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A Koval - One of the best experts on this subject based on the ideXlab platform.
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a comparison of alpha particle and proton beam differential flows in Collisionally young solar wind
The Astrophysical Journal, 2018Co-Authors: B L Alterman, J C Kasper, M L Stevens, A KovalAbstract:In fast wind or when the local Coulomb Collision frequency is low, observations show that solar wind minor ions and ion sub-populations flow with different bulk velocities. Measurements indicate that the drift speed of both alpha particles and proton beams with respect to the bulk or core protons rarely exceeds the local Alfven speed, suggesting that a magnetic instability or other wave-particle process limits their maximum drift. We compare simultaneous alpha particle, proton beam, and proton core observations from instruments on the Wind spacecraft spanning over 20 years. In nearly Collisionless solar wind, we find that the normalized alpha particle drift speed is slower than the normalized proton beam speed; no correlation between fluctuations in both species' drifts about their means; and a strong anti-correlation between Collisional age and alpha-proton differential flow, but no such correlation with proton beam-core differential flow. Controlling for the Collisional dependence, both species' normalized drifts exhibit similar statistical distributions. In the asymptotic, zero Coulomb Collision limit, the youngest measured differential flows most strongly correlate with an approximation of the Alfven speed that includes proton pressure anisotropy. In this limit and with this most precise representation, alpha particles drift at 67% and proton beam drift is approximately 105% of the local Alfven speed. We posit that one of two physical explanations is possible. Either (1) an Alfvenic process preferentially accelerates or sustains proton beams and not alphas or (2) alpha particles are more susceptible to either an instability or Coulomb drag than proton beams.
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a comparison of alpha particle and proton beam differential flow in Collisionally young solar wind
arXiv: Solar and Stellar Astrophysics, 2018Co-Authors: B L Alterman, J C Kasper, M L Stevens, A KovalAbstract:In fast wind or when the local Coulomb Collision frequency is low, observations show that solar wind minor ions and ion sub-populations flow with different bulk velocities. Measurements indicate that the drift speed of both alpha particles and proton beams with respect to the bulk or core protons rarely exceeds the local Alfven speed, suggesting that a magnetic instability or other wave-particle process limits their maximum drift. We compare simultaneous alpha particle, proton beam, and proton core observations from instruments on the Wind spacecraft spanning over 20 years. In nearly Collisionless solar wind, we find that the normalized alpha particle drift speed is slower than the normalized proton beam speed; no correlation between fluctuations in both species' drifts about their means; and a strong anti-correlation between Collisional age and alpha-proton differential flow, but no such correlation with proton beam-core differential flow. Controlling for the Collisional dependence, both species' normalized drifts exhibit similar statistical distributions. In the asymptotic, zero Coulomb Collision limit, the youngest measured differential flows most strongly correlate with an approximation of the Alfven speed that includes proton pressure anisotropy. In this limit and with this most precise representation, alpha particles drift at 67% and proton beam drift is approximately 105% of the local Alfven speed. We posit that one of two physical explanations is possible. Either (1) an Alfvenic process preferentially accelerates or sustains proton beams and not alphas or (2) alpha particles are more susceptible to either an instability or Coulomb drag than proton beams.
E D Held - One of the best experts on this subject based on the ideXlab platform.
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unified form for parallel ion viscous stress in magnetized plasmas
Physics of Plasmas, 2003Co-Authors: E D HeldAbstract:In this work a unified form for the parallel ion viscous stress in a magnetized plasma is presented. Approximately valid for arbitrary Collisionality, the integral nature of this generalized closure results from assuming the maximal ordering between Collisional pitch-angle scattering and free streaming effects and from taking a Chapman–Enskog-type approach which includes the parallel ion viscous stress itself as a drive. The ion drift kinetic equation is solved in a sheared slab using an expansion in eigenfunctions of the Lorentz scattering operator. Integrating the coefficient equations in space and taking the proper velocity space moments couples the parallel viscous stress closure to an integral momentum restoring term, thus generalizing the concept of momentum conservation for simplified Coulomb Collision operators. The integral closure involves following ions along magnetic field lines which are the ideal, time-independent characteristics of the perturbed distribution function. The fact that the visc...
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unified form for parallel ion viscous stress in magnetized plasmas
Physics of Plasmas, 2003Co-Authors: E D HeldAbstract:In this work a unified form for the parallel ion viscous stress in a magnetized plasma is presented. Approximately valid for arbitrary Collisionality, the integral nature of this generalized closure results from assuming the maximal ordering between Collisional pitch-angle scattering and free streaming effects and from taking a Chapman–Enskog-type approach which includes the parallel ion viscous stress itself as a drive. The ion drift kinetic equation is solved in a sheared slab using an expansion in eigenfunctions of the Lorentz scattering operator. Integrating the coefficient equations in space and taking the proper velocity space moments couples the parallel viscous stress closure to an integral momentum restoring term, thus generalizing the concept of momentum conservation for simplified Coulomb Collision operators. The integral closure involves following ions along magnetic field lines which are the ideal, time-independent characteristics of the perturbed distribution function. The fact that the visc...
