The Experts below are selected from a list of 259287 Experts worldwide ranked by ideXlab platform
Scotti U Di Uccio - One of the best experts on this subject based on the ideXlab platform.
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effects of oxygen Background Pressure on the stoichiometry of a lagao3 laser ablation plume investigated by time and spectrally resolved two dimensional imaging
Journal of Applied Physics, 2016Co-Authors: A. Sambri, E. Di Gennaro, Miletto F Granozio, Scotti U Di Uccio, C Aruta, X Wang, S AmorusoAbstract:The plume expansion dynamics strongly affects the growth and the chemistry of pulsed laser deposited thin films. The interaction with the Background gas determines the kinetic energy of the species impinging on the substrate, their angular broadening, the plasma chemistry, and eventually the cations stoichiometric ratio in oxide films. Here, we exploit two-dimensional, spectrally resolved plume imaging to characterize the diverse effects of the oxygen Background Pressure on the expansion dynamics of La, Ga, and LaO species during pulsed laser deposition of LaGaO3. The propagation of the ablated species towards the substrate is studied for Background oxygen Pressures ranging from high vacuum up to ≈10−1 mbar. Our experimental results show specie-dependent effects of the Background gas on the angular distribution of the precursors within the plume. These findings suggest that even in the presence of a stoichiometric ablation and of a globally stoichiometric plume, cations off-stoichiometry can take place in the forefront portion of the plume impinging on the substrate. We show that such effect can be compensated by a proper choice of process parameters.
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oxygen Background gas influence on pulsed laser deposition process of laalo3 and lagao3
Applied Surface Science, 2012Co-Authors: S Amoruso, Miletto F Granozio, C Aruta, X Wang, P Aurino, R Bruzzese, Scotti U Di UccioAbstract:Abstract We investigate pulsed laser ablation of LaAlO 3 and LaGaO 3 with a focus on the influence of oxygen Background gas Pressure on the plume expansion dynamics and deposition rate. The ablation plume is characterized by exploiting fast photography and time- and space-resolved optical emission spectroscopy. The variation of the deposition rate with the oxygen Background Pressure was obtained at 800 °C by reflection high-energy electron diffraction, and compared to that measured at room temperature by means of a quartz crystal microbalance. The experimental findings allow one to address the various stages of plume expansion as a function of the Background oxygen Pressure as well as the changes induced on the plume species kinetic energy and composition. On the base of our experimental results, the possible influence of various mechanisms, such as subplantation and oxygen vacancy formation, on the growth of oxides interfaces is addressed.
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critical influence of target to substrate distance on conductive properties of lagao3 srtio3 interfaces deposited at 10 1 mbar oxygen Pressure
Applied Physics Letters, 2012Co-Authors: Carmela Aruta, Salvatore Amoruso, Giovanni Ausanio, Riccardo Bruzzese, E. Di Gennaro, M. Lanzano, Muhammad Riaz, A. Sambri, Miletto F Granozio, Scotti U Di UccioAbstract:We investigate pulsed laser deposition of LaGaO3/SrTiO3 at 10−1 mbar oxygen Background Pressure, demonstrating the critical effect of the target-to-substrate distance, dTS, on the interface sheet resistance, Rs. The interface turns from insulating to metallic by progressively decreasing dTS. The analysis of the LaGaO3 plume evidences the important role of the plume propagation dynamics on the interface properties. These results demonstrate the growth of conducting interfaces at an oxygen Pressure of 10−1 mbar, an experimental condition where a well-oxygenated heterostructures with a reduced content of oxygen defects is expected.
N A Adams - One of the best experts on this subject based on the ideXlab platform.
