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## Multifractality in plasma edge electrostatic turbulence

Fonte: AMER INST PHYSICS; NEW YORK
Publicador: AMER INST PHYSICS; NEW YORK

Tipo: Artigo de Revista Científica

ENG

Relevância na Pesquisa

45.85%

#TIME CORRELATIONS#DRIFT WAVES#TRANSPORT#RANGE#RECURRENCE#TOKAMAK#INTERMITTENCY#STATISTICS#WAVELETS#DEVICES#Physics, Fluids & Plasmas

Plasma edge turbulence in Tokamak Chauffage Alfven Bresilien (TCABR) [R. M. O. Galvao et al., Plasma Phys. Contr. Fusion 43, 1181 (2001)] is investigated for multifractal properties of the fluctuating floating electrostatic potential measured by Langmuir probes. The multifractality in this signal is characterized by the full multifractal spectra determined by applying the wavelet transform modulus maxima. In this work, the dependence of the multifractal spectrum with the radial position is presented. The multifractality degree inside the plasma increases with the radial position reaching a maximum near the plasma edge and becoming almost constant in the scrape-off layer. Comparisons between these results with those obtained for random test time series with the same Hurst exponents and data length statistically confirm the reported multifractal behavior. Moreover, the persistence of these signals, characterized by their Hurst exponent, present radial profile similar to the deterministic component estimated from analysis based on dynamical recurrences. (C) 2008 American Institute of Physics.

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## Possible states in the flow around two circular cylinders in tandem with separations in the vicinity of the drag inversion spacing

Fonte: AMER INST PHYSICS
Publicador: AMER INST PHYSICS

Tipo: Artigo de Revista Científica

ENG

Relevância na Pesquisa

45.85%

#drag#external flows#flow instability#flow separation#flow simulation#numerical analysis#vortices#ARRANGEMENTS#WAKE#3-DIMENSIONALITY#INTERFERENCE

The possible states in the flow around two identical circular cylinders in tandem arrangements are investigated for configurations in the vicinity of the drag inversion separation. By means of numerical simulations, the hysteresis in the transition between the shedding regimes is studied and the relationship between (three-dimensional) secondary instabilities and shedding regime determination is addressed. The differences observed in the behavior of two- and three-dimensional flows are analyzed, and the regions of bistable flow are delimited. Very good agreement is found between the proposed scenario and results available in the literature. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3420111]; CAPES-Brazil; FAPESP; CNPq; Finep; Petrobras; EPSRC-GB

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## Analytical solutions for Tokamak equilibria with reversed toroidal current

Fonte: AMER INST PHYSICS
Publicador: AMER INST PHYSICS

Tipo: Artigo de Revista Científica

ENG

Relevância na Pesquisa

45.85%

#plasma magnetohydrodynamics#plasma toroidal confinement#plasma transport processes#Tokamak devices#SHEAR#Physics, Fluids & Plasmas

In tokamaks, an advanced plasma confinement regime has been investigated with a central hollow electric current with negative density which gives rise to non-nested magnetic surfaces. We present analytical solutions for the magnetohydrodynamic equilibria of this regime in terms of non-orthogonal toroidal polar coordinates. These solutions are obtained for large aspect ratio tokamaks and they are valid for any kind of reversed hollow current density profiles. The zero order solution of the poloidal magnetic flux function describes nested toroidal magnetic surfaces with a magnetic axis displaced due to the toroidal geometry. The first order correction introduces a poloidal field asymmetry and, consequently, magnetic islands arise around the zero order surface with null poloidal magnetic flux gradient. An analytic expression for the magnetic island width is deduced in terms of the equilibrium parameters. We give examples of the equilibrium plasma profiles and islands obtained for a class of current density profile. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3624551]; Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES); CNPq; FAPESP

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## Alfveacuten continuum deformation by kinetic geodesic effect in rotating tokamak plasmas

