The Experts below are selected from a list of 141 Experts worldwide ranked by ideXlab platform
Ralf Schneider - One of the best experts on this subject based on the ideXlab platform.
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Self-similarity in Hall plasma discharges: Applications to particle models
Physics of Plasmas, 2005Co-Authors: Francesco Taccogna, Mario Capitelli, Savino Longo, Ralf SchneiderAbstract:Electron transport is a key process in the physics of Hall thruster discharges. Therefore, a kinetic description of the heavy particles (Xe) as well as electrons is required. The ideal numerical model would be a particle model for all the species. Nowadays, such a model is unpractical because it would need too large an amount of computation time due to the very different time scales of electrons and heavy particles dynamics. For this purpose two scalings to speed-up the execution time of a two-dimensional fully kinetic Particle-in-Cell/Monte Carlo Collision simulation of the Hall thruster SPT-100 are proposed. These two different scaling schemes generate self-similar systems of the acceleration channel including the process of secondary electron emission from the dielectric walls. Instead of using the common approach of a smaller neutral and ion mass or a larger Vacuum Permittivity the channel dimensions are reduced keeping the main dimensionless physics parameters constant. This leads to scaling laws for...
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Plasma flow in a Hall thruster
Physics of Plasmas, 2005Co-Authors: Francesco Taccogna, Mario Capitelli, Savino Longo, Ralf SchneiderAbstract:This work represents a two-dimensional (r,z)-3V axisymmetric fully kinetic particle-in-cell/Monte Carlo collision model of the plasmadynamics in the acceleration channel of a stationary plasma thruster. The model includes the process of secondary electron emission from the dielectric walls. In order to allow for a realistic simulation, differently from the previous fully kinetic model using a dummy mass ratio and Vacuum Permittivity or neglecting radial effects, a geometrical scaling of the channel is applied keeping the main dimensionless physics parameters constant. By this, the problem of the computational limits due to the very fast electron dynamics can be overcome. This model is able to give a clear picture of the plasma flow inside the acceleration channel. The results confirm the existence of an anode sheath with reverse ion flow, an ionization and acceleration region separated by a sonic transition point, and the ion flux distribution hitting the walls. Furthermore, the code is able to reproduce ...
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Plasma flow in a Hall thruster
Physics of Plasmas, 2005Co-Authors: Francesco Taccogna, Salvatore Longo, Mario Capitelli, Ralf SchneiderAbstract:This work represents a two-dimensional (r,z) -3V axisymmetric fully kinetic particle-in-cell/Monte Carlo collision model of the plasmadynamics in the acceleration channel of a stationary plasma thruster. The model includes the process of secondary electron emission from the dielectric walls. In order to allow for a realistic simulation, differently from the previous fully kinetic model using a dummy mass ratio and Vacuum Permittivity or neglecting radial effects, a geometrical scaling of the channel is applied keeping the main dimensionless physics parameters constant. By this, the problem of the computational limits due to the very fast electron dynamics can be overcome. This model is able to give a clear picture of the plasma flow inside the acceleration channel. The results confirm the existence of an anode sheath with reverse ion flow, an ionization and acceleration region separated by a sonic transition point, and the ion flux distribution hitting the walls. Furthermore, the code is able to reproduce the observed two populations of electrons and to calculate the ion distribution on the exit plane used as input data for plume simulations. © 2005 American Institute of Physics.
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Self-similarity in Hall plasma discharges: Applications to particle models
Physics of Plasmas, 2005Co-Authors: Francesco Taccogna, Salvatore Longo, Mario Capitelli, Ralf SchneiderAbstract:Electron transport is a key process in the physics of Hall thruster discharges. Therefore, a kinetic description of the heavy particles Xe as well as electrons is required. The ideal numerical model would be a particle model for all the species. Nowadays, such a model is unpractical because it would need too large an amount of computation time due to the very different time scales of electrons and heavy particles dynamics. For this purpose two scalings to speed-up the execution time of a two-dimensional fully kinetic Particle-in-Cell/Monte Carlo Collision simulation of the Hall thruster SPT-100 are proposed. These two different scaling schemes generate self-similar systems of the acceleration channel including the process of secondary electron emission from the dielectric walls. Instead of using the common approach of a smaller neutral and ion mass or a larger Vacuum Permittivity the channel dimensions are reduced keeping the main dimensionless physics parameters constant. This leads to scaling laws for the input magnetic field, mass flow rate, current and voltage discharge, etc. and output parameters obeying self-similarity. This scaling methodology makes the simulation faster and allows improved modeling of electron interactions and fundamental processes. This model has demonstrated its outstanding capability in improving the physics insight into the processes in SPT-100 under the scaling constraints for the geometrical reduction. The application to particle models of different plasma based devices is suggested for such systems where a linearization of the Boltzmann equation is possible.
