of Cloud models in atmospheric simulations is large and it is not always clear how the underlying physics of the various models compare. Likewise the observational consequences of different modeling approaches can be masked by other model differences, making objective comparisons challenging. In order to clarify the current state of the modeling approaches, this paper compares five different Cloud models in two sets of tests. Test case 1 tests the Dust Cloud models for a prescribed L, L--T, and T-dwarf atmospheric (temperature T, pressure p, convective velocity vconv)-structures. Test case 2 compares complete model atmosphere results for given (effective temperature Teff, surface gravity log g). All models agree on the global Cloud structure but differ in opacity-relevant details like grain size, amount of Dust, Dust and gas-phase composition. Comparisons of synthetic photometric fluxes translate into an modelling uncertainty in apparent magnitudes for our L-dwarf (T-dwarf) test case of 0.25 < \Delta m < 0.875 (0.1 < \Delta m M 1.375) taking into account the 2MASS, the UKIRT WFCAM, the Spitzer IRAC, and VLT VISIR filters with UKIRT WFCAM being the most challenging for the models. (abr.)
Marjorie Cavarroc - One of the best experts on this subject based on the ideXlab platform.
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Nonlinear Oscillations of a Dust Cloud in a rf Plasma
2010Co-Authors: Maxime Mikikian, Laifa Boufendi, LÉnaÏc Couedel, Marjorie Cavarroc, Yves Tessier, Olivier ValléeAbstract:In a plasma, Dust particles acquire a negative charge. Thus, a high density of Dust particles strongly reduces the free electron density and can drastically alter the plasma equilibrium leading to a wide variety of instabilities (as in electronegative plasmas). One of these instabilities concerns the Dust-free region (void) often appearing in the center of the discharge. This void is maintained by two forces of opposite directions and a break in this equilibrium can lead to strongly nonlinear oscillations of the void size. In this presentation we analyze these low-frequency oscillations on the Dust Cloud and the plasma thanks to high-speed imaging. Correlations are made with the evolution of the discharge current which shows a nonlinear behavior similar to mixed-mode oscillations (MMOs) well- known in other fields like chemistry or neuronal science. We perform an analogy between MMOs in these fields and the ones we obtained. These MMOs are also highly studied through dynamical system theories which can provide a new approach for studying plasma instabilities.
-
Threshold phenomena in a throbbing Dusty plasma
2010Co-Authors: Maxime Mikikian, LÉnaÏc Couedel, Marjorie Cavarroc, Yves Tessier, Laifa BoufendiAbstract:A Dust Cloud trapped in a plasma often contains a Dust-free region ("void") near the plasma center. This void has important effects: it induces a spatial inhomogeneity of the Dust particle distribution and is at the origin of many intricate unstable phenomena. One of this behavior is the heartbeat instability consisting of successive contractions and expansions of the void. This instability is characterized by a strong nonlinear dynamics which can reveal the occurrence of incomplete sequences corresponding to failed contractions. Experimental results based on high-speed imaging are presented for the first time and underline this threshold effect in both the Dust Cloud motion and the evolution of the plasma light emission.
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Dusty plasmas: synthesis, structure and dynamics of a Dust Cloud in a plasma
European Physical Journal: Applied Physics, 2010Co-Authors: Maxime Mikikian, LÉnaÏc Couedel, Marjorie Cavarroc, Yves Tessier, Laifa BoufendiAbstract:Plasmas are energetic media that can give birth to Dust particles due to the presence of reactive gases or plasma-surface interactions. InDustrial plasmas are often concerned by these Dust particles that can be either unwanted or useful for the process. For fusion plasmas, production of Dust particles from wall erosion is a serious issue for performance and safety reasons. In this article, some aspects of Dusty plasmas with potential implications for plasma experimenters will be discussed. Convenient ways for detecting the presence or the growth of Dust particles will be presented. The spatial distribution of the Dust Cloud during the plasma phase determines the subsequent Dust particle deposition. It will be shown that some reactor regions can attract or repeal these Dust particles. Finally, the Dust particle dynamics after the plasma extinction will be investigated. A special attention will be paid on the residual electric charge that can stay attached on the Dust particle surface and on its implications for Dust particle control or deposition.
-
Dust Successive Generations in Ar/SiH4: Dust Cloud Dynamics
2008Co-Authors: Marjorie Cavarroc, Maxime Mikikian, Yves Tessier, Laifa BoufendiAbstract:Successive generations of Dust particles in an Ar/SiH4 plasma, are shown to take place in the void region. We evidence that this cyclic phenomenon is also related to self-excited low frequency oscillations. These different results are obtained by correlating several diagnostics. We studied Dust particle successive generations and the related Dust Cloud dynamics in silane based plasmas. Indeed, the growth of silicon nanoparticles is known to follow a well-defined cycle. Thanks to the correlation of various diagnostics (electrical, optical, ex-situ SEM), we evidenced a void region in the plasma and its specific structure. We especially showed that Dust new generations grow inside this void region close to the plasma center. Moreover, an instability phenomenon linked to this cyclic growth in the void has been brought to the fore.
-
Successive Generations of Dust in Complex Plasmas: A Cyclic Phenomenon in the Void Region
Physical Review Letters, 2008Co-Authors: Marjorie Cavarroc, Maxime Mikikian, Yves Tessier, Laifa BoufendiAbstract:Dust formation and growth in plasmas are in most cases continuous cyclic phenomena. We show that the growth of new Dust generations takes place in a Dust-free region, usually called a void, in the Dust Cloud. The three-step process of new Dust generation is detailed thanks to the correlation between electrical, optical, and ex situ diagnostics. The strong inhomogeneity of both the plasma and the Dust Cloud during this process is underlined.