Rogerio Jorge - One of the best experts on this subject based on the ideXlab platform.
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Nonlinear Gyrokinetic Coulomb Collision Operator
Journal of Plasma Physics, 2019Co-Authors: Rogerio Jorge, Baptiste Jimmy Frei, Paolo RicciAbstract:A gyrokinetic Coulomb Collision operator is derived, which is particularly useful to describe the plasma dynamics at the periphery region of magnetic confinement fusion devices. The derived operator is able to describe Collisions occurring in distribution functions arbitrarily far from equilibrium with variations on spatial scales at and below the particle Larmor radius. A multipole expansion of the Rosenbluth potentials is used in order to derive the dependence of the full Coulomb Collision operator on the particle gyroangle. The full Coulomb Collision operator is then expressed in gyrocentre phase-space coordinates, and a closed formula for its gyroaverage in terms of the moments of the gyrocentre distribution function in a form ready to be numerically implemented is provided. Furthermore, the Collision operator is projected onto a Hermite–Laguerre velocity space polynomial basis and expansions in the small electron-to-ion mass ratio are provided.
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linear theory of electron plasma waves at arbitrary Collisionality
Journal of Plasma Physics, 2019Co-Authors: Rogerio Jorge, Paolo Ricci, S Brunner, S Gamba, V Konovets, Nuno Loureiro, L M Perrone, N TeixeiraAbstract:The dynamics of electron-plasma waves is described at arbitrary Collisionality by considering the full Coulomb Collision operator. The description is based on a Hermite–Laguerre decomposition of the velocity dependence of the electron distribution function. The damping rate, frequency and eigenmode spectrum of electron-plasma waves are found as functions of the Collision frequency and wavelength. A comparison is made between the Collisionless Landau damping limit, the Lenard–Bernstein and Dougherty Collision operators and the electron–ion Collision operator, finding large deviations in the damping rates and eigenmode spectra. A purely damped entropy mode, characteristic of a plasma where pitch-angle scattering effects are dominant with respect to Collisionless effects, is shown to emerge numerically, and its dispersion relation is analytically derived. It is shown that such a mode is absent when simplified Collision operators are used, and that like-particle Collisions strongly influence the damping rate of the entropy mode.
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linear theory of electron plasma waves at arbitrary Collisionality
arXiv: Plasma Physics, 2018Co-Authors: Rogerio Jorge, Paolo Ricci, S Brunner, S Gamba, V Konovets, Nuno Loureiro, L M Perrone, N TeixeiraAbstract:The dynamics of electron-plasma waves are described at arbitrary Collisionality by considering the full Coulomb Collision operator. The description is based on a Hermite-Laguerre decomposition of the velocity dependence of the electron distribution function. The damping rate, frequency, and eigenmode spectrum of electron-plasma waves are found as functions of the Collision frequency and wavelength. A comparison is made between the Collisionless Landau damping limit, the Lenard-Bernstein and Dougherty Collision operators, and the electron-ion Collision operator, finding large deviations in the damping rates and eigenmode spectra. A purely damped entropy mode, characteristic of a plasma where pitch-angle scattering effects are dominant with respect to Collisionless effects, is shown to emerge numerically, and its dispersion relation is analytically derived. It is shown that such a mode is absent when simplified Collision operators are used, and that like-particle Collisions strongly influence the damping rate of the entropy mode.
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theory of the drift wave instability at arbitrary Collisionality
Physical Review Letters, 2018Co-Authors: Rogerio Jorge, Paolo Ricci, Nuno LoureiroAbstract:A numerically efficient framework that takes into account the effect of the Coulomb Collision operator at arbitrary Collisionalities is introduced. Such a model is based on the expansion of the distribution function on a Hermite-Laguerre polynomial basis to study the effects of Collisions on magnetized plasma instabilities at arbitrary mean-free path. Focusing on the drift-wave instability, we show that our framework allows retrieving established Collisional and Collisionless limits. At the intermediate Collisionalities relevant for present and future magnetic nuclear fusion devices, deviations with respect to Collision operators used in state-of-the-art turbulence simulation codes show the need for retaining the full Coulomb operator in order to obtain both the correct instability growth rate and eigenmode spectrum, which, for example, may significantly impact quantitative predictions of transport. The exponential convergence of the spectral representation that we propose makes the representation of the velocity space dependence, including the full Collision operator, more efficient than standard finite difference methods.
