Plasma-beta dependence of the fast reconnection mechanism in an initially force-free current sheet

2011 ◽  
Vol 18 (10) ◽  
pp. 102903 ◽  
Author(s):  
M. Ugai
Keyword(s):  
Current Sheet ◽  
Free Current ◽  
Fast Reconnection

scholarly journals Collisionless distribution functions for force-free current sheets: using a pressure transformation to lower the plasma beta

2018 ◽  
Vol 84 (3) ◽  
Author(s):  
F. Wilson ◽  
T. Neukirch ◽  
O. Allanson
Keyword(s):  
Distribution Function ◽  
Current Sheet ◽  
Plasma Phys ◽  
Distribution Functions ◽  
Hermite Functions ◽  
Slow Convergence ◽  
Nonlinear Force ◽  
Free Current ◽  
Transformed Distribution ◽  
General Method

So far, only one distribution function giving rise to a collisionless nonlinear force-free current sheet equilibrium allowing for a plasma beta less than one is known (Allansonet al.,Phys. Plasmas, vol. 22 (10), 2015, 102116; Allansonet al.,J. Plasma Phys., vol. 82 (3), 2016a, 905820306). This distribution function can only be expressed as an infinite series of Hermite functions with very slow convergence and this makes its practical use cumbersome. It is the purpose of this paper to present a general method that allows us to find distribution functions consisting of a finite number of terms (therefore easier to use in practice), but which still allow for current sheet equilibria that can, in principle, have an arbitrarily low plasma beta. The method involves using known solutions and transforming them into new solutions using transformations based on taking integer powers ($N$) of one component of the pressure tensor. The plasma beta of the current sheet corresponding to the transformed distribution functions can then, in principle, have values as low as$1/N$. We present the general form of the distribution functions for arbitrary$N$and then, as a specific example, discuss the case for$N=2$in detail.

scholarly journals A two-fluid study of oblique tearing modes in a force-free current sheet

2016 ◽  
Vol 23 (1) ◽  
pp. 012112 ◽  
Author(s):  
Cihan Akçay ◽  
William Daughton ◽  
Vyacheslav S. Lukin ◽  
Yi-Hsin Liu
Keyword(s):  
Current Sheet ◽  
Tearing Modes ◽  
Free Current ◽  
Two Fluid

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.

Computer modelling of three-dimensional dynamics of fast reconnection

1991 ◽  
Vol 45 (2) ◽  
pp. 251-266 ◽  
Author(s):  
M. Ugai
Keyword(s):  
Current Sheet ◽  
Computer Modelling ◽  
Neutral Line ◽  
Current System ◽  
Three Dimensional ◽  
Dimensional Structure ◽  
Reconnection Process ◽  
Reconnection Region ◽  
Set Up ◽  
Fast Reconnection

Computer simulations are used to investigate the basic three-dimensional structure of the fast reconnection mechanism spontaneously developing from a long current sheet. It is shown that if three-dimensional effects (∂sol;∂z ≠ 0) are not so strong, a locally enhanced resistivity results in current-sheet thinning, and a fast reconnection process, involving switch-off shocks, is eventually set up in a region limited in the z direction. The fast reconnection process near the z = 0 plane becomes quasi-steady and two-dimensional (∂/∂z = 0), so that the well-known Petschek mechanism is fully applicable. Distinct plasma rarefaction occurs inside the fast reconnection region, so that fast-mode expansion may propagate in the z direction, and the resulting inflow velocity uz takes the magnetic field into the fast reconnection region and contracts the latter. The global current system undergoes drastic changes during the fast-reconnection development. The current flow, initially directed in the z direction, first converges towards the neutral line, and is then largely deflected away from this line in the inner reconnection region.

Conversion of magnetic energy and the width of current sheets

2002 ◽  
Vol 68 (1) ◽  
pp. 53-58
Author(s):  
MANUEL NÚÑEZ
Keyword(s):  
Energy Transfer ◽  
Magnetic Reconnection ◽  
Current Sheet ◽  
Magnetic Energy ◽  
Plasma Conductivity ◽  
Constant Rate ◽  
Classical Models ◽  
Field Lines ◽  
A Current ◽  
Fast Reconnection

Magnetic reconnection is one of the most efficient ways of transforming magnetic into kinetic and thermal energies. We prove a general identity relating the energy transfer in a neighborhood of a current sheet, where reconnection is assumed to occur. With some reasonable hypotheses regarding the geometry of stream and field lines, we prove that for a constant rate of transformation of magnetic energy, the width of the current sheet must grow with the plasma conductivity. Hence an enhanced diffusivity seems necessary for certain classical models of fast reconnection to work.

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).

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