Why is the current sheet of the earth's distant magnetotail
to be thinned, and why is a large amount of energy released ?
This is typically observed as magnetic reconnection in magneto-
spheric space.
However, this was haunted to Dr. Alfven as mysterious fluid-like
reconnection. Many theorists, there were many theories for this
reconnection, starting classical Dungey's theory to nuclear-fusion
oriented anomalous resistivity. Above them, Dr. Speicer paid
attention to the hypothesis of inertia resistivity to thinning the
current sheet, but his idea was highly criticized by public mass
of audience.
Later in 1994-1996 by the macro-particle simulation - the low-
frequency simulation of ion and electron dynamics, it became
clearly proved that inertia of ions and electrons controls over
input and output of magnetospheric X-point flows of magnetic
reconnection, resulting in the large energy release of earth's
magnetotail (Refs.1, 4).
The numerical simulation of magnetic recennection is written
below.
M. Tanaka, Physics of Plasmas, vol.2, 2920-2930 (1995)
>> Macro-particle low-frequency simulation for reconnection
An electromagnetic particle simulation code is utilized for solar
and magnetospheric space physics (Refs. 1,4-5). Both electric and
magnetic fields are solved at low frequencies by specifically a slightly
backward time decentering technique. The backward decentering
does not affect low frequency phenomena, \omega*Dt << 1 (Refs. 2,3).
The separation of electrons and outskirt ions at X-point as particles
is shown in the simulation.
Magnetic reconnection and the solar wind-earth magnetic field
coupling are quite suitable for applying this simulation code.
The code is available by the author under GPL-3.0 License at
https://github.com/Mtanaka77/ (Ref. 6).
Article: Macro‐particle simulations of collisionless magnetic reconnection
M. Tanaka, Phys.Plasmas, 2, 2920-2930 (1995)
The basic process of collisionless reconnection is studied in terms of
coalescence of two flux bundles using an implicit particle simulation of
two‐dimensions. As the toroidal electric field is generated by magnetic
induction, an elongated current sheet whose width is a few electron skin
depths is formed. Sub‐Alfvénic plasma outflow off the reconnection region
is generated in the poloidal plane which spreads within the dual fans originating
at the X‐point. Significant toroidal acceleration and streaming of the
electrons without direct thermalization is observed in the current sheet.
The electron parallel transport is proved to enhance the reconnection rate
by comparing the implicit and hybrid‐particle simulations; in the latter
the electrons are spatially frozen to the ions. The reconnection rate is
insensitive to finite Larmor radii of the ions in the regime where the
magnetic flux merges constantly in time. The simulation results support
that the collisionless reconnection is mediated by the electron inertia.
Article: Asymmetry and thermal effects due to parallel motion of electrons
in collisionless magnetic reconnection
M. Tanaka, Phys.Plasmas, 3, 4010-4017 (1996).
Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
Fast collisionless reconnection of magnetic flux loops by the
macro‐particle simulation code shows significant asymmetry of the plasma
flow under an ambient toroidal magnetic field. The parallel motion of
electrons induced by the reconnection electric field is found to produce
large density and toroidal magnetic field inhomogeneities of a
quadrupole shape, δn/n0∼0.3, unlike the m=1 mode. The divergence of the plasma flow is locally not identical to zero with each species, ∇⋅V(s)≠0 (s=e,i),
due to the electron spatial movement along the magnetic field. This
internal structure results in a thick current layer and enhances the
reconnection process. A plasmoid that impedes magnetic reconnection is
created when the parallel mass diffusivity of electrons arising from
their thermal motion is suppressed (the fluid limit). The reconnection
rate becomes a smoothly increasing function of the ion mass and an
inverse of the toroidal magnetic field, the latter of which being due to
the compressional effect. The rate is drastically reduced when the ion
Larmor radius far exceeds the ion skin depth.
References
1. M. Tanaka, Macro-particle simulations of collisionless magnetic reconnection,
Phys.Plasmas, 2, 2920-2930 (1995).
2. M. Tanaka, A simulation of low-frequency electromagnetic phenomena in
kinetic plasmas of three dimensions, J.Comput. Phys., 107, 124-145 (1993).
3. M. Tanaka, Macro-EM particle simulation method and a study of collisionless
magnetic reconnection, Comput.Phys.Commun., 87, 117-138 (1995)
4. M. Tanaka, Asymmetry and thermal effects due to parallel motion of electrons
in collisionless magnetic reconnection, Phys.Plasmas, 3, 4010-4017 (1996).
5. H. Shimazu, M. Tanaka, and S. Machida, The behavior of heavy ions in
collisionless parallel shocks generated by the solar wind and planetary
plasma interactions, J.Geophys.Res., 101, 27565-27571 (1996).
6. M. Tanaka, Macro-Particle Simulation for Magnetic Reconnection, at
https://github.com/Mtanaka77/ (2023).
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