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a generalized transport velocity formulation for smoothed particle hydrodynamics
Journal of Computational Physics, 2017Co-Authors: Chi Zhang, N A AdamsAbstract:The standard smoothed particle hydrodynamics (SPH) method suffers from tensile instability. In fluid-dynamics simulations this instability leads to particle clumping and void regions when negative Pressure occurs. In solid-dynamics simulations, it results in unphysical structure fragmentation. In this work the transport-velocity formulation of Adami et al. (2013) [14] is generalized for providing a solution of this long-standing problem. Other than imposing a global Background Pressure, a variable Background Pressure is used to modify the particle transport velocity and eliminate the tensile instability completely. Furthermore, such a modification is localized by defining a shortened smoothing length. The generalized formulation is suitable for fluid and solid materials with and without free surfaces. The results of extensive numerical tests on both fluid and solid dynamics problems indicate that the new method provides a unified approach for multi-physics SPH simulations.
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a transport velocity formulation for smoothed particle hydrodynamics
Journal of Computational Physics, 2013Co-Authors: S Adami, N A AdamsAbstract:The standard weakly-compressible SPH method suffers from particle clumping and void regions for high Reynolds number flows and when negative Pressures occur in the flow. As a remedy, a new algorithm is proposed that combines the homogenization of the particle configuration by a Background Pressure while at the same time reduces artificial numerical dissipation. The transport or advection velocity of particles is modified and an effective stress term occurs in the momentum balance that accounts for the difference between advection velocity times particle density and actual particle momentum. The present formulation can be applied for internal flows where the density summation is applicable. A wide range of test cases demonstrates unprecedented accuracy and stability of the proposed modification even at previously infeasible conditions.
Hani Kamhawi - One of the best experts on this subject based on the ideXlab platform.
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performance facility Pressure effects and stability characterization tests of nasa s hall effect rocket with magnetic shielding thruster
52nd AIAA SAE ASEE Joint Propulsion Conference, 2016Co-Authors: Hani Kamhawi, Wensheng Huang, Thomas W Haag, Daniel A Herman, George J Williams, James H Gilland, Peter Y Peterson, Richard R Hofer, Ioannis G MikellidesAbstract:NASA's Hall Effect Rocket with Magnetic Shielding (HERMeS) 12.5 kW Technology Demonstration Unit-1 (TDU-1) has been the subject of extensive technology maturation in preparation for flight system development. Part of the technology maturation effort included experimental evaluation of the TDU-1 thruster with conducting and dielectric front pole cover materials in two different electrical configurations. A graphite front magnetic pole cover thruster configuration with the thruster body electrically tied to cathode, and an alumina front pole cover thruster configuration with the thruster body floating were evaluated. Both configurations were also evaluated at different facility Background Pressure conditions to evaluate Background Pressure effects on thruster operation. Performance characterization tests found that higher thruster performance was attained with the graphite front pole cover configuration with the thruster electrically tied to cathode. A total thrust efficiency of 68% and a total specific impulse of 2,820 s was demonstrated at a discharge voltage of 600 V and a discharge power of 12.5 kW. Thruster stability regimes were characterized with respect to the thruster discharge current oscillations and with maps of the discharge current-voltage-magnetic field (IVB). Analysis of TDU-1 discharge current waveforms found that lower normalized discharge current peak-to-peak and root mean square magnitudes were attained when the thruster was electrically floated with alumina front pole covers. Background Pressure effects characterization tests indicated that the thruster performance and stability were mostly invariant to changes in the facility Background Pressure for vacuum chamber Pressure below 110-5 Torr-Xe (for thruster flow rates of 20.5 mg/s). Power spectral density analysis of the discharge current waveforms showed that increasing the vacuum chamber Background Pressure resulted in a higher discharge current dominant breathing mode frequency. Finally, IVB maps of the TDU-1 thruster indicated that the discharge current became more oscillatory with higher discharge current peak-to-peak and RMS values with increased facility Background Pressure at lower thruster mass flow rates; thruster operation at higher flow rates resulted in less change to the thruster's IVB characteristics with elevated Background Pressure.