Fonte: AMER INST PHYSICS
Publicador: AMER INST PHYSICS

Tipo: Artigo de Revista Científica

ENG

Relevância na Pesquisa

56.06%

#plasma Alfven waves#plasma instability#plasma ion acoustic waves#plasma kinetic theory#plasma magnetohydrodynamics#plasma temperature#plasma toroidal confinement#Tokamak devices#Vlasov equation#MODES#WAVES

Using a quasitoroidal set of coordinates with coaxial circular magnetic surfaces, Vlasov equation is solved for collisionless plasmas in drift approach and a perpendicular dielectric tensor is found for large aspect ratio tokamaks in a low frequency band. Taking into account plasma rotation and charge separation parallel electric field, it is found that an ion geodesic effect deform Alfveacuten wave continuum producing continuum minimum at the rational magnetic surfaces, which depends on the plasma rotation and poloidal mode numbers. In kinetic approach, the ion thermal motion defines the geodesic effect but the mode frequency also depends on electron temperature. A geodesic ion Alfveacuten mode predicted below the continuum minimum has a small Landau damping in plasmas with Maxwell distribution but the plasma rotation may drive instability.; CNPq; (CNPq) National Council of Brazil for Science and Technology Development

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## Bicoherence in electrostatic turbulence driven by high magnetohydrodynamic activity in Tokamak Chauffage Alfven Bresilien

Fonte: AMER INST PHYSICS
Publicador: AMER INST PHYSICS

Tipo: Artigo de Revista Científica

ENG

Relevância na Pesquisa

45.98%

#SCRAPE-OFF LAYER#PLASMA EDGE TURBULENCE#DRIFT WAVES#PHASE SYNCHRONIZATION#BISPECTRAL ANALYSIS#RECURRENCE PLOTS#TOROIDAL PLASMA#FUSION PLASMAS#TCABR TOKAMAK#MODE#Physics, Fluids & Plasmas

During some discharges in Tokamak Chauffage Alfven Bresilien [R. M. O. Galvao et al., Plasma Phys. Controlled Fusion 43, 1181 (2001)] high magnetohydrodynamic activity may appear with a peaked frequency spectrum. Whenever this peak occurs, the ambient broadband electrostatic turbulence is remarkably modified, synchronizing into the dominant magnetic fluctuation frequency and presenting high bicoherence in the whole plasma edge with a maximum bicoherence inside the plasma. A phenomenological model is introduced to investigate this driven turbulence bicoherence, consisting of nonlinearly coupled phase-randomized drift modes with time-periodic external driving at the dominant magnetic fluctuation frequency. The bicoherence spectrum of this model can mimic features of the experimental results. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3099701]; FAPESP; CNPq; Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES); FINEP/CNEN

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## Kinetic ion effect on geodesic acoustic Alfven modes in tokamaks

Fonte: AMER INST PHYSICS
Publicador: AMER INST PHYSICS

Tipo: Artigo de Revista Científica

ENG

Relevância na Pesquisa

45.95%

#plasma Alfven waves#plasma toroidal confinement#Tokamak devices#Vlasov equation#Physics, Fluids & Plasmas

Using a quasitoroidal set of coordinates with coaxial circular magnetic surfaces, the Vlasov equation is solved for collisionless plasmas, and the dielectric tensor is found for large aspect ratio tokamaks in a low frequency band. Taking into account q-profile and charge separation parallel electric field, it is found that the Alfven wave continuum is deformed by ion geodesic effects producing continuum minimum at the rational magnetic surfaces. Low frequency geodesic ion induced Alfven waves are found below the continuum minimum where collisionless damping has a gap for Maxwell distribution. In kinetic approach, the ion thermal motion defines the geodesic effect but the mode frequency is strongly corrected due to parallel motion of electrons.; CNPq (National Council of Brazil for Science and Technology Development)

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## Kinetic effect on low frequency Alfven continuum in tokamaks