Vladimir Nesterov - One of the best experts on this subject based on the ideXlab platform.
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A nanonewton force facility and a novel method for measurements of the air and Vacuum Permittivity at zero frequencies
Measurement Science and Technology, 2009Co-Authors: Vladimir NesterovAbstract:A nanonewton force facility, based on a disk-pendulum with electrostatic stiffness reduction and electrostatic force compensation, for the measurement of horizontal forces in the range below 1 µN, is presented. It consists of a measuring system and an identical reference system. Recent experiments with the nanonewton force facility have achieved agreement between an electrostatic force and a gravitational force of 80 nN with an uncertainty of less than 3%. A novel method for measurements of the air (Vacuum) Permittivity at zero frequencies by means of the nanonewton force facility is presented. First measurements in air show a Permittivity of the air e ≈ 8.71 × 10−12 F m−1 with an uncertainty of 3%. From a theoretical analysis, it follows that this method can be used for the measurement of the Vacuum Permittivity e0 at zero frequencies with a relative uncertainty of about 10−5. The precise measurement of the Vacuum Permittivity e0 for an electrostatic field would be another test for the correctness of Maxwell's equations.
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A nanonewton force facility and a novel method for measurements of the air and Vacuum Permittivity at zero frequencies
Measurement Science and Technology, 2009Co-Authors: Vladimir NesterovAbstract:A nanonewton force facility, based on a disk-pendulum with electrostatic stiffness reduction and electrostatic force compensation, for the measurement of horizontal forces in the range below 1 mu N, is presented. It consists of a measuring system and an identical reference system. Recent experiments with the nanonewton force facility have achieved agreement between an electrostatic force and a gravitational force of 80 nN with an uncertainty of less than 3%. A novel method for measurements of the air (Vacuum) Permittivity at zero frequencies by means of the nanonewton force facility is presented. First measurements in air show a Permittivity of the air epsilon approximate to 8.71 x 10(-12) F m(-1) with an uncertainty of 3%. From a theoretical analysis, it follows that this method can be used for the measurement of the Vacuum Permittivity epsilon(0) at zero frequencies with a relative uncertainty of about 10(-5). The precise measurement of the Vacuum Permittivity epsilon(0) for an electrostatic field would be another test for the correctness of Maxwell's equations.
A. M. Gañán-calvo - One of the best experts on this subject based on the ideXlab platform.
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TAYLOR CONE ELECTROHYDRODYNAMICS. THE MINIMUM AND MAXIMUM FLOW RATES IN ELECTROSPRAYING
Journal of Aerosol Science, 1999Co-Authors: Antonio Barrero, A. M. Gañán-calvoAbstract:The surface charge at the liquid–gas interface in cone-jet electrospraying, almost relaxed from an electrochemical point of view, is driven by the radial electric field created to supply the current to the cone tip that the microjet withdraws. The electric stress applied on the liquid surface provokes a low or high Reynolds number motions in the electrified meniscus depending on a dimensionless parameter which relates the liquid viscosity and its electrical conductivity. The analysis of the surface motion is essential to quantify the surface current convected to the cone’s tip, which is shown to be negligible compared to the one driven by bulk conduction. In the case of high Reynolds number motions, we show mathematically, and also experimentally, the emergence of an interesting self-rotation phenomenon. In addition, an analysis of the equations governing the electrohydrodynamics of the charged liquid ligament issuing from the tip of an electrified meniscus in a steady cone-jet suggests the mechanisms which set the stability limits of this steady regime. It is shown that for low and moderate liquid polarities (less than 40 times the Vacuum Permittivity), the minimum liquid flow rate that can be electrosprayed in a steady cone-jet is reached when the surface tension stress at the cusp from which the jet issues, which provokes a resulting pressure gradient against the flow, overcomes the electrostatic “suction” effect. To show the role of the different forces involved, we have carried the calculation of the intervening ones in the momentum equation using the digitized shape of a cone-jet close to the minimum flow rate in the case of a Permittivity 6.5 times larger than the Vacuum one. For larger polarities, which impose large electrical conductivities as well, the role of viscous forces, polarization forces, and charge relaxation effects is discussed. In addition, we have carried out experimental measurements of the minimum flow rate using several different liquids. These results are discussed and compared with the experimental data from different authors, as well as with other previously given scaling laws and estimations of the minimum flow rate in cone-jet electrospraying.