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facility effect characterization test of nasa s hermes hall thruster
52nd AIAA SAE ASEE Joint Propulsion Conference, 2016Co-Authors: Thomas W Haag, Wensheng Huang, Ioannis G Mikellides, Alejandro Lopez Ortega, Hani KamhawiAbstract:A test to characterize the effect of varying Background Pressure on NASA's 12.5-kW Hall Effect Rocket with Magnetic Shielding had being completed. This thruster is the baseline propulsion system for the Solar Electric Propulsion Technology Demonstration Mission (SEP TDM). Potential differences in thruster performance and oscillation characteristics when in ground facilities versus on-orbit are considered a primary risk for the propulsion system of the Asteroid Redirect Robotic Mission, which is a candidate for SEP TDM. The first primary objective of this test was to demonstrate that the tools being developed to predict the zero-Background-Pressure behavior of the thruster can provide self-consistent results. The second primary objective of this test was to provide data for refining a physics-based model of the thruster plume that will be used in spacecraft interaction studies. Diagnostics deployed included a thrust stand, Faraday probe, Langmuir probe, retarding potential analyzer, Wien filter spectrometer, and high-speed camera. From the data, a physics-based plume model was refined. Comparisons of empirical data to modeling results are shown.
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effect of Background Pressure on the plasma oscillation characteristics of the hivhac hall thruster
50th AIAA ASME SAE ASEE Joint Propulsion Conference, 2014Co-Authors: Wensheng Huang, Hani Kamhawi, Robert B Lobbia, Daniel L BrownAbstract:Abstract : During a single-string integration test of the NASA HiVHAc Hall thruster, a number of plasma diagnostics were implemented to study the effect of varying facility Background Pressure on thruster operation. These diagnostics characterized the thruster performance, the plume, and the plasma oscillations in the thruster. Thruster performance and plume characteristics as functions of Background Pressure were previously published. This paper will focus on changes in the plasma oscillation characteristics with changing Background Pressure. The diagnostics used to study plasma oscillations include a high-speed camera and a set of high-speed Langmuir probes. The results show a rise in the oscillation frequency of the breathing mode with rising Background Pressure, which is hypothesized to be due to a shortening acceleration/ionization zone. An attempt is made to apply a simplified ingestion model to the data. The combined results are used to estimate the maximum acceptable Background Pressure for performance and wear testing.
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investigation of the effects of facility Background Pressure on the performance and operation of the high voltage hall accelerator
50th AIAA ASME SAE ASEE Joint Propulsion Conference, 2014Co-Authors: Hani Kamhawi, Wensheng Huang, Thomas W Haag, Rotislav SpektorAbstract:The National Aeronautics and Space Administration (NASA) Science Mission Directorate In-Space Propulsion Technology office is sponsoring NASA Glenn Research Center to develop a 4 kW-class Hall thruster propulsion system for implementation in NASA science missions. A study was conducted to assess the impact of varying the facility Background Pressure on the High Voltage Hall Accelerator (HiVHAc) thruster performance and voltage-current characteristics. This present study evaluated the HiVHAc thruster performance in the lowest attainable Background Pressure condition at NASA GRC Vacuum Facility 5 to best simulate space-like conditions. Additional tests were performed at selected thruster operating conditions to investigate and elucidate the underlying physics that change during thruster operation at elevated facility Background Pressure. Tests were performed at Background Pressure conditions that are three and ten times higher than the lowest realized Background Pressure. Results indicated that the thruster discharge specific impulse and efficiency increased with elevated facility Background Pressure. The voltage-current profiles indicated a narrower stable operating region with increased Background Pressure. Experimental observations of the thruster operation indicated that increasing the facility Background Pressure shifted the ionization and acceleration zones upstream towards the thruster’s anode. Future tests of the HiVHAc thruster are planned at Background Pressure conditions that are expected to be two to three times lower than what was achieved during this test campaign. These tests will not only assess the impact of reduced facility Background Pressure on thruster performance, voltage-current characteristics, and plume properties; but will also attempt to quantify the magnitude of the ionization and acceleration zones upstream shifting as a function of increased Background Pressure.