Fonte: AMER INST PHYSICS
Publicador: AMER INST PHYSICS

Tipo: Artigo de Revista Científica

ENG

Relevância na Pesquisa

46.05%

Using a quasi-toroidal set of coordinates in plasmas with coaxial circular magnetic surfaces, the Vlasov equation is solved, and dielectric tensor is found for large aspect ratio tokamaks in a low frequency band. Taking into account the q-profile and drift effects, Alfven wave continuum deformation by geodesic effects is analyzed. It is shown that the Alfven continuum has a minimum defined by the ion thermal velocity at the rational magnetic surfaces q(s)=-M/N, where M and N are the poloidal and toroidal mode numbers, respectively, and the parallel wave number is zero. Low frequency global Alfven waves are found below the continuum minimum. In hot ion plasmas, the geodesic term changes sign, provoking some deformation of Alfven velocity by a factor (1+q(2))(-1/2), and the continuum minimum disappears. (C) 2008 American Institute of Physics.

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## Nonaxisymmetric magnetorotational instability in ideal and viscous plasmas

Fonte: AMER INST PHYSICS
Publicador: AMER INST PHYSICS

Tipo: Artigo de Revista Científica

ENG

Relevância na Pesquisa

56.14%

#WEAKLY MAGNETIZED DISKS#LOCAL SHEAR INSTABILITY#CYLINDRICAL PLASMA#ACCRETION DISKS#STABILITY#FLOWS#EQUILIBRIUM#GEOMETRY#Physics, Fluids & Plasmas

The excitation of magnetorotational instability (MRI) in rotating laboratory plasmas is investigated. In contrast to astrophysical plasmas, in which gravitation plays an important role, in laboratory plasmas it can be neglected and the plasma rotation is equilibrated by the pressure gradient. The analysis is restricted to the simple model of a magnetic confinement configuration with cylindrical symmetry, in which nonaxisymmetric perturbations are investigated using the local approximation. Starting from the simplest case of an ideal plasma, the corresponding dispersion relations are derived for more complicated models including the physical effects of parallel and perpendicular viscosities. The Friemann-Rotenberg approach used for ideal plasmas is generalized for the viscous model and an analytical expression for the instability boundary is obtained. It is shown that, in addition to the standard effect of radial derivative of the rotation frequency (the Velikhov effect), which can be destabilizing or stabilizing depending on the sign of this derivative in the ideal plasma, there is a destabilizing effect proportional to the fourth power of the rotation frequency, or, what is the same, to the square of the plasma pressure gradient, and to the square of the azimuthal mode number of the perturbations. It is shown that the instability boundary also depends on the product of the plasma pressure and density gradients...

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## Identification of geodesic chirping Alfven modes and q-factor estimation in hot core tokamak plasmas in ASDEX Upgrade

Fonte: IOP PUBLISHING LTD
Publicador: IOP PUBLISHING LTD

Tipo: Artigo de Revista Científica

ENG

Relevância na Pesquisa

46.02%

Alfven eigenmodes (AE) driven by ion cyclotron resonance heating are usually registered by different diagnostic channels in the hot core plasmas of large tokamaks like JET and ASDEX Upgrade. These AE appear very near to the extremum points of Alfven wave continuum, which is modified by the geodesic effect due to poloidal mode coupling. It is shown that the AE spectrum may be explored as the magnetic spectroscopy (like Alfven cascades by Sharapov et al 2001 Phys. Lett. A 289 127) to determine the q-factor minimum and geodesic frequency at the magnetic axis in standard sawtoothed discharges without reversed shear.; CNPq (National Council of Brazil for Science and Technology Development); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

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## Rotation effect on geodesic and zonal flow modes in tokamak plasmas with isothermal magnetic surfaces

