scholarly journals Hamiltonian magnetic reconnection with parallel electron heat flux dynamics

2015 ◽  
Vol 81 (5) ◽  
Author(s):  
D. Grasso ◽  
E. Tassi
Keyword(s):  
Heat Flux ◽  
Magnetic Reconnection ◽  
Magnetic Energy ◽  
Fluid Model ◽  
Temperature Fluctuations ◽  
Skin Depth ◽  
Density Fluctuations ◽  
Larmor Radius ◽  
Flux Dynamics ◽  
Isothermal Fluid

We analyse, both analytically and numerically, a two-dimensional six-field fluid model for collisionless magnetic reconnection, accounting for temperature and heat flux fluctuations along the direction of the magnetic guide field. We show that the model possesses a Hamiltonian structure with a non-canonical Poisson bracket. This bracket is characterized by the presence of six infinite families of Casimirs, associated with Lagrangian invariants. This reveals that the model can be reformulated as a system of advection equations, thus generalizing previous results obtained for Hamiltonian isothermal fluid models for reconnection. Numerical simulations indicate that the presence of heat flux and temperature fluctuations yields slightly larger growth rates and similar saturated island amplitudes, with respect to the isothermal models. For values of the sonic Larmor radius much smaller than the electron skin depth, heat flux fluctuations tend to be suppressed and temperature fluctuations follow density fluctuations. Increasing the sonic Larmor radius results in an increasing fraction of magnetic energy converted into heat flux, at the expense of temperature fluctuations. In particular, heat flux fluctuations tend to become relevant along the magnetic island separatrices. The qualitative structures associated with the electron field variables are also reinterpreted in terms of the rotation of the Lagrangian invariants of the system.

scholarly journals A reduced Landau-gyrofluid model for magnetic reconnection driven by electron inertia

2018 ◽  
Vol 84 (4) ◽  
Author(s):  
E. Tassi ◽  
D. Grasso ◽  
D. Borgogno ◽  
T. Passot ◽  
P. L. Sulem
Keyword(s):  
Kinetic Energy ◽  
Electron Temperature ◽  
Magnetic Reconnection ◽  
Magnetic Energy ◽  
Temperature Fluctuations ◽  
The Other ◽  
Landau Damping ◽  
Larmor Radius ◽  
Electron Inertia ◽  
Other Hand

An electromagnetic reduced gyrofluid model for collisionless plasmas, accounting for electron inertia, finite ion Larmor radius effects and Landau-fluid closures for the electron fluid is derived by means of an asymptotic expansion from a parent gyrofluid model. In the absence of terms accounting for Landau damping, the model is shown to possess a non-canonical Hamiltonian structure. The corresponding Casimir invariants are derived and use is made thereof, in order to obtain a set of normal field variables, in terms of which the Poisson bracket and the model equations take a remarkably simple form. The inclusion of perpendicular temperature fluctuations generalizes previous Hamiltonian reduced fluid models and, in particular, the presence of ion perpendicular gyrofluid temperature fluctuations reflects into the presence of two new Lagrangian invariants governing the ion dynamics. The model is applied, in the cold-ion limit, to investigate numerically a magnetic reconnection problem. The Landau damping terms are shown to reduce, by decreasing the electron temperature fluctuations, the linear reconnection rate and to delay the nonlinear island growth. The saturated island width, on the other hand, is independent of Landau damping. The fraction of magnetic energy converted into perpendicular kinetic energy also appears to be unaffected by the Landau damping terms, which, on the other hand, dissipate parallel kinetic energy as well as free energy due to density and electron temperature fluctuations.