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investigation of the effects of facility Background Pressure on the performance and voltage current characteristics of the high voltage hall accelerator
AIAA ASME SAE ASEE Joint Propulsion Conference, 2014Co-Authors: Hani Kamhawi, Wensheng Huang, Thomas W Haag, Rostislav SpektorAbstract:The National Aeronautics and Space Administration (NASA) Science Mission Directorate In-Space Propulsion Technology office is sponsoring NASA Glenn Research Center to develop a 4 kW-class Hall thruster propulsion system for implementation in NASA science missions. A study was conducted to assess the impact of varying the facility Background Pressure on the High Voltage Hall Accelerator (HiVHAc) thruster performance and voltage-current characteristics. This present study evaluated the HiVHAc thruster performance in the lowest attainable Background Pressure condition at NASA GRC Vacuum Facility 5 to best simulate space-like conditions. Additional tests were performed at selected thruster operating conditions to investigate and elucidate the underlying physics that change during thruster operation at elevated facility Background Pressure. Tests were performed at Background Pressure conditions that are three and ten times higher than the lowest realized Background Pressure. Results indicated that the thruster discharge specific impulse and efficiency increased with elevated facility Background Pressure. The voltage-current profiles indicated a narrower stable operating region with increased Background Pressure. Experimental observations of the thruster operation indicated that increasing the facility Background Pressure shifted the ionization and acceleration zones upstream towards the thruster's anode. Future tests of the HiVHAc thruster are planned at Background Pressure conditions that are expected to be two to three times lower than what was achieved during this test campaign. These tests will not only assess the impact of reduced facility Background Pressure on thruster performance, voltage-current characteristics, and plume properties; but will also attempt to quantify the magnitude of the ionization and acceleration zones upstream shifting as a function of increased Background Pressure.
S Amoruso - One of the best experts on this subject based on the ideXlab platform.
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effects of oxygen Background Pressure on the stoichiometry of a lagao3 laser ablation plume investigated by time and spectrally resolved two dimensional imaging
Journal of Applied Physics, 2016Co-Authors: A. Sambri, E. Di Gennaro, Miletto F Granozio, Scotti U Di Uccio, C Aruta, X Wang, S AmorusoAbstract:The plume expansion dynamics strongly affects the growth and the chemistry of pulsed laser deposited thin films. The interaction with the Background gas determines the kinetic energy of the species impinging on the substrate, their angular broadening, the plasma chemistry, and eventually the cations stoichiometric ratio in oxide films. Here, we exploit two-dimensional, spectrally resolved plume imaging to characterize the diverse effects of the oxygen Background Pressure on the expansion dynamics of La, Ga, and LaO species during pulsed laser deposition of LaGaO3. The propagation of the ablated species towards the substrate is studied for Background oxygen Pressures ranging from high vacuum up to ≈10−1 mbar. Our experimental results show specie-dependent effects of the Background gas on the angular distribution of the precursors within the plume. These findings suggest that even in the presence of a stoichiometric ablation and of a globally stoichiometric plume, cations off-stoichiometry can take place in the forefront portion of the plume impinging on the substrate. We show that such effect can be compensated by a proper choice of process parameters.
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oxygen Background gas influence on pulsed laser deposition process of laalo3 and lagao3
Applied Surface Science, 2012Co-Authors: S Amoruso, Miletto F Granozio, C Aruta, X Wang, P Aurino, R Bruzzese, Scotti U Di UccioAbstract:Abstract We investigate pulsed laser ablation of LaAlO 3 and LaGaO 3 with a focus on the influence of oxygen Background gas Pressure on the plume expansion dynamics and deposition rate. The ablation plume is characterized by exploiting fast photography and time- and space-resolved optical emission spectroscopy. The variation of the deposition rate with the oxygen Background Pressure was obtained at 800 °C by reflection high-energy electron diffraction, and compared to that measured at room temperature by means of a quartz crystal microbalance. The experimental findings allow one to address the various stages of plume expansion as a function of the Background oxygen Pressure as well as the changes induced on the plume species kinetic energy and composition. On the base of our experimental results, the possible influence of various mechanisms, such as subplantation and oxygen vacancy formation, on the growth of oxides interfaces is addressed.
