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.

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.

The magnetic flux and self-inductivity of a thick toroidal current

2007 ◽  
Vol 73 (5) ◽  
pp. 741-756 ◽  
Author(s):  
TOMISLAV ŽIC ◽  
BOJAN VRŠNAK ◽  
MARINA SKENDER
Keyword(s):  
Aspect Ratio ◽  
Magnetic Flux ◽  
Magnetic Energy ◽  
The Other ◽  
Poloidal Field ◽  
Other Hand ◽  
Radial Profiles ◽  
Internal Flux ◽  
The Difference ◽  
Better Than

AbstractWe investigate numerically the magnetic flux and self-inductivity of a toroidal current I of arbitrary aspect ratio (R0/r0 = 1/η, where R0 and r0 are the major and the minor torus radii, respectively). The total flux Ψ is represented by the sum of the flux outside the torus envelope (Ψo) and the internal flux within the torus body (Ψi). Analogously, the total inductivity is expressed as L = Lo + Li. The outside self-inductivity is determined directly from the magnetic flux Ψo, utilizing Ψo = LoI. On the other hand, the internal inductivity is evaluated as the magnetic energy contained in the poloidal field. The calculations are performed for three different radial profiles of the current density, j(r).It is found that Ψo(η) and Lo (η) depend only very weakly on the form of j(r). On the other hand, Ψi and Li do not depend on η, but depend on the form of j(r). In the range 0.02 ≲ η ≲ 0.5, the numerical values of Lo can be very well fitted by the function of the form Lofit1(η) = −A log(η) − B. Such a relation is analogous to that for a slender torus, although the coefficients are different. For η ≲ 0.01 the slender-torus approximation (Lo*) matches the numerical results better than our function Lofit1, whereas for thicker tori, Lofit1 becomes more appropriate. It is shown that, beyond η ≳ 0.1, the departure of the slender-torus analytical expression from the numerical values becomes greater than 10%, and the difference becomes larger than 100% at η 0.55. In the range η 0.5, the numerical values of Lo can be very well expressed by the function Lofit2(η)=c1 (1 − η)c2. Furthermore, since the internal flux and inductivity become larger than that outside the envelope, Ψi and Li become larger than Ψo and Lo. The total inductivity Ltotfit = Lofit + Li, calculated by appropriately employing our functions Lofit1 and Lofit2, never deviates by more than 1% from the numerically determined values of Ltot.

scholarly journals Three-dimensional magnetic reconnection and its application to solar flares

2017 ◽  
Vol 83 (1) ◽  
Author(s):  
Miho Janvier
Keyword(s):  
Kinetic Energy ◽  
Numerical Simulations ◽  
Magnetic Reconnection ◽  
Solar Flares ◽  
Magnetic Energy ◽  
Three Dimensional ◽  
Three Dimensions ◽  
Current Layer ◽  
Solar Observations ◽  
The Universe

Solar flares are powerful radiations occurring in the Sun’s atmosphere. They are powered by magnetic reconnection, a phenomenon that can convert magnetic energy into other forms of energy such as heat and kinetic energy, and which is believed to be ubiquitous in the universe. With the ever increasing spatial and temporal resolutions of solar observations, as well as numerical simulations benefiting from increasing computer power, we can now probe into the nature and the characteristics of magnetic reconnection in three dimensions to better understand the phenomenon’s consequences during eruptive flares in our star’s atmosphere. We review in the following the efforts made on different fronts to approach the problem of magnetic reconnection. In particular, we will see how understanding the magnetic topology in three dimensions helps in locating the most probable regions for reconnection to occur, how the current layer evolves in three dimensions and how reconnection leads to the formation of flux ropes, plasmoids and flaring loops.

High Performance Fabrics in Body Protective Systems

2016 ◽  
Vol 880 ◽  
pp. 132-135 ◽  
Author(s):  
Selim Gürgen ◽  
Melih Cemal Kuşhan
Keyword(s):  
Kinetic Energy ◽  
High Performance ◽  
The Other ◽  
Body Armor ◽  
Personal Protection ◽  
Military Vehicles ◽  
Living Space ◽  
Other Hand ◽  
Lightweight Structure ◽  
Protective Systems

High performance fabrics are preferable for armor systems due to their lightweight structure and flexibility. High performance fabrics are generally used in body armor design for personal protection. However, these fabrics are utilized to cover the living space in military vehicles such as helicopters and armored vehicles. Besides, pilot seats in combat helicopters are included in utilization area of high performance fabrics. On the other hand armor is defined as a defensive covering to protect body or something against attacking threats. Protection is provided by absorbing the kinetic energy of the attacking threats and stopping them before any damage occurs in the target. This paper offers an overview of high performance fabrics in armor systems.

scholarly journals Characterization of Shock Wave Damages in Explosion Welded Mo/Cu Clads

Metals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 501
Author(s):  
Pradeep Kumar Parchuri ◽  
Shota Kotegawa ◽  
Kazuhiro Ito ◽  
Hajime Yamamoto ◽  
Akihisa Mori ◽  
...  
Keyword(s):  
Shock Wave ◽  
Kinetic Energy ◽  
Plastic Strain ◽  
Intermediate Layer ◽  
Explosive Welding ◽  
The Other ◽  
Group Vi ◽  
Bending Tests ◽  
Other Hand

The shock wave damage during explosive welding has not been reported in a flyer Mo plate of the Mo/Cu clads. However, it would be an inevitable problem in group VI elements. This study was aimed to characterize the shock wave damage in the Mo plate, that is less brittle than a W plate, of explosive welded Mo/Cu clads. Cladding at low horizontal collision velocities leading to high collision angles was expected to enhance the shock wave damage, and the clads resulted in less elongation in bending tests. On the other hand, in the clads obtained at high horizontal collision velocities (HCVs) with low collision angles, their bending elongation increased significantly. The shock wave damage penetrated from the surface of a Mo plate to the Mo/Cu interface, and thus reducing thickness of a Mo plate of bending specimens increased bending plastic strain. The shock wave damage is associated with kinetic energy imparted to the flyer Mo plate, and thus loss of kinetic energy due to formation of an intermediate layer at the interface and reducing thickness of a flyer Mo plate would be very helpful for decrease of shock wave damage.