ELECTRON PARALLEL COMPRESSIBILITY IN THE NONLINEAR DEVELOPMENT OF TWO-DIMENSIONAL COLLISIONLESS MAGNETOHYDRODYNAMIC RECONNECTION

2006 ◽  
Vol 20 (16) ◽  
pp. 931-961 ◽  
Author(s):  
DANIELE DEL SARTO ◽  
F. CALIFANO ◽  
F. PEGORARO
Keyword(s):  
Magnetic Reconnection ◽  
Fluid Model ◽  
Density Fluctuations ◽  
Larmor Radius ◽  
Small Scale ◽  
Two Dimensional ◽  
Guide Field ◽  
Fluid Instabilities ◽  
Two Fluid Model ◽  
Two Fluid

Some topological aspects of the magnetic reconnection phenomenon are summarized and recent numerical results, derived within a two-fluid model, of two-dimensional collisionless magnetic reconnection in presence of a strong guide field are reported. Both the Alfvèn and the whistler frequency range are investigated by including electron parallel compressibility effects that are related respectively to thermal effects and to density fluctuations. The Hamiltonian character of the system is emphasized as it drives the small scale dynamics through the presence of topological invariants. These determine the formation and the shape of small scale current and vorticity layers inside the magnetic island. Secondary fluid instabilities, mainly of the Kelvin–Helmholtz type, can destabilize these layers when a hydrodynamic type regime is achieved. The inclusion of parallel electron compressibility has stabilizing effects. In view of the limitations of the two-fluid modelling, possible developments are briefly discussed such as the inclusion of Larmor-radius corrections, in lieu of a fully kinetic approach.

scholarly journals An introductory guide to fluid models with anisotropic temperatures. Part 1. CGL description and collisionless fluid hierarchy

2019 ◽  
Vol 85 (6) ◽  
Author(s):  
P. Hunana ◽  
A. Tenerani ◽  
G. P. Zank ◽  
E. Khomenko ◽  
M. L. Goldstein ◽  
...  
Keyword(s):  
Heat Flux ◽  
Evolution Equations ◽  
Fluid Model ◽  
Maximum Growth ◽  
Maximum Growth Rate ◽  
Normal Closure ◽  
Larmor Radius ◽  
Order Moment ◽  
Fourth Moment ◽  
Fluid Models

We present a detailed guide to advanced collisionless fluid models that incorporate kinetic effects into the fluid framework, and that are much closer to the collisionless kinetic description than traditional magnetohydrodynamics. Such fluid models are directly applicable to modelling the turbulent evolution of a vast array of astrophysical plasmas, such as the solar corona and the solar wind, the interstellar medium, as well as accretion disks and galaxy clusters. The text can be viewed as a detailed guide to Landau fluid models and it is divided into two parts. Part 1 is dedicated to fluid models that are obtained by closing the fluid hierarchy with simple (non-Landau fluid) closures. Part 2 is dedicated to Landau fluid closures. Here in Part 1, we discuss the fluid model of Chew–Goldberger–Low (CGL) in great detail, together with fluid models that contain dispersive effects introduced by the Hall term and by the finite Larmor radius corrections to the pressure tensor. We consider dispersive effects introduced by the non-gyrotropic heat flux vectors. We investigate the parallel and oblique firehose instability, and show that the non-gyrotropic heat flux strongly influences the maximum growth rate of these instabilities. Furthermore, we discuss fluid models that contain evolution equations for the gyrotropic heat flux fluctuations and that are closed at the fourth-moment level by prescribing a specific form for the distribution function. For the bi-Maxwellian distribution, such a closure is known as the ‘normal’ closure. We also discuss a fluid closure for the bi-kappa distribution. Finally, by considering one-dimensional Maxwellian fluid closures at higher-order moments, we show that such fluid models are always unstable. The last possible non Landau fluid closure is therefore the ‘normal’ closure, and beyond the fourth-order moment, Landau fluid closures are required.