Fonte: IOP PUBLISHING LTD
Publicador: IOP PUBLISHING LTD

Tipo: Artigo de Revista Científica

ENG

Relevância na Pesquisa

46.09%

The electrostatic geodesic mode oscillations are investigated in rotating large aspect ratio tokamak plasmas with circular isothermal magnetic surfaces. The analysis is carried out within the magnetohydrodynamic model including heat flux to compensate for the non-adiabatic pressure distribution along the magnetic surfaces in plasmas with poloidal rotation. Instead of two standard geodesic modes, three geodesic continua are found. The two higher branches of the geodesic modes have a small frequency up-shift from ordinary geodesic acoustic and sonic modes due to rotation. The lower geodesic continuum is a newzonal flowmode (geodesic Doppler mode) in plasmas with mainly poloidal rotation. Limits to standard geodesic modes are found. Bifurcation of Alfven continuum by geodesic modes at the rational surfaces is also discussed. Due to that, the frequency of combined geodesic continuum extends from the poloidal rotation frequency to the ion-sound band that can have an important role in suppressing plasma turbulence.; Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); CNPq (National Council of Brazil for Science and Technology Development); Financiadora de Estudos e Projetos (FINEP); FINEP (Financiadora de Estudos e Projetos)

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## Anisotropy of thermal stresses in confined dusty plasmas

Fonte: IOP PUBLISHING LTD
Publicador: IOP PUBLISHING LTD

Tipo: Artigo de Revista Científica

ENG

Relevância na Pesquisa

45.97%

#COLLISIONAL PLASMA#VARIABLE CHARGES#PARTICLES#WAVES#DISCHARGES#ROTATION#SHEATH#Physics, Fluids & Plasmas

Anisotropy of thermal stresses in confined dusty plasmas is considered. It is shown that in a multi-component low-temperature plasma containing electrons, ions and dust, the complicated dependence of the ion viscosity on ion temperature gradients leads to a plasma equilibrium state with anisotropic pressure. This pressure anisotropy can be of the order of the ion pressure in some limiting cases, in which the ion Larmor radius or the ion mean free path are of the order of the characteristic length of the plasma nonuniformity. For a sufficiently large dust number density, they contribute to the plasma pressure anisotropy and to its spatial dependence. Currently, it is not yet clear whether this equilibrium state is stable or not. Under these conditions, some convective plasma flows can arise in confinement devices. Therefore, this question needs special consideration.

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## Effective transport barriers in nontwist systems

Fonte: AMER PHYSICAL SOC; COLLEGE PK
Publicador: AMER PHYSICAL SOC; COLLEGE PK

Tipo: Artigo de Revista Científica

ENG

Relevância na Pesquisa

46.06%

In fluids and plasmas with zonal flow reversed shear, a peculiar kind of transport barrier appears in the shearless region, one that is associated with a proper route of transition to chaos. These barriers have been identified in symplectic nontwist maps that model such zonal flows. We use the so-called standard nontwist map, a paradigmatic example of nontwist systems, to analyze the parameter dependence of the transport through a broken shearless barrier. On varying a proper control parameter, we identify the onset of structures with high stickiness that give rise to an effective barrier near the broken shearless curve. Moreover, we show how these stickiness structures, and the concomitant transport reduction in the shearless region, are determined by a homoclinic tangle of the remaining dominant twin island chains. We use the finite-time rotation number, a recently proposed diagnostic, to identify transport barriers that separate different regions of stickiness. The identified barriers are comparable to those obtained by using finite-time Lyapunov exponents.; FAPESP; FAPESP; CNPq; CNPq; CAPES; CAPES; MCT/CNEN (Rede Nacional de Fusao); MCT/CNEN (Rede Nacional de Fusao); Fundacao Araucaria; Fundacao Araucaria; US Department of Energy; US Department of Energy [DE-FG05-80ET-53088]

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## Shearless transport barriers in magnetically confined plasmas

Fonte: IOP PUBLISHING LTD; BRISTOL
Publicador: IOP PUBLISHING LTD; BRISTOL

Tipo: Artigo de Revista Científica

ENG

Relevância na Pesquisa

46.06%

#FIELD LINES#CHAOTIC TRANSPORT#TOKAMAKS#STOCHASTICITY#HELIMAK#SYSTEMS#WAVES#MODEL#PHYSICS, FLUIDS & PLASMAS#PHYSICS, NUCLEAR

