scholarly journals Collapse of the neutral current sheet and reconnection at micro-scales

2008 ◽  
Vol 74 (2) ◽  
pp. 215-232 ◽  
Author(s):  
I. F. SHAIKHISLAMOV
Keyword(s):  
Current Sheet ◽  
Large Scale ◽  
Numerical Solutions ◽  
Neutral Current ◽  
Static Solution ◽  
New Process ◽  
Maximum Current ◽  
Nonlinear Static ◽  
Field Lines ◽  
Two Fluid

AbstractReconnection physics at micro-scales is investigated in an electron magnetohydrodynamics frame. A new process of collapse of the neutral current sheet is demonstrated by means of analytical and numerical solutions. It shows how at scales smaller than ion inertia length a compression of the sheet triggers an explosive evolution of current perturbation. Collapse results in the formation of a intense sub-sheet and then an X-point structure embedded into the equilibrium sheet. Hall currents associated with this structure support high reconnection rates. Nonlinear static solution at scales of the electron skin reveals that electron inertia and small viscosity provide an efficient mechanism of field lines breaking. The reconnection rate does not depend on the actual value of viscosity, while the maximum current is found to be restricted even for space plasmas with extremely rare collisions. The results obtained are verified by a two-fluid large-scale numerical simulation.

scholarly journals The structure and dynamics of a large-scale plasmoid generated by fast reconnection in the geomagnetic tail

2011 ◽  
Vol 29 (1) ◽  
pp. 147-156 ◽  
Author(s):  
M. Ugai
Keyword(s):  
Magnetic Field ◽  
Current Sheet ◽  
Large Scale ◽  
Field Component ◽  
The North ◽  
Reconnection Region ◽  
Field Lines ◽  
The Magnetic Field ◽  
East West ◽  
Fast Reconnection

Abstract. As a sequence of Ugai (2010b), the present paper studies in detail the structure and dynamics of large-scale (principal) plasmoid, generated by the fast reconnection evolution in a sheared current sheet with no initial northward field component. The overall plasmoid domain is divided into the plasmoid reconnection region P and the plasmoid core region C. In the region P, the magnetized plasma with reconnected field lines are accumulated, whereas in the region C, the plasma, which was intially embedded in the current sheet and has been ejected away by the reconnection jet, is compressed and accumulated. In the presence of the sheared magnetic field in the east-west direction in the current sheet, the upper and lower parts of the reconnection region P are inversely shifted in the east-west directions. Accordingly, the plasmoid core region C with the accumulated sheared field lines is bent in the north-south direction just ahead of the plasmoid center x=XC, causing the magnetic field component in the north-south direction, whose sign is always opposite to that of the reconnected field lines. Therefore, independently of the sign of the initial sheared field, the magnetic field component Bz in the north-south direction has the definite bipolar profile around XC along the x-axis. At x=XC, the sheared field component has the peak value, and as the sheared fields accumulated in the region C become larger, the bipolar field profile becomes more distinct.

scholarly journals Reconnection current sheet structure in a turbulent medium

2012 ◽  
Vol 19 (6) ◽  
pp. 605-610 ◽  
Author(s):  
E. T. Vishniac ◽  
S. Pillsworth ◽  
G. Eyink ◽  
G. Kowal ◽  
A. Lazarian ◽  
...  
Keyword(s):  
Current Sheet ◽  
Large Scale ◽  
Transport Coefficients ◽  
Cumulative Effect ◽  
High Energy ◽  
Turbulent Medium ◽  
Laminar Flows ◽  
High Energy Particle ◽  
Mhd Turbulence ◽  
Field Lines