The scaling of reconnection rate in the two-fluid model of a collisionless forced magnetic reconnection

2013 ◽  
Vol 79 (5) ◽  
pp. 519-524 ◽  
Author(s):  
M. HOSSEINPOUR
Keyword(s):  
Magnetic Field ◽  
Magnetic Reconnection ◽  
Fluid Model ◽  
Skin Depth ◽  
Main Stage ◽  
Field Reversal ◽  
Two Fluid Model ◽  
Hall Reconnection ◽  
Forced Magnetic Reconnection ◽  
Two Fluid

AbstractThe two-fluid model of collisionless forced magnetic reconnection is considered where breaking the frozen-in flow constraint for magnetic field lines is provided by electron inertia. Following the Taylor problem, a tearing stable slab of plasma with a magnetic field reversal is subjected to a small-amplitude boundary perturbation that drives magnetic reconnection at the neutral surface within the plasma. It has been shown that unlike the resistive regime, where the two-fluid magnetohydrodynamics (MHD) description reduces to the single-fluid MHD regime at sufficiently small values of the ion inertial skin-depth, di ≡ c/ωpi (with ωpi as the ion plasma frequency), there is no room for the single-fluid MHD reconnection in the collisionless case, even at very small values of di. Meanwhile, contradictory to the resistive reconnection, the rate of collisionless Hall reconnection always decreases with time as reconnection proceeds. In particular, in the main stage of Hall reconnection, when transition between two main equilibria states are taking place, it scales as t−1/2.

scholarly journals Extended Magnetohydrodynamic Simulations of Decaying, Homogeneous, Approximately-Isotropic and Incompressible Turbulence

Fluids ◽  
2019 ◽  
Vol 4 (1) ◽  
pp. 46 ◽  
Author(s):  
Hideaki Miura
Keyword(s):  
Energy Transfer ◽  
Isotropic Turbulence ◽  
Magnetic Energy ◽  
Fluid Dynamic ◽  
Skin Depth ◽  
Wave Number ◽  
Larmor Radius ◽  
Mhd Turbulence ◽  
High Wave Number ◽  
Extended Mhd

Incompressible magnetohydrodynamic (MHD) turbulence under influences of the Hall and the gyro-viscous terms was studied by means of direct numerical simulations of freely decaying, homogeneous and approximately isotropic turbulence. Numerical results were compared among MHD, Hall MHD, and extended MHD models focusing on differences of Hall and extended MHD turbulence from MHD turbulence at a fully relaxed state. Magnetic and kinetic energies, energy spectra, energy transfer, vorticity and current structures were studied. The Hall and gyro-viscous terms change the energy transfer in the equations of motions to be forward-transfer-dominant while the magnetic energy transfer remains backward-transfer-dominant. The gyro-viscosity works as a kind of hyper-diffusivity, attenuating the kinetic energy spectrum sharply at a high wave-number region. However, this term also induces high-vorticity events more frequently than MHD turbulence, making the turbulent field more intermittent. Vortices and currents were found to be transformed from sheet to tubular structures under the influences of the Hall and/or the gyro-viscous terms. These observations highlight features of fluid-dynamic aspect of turbulence in sub-ion-scales where turbulence is governed by the ion skin depth and ion Larmor radius.

The scaling of collisionless magnetic reconnection in an electron–positron plasma with non-scalar pressure

2012 ◽  
Vol 79 (5) ◽  
pp. 473-477 ◽  
Author(s):  
M. HOSSEINPOUR ◽  
M. A. MOHAMMADI ◽  
S. BIABANI
Keyword(s):  
Magnetic Reconnection ◽  
Skin Depth ◽  
Larmor Radius ◽  
Anisotropic Pressure ◽  
Diffusion Region ◽  
Pair Plasma ◽  
Tearing Instability ◽  
Electron Positron ◽  
Sheet Width ◽  
Field Lines