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a drift kinetic analytical model for scrape off layer plasma dynamics at arbitrary Collisionality
Journal of Plasma Physics, 2017Co-Authors: Rogerio Jorge, Paolo Ricci, Nuno LoureiroAbstract:A drift-kinetic model to describe the plasma dynamics in the scrape-off layer region of tokamak devices at arbitrary Collisionality is derived. Our formulation is based on a gyroaveraged Lagrangian description of the charged particle motion, and the corresponding drift-kinetic Boltzmann equation that includes a full Coulomb Collision operator. Using a Hermite–Laguerre velocity space decomposition of the gyroaveraged distribution function, a set of equations to evolve the coefficients of the expansion is presented. By evaluating explicitly the moments of the Coulomb Collision operator, distribution functions arbitrarily far from equilibrium can be studied at arbitrary Collisionalities. A fluid closure in the high-Collisionality limit is presented, and the corresponding fluid equations are compared with previously derived fluid models.
Paolo Ricci - One of the best experts on this subject based on the ideXlab platform.
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Nonlinear Gyrokinetic Coulomb Collision Operator
Journal of Plasma Physics, 2019Co-Authors: Rogerio Jorge, Baptiste Jimmy Frei, Paolo RicciAbstract:A gyrokinetic Coulomb Collision operator is derived, which is particularly useful to describe the plasma dynamics at the periphery region of magnetic confinement fusion devices. The derived operator is able to describe Collisions occurring in distribution functions arbitrarily far from equilibrium with variations on spatial scales at and below the particle Larmor radius. A multipole expansion of the Rosenbluth potentials is used in order to derive the dependence of the full Coulomb Collision operator on the particle gyroangle. The full Coulomb Collision operator is then expressed in gyrocentre phase-space coordinates, and a closed formula for its gyroaverage in terms of the moments of the gyrocentre distribution function in a form ready to be numerically implemented is provided. Furthermore, the Collision operator is projected onto a Hermite–Laguerre velocity space polynomial basis and expansions in the small electron-to-ion mass ratio are provided.
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linear theory of electron plasma waves at arbitrary Collisionality
Journal of Plasma Physics, 2019Co-Authors: Rogerio Jorge, Paolo Ricci, S Brunner, S Gamba, V Konovets, Nuno Loureiro, L M Perrone, N TeixeiraAbstract:The dynamics of electron-plasma waves is described at arbitrary Collisionality by considering the full Coulomb Collision operator. The description is based on a Hermite–Laguerre decomposition of the velocity dependence of the electron distribution function. The damping rate, frequency and eigenmode spectrum of electron-plasma waves are found as functions of the Collision frequency and wavelength. A comparison is made between the Collisionless Landau damping limit, the Lenard–Bernstein and Dougherty Collision operators and the electron–ion Collision operator, finding large deviations in the damping rates and eigenmode spectra. A purely damped entropy mode, characteristic of a plasma where pitch-angle scattering effects are dominant with respect to Collisionless effects, is shown to emerge numerically, and its dispersion relation is analytically derived. It is shown that such a mode is absent when simplified Collision operators are used, and that like-particle Collisions strongly influence the damping rate of the entropy mode.
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linear theory of electron plasma waves at arbitrary Collisionality
arXiv: Plasma Physics, 2018Co-Authors: Rogerio Jorge, Paolo Ricci, S Brunner, S Gamba, V Konovets, Nuno Loureiro, L M Perrone, N TeixeiraAbstract:The dynamics of electron-plasma waves are described at arbitrary Collisionality by considering the full Coulomb Collision operator. The description is based on a Hermite-Laguerre decomposition of the velocity dependence of the electron distribution function. The damping rate, frequency, and eigenmode spectrum of electron-plasma waves are found as functions of the Collision frequency and wavelength. A comparison is made between the Collisionless Landau damping limit, the Lenard-Bernstein and Dougherty Collision operators, and the electron-ion Collision operator, finding large deviations in the damping rates and eigenmode spectra. A purely damped entropy mode, characteristic of a plasma where pitch-angle scattering effects are dominant with respect to Collisionless effects, is shown to emerge numerically, and its dispersion relation is analytically derived. It is shown that such a mode is absent when simplified Collision operators are used, and that like-particle Collisions strongly influence the damping rate of the entropy mode.