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THE ELECTROHYDRODYNAMICS OF THE CHARGED LIQUID JET ISSUING FROM AN ELECTRIFIED TAYLOR CONE. UNIVERSAL SCALING LAWS
Journal of Aerosol Science, 1999Co-Authors: A. M. Gañán-calvoAbstract:A hybrid experimental–numerical approach to study the dynamics of capillary electrified jets, which uses a quasi-one-dimensional model and the experimentally measured shape of an actual liquid thread (Gañán-Calvo (1997) J. Fluid Mech. 335, 165–188) has been employed in this work to analyze the electrohydrodynamics of the liquid micro-jets issuing from Taylor cones. Different liquids have been used in this study, with electrical permittivities from 6.5 to 38 times the Vacuum Permittivity, and electrical conductivities ranging from 8.5 to 4.5e-4Sm-1. Up to 25 different jet shapes corresponding to steady and absolutely stable conditions have been digitized, and the corresponding surface charge distribution, normal external and internal electric fields at the surface, the axial electric field (the slender approach allows to consider the axial electric field constant in the transversal direction), the liquid velocity distribution, the electric current convected by the surface and the one driven through the bulk by Ohmic conduction at each axial point have been calculated. In particular, one of the liquid jets analyzed corresponded to the onset of stability of the steady cone-jet mode, where we supply just the (minimum) liquid flow rate that the electrostatic suction effect at the cone-jet neck is able to withdraw at the minimum needle–electrode potential difference for a given stable cone elongation. This has revealed a surprising result: even in this critical situation, the inner normal electric displacement is at most a mere 15% of the outer one, and this happens only at one point of the whole cone-jet, located close to the point at which the convected electric current equals the current driven by bulk conduction (i.e. a little downstream of the cone-jet neck), being the inner displacement at other points of the jet and the cone hundreds of times smaller than the outer displacement. As one increases the liquid flow rate, the ratio of the maximum inner displacement to the outer displacement becomes proportionally smaller. This result clarifies for the first time the controversy about charge relaxation phenomena in cone-jet electrosprays, since it can be used to show from a physicochemical argument that the charge layer at the whole cone-jet surface is almost relaxed even at the onset of stability, at least for liquid permittivities of the order of the ones used in this study. This result also guarantees a homogeneous bulk conductivity along the hole cone-jet. Secondly, and similarly interesting, the kinetic energy per unit volume acquired by the liquid in the jet results independent of the flow rate for a given liquid and a cone elongation, explained by the fact that the normal electric field (or surface charge distribution) which provokes the main acceleration force (the electrostatic suction effect, at the cone-jet neck and the beginning of the jet) results independent of the flow rate as well. A universal scaling of the electro-hydrodynamic variables, jet size and total emitted electric current is proposed, and the experimental results are collapsed into a universal collection of distributions of non-dimensional variables along the axis. The resulting droplet size, also measured in the same experiments, scales as the jet radius, and the droplet charge results proportional to its surface, a result shown by many investigators but never explained. Other previously used electrohydro-dynamic hypotheses and scaling laws are discussed under these new results.
Antonio Barrero - One of the best experts on this subject based on the ideXlab platform.
