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## Magnetic field amplification and evolution in turbulent collisionless magnetohydrodynamics: an application to the intracluster medium

Santos-Lima, R.; Pino, Elisabete Maria de Gouveia Dal; Kowal, Grzegorz; Gonçalves, Diego Antonio Falceta; Lazarian, A.; Nakwacki, M. S.
Fonte: American Astronomical Society; Chicago Publicador: American Astronomical Society; Chicago
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
36.35%
The amplification of magnetic fields (MFs) in the intracluster medium (ICM) is attributed to turbulent dynamo (TD) action, which is generally derived in the collisional-MHD framework. However, this assumption is poorly justified a priori, since in the ICM the ion mean free path between collisions is of the order of the dynamical scales, thus requiring a collisionless MHD description. The present study uses an anisotropic plasma pressure that brings the plasma within a parametric space where collisionless instabilities take place. In this model, a relaxation term of the pressure anisotropy simulates the feedback of the mirror and firehose instabilities, in consistency with empirical studies.Our three-dimensional numerical simulations of forced transonic turbulence, aiming themodeling of the turbulent ICM, were performed for different initial values of the MF intensity and different relaxation rates of the pressure anisotropy. We found that in the high-β plasma regime corresponding to the ICM conditions, a fast anisotropy relaxation rate gives results that are similar to the collisional-MHD model, as far as the statistical properties of the turbulence are concerned. Also, the TD amplification of seed MFs was found to be similar to the collisional-MHD model. The simulations that do not employ the anisotropy relaxation deviate significantly from the collisional-MHD results and show more power at the small-scale fluctuations of both density and velocity as a result of the action of the instabilities. For these simulations...

## Magnetohydrodynamics in solar and space physics

Gomez, Daniel Osvaldo; Martin, Luis Nicolas; Dmitruk, Pablo Ariel
Fonte: Elsevier Publicador: Elsevier
Tipo: info:eu-repo/semantics/article; info:ar-repo/semantics/artículo; info:eu-repo/semantics/publishedVersion Formato: application/pdf
ENG
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36.49%
Because of its proximity, our Sun provides a unique opportunity to perform high resolution observations of its outer layers throughout the whole electromagnetic spectrum. We can also theoretically model most of the fascinating physical phenomena taking place on the Sun, as well as their impact on the solar system. Many of these phenomena can be properly studied within the framework of magnetohydrodynamics. More specifically, we assume a fully ionized hydrogen plasma and adopt the more comprehensive two-fluid magnetohydrodynamic approximation. For problems such as the solar wind or magnetic loops in the solar corona, which are shaped by a relatively strong mean magnetic field, the reduced magnetohydrodynamic approximation is often used. We will review the basic features of both two-fluid and one-fluid magnetohydrodynamics, and focus on two particular applications: the turbulent heating of coronal active regions and the dynamics of the solar wind.; Fil: Gomez, Daniel Osvaldo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio(i); Argentina; Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentina;; Fil: Martin...

## Barotropic Magnetohydrodynamics as a Four Function Field Theory with Non-Trivial Topology and Aharonov-Bohm Effects

Yahalom, Asher
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
36.38%
Variational principles for magnetohydrodynamics were introduced by previous authors both in Lagrangian and Eulerian form. In previous works [1] Yahalom & Lynden-Bell and later Yahalom [2] introduced a simpler Eulerian variational principle from which all the relevant equations of Magnetohydrodynamics can be derived. The variational principles were given in terms of four independent functions for non-stationary flows and three independent functions for stationary flows. This is less than the seven variables which appear in the standard equations of magnetohydrodynamics which are the magnetic field, the velocity field and the density . In the case that the magnetohydrodynamic flow has a non trivial topology such as when the magnetic lines are knotted or magnetic and stream lines are knotted, some of the functions appearing in the Lagrangian are non-single valued. Those functions play the same rule as the phase in the Aharonov-Bohm celebrated effect [3].; Comment: 10 pages, 3 figures, submitted to MMT 2010

## A Four Function Variational Principle for Barotropic Magnetohydrodynamics

Yahalom, Asher
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
36.43%
Variational principles for magnetohydrodynamics were introduced by previous authors both in Lagrangian and Eulerian form. In a previous work Yahalom & Lynden-Bell introduced a simpler Eulerian variational principles from which all the relevant equations of magnetohydrodynamics can be derived. The variational principle was given in terms of six independent functions for non-stationary flows and three independent functions for stationary flows. This is less then the seven variables which appear in the standard equations of magnetohydrodynamics which are the magnetic field $\vec B$ the velocity field $\vec v$ and the density $\rho$. In this work I will improve on the previous results showing that non-stationary magnetohydrodynamics should be described by four functions .; Comment: 11 pages no figures