EFFECTS OF A LARGE-SCALE MEAN FLOW IN A SHELL MODEL OF TURBULENT CONVECTION

2007 ◽  
Vol 21 (23n24) ◽  
pp. 4178-4183 ◽  
Author(s):  
EMILY S. C. CHING ◽  
H. GUO
Keyword(s):  
Shell Model ◽  
Large Scale ◽  
Temperature Fluctuations ◽  
Scaling Behavior ◽  
The Other ◽  
Turbulent Convection ◽  
Mean Flow ◽  
Mean Velocity ◽  
Other Hand ◽  
Flow Reversals

The possible effects of a large-scale mean flow, represented as a non-zero mean velocity in the shell of the largest scale, are studied using a shell model of turbulent convection. In the regime where buoyancy is dynamically important, flow reversals are not observed. On the other hand, flow reversals are found in the regime where buoyancy is not dynamically important. In both regimes, the presence of such a large-scale mean flow does not change the scaling behavior of the velocity and temperature fluctuations.

scholarly journals Binaries in Globular Clusters

1998 ◽  
Vol 11 (2) ◽  
pp. 616-621 ◽  
Author(s):  
S. L. W. Mcmillan ◽  
C. Pryor ◽  
E. S. Phinney
Keyword(s):  
Kinetic Energy ◽  
Globular Cluster ◽  
Binary Stars ◽  
Formation Process ◽  
Globular Clusters ◽  
The Other ◽  
Energy Distributions ◽  
Other Hand ◽  
Mass Segregation ◽  
Three Body

Binary stars in a globular cluster (hereafter, GC) may be primordial (i.e. formed along with the cluster), or the result of cluster dynamics. “Dynamical” binaries can result from conservative three-body encounters (e.g. Spitzer, 1987) if a third star can carry away enough kinetic energy to leave two others bound, or from dissipative two-body encounters, if two stars happen to pass within a few stellar radii of one other (Fabian, Pringle, & Rees, 1975). Such non-primordial systems are likely to be found primarily in evolved GC cores, both because conditions are more favorable for making them there, and because of mass segregation. Knowledge of the formation process allows reasonable estimates to be made of their mass and energy distributions. The initial spatial, mass, and energy distributions of primordial binaries, on the other hand, are largely unknown.

scholarly journals Fission observables from 4D Langevin calculations with macroscopic transport coefficients

2018 ◽  
Vol 169 ◽  
pp. 00027 ◽  
Author(s):  
Mark D. Usang ◽  
Fedir A. Ivanyuk ◽  
Chikako Ishizuka ◽  
Satoshi Chiba ◽  
Joachim A. Maruhn
Keyword(s):  
Kinetic Energy ◽  
Transport Coefficients ◽  
Considerable Improvement ◽  
The Other ◽  
Total Kinetic Energy ◽  
Langevin Equations ◽  
Preliminary Results ◽  
Fission Fragments ◽  
Other Hand ◽  
The Moment

We have extended the Langevin equations to 4 dimensions (4D) by allowing the independent deformation for the left (δ1) and right fragments (δ2) of the fissioning nucleus. At the moment we are only able to use them in conjunction with the macroscopic transport coefficients. Nevertheless, we can see a considerable improvement in the preliminary results for the fission observables, especially those related to the total kinetic energy (TKE) of fission fragments. By plotting the TKE distributions we have revealed the super-long fission modes in 236U and super-short fission modes in 257Fm. By plotting the distribution of δ against the fragment’s TKE we have noted a correlation between the values of δ and Brosa’s fission modes. We have found that the standard fission modes correspond to prolate tips of the light fragments while the complementary heavy fragments have oblate fission tips. On the other hand, if both fragments were prolate at the tips, we get super-long fission modes. If both fragments were oblate at the tips, we get super-short fission modes.

scholarly journals Separatrices: The crux of reconnection

2014 ◽  
Vol 81 (1) ◽  
Author(s):  
Giovanni Lapenta ◽  
Stefano Markidis ◽  
Andrey Divin ◽  
David Newman ◽  
Martin Goldman
Keyword(s):  
Magnetic Field ◽  
Kinetic Energy ◽  
Magnetic Reconnection ◽  
Electromagnetic Fields ◽  
Plasma Flow ◽  
Magnetic Energy ◽  
Laboratory Plasmas ◽  
Field Lines ◽  
Kinetic Physics ◽  
Over Time

Magnetic reconnection is one of the key processes in astrophysical and laboratory plasmas: it is the opposite of a dynamo. Looking at energy, a dynamo transforms kinetic energy in magnetic energy while reconnection takes magnetic energy and returns it to its kinetic form. Most plasma processes at their core involve first storing magnetic energy accumulated over time and then releasing it suddenly. We focus here on this release. A key concept in analysing reconnection is that of the separatrix, a surface (line in 2D) that separates the fresh unperturbed plasma embedded in magnetic field lines not yet reconnected with the hotter exhaust embedded in reconnected field lines. In kinetic physics, the separatrices become a layer where many key processes develop. We present here new results relative to the processes at the separatrices that regulate the plasma flow, the energization of the species, the electromagnetic fields and the instabilities developing at the separatrices.

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.

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