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TAYLOR CONE ELECTROHYDRODYNAMICS. THE MINIMUM AND MAXIMUM FLOW RATES IN ELECTROSPRAYING
Journal of Aerosol Science, 1999Co-Authors: Antonio Barrero, A. M. Gañán-calvoAbstract:The surface charge at the liquid–gas interface in cone-jet electrospraying, almost relaxed from an electrochemical point of view, is driven by the radial electric field created to supply the current to the cone tip that the microjet withdraws. The electric stress applied on the liquid surface provokes a low or high Reynolds number motions in the electrified meniscus depending on a dimensionless parameter which relates the liquid viscosity and its electrical conductivity. The analysis of the surface motion is essential to quantify the surface current convected to the cone’s tip, which is shown to be negligible compared to the one driven by bulk conduction. In the case of high Reynolds number motions, we show mathematically, and also experimentally, the emergence of an interesting self-rotation phenomenon. In addition, an analysis of the equations governing the electrohydrodynamics of the charged liquid ligament issuing from the tip of an electrified meniscus in a steady cone-jet suggests the mechanisms which set the stability limits of this steady regime. It is shown that for low and moderate liquid polarities (less than 40 times the Vacuum Permittivity), the minimum liquid flow rate that can be electrosprayed in a steady cone-jet is reached when the surface tension stress at the cusp from which the jet issues, which provokes a resulting pressure gradient against the flow, overcomes the electrostatic “suction” effect. To show the role of the different forces involved, we have carried the calculation of the intervening ones in the momentum equation using the digitized shape of a cone-jet close to the minimum flow rate in the case of a Permittivity 6.5 times larger than the Vacuum one. For larger polarities, which impose large electrical conductivities as well, the role of viscous forces, polarization forces, and charge relaxation effects is discussed. In addition, we have carried out experimental measurements of the minimum flow rate using several different liquids. These results are discussed and compared with the experimental data from different authors, as well as with other previously given scaling laws and estimations of the minimum flow rate in cone-jet electrospraying.
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current and droplet size in the electrospraying of liquids scaling laws
Journal of Aerosol Science, 1997Co-Authors: Alfonso M Ganancalvo, Jorge Davila, Antonio BarreroAbstract:Measurements of the current and size of the primary droplets of sprays generated by electrostatic atomization of a variety of liquids with different electrical conductivities, permittivities, liquid-gas surface tensions, densities and viscosities have been carried out. Scaling laws of the spray current as well as the charge and size of the droplets have been obtained from a theoretical model of the charge transport. Comparisons between experimental and theoretical results are good. We have found that there are two different behaviours strongly related to the viscosity and electrical conductivity of the liquid. The separation between both behaviours is governed by the dimensionless parameter δμδ1/3=[ɛ02γ3/(K2μ3Q)]1/3; Q, μ, K, γ, and ɛ0 are the flow rate, viscosity, electrical conductivity, surface tension of the gas-liquid interface and Vacuum Permittivity, respectively. For liquids with high enough conductivities and viscosities (δμδ1/3 ≪ 1), the spray current and droplet size are approximately given by I/I0 = 6.2[Q/(β-1)1/2Q0]1/2 - 2.0 and d/(β-1)1/3d0 = 1.6[Q/ (β - 1)1/2Q0]1/3 - 1.0, where βɛ0 is the liquid Permittivity and I0 = (ɛ0γ2/ρ)1/2,d0 = [γɛ02/(ρK2)]1/3 and Q0 = γɛ0/ρK are a reference intensity, droplet size and flow rate, respectively. In the opposite limit, we have found I/I0= 11.0(Q/Q0)1/4 - 5.0 and d/d0 = 1.2(Q/Q0)1/2 -0.3. Comparisons with experimental data reported in the literature are also satisfactory
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Current and Droplet Size in the Elctrospraying of Liquids. Scaling Laws
Journal of Aerosol Science, 1997Co-Authors: Jorge Davila, Antonio BarreroAbstract:Measurements of the current and size of the primary droplets of sprays generated by electrostatic atomization of a variety of liquids with different electrical condutivities, permittivities, liquid-gas surface tensions, densities and viscosities have been carried out. Scaling laws of the spray current as well as the charge and size of the droplets have been obtained from a theoretical model of the charge transport. Comparisons between experimental and theoretical results are good. We have found that there are two different behaviours strongly related to the viscosity and electrical conductivity of the liquid. The separation between both behaviours is governed by the dimensionless parameter deltaµ delta1/3, and 0 are the flow rate, viscosity, electrical conductivity, surface tension of the gas-liquid interface and Vacuum Permittivity, respectively. For liquids with high enough conductivities and viscosities (
Francesco Taccogna - One of the best experts on this subject based on the ideXlab platform.