## Variational formulation of relaxed and multi-region relaxed magnetohydrodynamics

Dewar, Robert L.; Yoshida, Zensho; Bhattacharjee, Amitava; Hudson, Stuart R.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
36.55%
Ideal magnetohydrodynamics (IMHD) is strongly constrained by an infinite number of microscopic constraints expressing mass, entropy and magnetic flux conservation in each infinitesimal fluid element, the latter preventing magnetic reconnection. By contrast, in the Taylor relaxation model for formation of macroscopically self-organized plasma equilibrium states, all these constraints are relaxed save for global magnetic fluxes and helicity. A Lagrangian variational principle is presented that leads to a new, fully dynamical, \emph{relaxed magnetohydrodynamics} (RxMHD), such that all static solutions are Taylor states but also allows flow. By postulating that some long-lived macroscopic current sheets can act as barriers to relaxation, separating the plasma into multiple relaxation regions, a further generalization, \emph{multi-region relaxed magnetohydrodynamics} (MRxMHD) is developed.; Comment: 21 pages, 2 figures

## Plasma Relaxation and Topological Aspects in Hall Magnetohydrodynamics

Shivamoggi, B. K.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
36.35%
Parker's formulation of isotopological plasma relaxation process in magnetohydrodynamics (MHD) is extended to Hall MHD. The torsion coefficient alpha in the Hall MHD Beltrami condition turns out now to be proportional to the "potential vorticity." The Hall MHD Beltrami condition becomes equivalent to the "potential vorticity" conservation equation in two-dimensional (2D) hydrodynamics if the Hall MHD Lagrange multiplier beta is taken to be proportional to the "potential vorticity" as well. The winding pattern of the magnetic field lines in Hall MHD then appears to evolve in the same way as "potential vorticity" lines in 2D hydrodynamics.

## Minimum energy states of the plasma pinch in standard and Hall magnetohydrodynamics

Khalzov, I. V.; Ebrahimi, F.; Schnack, D. D.; Mirnov, V. V.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
36.35%
Axisymmetric relaxed states of a cylindrical plasma column are found analytically in both standard and Hall magnetohydrodynamics (MHD) by complete minimization of energy with constraints imposed by invariants inherent in corresponding models. It is shown that the relaxed state in Hall MHD is the force-free magnetic field with uniform axial flow and/or rigid azimuthal rotation. The relaxed states in standard MHD are more complex due to the coupling between velocity and magnetic field. Application of these states for reversed-field pinches (RFP) is discussed.

## Variational Integrators in Plasma Physics

Kraus, Michael
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
36.41%
Variational integrators are a special kind of geometric discretisation methods applicable to any system of differential equations that obeys a Lagrangian formulation. In this thesis, variational integrators are developed for several important models of plasma physics: guiding centre dynamics (particle dynamics), the Vlasov-Poisson system (kinetic theory), and ideal magnetohydrodynamics (plasma fluid theory). Special attention is given to physical conservation laws like conservation of energy and momentum. Most systems in plasma physics do not possess a Lagrangian formulation to which the variational integrator methodology is directly applicable. Therefore the theory is extended towards nonvariational differential equations by linking it to Ibragimov's theory of integrating factors and adjoint equations. It allows us to find a Lagrangian for all ordinary and partial differential equations and systems thereof. Consequently, the applicability of variational integrators is extended to a much larger family of systems than envisaged in the original theory. This approach allows for the application of Noether's theorem to analyse the conservation properties of the system, both at the continuous and the discrete level. In numerical examples...