AbstractCollisionless magnetic reconnection via tearing instability in non-relativistic electron–positron (pair) plasma with an anisotropic pressure is investigated. The equilibrium magnetic field is considered to be sheared force-free, and a set of linearized collisionless Magnetohydrodynamics equations describes the evolution of reconnection dynamics. A linear analytical analysis, based on scaling, demonstrates that in such a pair plasma, breaking the frozen in flow constraint for field lines can be mainly provided by the non-gyrotropic pressure of electrons and positrons (rather than the particle bulk inertia) when the current sheet width is smaller than the particle Larmor radius (Δx < rL). This condition is satisfied when β > d2 (d = c/ωp is the particle skin-depth with the electron/positron frequency ωp and β = 8πP(0)/B02 ⪡ 1). Meanwhile, on top of the Lorentz force and in the absence of the reconnection facilitating mechanism of the Hall effect, non-scalar pressure force can accelerate bulk plasma into the diffusion region at the scale lengths of the order of dx. Therefore, the respective regime of tearing instability proceeds much faster compared with the case of an isotropic pressure with a new dimensionless growth rate of (γτA) ~ d.

scholarly journals Ion and electron heating during magnetic reconnection in weakly collisional plasmas

2014 ◽  
Vol 81 (2) ◽  
Author(s):  
Ryusuke Numata ◽  
N. F. Loureiro
Keyword(s):  
Magnetic Reconnection ◽  
Current Sheet ◽  
Magnetic Energy ◽  
Appreciable Amount ◽  
Larmor Radius ◽  
Ion Heating ◽  
Electron Heating ◽  
Phase Mixing ◽  
Finite Larmor Radius ◽  
Gyrokinetic Simulations

Magnetic reconnection and associated heating of ions and electrons in strongly magnetized, weakly collisional plasmas are studied by means of gyrokinetic simulations. It is shown that an appreciable amount of the released magnetic energy is dissipated to yield (irreversible) electron and ion heating via phase mixing. Electron heating is mostly localized to the magnetic island, not the current sheet, and occurs after the dynamical reconnection stage. Ion heating is comparable to electron heating only in high-β plasmas, and results from both parallel and perpendicular phase mixing due to finite Larmor radius (FLR) effects; in space, ion heating is mostly localized to the interior of a secondary island (plasmoid) that arises from the instability of the current sheet.

The role of electron heat flux in guide-field magnetic reconnection

2004 ◽  
Vol 11 (12) ◽  
pp. 5387-5397 ◽  
Author(s):  
Michael Hesse ◽  
Masha Kuznetsova ◽  
Joachim Birn
Keyword(s):  
Heat Flux ◽  
Magnetic Reconnection ◽  
Guide Field ◽  
Electron Heat

scholarly journals Multicomponent fluid model for two-temperature plasmas derived from kinetic theory : application to magnetic reconnection

2018 ◽  
Vol 1125 ◽  
pp. 012021 ◽  
Author(s):  
Q. Wargnier ◽  
A. Alvarez Laguna ◽  
P. Kestener ◽  
B. Graille ◽  
N. N. Mansour ◽  
...  
Keyword(s):  
Kinetic Theory ◽  
Magnetic Reconnection ◽  
Fluid Model ◽  
Multicomponent Fluid ◽  
Theory Application ◽  
Two Temperature

Experimental Measurements and CFD Evaluation of the Onset Flow Boiling at Low Pressure and High Subcooling Flow of R-11 Within Vertical Annulus

2014 ◽  
Author(s):  
Y. Bouaichaoui ◽  
R. Kibboua ◽  
M. Matkovič
Keyword(s):  
Heat Flux ◽  
Liquid Velocity ◽  
Flow Boiling ◽  
Fluid Model ◽  
Computer Code ◽  
Computational Method ◽  
Subcooled Boiling ◽  
Two Phase ◽  
Local Flow ◽  
Wide Range

The knowledge of the onset of subcooled boiling in forced convective flow at high liquid velocity and subcooling is of importance in thermal hydraulic studies. Measurements were performed under various conditions of mass flux, heat flux, and inlet subcooling, which enabled to study the influence of different boundary conditions on the development of local flow parameters. Also, some measurements have been compared to the predictions by the three-dimensional two-fluid model of subcooled boiling flow carried out with the computer code ANSYS-CFX-13. A computational method based on theoretical studies of steady state two phase forced convection along a test section loop was released. The calculation model covers a wide range of two phase flow conditions. It predicts the heat transfer rates and transitions points such as the Onset of Critical Heat Flux.

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