Abstract. In the presence of turbulence, magnetic field lines lose their dynamical identity and particles entrained on field lines diffuse through space at a rate determined by the amplitude of the turbulence. In previous work (Lazarian and Vishniac, 1999; Kowal et al., 2009; Eyink et al., 2011) we showed that this leads to reconnection speeds which are independent of resistivity. In particular, in Kowal et al. (2009) we showed that numerical simulations were consistent with the predictions of this model. Here we examine the structure of the current sheet in simulations of turbulent reconnection. Laminar flows consistent with the Sweet-Parker reconnection model produce very thin and well ordered currents sheets. On the other hand, the simulations of Kowal et al. (2009) show a strongly disordered state even for relatively low levels of turbulence. Comparing data cubes with and without reconnection, we find that large scale field reversals are the cumulative effect of many individual eddies, each of which has magnetic properties which are not very different from turbulent eddies in a homogeneous background. This implies that the properties of stationary and homogeneous MHD turbulence are a reasonable guide to understanding turbulence during large scale magnetic reconnection events. In addition, dissipation and high energy particle acceleration during reconnection events take place over a macroscopic volume, rather than being confined to a narrow zone whose properties depend on microscopic transport coefficients.

scholarly journals Magnetic field structure of large-scale plasmoid generated by the fast reconnection mechanism in a sheared current sheet

2010 ◽  
Vol 28 (8) ◽  
pp. 1511-1521 ◽  
Author(s):  
M. Ugai
Keyword(s):  
Magnetic Field ◽  
Current Sheet ◽  
Large Scale ◽  
Field Component ◽  
Three Dimensional ◽  
Magnetized Plasma ◽  
The North ◽  
Magnetic Field Region ◽  
Field Lines ◽  
Fast Reconnection

Abstract. On the basis of the spontaneous fast reconnection model, three-dimensional magnetic field profiles associated with a large-scale plasmoid propagating along the antiparallel magnetic fields are studied in the general sheared current sheet system. The plasmoid is generated ahead of the fast reconnection jet as a result of distinct compression of the magnetized plasma. Inside the plasmoid, the sheared (east-west) field component has the peak value at the plasmoid center located at x=XC, where the north-south field component changes its sign. The plasmoid center corresponds to the so-called contact discontinuity that bounds the reconnected field lines in x<XC and the field lines without reconnection in x>XC. Hence, contray to the conventional prediction, the reconnected sheared field lines in x<XC are not spiral or helical, since they cannot be topologically connected to the field lines in x>XC. It is demonstrated that the resulting profiles of magnetic field components inside the plasmoid are, in principle, consistent with satellite observations. In the ambient magnetic field region outside the plasmoid too, the magnetic field profiles are in good agreement with the well-known observations of traveling compression regions (TCRs).

scholarly journals Disruption of magnetospheric current sheet by quasi-electrostatic field

2009 ◽  
Vol 27 (5) ◽  
pp. 1941-1950 ◽  
Author(s):  
W. W. Liu ◽  
J. Liang
Keyword(s):  
Current Sheet ◽  
Drift Velocity ◽  
Electrostatic Field ◽  
Numerical Solutions ◽  
External Perturbation ◽  
Ion Drift ◽  
Current Disruption ◽  
Local Current ◽  
Fluid Theory ◽  
Two Fluid

Abstract. Recent observational evidence has indicated that local current sheet disruptions are excited by an external perturbation likely associated with the kinetic ballooning (KB) instability initiating at the transition region separating the dipole- and tail-like geometries. Specifically a quasi-electrostatic field pointing to the neutral sheet was identified in the interval between the arrival of KB perturbation and local current disruption. How can such a field drive the local current sheet unstable? This question is considered through a fluid treatment of thin current sheet (TCS) where the generalized Ohm's law replaces the frozen-in-flux condition. A perturbation with the wavevector along the current is applied, and eigenmodes with frequency much below the ion gyrofrequency are sought. We show that the second-order derivative of ion drift velocity along the thickness of the current sheet is a critical stability parameter. In an E-field-free Harris sheet in which the drift velocity is constant, the current sheet is stable against this particular mode. As the electrostatic field grows, however, potential for instability arises. The threshold of instability is identified through an approximate analysis of the theory. For a nominal current sheet half-thickness of 1000 km, the estimated instability threshold is E~4 mV/m. Numerical solutions indicate that the two-fluid theory gives growth rate and wave period consistent with observations.