Thomas W Haag - One of the best experts on this subject based on the ideXlab platform.
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effects of Background Pressure on spt 140 hall thruster performance
Journal of Propulsion and Power, 2020Co-Authors: John Steven Snyder, Thomas W Haag, Giovanni Lenguito, Jason D Frieman, Jonathan A MackeyAbstract:The performance of many Hall thrusters has been shown to exhibit sensitivity to Background Pressure in ground-based test facilities, and this property can have an impact on the prediction of in-spa...
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performance facility Pressure effects and stability characterization tests of nasa s hall effect rocket with magnetic shielding thruster
52nd AIAA SAE ASEE Joint Propulsion Conference, 2016Co-Authors: Hani Kamhawi, Wensheng Huang, Thomas W Haag, Daniel A Herman, George J Williams, James H Gilland, Peter Y Peterson, Richard R Hofer, Ioannis G MikellidesAbstract:NASA's Hall Effect Rocket with Magnetic Shielding (HERMeS) 12.5 kW Technology Demonstration Unit-1 (TDU-1) has been the subject of extensive technology maturation in preparation for flight system development. Part of the technology maturation effort included experimental evaluation of the TDU-1 thruster with conducting and dielectric front pole cover materials in two different electrical configurations. A graphite front magnetic pole cover thruster configuration with the thruster body electrically tied to cathode, and an alumina front pole cover thruster configuration with the thruster body floating were evaluated. Both configurations were also evaluated at different facility Background Pressure conditions to evaluate Background Pressure effects on thruster operation. Performance characterization tests found that higher thruster performance was attained with the graphite front pole cover configuration with the thruster electrically tied to cathode. A total thrust efficiency of 68% and a total specific impulse of 2,820 s was demonstrated at a discharge voltage of 600 V and a discharge power of 12.5 kW. Thruster stability regimes were characterized with respect to the thruster discharge current oscillations and with maps of the discharge current-voltage-magnetic field (IVB). Analysis of TDU-1 discharge current waveforms found that lower normalized discharge current peak-to-peak and root mean square magnitudes were attained when the thruster was electrically floated with alumina front pole covers. Background Pressure effects characterization tests indicated that the thruster performance and stability were mostly invariant to changes in the facility Background Pressure for vacuum chamber Pressure below 110-5 Torr-Xe (for thruster flow rates of 20.5 mg/s). Power spectral density analysis of the discharge current waveforms showed that increasing the vacuum chamber Background Pressure resulted in a higher discharge current dominant breathing mode frequency. Finally, IVB maps of the TDU-1 thruster indicated that the discharge current became more oscillatory with higher discharge current peak-to-peak and RMS values with increased facility Background Pressure at lower thruster mass flow rates; thruster operation at higher flow rates resulted in less change to the thruster's IVB characteristics with elevated Background Pressure.
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facility effect characterization test of nasa s hermes hall thruster
52nd AIAA SAE ASEE Joint Propulsion Conference, 2016Co-Authors: Thomas W Haag, Wensheng Huang, Ioannis G Mikellides, Alejandro Lopez Ortega, Hani KamhawiAbstract:A test to characterize the effect of varying Background Pressure on NASA's 12.5-kW Hall Effect Rocket with Magnetic Shielding had being completed. This thruster is the baseline propulsion system for the Solar Electric Propulsion Technology Demonstration Mission (SEP TDM). Potential differences in thruster performance and oscillation characteristics when in ground facilities versus on-orbit are considered a primary risk for the propulsion system of the Asteroid Redirect Robotic Mission, which is a candidate for SEP TDM. The first primary objective of this test was to demonstrate that the tools being developed to predict the zero-Background-Pressure behavior of the thruster can provide self-consistent results. The second primary objective of this test was to provide data for refining a physics-based model of the thruster plume that will be used in spacecraft interaction studies. Diagnostics deployed included a thrust stand, Faraday probe, Langmuir probe, retarding potential analyzer, Wien filter spectrometer, and high-speed camera. From the data, a physics-based plume model was refined. Comparisons of empirical data to modeling results are shown.