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Self-similarity in Hall plasma discharges: Applications to particle models
Physics of Plasmas, 2005Co-Authors: Francesco Taccogna, Mario Capitelli, Savino Longo, Ralf SchneiderAbstract:Electron transport is a key process in the physics of Hall thruster discharges. Therefore, a kinetic description of the heavy particles (Xe) as well as electrons is required. The ideal numerical model would be a particle model for all the species. Nowadays, such a model is unpractical because it would need too large an amount of computation time due to the very different time scales of electrons and heavy particles dynamics. For this purpose two scalings to speed-up the execution time of a two-dimensional fully kinetic Particle-in-Cell/Monte Carlo Collision simulation of the Hall thruster SPT-100 are proposed. These two different scaling schemes generate self-similar systems of the acceleration channel including the process of secondary electron emission from the dielectric walls. Instead of using the common approach of a smaller neutral and ion mass or a larger Vacuum Permittivity the channel dimensions are reduced keeping the main dimensionless physics parameters constant. This leads to scaling laws for...
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Plasma flow in a Hall thruster
Physics of Plasmas, 2005Co-Authors: Francesco Taccogna, Mario Capitelli, Savino Longo, Ralf SchneiderAbstract:This work represents a two-dimensional (r,z)-3V axisymmetric fully kinetic particle-in-cell/Monte Carlo collision model of the plasmadynamics in the acceleration channel of a stationary plasma thruster. The model includes the process of secondary electron emission from the dielectric walls. In order to allow for a realistic simulation, differently from the previous fully kinetic model using a dummy mass ratio and Vacuum Permittivity or neglecting radial effects, a geometrical scaling of the channel is applied keeping the main dimensionless physics parameters constant. By this, the problem of the computational limits due to the very fast electron dynamics can be overcome. This model is able to give a clear picture of the plasma flow inside the acceleration channel. The results confirm the existence of an anode sheath with reverse ion flow, an ionization and acceleration region separated by a sonic transition point, and the ion flux distribution hitting the walls. Furthermore, the code is able to reproduce ...
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Plasma flow in a Hall thruster
Physics of Plasmas, 2005Co-Authors: Francesco Taccogna, Salvatore Longo, Mario Capitelli, Ralf SchneiderAbstract:This work represents a two-dimensional (r,z) -3V axisymmetric fully kinetic particle-in-cell/Monte Carlo collision model of the plasmadynamics in the acceleration channel of a stationary plasma thruster. The model includes the process of secondary electron emission from the dielectric walls. In order to allow for a realistic simulation, differently from the previous fully kinetic model using a dummy mass ratio and Vacuum Permittivity or neglecting radial effects, a geometrical scaling of the channel is applied keeping the main dimensionless physics parameters constant. By this, the problem of the computational limits due to the very fast electron dynamics can be overcome. This model is able to give a clear picture of the plasma flow inside the acceleration channel. The results confirm the existence of an anode sheath with reverse ion flow, an ionization and acceleration region separated by a sonic transition point, and the ion flux distribution hitting the walls. Furthermore, the code is able to reproduce the observed two populations of electrons and to calculate the ion distribution on the exit plane used as input data for plume simulations. © 2005 American Institute of Physics.
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Self-similarity in Hall plasma discharges: Applications to particle models
Physics of Plasmas, 2005Co-Authors: Francesco Taccogna, Salvatore Longo, Mario Capitelli, Ralf SchneiderAbstract:Electron transport is a key process in the physics of Hall thruster discharges. Therefore, a kinetic description of the heavy particles Xe as well as electrons is required. The ideal numerical model would be a particle model for all the species. Nowadays, such a model is unpractical because it would need too large an amount of computation time due to the very different time scales of electrons and heavy particles dynamics. For this purpose two scalings to speed-up the execution time of a two-dimensional fully kinetic Particle-in-Cell/Monte Carlo Collision simulation of the Hall thruster SPT-100 are proposed. These two different scaling schemes generate self-similar systems of the acceleration channel including the process of secondary electron emission from the dielectric walls. Instead of using the common approach of a smaller neutral and ion mass or a larger Vacuum Permittivity the channel dimensions are reduced keeping the main dimensionless physics parameters constant. This leads to scaling laws for the input magnetic field, mass flow rate, current and voltage discharge, etc. and output parameters obeying self-similarity. This scaling methodology makes the simulation faster and allows improved modeling of electron interactions and fundamental processes. This model has demonstrated its outstanding capability in improving the physics insight into the processes in SPT-100 under the scaling constraints for the geometrical reduction. The application to particle models of different plasma based devices is suggested for such systems where a linearization of the Boltzmann equation is possible.