Finding the drivers for a non-steady state and large-scale stresses acting on the Saturnian magnetosphere

2020 ◽  
Author(s):  
Ned Staniland ◽  
Michele Dougherty ◽  
Adam Masters
Keyword(s):  
Magnetic Field ◽  
Steady State ◽  
Current Sheet ◽  
Ground State ◽  
Large Scale ◽  
Internal Field ◽  
Global Dynamics ◽  
Complete Dataset ◽  
Field Lines ◽  
Inner Region

&lt;p&gt;In the inner region of Saturn&amp;#8217;s rotationally-dominated magnetosphere, the governing magnetic field contributors are the internal magnetic field and the magnetodisc current sheet. The equatorially confined plasma sourced predominantly by the moon Enceladus stretches Saturn&amp;#8217;s magnetic field lines into the characteristic &amp;#8216;magnetodisc&amp;#8217; geometry. The extent of this effect varies due to both external and internal dynamical processes that perturb the system.&lt;/p&gt;&lt;p&gt;In this study, we use the complete dataset collected by the Cassini spacecraft to determine whether the magnetosphere is compressed, stretched or near some prescribed ground state. We find that there is an underlying dawn-dusk asymmetry in the ground state of Saturn&amp;#8217;s magnetosphere, where the field is more compressed at dusk compared to dawn. Whilst Saturn spent a significant period of the Cassini mission near its ground state, we find evidence for large-scale stresses acting on the system, including large compression events that coincide with the declining phase of the solar cycle. These results are then compared to propagated solar wind data. In addition, approximately two thirds of our dataset is well described by the internal field and current sheet models, signifying the system was in steady-state during these passes. We further discuss the drivers for the non-steady state periods at Saturn and what this implies for the global dynamics of Saturn's magnetosphere.&lt;/p&gt;

Room Temperature Solvent-Free Synthesis of Monodisperse Magnetite Nanocrystals

2006 ◽  
Vol 6 (3) ◽  
pp. 852-856 ◽  
Author(s):  
X. R. Ye ◽  
C. Daraio ◽  
C. Wang ◽  
J. B. Talbot ◽  
S. Jin
Keyword(s):  
Oleic Acid ◽  
Solid State ◽  
Large Scale ◽  
Room Temperature ◽  
Solvent Free ◽  
Two Dimensional ◽  
New Process ◽  
High Boiling Point ◽  
Magnetite Nanocrystals ◽  
Solvent Free Synthesis

We have successfully demonstrated a facile, solvent-free synthesis of highly crystalline and monodisperse Fe3O4 nanocrystallites at ambient temperature avoiding any heating. Solid state reaction of inorganic Fe(II) and Fe(III) salts with NaOH was found to produce highly crystalline Fe3O4 nanoparticles. The reaction, if carried out in the presence of surfactant such as oleic acid–oleylamine adduct, generated monodisperse Fe3O4 nanocrystals extractable directly from the reaction mixture. The extracted nanoparticles were capable of forming self-assembled, two-dimensional and uniform periodic array. The new process utilizes inexpensive and nontoxic starting materials, and does not require a use of high boiling point and toxic solvents, thus is amenable to an environmentally desirable, large-scale synthesis of nanocrystals.

scholarly journals The development of magnetic field line wander by plasma turbulence

2017 ◽  
Vol 83 (4) ◽  
Author(s):  
Gregory G. Howes ◽  
Sofiane Bourouaine
Keyword(s):  
Magnetic Field ◽  
Field Line ◽  
Magnetic Field Line ◽  
Large Scale ◽  
Magnetic Energy ◽  
Plasma Turbulence ◽  
Alfven Wave ◽  
Astrophysical Plasmas ◽  
Field Lines ◽  
The Magnetic Field

