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A. Case - One of the best experts on this subject based on the ideXlab platform.
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Wave-particle interaction
Plasma Physics and Controlled Fusion, 2000Co-Authors: Fred Skiff, W. A. Noonan, C. S. Ng, Amitava Bhattacharjee, A. CaseAbstract:We seek a description of plasma wave-particle interactions in the weakly Collisional regime. Because weak collisions produce a qualitative change in the plasma degrees of freedom without totally suppressing kinetic effects, neither the Vlasov limit nor the fluid moment limit are found to be an adequate description of experimental data. Illustrative examples of data that require a weakly Collisional description are discussed.
Francois Lique - One of the best experts on this subject based on the ideXlab platform.
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Inelastic rate coefficients for collisions of N$_2$H$^+$ with H$_2$
Monthly Notices of the Royal Astronomical Society, 2020Co-Authors: C. Balança, Yohann Scribano, Francois Lique, Jérôme Loreau, Nicole FeautrierAbstract:N$_2$H$^+$ is one of the first molecular ion observed in the interstellar medium and it is found of particular interest to probe the physical conditions of cold molecular clouds. Accurate modelling of the observed lines requires the knowledge of Collisional exci- tation rate coefficients. Thus, we have calculated rate coefficients for the excitation of N$_2$H$^+$ by H$_2$, the most abundant Collisional partner.
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C-type shock modelling -- the effect of new H$_2$--H Collisional rate coefficients
Monthly Notices of the Royal Astronomical Society, 2019Co-Authors: A. Nesterenok, Duncan Bossion, Yohann Scribano, Francois LiqueAbstract:We consider Collisional excitation of H$_2$ molecules in C-type shocks propagating in dense molecular clouds. New data on Collisional rate coefficients for (de-)excitation of H$_2$ molecule in collisions with H atoms and new H$_2$ dissociation rates are used. The new H$_2$–H Collisional data are state of the art and are based on the most accurate H$_3$ potential energy surface.
Fred Skiff - One of the best experts on this subject based on the ideXlab platform.
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Wave-particle interaction
Plasma Physics and Controlled Fusion, 2000Co-Authors: Fred Skiff, W. A. Noonan, C. S. Ng, Amitava Bhattacharjee, A. CaseAbstract:We seek a description of plasma wave-particle interactions in the weakly Collisional regime. Because weak collisions produce a qualitative change in the plasma degrees of freedom without totally suppressing kinetic effects, neither the Vlasov limit nor the fluid moment limit are found to be an adequate description of experimental data. Illustrative examples of data that require a weakly Collisional description are discussed.
Pierluigi Veltri - One of the best experts on this subject based on the ideXlab platform.
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Collisional Relaxation of Fine Velocity Structures in Plasmas.
Physical Review Letters, 2016Co-Authors: Oreste Pezzi, Francesco Valentini, Pierluigi VeltriAbstract:The existence of several characteristic times during the Collisional relaxation of fine velocity structures is investigated by means of Eulerian numerical simulations of a spatially homogeneous force-free weakly Collisional plasma. The effect of smoothing out velocity gradients on the evolution of global quantities, such as temperature and entropy, is discussed, suggesting that plasma Collisionality can locally increase due to velocity space deformations of the particle velocity distribution function. These results support the idea that high-resolution measurements of the particle velocity distribution function are crucial for an accurate description of weakly Collisional systems, such as the solar wind, in order to answer relevant scientific questions, related, for example, to particle heating and energization.
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Numerical approach to Collisional plasmas: Collisional effects on electrostatic plasma waves
2007Co-Authors: Oreste Pezzi, F. Valentini, D. Perrone, Pierluigi VeltriAbstract:The problem of collisions in a plasma is a wide subject with a huge historical literature. The description of realistic plasmas is a tough problem to attac h, both from the theoretical and the numerical point of view. In fact the Landau operator [1], that describes Coulomb interactions, is nonlinear in nature and multi-dimensional. In order to overcome these difficulties, some analytical results have been obtained by approximating the original Landau integral by simplified differential operators in reduced dimensionality. We present here a Eulerian time-splitting algorithm [2] for the study of the propagation of electrostatic waves in Collisional plasmas. At first we focu s on one-dimensional operators of the Fokker-Planck type in 1D 1V phase space (1D in physical space, 1D in velocity space). The accuracy of the numerical code is discussed by comparing the numerical results to the analytical predictions obtained in some limit cases when trying to evaluate the effects of collisions in the phenomenon of wave plasma echo and Collisional dissipation of Bernstein-Greene-Kruskal waves. Particular attention is devoted to the study of the nonlinea r Dougherty Collisional operator, recently used to describe the Collisional dissipation of electron pl asma waves in a pure electron plasma column [3]. A receipt to prevent the filamentation problem in Eulerian algorithms is provided by exploiting the property of velocity diffusion operators to smooth out small velocity scales. Finally we show the effects of the whole Landau operator on the propagation of plasma waves by implementing an algorithm in 1D 3V phase space. In order to evaluate the Landau Collisional integral Pareschi et al. [2] proposed a spectral method in velocity space based on the use of Fast Fourier Transform (FFT) routines. Despite the usual reduction of the computation cost that one obtains using FFT routines, these authors needed to periodize the distribution function in the velocity domain as well as the Landau operator, thus introducing unphysical effects of fake binary collisions. Instead here we model collisions through the di rect evaluation of the Landau Collisional integral in velocity space.
J E Colwell - One of the best experts on this subject based on the ideXlab platform.
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Collisional erosion in the primordial edgeworth kuiper belt and the generation of the 30 50 au kuiper gap
The Astrophysical Journal, 1997Co-Authors: Alan S Stern, J E ColwellAbstract:One of the oustanding questions about the architecture of the outer solar system is how the trans-Neptunian disk of comets and small planet-scale objects known as the solar system's Edgeworth-Kuiper Belt (EKB) originated and evolved to its present mass and architecture. Applying a time-dependent model of collisonal evolution of the EKB, we find that under a wide range of assumptions, Collisional evolution should have depleted the mass of the 30-50 AU zone by >90% early in the history of the solar system, thereby creating a deep scar or gap in the surface mass density across a wide region beyond Neptune, much like what is observed today. Dynamical erosion may have further accelerated the depletion process. Given the fact that Neptune has had far less dynamical influence beyond 50 AU, our results also suggest that unless the solar nebula was truncated near 50 AU, then surface mass density of solids somewhere beyond ~50 AU may increase again, most likely dramatically.