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

Fonte: American Astronomical Society; Chicago
Publicador: American Astronomical Society; Chicago

Tipo: Artigo de Revista Científica

ENG

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#galaxies: clusters: intracluster medium#magnetic fields#magnetohydrodynamics (MHD)#turbulence#AGLOMERADOS DE GALÁXIAS#CAMPO MAGNÉTICO#MAGNETOHIDRODINÂMICA#TURBULÊNCIA

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...

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## Magnetohydrodynamics in solar and space physics

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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#SPACE#SOLAR#TURBULENCE#MHD#MAGNETOHYDRODYNAMICS#SOLAR PHYSICS#SPACE PHYSICS#Astronomía#Ciencias Físicas#CIENCIAS NATURALES Y EXACTAS#Física de los Fluidos y Plasma

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...

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

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 21/05/2010

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36.38%

#Physics - Plasma Physics#Astrophysics - Solar and Stellar Astrophysics#Mathematical Physics#Quantum Physics

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

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## A Four Function Variational Principle for Barotropic Magnetohydrodynamics

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 14/11/2008

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36.43%

#Physics - Plasma Physics#Astrophysics#Mathematical Physics#Physics - Fluid Dynamics#Physics - Space Physics

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

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

Fonte: Universidade Cornell
Publicador: Universidade Cornell

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

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## Plasma Relaxation and Topological Aspects in Hall Magnetohydrodynamics

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

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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.

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

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 14/08/2010

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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.

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## Variational Integrators in Plasma Physics

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

36.41%

#Mathematics - Numerical Analysis#Mathematical Physics#Physics - Plasma Physics#65M06, 65P10, 35A15, 70S05, 70S10

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...

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## Variational Integrators for Reduced Magnetohydrodynamics

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 30/11/2015

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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...

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## Quantum Magnetohydrodynamics

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 02/03/2005

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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

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

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

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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

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

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 07/10/2008

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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

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

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 13/11/2010

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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

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## Multi-region relaxed magnetohydrodynamics with anisotropy and flow

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 30/04/2014

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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

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

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 06/12/2015

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#Astrophysics - Solar and Stellar Astrophysics#Physics - Fluid Dynamics#Physics - Plasma Physics#Physics - Space Physics

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...

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## Simplified Variational Principles for Barotropic Magnetohydrodynamics

Fonte: Universidade Cornell
Publicador: Universidade Cornell

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

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## Duality Invariant Magnetohydrodynamics And Dyons

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 29/03/1996

Relevância na Pesquisa

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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

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## Simplified Variational Principles for non-Barotropic Magnetohydrodynamics

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 29/09/2015

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

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

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 03/08/2013

Relevância na Pesquisa

36.35%

Stability conditions of magnetized plasma flows are obtained by exploiting
the Hamiltonian structure of the magnetohydrodynamics (MHD) equations and, in
particular, by using three kinds of energy principles. First, the Lagrangian
variable energy principle is described and sufficient stability conditions are
presented. Next, plasma flows are described in terms of Eulerian variables and
the noncanonical Hamiltonian formulation of MHD is exploited. For symmetric
equilibria, the energy-Casimir principle is expanded to second order and
sufficient conditions for stability to symmetric perturbation are obtained.
Then, dynamically accessible variations, i.e. variations that explicitly
preserve invariants of the system, are introduced and the respective energy
principle is considered. General criteria for stability are obtained, along
with comparisons between the three different approaches.

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## Multi-region relaxed magnetohydrodynamics with flow

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

36.47%

We present an extension of the multi-region relaxed magnetohydrodynamics
(MRxMHD) equilibrium model that includes plasma flow. This new model is a
generalization of Woltjer's model of relaxed magnetohydrodynamics equilibria
with flow. We prove that as the number of plasma regions becomes infinite our
extension of MRxMHD reduces to ideal MHD with flow. We also prove that some
solutions to MRxMHD with flow are not time-independent in the laboratory frame,
and instead have 3D structure which rotates in the toroidal direction with
fixed angular velocity. This capability gives MRxMHD potential application to
describing rotating 3D MHD structures such as 'snakes' and long-lived modes.; Comment: 11 pages, 2 figures

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