## Variational Integrators for Reduced Magnetohydrodynamics

Kraus, Michael; Tassi, Emanuele; Grasso, Daniela
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
36.38%
Reduced magnetohydrodynamics is a simplified set of magnetohydrodynamics equations with applications to both fusion and astrophysical plasmas, possessing a noncanonical Hamiltonian structure and consequently a number of conserved functionals. We propose a new discretisation strategy for these equations based on a discrete variational principle applied to a formal Lagrangian. The resulting integrator preserves important quantities like the total energy, magnetic helicity and cross helicity exactly (up to machine precision). As the integrator is free of numerical resistivity, spurious reconnection along current sheets is absent in the ideal case. If effects of electron inertia are added, reconnection of magnetic field lines is allowed, although the resulting model still possesses a noncanonical Hamiltonian structure. After reviewing the conservation laws of the model equations, the adopted variational principle with the related conservation laws are described both at the continuous and discrete level. We verify the favourable properties of the variational integrator in particular with respect to the preservation of the invariants of the models under consideration and compare with results from the literature. In the case of reduced magnetohydrodynamics with electron inertia effects...

## Quantum Magnetohydrodynamics

Haas, Fernando
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
36.38%
The quantum hydrodynamic model for charged particle systems is extended to the cases of non zero magnetic fields. In this way, quantum corrections to magnetohydrodynamics are obtained starting from the quantum hydrodynamical model with magnetic fields. The quantum magnetohydrodynamics model is analyzed in the infinite conductivity limit. The conditions for equilibrium in ideal quantum magnetohydrodynamics are established. Translationally invariant exact equilibrium solutions are obtained in the case of the ideal quantum magnetohydrodynamic model.; Comment: 2 figures

## Emergence of High Peaks in the Axial Velocity for an Ideal Magnetohydrodynamics Disk Configuration

Montani, Giovanni; Carlevaro, Nakia
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
36.41%
We study the profile of a thin disk configuration as described by an axisymmetric ideal magnetohydrodynamics steady equilibrium. We consider the disk like a differentially rotating system dominated by the Keplerian term, but allowing for a non-zero radial and vertical matter flux. As a result, the steady state allows for the existence of local peaks for the vertical velocity of the plasma particles, though it prevents the radial matter accretion rate. This ideal magnetohydrodynamics scheme is therefore unable to solve the angular momentum-transport problem, but we suggest that it provides a mechanism for the generation of matter-jet seeds.; Comment: 8 pages, 1 figure

## Propagation of Electromagnetic Waves in Resistive Pair Plasma and Causal Relativistic Magnetohydrodynamics

Koide, Shinji
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
36.41%
We investigate the propagation of electromagnetic waves in resistive pair plasmas using a onefluid theory derived from the relativistic two-fluid equations. When the resistivity normalized by the electron/positron inertia variable exceeds a critical value, the dispersion relation for electromagnetic waves shows that the group velocity is larger than the light speed in vacuum. However, in such a case, it also is found that the plasma parameter is less than unity: that is, the electron-positron pair medium no longer can be treated as plasma. Thus the simple two-fluid approximation is invalid. This confirms that superluminal propagation of electromagnetic wave is forbidden in a plasma -- a conclusion consistent with the relativistic principle of causality. As an alternative, we propose a new set of equations for causal relativistic magnetohydrodynamics", which both have non-zero resistivity and yet are consistent with the causality principle.; Comment: to be published in Physical Review D

## Exact Solutions of the Self-consistent System of Relativistic Magnetohydrodynamics Equations for an Anisotropic Plasma on the Background of Bondi-Pirani-Robinson's Metric

Ignatyev, Yurii; Agathonov, Alexander
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
36.38%
Exact solutions of the self-consistent relativistic magnetohydrodynamics equations for an anisotropic magnetized plasma on the background of Bondi-Pirani-Robinson's vacuum plane gravitational wave (PGW) metric with an arbitrary polarization are obtained, which generalize the results obtained earlier by one of the authors for the transverse polarization of a gravitational wave. Based on the reformulated energobalance equation it is shown that in the linear approximation by gravitational wave amplitude only the transverse polarization of PGW interacts with magnetized plasma.; Comment: 20 pages

## Multi-region relaxed magnetohydrodynamics with anisotropy and flow

Dennis, Graham R.; Hudson, Stuart R.; Dewar, Robert L.; Hole, Matthew J.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
36.38%
We present an extension of the multi-region relaxed magnetohydrodynamics (MRxMHD) equilibrium model that includes pressure anisotropy and general plasma flows. This anisotropic extension to our previous isotropic model is motivated by Sun and Finn's model of relaxed anisotropic magnetohydrodynamic equilibria. We prove that as the number of plasma regions becomes infinite, our anisotropic extension of MRxMHD reduces to anisotropic ideal MHD with flow. The continuously nested flux surface limit of our MRxMHD model is the first variational principle for anisotropic plasma equilibria with general flow fields.; Comment: 11 pages, 2 figures. arXiv admin note: text overlap with arXiv:1401.3076