Plasma turbulence occurs ubiquitously in space and astrophysical plasmas, mediating the nonlinear transfer of energy from large-scale electromagnetic fields and plasma flows to small scales at which the energy may be ultimately converted to plasma heat. But plasma turbulence also generically leads to a tangling of the magnetic field that threads through the plasma. The resulting wander of the magnetic field lines may significantly impact a number of important physical processes, including the propagation of cosmic rays and energetic particles, confinement in magnetic fusion devices and the fundamental processes of turbulence, magnetic reconnection and particle acceleration. The various potential impacts of magnetic field line wander are reviewed in detail, and a number of important theoretical considerations are identified that may influence the development and saturation of magnetic field line wander in astrophysical plasma turbulence. The results of nonlinear gyrokinetic simulations of kinetic Alfvén wave turbulence of sub-ion length scales are evaluated to understand the development and saturation of the turbulent magnetic energy spectrum and of the magnetic field line wander. It is found that turbulent space and astrophysical plasmas are generally expected to contain a stochastic magnetic field due to the tangling of the field by strong plasma turbulence. Future work will explore how the saturated magnetic field line wander varies as a function of the amplitude of the plasma turbulence and the ratio of the thermal to magnetic pressure, known as the plasma beta.

scholarly journals Modelling of mirror mode structures as propagating slow magnetosonic solitons

2009 ◽  
Vol 27 (12) ◽  
pp. 4379-4389 ◽  
Author(s):  
K. Stasiewicz ◽  
C. Z. Cheng
Keyword(s):  
Numerical Modelling ◽  
Excellent Agreement ◽  
Plasma Flow ◽  
Numerical Solutions ◽  
Small Subset ◽  
Instability Condition ◽  
Magnetic Pulsations ◽  
Fluid Theory ◽  
Mirror Mode ◽  
Two Fluid

Abstract. Cluster measurements in the magnetosheath with spacecraft separations of 2000 km indicate that magnetic pulsations interpreted as mirror mode structures are not frozen in plasma flow, but do propagate with speeds of up to ~50 km/s. Properties of these pulsations are shown to be consistent with propagating slow magnetosonic solitons. By using nonlinear two fluid theory we demonstrate that the well known classical mirror instability condition corresponds to a small subset in a continuum of exponentially varying solutions. With the measured plasma moments we have determined parameters of the polybaric pressure model in the region of occurrence of mirror type structures and applied it to numerical modelling of these structures. In individual cases we obtain excellent agreement between observed mirror mode structures and numerical solutions for magnetosonic solitons.

scholarly journals Numerical study of the reconnection process between magnetic cloud and heliospheric current sheet

2018 ◽  
Vol 619 ◽  
pp. A82
Author(s):  
Man Zhang ◽  
Yu Fen Zhou ◽  
Xue Shang Feng ◽  
Bo Li ◽  
Ming Xiong
Keyword(s):  
Magnetic Reconnection ◽  
Current Sheet ◽  
Dynamic Process ◽  
Large Scale ◽  
Magnetic Cloud ◽  
Numerical Study ◽  
Three Dimensional ◽  
Heliospheric Current Sheet ◽  
Reconnection Process ◽  
Magnetic Filed

In this paper, we have used a three-dimensional numerical magnetohydrodynamics model to study the reconnection process between magnetic cloud and heliospheric current sheet. Within a steady-state heliospheric model that gives a reasonable large-scale structure of the solar wind near solar minimum, we injected a spherical plasmoid to mimic a magnetic cloud. When the magnetic cloud moves to the heliospheric current sheet, the dynamic process causes the current sheet to become gradually thinner and the magnetic reconnection begin. The numerical simulation can reproduce the basic characteristics of the magnetic reconnection, such as the correlated/anticorrelated signatures in V and B passing a reconnection exhaust. Depending on the initial magnetic helicity of the cloud, magnetic reconnection occurs at points along the boundary of the two systems where antiparallel field lines are forced together. We find the magnetic filed and velocity in the MC have a effect on the reconnection rate, and the magnitude of velocity can also effect the beginning time of reconnection. These results are helpful in understanding and identifying the dynamic process occurring between the magnetic cloud and the heliospheric current sheet.

Sign in / Sign up

Export Citation Format

Share Document