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investigation of the effects of facility Background Pressure on the performance and operation of the high voltage hall accelerator
50th AIAA ASME SAE ASEE Joint Propulsion Conference, 2014Co-Authors: Hani Kamhawi, Wensheng Huang, Thomas W Haag, Rotislav SpektorAbstract:The National Aeronautics and Space Administration (NASA) Science Mission Directorate In-Space Propulsion Technology office is sponsoring NASA Glenn Research Center to develop a 4 kW-class Hall thruster propulsion system for implementation in NASA science missions. A study was conducted to assess the impact of varying the facility Background Pressure on the High Voltage Hall Accelerator (HiVHAc) thruster performance and voltage-current characteristics. This present study evaluated the HiVHAc thruster performance in the lowest attainable Background Pressure condition at NASA GRC Vacuum Facility 5 to best simulate space-like conditions. Additional tests were performed at selected thruster operating conditions to investigate and elucidate the underlying physics that change during thruster operation at elevated facility Background Pressure. Tests were performed at Background Pressure conditions that are three and ten times higher than the lowest realized Background Pressure. Results indicated that the thruster discharge specific impulse and efficiency increased with elevated facility Background Pressure. The voltage-current profiles indicated a narrower stable operating region with increased Background Pressure. Experimental observations of the thruster operation indicated that increasing the facility Background Pressure shifted the ionization and acceleration zones upstream towards the thruster’s anode. Future tests of the HiVHAc thruster are planned at Background Pressure conditions that are expected to be two to three times lower than what was achieved during this test campaign. These tests will not only assess the impact of reduced facility Background Pressure on thruster performance, voltage-current characteristics, and plume properties; but will also attempt to quantify the magnitude of the ionization and acceleration zones upstream shifting as a function of increased Background Pressure.
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investigation of the effects of facility Background Pressure on the performance and voltage current characteristics of the high voltage hall accelerator
AIAA ASME SAE ASEE Joint Propulsion Conference, 2014Co-Authors: Hani Kamhawi, Wensheng Huang, Thomas W Haag, Rostislav SpektorAbstract:The National Aeronautics and Space Administration (NASA) Science Mission Directorate In-Space Propulsion Technology office is sponsoring NASA Glenn Research Center to develop a 4 kW-class Hall thruster propulsion system for implementation in NASA science missions. A study was conducted to assess the impact of varying the facility Background Pressure on the High Voltage Hall Accelerator (HiVHAc) thruster performance and voltage-current characteristics. This present study evaluated the HiVHAc thruster performance in the lowest attainable Background Pressure condition at NASA GRC Vacuum Facility 5 to best simulate space-like conditions. Additional tests were performed at selected thruster operating conditions to investigate and elucidate the underlying physics that change during thruster operation at elevated facility Background Pressure. Tests were performed at Background Pressure conditions that are three and ten times higher than the lowest realized Background Pressure. Results indicated that the thruster discharge specific impulse and efficiency increased with elevated facility Background Pressure. The voltage-current profiles indicated a narrower stable operating region with increased Background Pressure. Experimental observations of the thruster operation indicated that increasing the facility Background Pressure shifted the ionization and acceleration zones upstream towards the thruster's anode. Future tests of the HiVHAc thruster are planned at Background Pressure conditions that are expected to be two to three times lower than what was achieved during this test campaign. These tests will not only assess the impact of reduced facility Background Pressure on thruster performance, voltage-current characteristics, and plume properties; but will also attempt to quantify the magnitude of the ionization and acceleration zones upstream shifting as a function of increased Background Pressure.