## Parametric Instabilities in Shallow Water Magnetohydrodynamics Of Astrophysical Plasma in External Magnetic Field

Klimachkov, Dmitry; Petrosyan, Arakel
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
36.43%
This letter discusses rotating magnetohydrodynamics (MHD) of a thin layer of astrophysical plasma. To describe a thin plasma layer with a free surface in a vertical external magnetic field we use the shallow water ap- proximation. The presence of a vertical magnetic field essentially changed the wave processes dynamics in astrophysical plasma compared to the neu- tral uid and plasma layer in a thoroidal magnetic field. In present case thre are three-waves nonlinear interactions. Using the asymptotic mul- tiscale we deduced nonlinear wave packets interaction equations: three magneto-Poincare waves interaction, three magnetostrophic waves inter- action, the interaction of two magneto-Poincare and one magnetostrophic wave and two magnetostrophic and one magneto-Poincare wave interac- tion. The existence of decay instabilities and parametric amplifications is predicted. We found following four types of decay instabilities: magneto- Poincare wave decays into two magneto-Poincare waves, magnetostrophic wave decays into two magnetostrophic waves, magneto-Poincare wave de- cays into one magneto-Poincare wave and one magnetostrophic wave, magnetostrophic wave decays into one magnetostrophic wave and one magneto-Poincare wave. Also following mechanisms of parametric amplifications were found: parametric amplification of magneto-Poincare waves...

## Simplified Variational Principles for Barotropic Magnetohydrodynamics

Yahalom, Asher; Lynden-Bell, Donald
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
36.47%
Variational principles for magnetohydrodynamics were introduced by previous authors both in Lagrangian and Eulerian form. In this paper we introduce simpler Eulerian variational principles from which all the relevant equations of barotropic magnetohydrodynamics can be derived. The variational principle is given in terms of six independent functions for non-stationary barotropic flows and three independent functions for stationary barotropic flows. This is less then the seven variables which appear in the standard equations of barotropic magnetohydrodynamics which are the magnetic field $\vec B$ the velocity field $\vec v$ and the density $\rho$. The equations obtained for non-stationary barotropic magnetohydrodynamics resemble the equations of Frenkel, Levich & Stilman \cite{FLS}. The connection between the Hamiltonian formalism introduced in \cite{FLS} and the present Lagrangian formalism (with Eulerian variables) will be discussed. Finally the relations between barotropic magnetohydrodynamics topological constants and the functions of the present formalism will be elucidated.; Comment: 37 pages, 3 figures

## Duality Invariant Magnetohydrodynamics And Dyons

Coceal, Omduth; Sabra, Wafic A.; Thomas, Steven
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
36.35%
The theory of magnetohydrodynamics is extended to the cases of a plasma of separate magnetic and electric charges, as well as to a plasma of dyons respectively. In both these cases the system possesses electric-magnetic duality symmetry. In the former case we find that because of the existence of two independent generalized Ohm's law equations, the limit of infinite electric and magnetic conductivity results in the vanishing of both electric and magnetic fields, as well as the corresponding currents. In the dyonic case, we find that the resulting duality-invariant system of equations are equivalent to those of ordinary MHD, after suitable field redefinitions.; Comment: 11 pages, latex

## Simplified Variational Principles for non-Barotropic Magnetohydrodynamics

Yahalom, Asher
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
36.38%
Variational principles for magnetohydrodynamics were introduced by previous authors both in Lagrangian and Eulerian form. In this paper we introduce simpler Eulerian variational principles from which all the relevant equations of non-barotropic magnetohydrodynamics can be derived. The variational principle is given in terms of five independent functions for non-stationary barotropic flows. This is less then the eight variables which appear in the standard equations of barotropic magnetohydrodynamics which are the magnetic field $\vec B$ the velocity field $\vec v$, the entropy $s$ and the density $\rho$.; Comment: 16 pages. arXiv admin note: substantial text overlap with arXiv:physics/0603115, arXiv:0811.2309

## Hamiltonian Magnetohydrodynamics: Lagrangian, Eulerian, and Dynamically Accessible Stability - Theory

Andreussi, T.; Morrison, P. J.; Pegoraro, F.
Tipo: Artigo de Revista Científica