Shearless transport barriers appear in confined plasmas due to non-monotonic radial profiles and cause localized reduction of transport even after they have been broken. In this paper we summarize our recent theoretical and experimental research on shearless transport barriers in plasmas confined in toroidal devices. In particular, we discuss shearless barriers in Lagrangian magnetic field line transport caused by non-monotonic safety factor profiles. We also discuss evidence of particle transport barriers found in the TCABR Tokamak (University of Sao Paulo) and the Texas Helimak (University of Texas at Austin) in biased discharges with non-monotonic plasma flows.; US Department of Energy [DE-FG05-80ET-53088]

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## Non-linear magnetohydrodynamic simulations of density evolution in Tore Supra sawtoothing plasmas

Fonte: AMER INST PHYSICS; MELVILLE
Publicador: AMER INST PHYSICS; MELVILLE

Tipo: Artigo de Revista Científica

ENG

Relevância na Pesquisa

56.09%

#HIGH-TEMPERATURE PLASMAS#X-RAY TOMOGRAPHY#INTERNAL KINK#MAGNETIC RECONNECTION#M=1 RECONNECTION#TOKAMAK PLASMAS#OSCILLATIONS#DYNAMICS#COLLAPSE#MODE#PHYSICS, FLUIDS & PLASMAS

The plasma density evolution in sawtooth regime on the Tore Supra tokamak is analyzed. The density is measured using fast-sweeping X-mode reflectometry which allows tomographic reconstructions. There is evidence that density is governed by the perpendicular electric flows, while temperature evolution is dominated by parallel diffusion. Postcursor oscillations sometimes lead to the formation of a density plateau, which is explained in terms of convection cells associated with the kink mode. A crescent-shaped density structure located inside q = 1 is often visible just after the crash and indicates that some part of the density withstands the crash. 3D full MHD nonlinear simulations with the code XTOR-2F recover this structure and show that it arises from the perpendicular flows emerging from the reconnection layer. The proportion of density reinjected inside the q = 1 surface is determined, and the implications in terms of helium ash transport are discussed. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4766893]; European Communities; European Communities

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## Dynamical analysis of turbulence in fusion plasmas and nonlinear waves

Fonte: ELSEVIER SCIENCE BV; AMSTERDAM
Publicador: ELSEVIER SCIENCE BV; AMSTERDAM

Tipo: Artigo de Revista Científica

ENG

Relevância na Pesquisa

46.29%

#TURBULENCE#FLUIDS#PLASMAS#NONLINEAR WAVES#CHAOS#TOKAMAKS#ACTION PRINCIPLE FORMULATIONS#SELF-SUSTAINING PROCESS#SCRAPE-OFF LAYER#EDGE TURBULENCE#DRIFT WAVES

Turbulence is one of the key problems of classical physics, and it has been the object of intense research in the last decades in a large spectrum of problems involving fluids, plasmas, and waves. In order to review some advances in theoretical and experimental investigations on turbulence a mini-symposium on this subject was organized in the Dynamics Days South America 2010 Conference. The main goal of this mini-symposium was to present recent developments in both fundamental aspects and dynamical analysis of turbulence in nonlinear waves and fusion plasmas. In this paper we present a summary of the works presented at this mini-symposium. Among the questions to be addressed were the onset and control of turbulence and spatio-temporal chaos. (C) 2011 Elsevier B. V. All rights reserved.; FAPESP; FAPESP; CNPq; CNPq; CAPES; CAPES; Fundacao Araucarias; Fundacao Araucarias; RNF-CNEN (Brazilian Fusion Network); RNFCNEN (Brazilian Fusion Network)

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## Turbulence driven particle transport in Texas Helimak