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theory of the drift wave instability at arbitrary Collisionality
Physical Review Letters, 2018Co-Authors: Rogerio Jorge, Paolo Ricci, Nuno LoureiroAbstract:A numerically efficient framework that takes into account the effect of the Coulomb Collision operator at arbitrary Collisionalities is introduced. Such a model is based on the expansion of the distribution function on a Hermite-Laguerre polynomial basis to study the effects of Collisions on magnetized plasma instabilities at arbitrary mean-free path. Focusing on the drift-wave instability, we show that our framework allows retrieving established Collisional and Collisionless limits. At the intermediate Collisionalities relevant for present and future magnetic nuclear fusion devices, deviations with respect to Collision operators used in state-of-the-art turbulence simulation codes show the need for retaining the full Coulomb operator in order to obtain both the correct instability growth rate and eigenmode spectrum, which, for example, may significantly impact quantitative predictions of transport. The exponential convergence of the spectral representation that we propose makes the representation of the velocity space dependence, including the full Collision operator, more efficient than standard finite difference methods.
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a drift kinetic analytical model for scrape off layer plasma dynamics at arbitrary Collisionality
Journal of Plasma Physics, 2017Co-Authors: Rogerio Jorge, Paolo Ricci, Nuno LoureiroAbstract:A drift-kinetic model to describe the plasma dynamics in the scrape-off layer region of tokamak devices at arbitrary Collisionality is derived. Our formulation is based on a gyroaveraged Lagrangian description of the charged particle motion, and the corresponding drift-kinetic Boltzmann equation that includes a full Coulomb Collision operator. Using a Hermite–Laguerre velocity space decomposition of the gyroaveraged distribution function, a set of equations to evolve the coefficients of the expansion is presented. By evaluating explicitly the moments of the Coulomb Collision operator, distribution functions arbitrarily far from equilibrium can be studied at arbitrary Collisionalities. A fluid closure in the high-Collisionality limit is presented, and the corresponding fluid equations are compared with previously derived fluid models.
J C Kasper - One of the best experts on this subject based on the ideXlab platform.
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a comparison of alpha particle and proton beam differential flows in Collisionally young solar wind
The Astrophysical Journal, 2018Co-Authors: B L Alterman, J C Kasper, M L Stevens, A KovalAbstract:In fast wind or when the local Coulomb Collision frequency is low, observations show that solar wind minor ions and ion sub-populations flow with different bulk velocities. Measurements indicate that the drift speed of both alpha particles and proton beams with respect to the bulk or core protons rarely exceeds the local Alfven speed, suggesting that a magnetic instability or other wave-particle process limits their maximum drift. We compare simultaneous alpha particle, proton beam, and proton core observations from instruments on the Wind spacecraft spanning over 20 years. In nearly Collisionless solar wind, we find that the normalized alpha particle drift speed is slower than the normalized proton beam speed; no correlation between fluctuations in both species' drifts about their means; and a strong anti-correlation between Collisional age and alpha-proton differential flow, but no such correlation with proton beam-core differential flow. Controlling for the Collisional dependence, both species' normalized drifts exhibit similar statistical distributions. In the asymptotic, zero Coulomb Collision limit, the youngest measured differential flows most strongly correlate with an approximation of the Alfven speed that includes proton pressure anisotropy. In this limit and with this most precise representation, alpha particles drift at 67% and proton beam drift is approximately 105% of the local Alfven speed. We posit that one of two physical explanations is possible. Either (1) an Alfvenic process preferentially accelerates or sustains proton beams and not alphas or (2) alpha particles are more susceptible to either an instability or Coulomb drag than proton beams.
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a comparison of alpha particle and proton beam differential flow in Collisionally young solar wind
arXiv: Solar and Stellar Astrophysics, 2018Co-Authors: B L Alterman, J C Kasper, M L Stevens, A KovalAbstract:In fast wind or when the local Coulomb Collision frequency is low, observations show that solar wind minor ions and ion sub-populations flow with different bulk velocities. Measurements indicate that the drift speed of both alpha particles and proton beams with respect to the bulk or core protons rarely exceeds the local Alfven speed, suggesting that a magnetic instability or other wave-particle process limits their maximum drift. We compare simultaneous alpha particle, proton beam, and proton core observations from instruments on the Wind spacecraft spanning over 20 years. In nearly Collisionless solar wind, we find that the normalized alpha particle drift speed is slower than the normalized proton beam speed; no correlation between fluctuations in both species' drifts about their means; and a strong anti-correlation between Collisional age and alpha-proton differential flow, but no such correlation with proton beam-core differential flow. Controlling for the Collisional dependence, both species' normalized drifts exhibit similar statistical distributions. In the asymptotic, zero Coulomb Collision limit, the youngest measured differential flows most strongly correlate with an approximation of the Alfven speed that includes proton pressure anisotropy. In this limit and with this most precise representation, alpha particles drift at 67% and proton beam drift is approximately 105% of the local Alfven speed. We posit that one of two physical explanations is possible. Either (1) an Alfvenic process preferentially accelerates or sustains proton beams and not alphas or (2) alpha particles are more susceptible to either an instability or Coulomb drag than proton beams.