Fonte: AMER INST PHYSICS; MELVILLE
Publicador: AMER INST PHYSICS; MELVILLE

Tipo: Artigo de Revista Científica

ENG

Relevância na Pesquisa

45.98%

We analyze the turbulence driven particle transport in Texas Helimak [K. W. Gentle and H. He, Plasma Sci. Technol. 10, 284 (2008)], a toroidal plasma device with a one-dimensional equilibrium with magnetic curvature and shear. Alterations on the radial electric field, through an external voltage bias, change the spectral plasma characteristics inducing a dominant frequency for negative bias values and a broad band frequency spectrum for positive bias values. When applying a negative bias, the transport is high where the waves propagate with phase velocities near the plasma flow velocity, an indication that the transport is strongly affected by a wave particle resonant interaction. On the other hand, for positive bias values, the plasma has a reversed shear flow, and we observe that the transport is almost zero in the shearless radial region, an evidence of a transport barrier in this region. (c) 2012 American Institute of Physics. [doi:10.1063/1.3676607]; Brazilian agency CNPq; Brazilian agency CNPq; Brazilian agency CAPES; Brazilian agency CAPES; French agency CNRS; French agency CNRS; Brazilian agency FAPESP; Brazilian agency FAPESP

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## Self-duality of the asymptotic relaxation states of fluids and plasmas

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 08/08/2002

Relevância na Pesquisa

45.96%

The states of asymptotic relaxation of 2-dimensional fluids and plasma
present a high degree of regularity and obey to the sinh-Poisson equation. We
find that embedding the classical fluid description into a field-theoretical
framework, the same equation appears as a manifestation of the self-duality.; Comment: Latex 8 pages

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## Non-diffusive, non-local transport in fluids and plasmas

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 14/09/2010

Relevância na Pesquisa

56.11%

A review of non-diffusive transport in fluids and plasmas is presented. In
the fluid context, non-diffusive chaotic transport by Rossby waves in zonal
flows is studied following a Lagrangian approach. In the plasma physics context
the problem of interest is test particle transport in pressure-gradient-driven
plasma turbulence. In both systems the probability density function (PDF) of
particle displacements is strongly non-Gaussian and the statistical moments
exhibit super-diffusive anomalous scaling. Fractional diffusion models are
proposed and tested in the quantitative description of the non-diffusive
Lagrangian statistics of the fluid and plasma problems. Also, fractional
diffusion operators are used to construct non-local transport models exhibiting
up-hill transport, multivalued flux-gradient relations, fast pulse propagation
phenomena, and "tunneling" of perturbations across transport barriers.

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## Field theoretical approach to the description of the coherent structures in 2D fluids and plasmas

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

56.22%

Evolving from turbulent states the 2D fluids and the plasmas reach states
characterized by a high degree of order, consisting of few vortices. These
asymptotic states represent a small subset in the space of functions and are
characterised by properties that are difficult to identify in a direct
approach. The field theoretical approach to the dynamics and to the asymptotic
states of fluids and plasmas in 2D provides a considerable extension of the
usual perspective. The present works discusses a series of consequences of the
field theoretical approach, when it is applied to particular problems. The
discussion is developed around known physical problems: the current density
profiles in cylindrical plasma, the density pinch in tokamak and the
concentration of vorticity.; Comment: 64 pages, Latex and EPS figures included. New references added

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## Noether methods for fluids and plasmas

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 13/10/2004

Relevância na Pesquisa

56.06%

Two applications of the Noether method for fluids and plasmas are presented
based on the Euler-Lagrange and Euler-Poincare variational principles, which
depend on whether the dynamical fields are to be varied independently or not,
respectively. The relativistic cold laser-plasma equations, describing the
interaction between an intense laser field with a cold relativistic electron
plasma, provide a useful set of equations amenable to both variational
formulations. The derivation of conservation laws by Noether method proceeds
from the Noether equation, whose form depends on the variational formulation
used. As expected, the expressions for the energy-momentum conservation laws
are identical in both variational formulations. The connection between the two
Lagrangian densities is shown to involve the mass conservation and Lin
constraints associated with the cold relativistic electron fluid.; Comment: 16 pages

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